[Federal Register Volume 89, Number 143 (Thursday, July 25, 2024)]
[Proposed Rules]
[Pages 60498-60547]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2024-14970]



[[Page 60497]]

Vol. 89

Thursday,

No. 143

July 25, 2024

Part II





Department of Commerce





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National Oceanic and Atmospheric Administration





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50 CFR Parts 223 and 224





Endangered and Threatened Wildlife and Plants; Proposed Listing 
Determinations for Ten Species of Giant Clams Under the Endangered 
Species Act; Proposed Rule

  Federal Register / Vol. 89 , No. 143 / Thursday, July 25, 2024 / 
Proposed Rules  

[[Page 60498]]


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DEPARTMENT OF COMMERCE

National Oceanic and Atmospheric Administration

50 CFR Parts 223 and 224

[Docket No. 240626-0177; RTID 0648-XF174]


Endangered and Threatened Wildlife and Plants; Proposed Listing 
Determinations for Ten Species of Giant Clams Under the Endangered 
Species Act

AGENCY: National Marine Fisheries Service (NMFS), National Oceanic and 
Atmospheric Administration (NOAA), Commerce.

ACTION: Proposed rule; availability of status review; request for 
comments.

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SUMMARY: We, NMFS, have completed a comprehensive status review of 
seven species of giant clams (Hippopus hippopus, H. porcellanus, 
Tridacna derasa, T. gigas, T. mbalavuana, T. squamosa, and T. 
squamosina) in response to a petition to list these species as 
threatened or endangered under the Endangered Species Act (ESA). Based 
on the best scientific and commercial data available, including the 
Status Review Report, and after taking into account efforts being made 
to protect these species, we have determined that H. porcellanus, T. 
mbalavuana, and T. squamosina are in danger of extinction throughout 
the entirety of their respective ranges, T. derasa and T. gigas are in 
danger of extinction in a significant portion of their respective 
ranges, and H. hippopus is likely to become an endangered species 
within the foreseeable future throughout a significant portion of its 
range. Therefore, we propose to list H. porcellanus, T. mbalavuana, T. 
squamosina, T. derasa, and T. gigas as endangered species and H. 
hippopus as a threatened species under the ESA. We have determined that 
the fluted clam, T. squamosa, is not currently in danger of extinction 
throughout all or a significant portion of its range and is not likely 
to become so within the foreseeable future. Therefore, we find that T. 
squamosa does not meet the definition of a threatened or an endangered 
species under section 4(a) of the ESA. Further, we propose to exercise 
the discretionary authority of section 4(d) to extend the prohibitions 
of section 9 of the ESA to the proposed threatened species, H. 
hippopus. At this time, we do not propose to designate critical habitat 
for the three species proposed to be listed that occur within U.S. 
jurisdiction (H. hippopus, T. derasa, and T. gigas) because critical 
habitat for these species is not yet determinable. Using the authority 
of section 4(e) of the ESA, we also propose to list T. crocea, T. 
maxima, T. noae, and T. squamosa as threatened species due to the 
similarity of appearance of products derived from these species (e.g., 
meat, worked shell products, and pearls) to those derived from the six 
aforementioned species proposed to be listed based on their extinction 
risk. We propose a special rule to define activities that would and 
would not be prohibited with respect to these four species in order to 
mitigate the substantial enforcement challenge associated with this 
similarity of appearance concern. We solicit information to inform the 
final listing determination and to inform a future proposal for any 
determinable critical habitat.

DATES: Comments must be received by October 23, 2024.
    Public informational meetings and public hearings: In-person and 
virtual public hearings on this proposed rule will be held during the 
public comment period at dates, times, and locations to be announced in 
a forthcoming Federal Register notice.

ADDRESSES: You may submit data, information, or written comments on 
this document, identified by NOAA-NMFS-2017-0029, by either of the 
following methods:
     Electronic Submissions: Submit all electronic public 
comments via the Federal e-Rulemaking Portal. Go to https://www.regulations.gov and enter NOAA-NMFS-2017-0029 in the Search box. 
Click on the ``Comment'' icon, complete the required fields, and enter 
or attach your comments.
     Mail: Submit written comments to Endangered Species 
Division, Office of Protected Resources (F/PR3), National Marine 
Fisheries Service, 1315 East West Highway, Silver Spring, MD 20910, 
USA, Attn: Giant Clams Species Listing Proposed Rule.
    Instructions: Comments sent by any other method, to any other 
address or individual, or received after the end of the comment period, 
may not be considered by NMFS. All comments received are a part of the 
public record and will generally be posted for public viewing on 
https://www.regulations.gov without change. All personally identifying 
information (e.g., name, address, etc.), confidential business 
information, or otherwise sensitive information submitted voluntarily 
by the sender will be publicly accessible. NMFS will accept anonymous 
comments (enter ``N/A'' in the required fields if you wish to remain 
anonymous).
    The Status Review Report associated with this determination, its 
references, and the petition can be accessed electronically at: https://www.fisheries.noaa.gov/action/proposed-rule-10-species-giant-clams-under-endangered-species-act. The peer review plan, associated charge 
statement, and peer review report can be accessed electronically at: 
https://www.noaa.gov/information-technology/status-review-report-of-7-giant-clam-species-petitioned-under-us-endangered-species-act-hippopus. 
The draft Environmental Assessment and Initial Regulatory Flexibility 
Analysis associated with the proposed ESA section 4(d) regulation for 
T. crocea, T. maxima, T. noae, and T. squamosa can be accessed 
electronically via the Federal e-Rulemaking Portal by navigating to 
https://www.regulations.gov and entering NOAA-NMFS-2017-0029 in the 
Search box.

FOR FURTHER INFORMATION CONTACT: John Rippe, NMFS Office of Protected 
Resources, (301) 427-8467, [email protected].

SUPPLEMENTARY INFORMATION:

Background

    On August 7, 2016, we received a petition from Dwayne Meadows to 
list 10 species of giant clams (Cardiidae: Tridacninae) as threatened 
or endangered under the ESA throughout their respective ranges. The 
petitioner also requested that critical habitat be designated in waters 
subject to U.S. jurisdiction concurrently with listing under the ESA. 
On June 26, 2017, we published a 90-day finding (82 FR 28946) 
announcing that the petition presented substantial scientific or 
commercial information indicating that the petitioned action may be 
warranted for 7 of the 10 species listed in the petition: Hippopus 
hippopus (horse's hoof, bear paw, or strawberry clam), Hippopus 
porcellanus (porcelain or China clam), Tridacna derasa (smooth giant 
clam), Tridacna gigas (true giant clam), Tridacna mbalavuana (syn. T. 
tevoroa; devil or tevoro clam), Tridacna squamosa (fluted or scaly 
clam), and Tridacna squamosina (syn. T. costata; Red Sea giant clam), 
but that the petition did not present substantial scientific or 
commercial information indicating that the petitioned action may be 
warranted for the other 3 species (T. crocea, T. maxima, or T. noae). 
We also announced the initiation of a status review of the seven 
aforementioned giant clam species, as required by

[[Page 60499]]

section 4(b)(3)(A) of the ESA, and requested information to inform the 
agency's decision on whether these species warrant listing as 
endangered or threatened under the ESA. We received information from 
the public in response to the 90-day finding and incorporated the 
information into both the Status Review Report (Rippe et al., 2023) and 
this proposed rule. This information complemented our thorough review 
of the best available scientific and commercial data for these species 
(see Status Review below).

Listing Determinations Under the Endangered Species Act

    We are responsible for determining whether species are threatened 
or endangered under the ESA (16 U.S.C. 1531 et seq.). To be considered 
for listing under the ESA, a group of organisms must constitute a 
``species,'' which is defined in section 3 of the ESA to include any 
subspecies of fish or wildlife or plants, and any distinct population 
segment (DPS) of any species of vertebrate fish or wildlife which 
interbreeds when mature (16 U.S.C. 1532(16)). On February 7, 1996, NMFS 
and the U.S. Fish and Wildlife Service (USFWS; together, the Services) 
adopted a policy describing what constitutes a DPS of a taxonomic 
species (``DPS Policy,'' 61 FR 4722). The joint DPS Policy identifies 
two elements that must be considered when identifying a DPS: (1) The 
discreteness of the population segment in relation to the remainder of 
the taxon to which it belongs; and (2) the significance of the 
population segment to the remainder of the taxon to which it belongs. 
Because giant clams are invertebrates they cannot be listed as DPSs, 
and the DPS Policy does not apply here.
    Section 3 of the ESA defines an endangered species as ``any species 
which is in danger of extinction throughout all or a significant 
portion of its range'' and a threatened species as one ``which is 
likely to become an endangered species within the foreseeable future 
throughout all or a significant portion of its range.'' Thus, we 
interpret an ``endangered species'' to be one that is presently in 
danger of extinction. A ``threatened species,'' on the other hand, is 
not presently in danger of extinction, but is likely to become so 
within the foreseeable future (that is, at a later time). In other 
words, the primary statutory difference between a threatened and 
endangered species is the timing of when a species is in danger of 
extinction, either presently (endangered) or in the foreseeable future 
(threatened).
    Under section 4(a)(1) of the ESA, we must determine whether any 
species is endangered or threatened as a result of any one or a 
combination of any of the following factors: (A) the present or 
threatened destruction, modification, or curtailment of its habitat or 
range; (B) overutilization for commercial, recreational, scientific, or 
educational purposes; (C) disease or predation; (D) the inadequacy of 
existing regulatory mechanisms; or (E) other natural or manmade factors 
affecting its continued existence (16 U.S.C. 1533(a)(1)); 50 CFR 
424.11(c). We are also required to make listing determinations based 
solely on the best scientific and commercial data available, after 
conducting a review of the species' status and after taking into 
account efforts, if any, being made by any State or foreign nation (or 
subdivision thereof) to protect the species (16 U.S.C. 1533(b)(1)(A)).
    On July 5, 2022, the U.S. District Court for the Northern District 
of California issued an order vacating the ESA section 4 implementing 
regulations that were revised or added to 50 CFR part 424 in 2019 
(``2019 regulations,'' see 84 FR 45020, August 27, 2019) without making 
a finding on the merits. On September 21, 2022, the U.S. Court of 
Appeals for the Ninth Circuit granted a temporary stay of the district 
court's July 5 order. On November 14, 2022, the Northern District of 
California issued an order granting the government's request for 
voluntary remand without vacating the 2019 regulations. On April 5, 
2024, the Services published a final rule revising the section 4 
implementing regulations (89 FR 24300). Because the 2024 revised 
regulations became effective on May 6, 2024, we considered them during 
the development of this proposed rule. For purposes of this 
determination and in an abundance of caution, we considered whether the 
analysis or its conclusions would be any different under the pre-2019 
regulations. We have determined that our analysis and conclusions 
presented here would not be any different.

Status Review

    To determine whether each of the seven giant clam species warrants 
listing under the ESA, we completed a Status Review Report, which 
summarizes information on each species' taxonomy, distribution, 
abundance, life history, and biology; identifies threats or stressors 
affecting the status of each species; and assesses the species' current 
and future extinction risk. We appointed a biologist in the Office of 
Protected Resources Endangered Species Conservation Division to compile 
and complete a scientific review of the best scientific and commercial 
data available on the giant clam species, including information 
received in response to our request for information (82 FR 28946, June 
26, 2017).
    The Status Review Report was subject to independent peer review 
pursuant to the Office of Management and Budget Final Information 
Quality Bulletin for Peer Review (M-05-03; December 16, 2004). It was 
peer reviewed by four independent specialists selected from the 
academic and scientific community with expertise in giant clam biology, 
conservation, and management. The peer reviewers were asked to evaluate 
the adequacy, appropriateness, and application of data used in the 
Status Review Report, as well as the findings made in the ``Assessment 
of Extinction Risk'' section of the report. All peer reviewer comments 
were addressed prior to finalizing the Status Review Report and 
publication of this finding.
    We subsequently reviewed the Status Review Report, its cited 
references, and peer review comments, and conclude that it synthesizes 
the best available scientific and commercial data related to the seven 
giant clam species considered here. In making our determinations, we 
have applied the statutory provisions of the ESA, our regulations 
regarding listing determinations, and relevant policies identified 
herein.
    The Status Review Report and the peer review report are available 
on our website (see ADDRESSES section). Below is a summary of the 
information from the Status Review Report and our analysis of the 
status of the seven giant clam species.

Biological Review

Taxonomy and Species Descriptions

    Giant clams are a small but conspicuous group of the planet's 
largest and fastest growing marine bivalves. They fall within the order 
Veneroida, family Cardiidae, and subfamily Tridacninae (Schneider, 
1998). For many years, giant clams were considered to occupy their own 
family (Tridacnidae) sister to Cardiidae until molecular phylogenetics 
(Maruyama et al., 1998; Schneider & Foighil, 1999) and comparison of 
sperm ultrastructure (Keys & Healy, 2000) supported reclassifying the 
group as a subfamily within Cardiidae. This is the current, most widely 
accepted classification; however, Neo et al. (2017) note that others 
continue to argue that Tridacnidae should be retained as a full family 
based on its highly distinct

[[Page 60500]]

morphology (Huber & Eschner, 2011; Penny & Willan, 2014).
    Colloquially described as having `upside down' orientation (Penny & 
Willan, 2014), giant clams lie with the hinge of their shell facing 
downwards, allowing their byssus (i.e., filamentous threads) to attach 
the organism to the substrate while orienting their enlarged mantle 
upwards toward the sunlight (Soo & Todd, 2014). Additionally, most 
giant clam species have an epifaunal lifestyle (i.e., situated on top 
of the substrate) in contrast to the largely infaunal lifestyle of 
their cardiid ancestors.
    There are two extant genera of giant clams, Hippopus and Tridacna, 
which are distinguished by several shell and mantle characteristics. In 
Hippopus, a very narrow byssal orifice is bordered by interlocking 
teeth, while Tridacna exhibits a well-defined byssal gape without 
teeth. Additionally, when the clam is completely open, the mantle of 
Tridacna extends laterally beyond the margin of the shell, whereas the 
mantle of Hippopus does not (Lucas, 1988). A result of this difference 
is that Hippopus species tend to gape their valves further apart than 
Tridacna species, thus exposing more mantle surface area (Lucas, 1994).
    There are currently 12 species of giant clams recognized in the 
literature, though this number changes often as advances in molecular 
phylogenetics resolve evolutionary relationships (including cryptic 
speciation) that had been overlooked by traditional morphology-based 
taxonomies. Joseph Rosewater's seminal work in 1965 is widely cited as 
the authoritative material for early descriptions of giant clam species 
and includes six current species that remain valid to date: H. hippopus 
(Linnaeus, 1758), T. gigas (Linnaeus, 1758), T. derasa (R[ouml]ding, 
1798), T. maxima (R[ouml]ding, 1798), T. squamosa (Lamarck, 1819), and 
T. crocea (Lamarck, 1819). He later added H. porcellanus to this list 
after re-examining its classification (Rosewater, 1982).
    At the time of the 1965 report, T. mbalavuana had only been 
formally described from fossils on Viti Levu, Fiji. However, Fijians 
had long known of this species occurring in local waters as `tevoro', 
or devil clam. Thus, when Lucas et al. (1991) re-discovered the species 
in 1991, they described it as the new species T. tevoroa. It was not 
until 2000 that T. mbalavuana and T. tevoroa were re-classified as 
synonymous based on morphological similarities (Newman & Gomez, 2000). 
As in the Status Review Report, we refer to this species by its 
lectotype (i.e., its original classification), T. mbalavuana. 
Additionally, Richter et al. (2008) described a new species, T. 
costata, in 2008, but upon further analysis, it too was found to be 
synonymous with a previously described species, T. squamosina, first 
discovered by Rudolf Sturany (1899) during the early Austro-Hungarian 
expeditions of the Red Sea (Huber & Eschner, 2011). As in the Status 
Review Report, we refer to this species by its lectotype, T. 
squamosina.
    Based on the best available scientific and commercial data 
summarized above, we find that all seven species of giant clams (H. 
hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, T. 
squamosa, and T. squamosina) are currently considered taxonomically-
distinct species and, therefore, meet the definition of ``species'' 
pursuant to section 3 of the ESA. Distinguishing features of each 
species are summarized below.

Hippopus Hippopus

    Commonly referred to as the horse's hoof, bear paw, or strawberry 
clam, H. hippopus has a heavy, thick shell that features prominent 
reddish blotches in irregular concentric bands (Rosewater, 1965). The 
shell interior is porcellaneous white, frequently flushed with 
yellowish orange on the ventral margin (Kinch & Teitelbaum 2010; 
Rosewater, 1965). Primary radial sculpture consists of 13 or 14 
moderately convex rib-like folds over the surface of the valve, 
extending towards the ventral slope where they become obsolete 
(Rosewater, 1965). The mantle usually exhibits mottled patterns in 
green, yellow-brown or grey, and the incurrent siphon lacks guard 
tentacles (Neo et al., 2017). Juveniles and young, smaller adults are 
usually attached to coral rubble by their byssus, whereas older 
(larger, heavier) individuals are typically found unattached on the 
substratum being held in place by their weight (Rosewater, 1965; Neo et 
al., 2017). The largest reported shell length for H. hippopus is 50 cm, 
which was documented at the Bolinao Marine Laboratory in the 
Philippines (Neo et al., 2017).

Hippopus Porcellanus

    Commonly referred to as the China clam, H. porcellanus grows to a 
maximum size of 40 cm, but is most commonly found at shell lengths of 
around 20 cm (Kinch & Teitelbaum, 2010). The shell exterior is off-
white, occasionally with scattered weak reddish blotches. The shell 
interior is porcellaneous white, often flushed with orange on the 
ventral margin, and the mantle ranges from a yellowish-brown to a dull 
green or grey (Kinch & Teitelbaum, 2010). This species is distinguished 
from its congener, H. hippopus, by its smoother and thinner valves and 
presence of fringing tentacles at the incurrent siphon (Neo, Eckman, et 
al., 2015).

Tridacna Derasa

    T. derasa, or the smooth giant clam, is the second largest giant 
clam species, with a maximum size of around 60 cm (Neo et al., 2017). 
T. derasa has a heavy, plain-colored shell and can be distinguished 
from other species by its low primary and secondary radial sculpture. 
Primary radial sculpture consists of 7-12 broad, shallow rib-like folds 
(usually 6-7 main folds), and the shells are often greatly thickened at 
the umbos (i.e., the oldest, most prominent point of the shell near the 
ventral margin) (Rosewater, 1965). The mantle is often characterized by 
elongate patterns of brilliant greens and blues, and the incurrent 
siphon is equipped with inconspicuous guard tentacles (Neo et al., 
2017).

Tridacna Gigas

    T. gigas is known as the true giant clam and is the largest of all 
the giant clam species, growing to a maximum shell length of 137 cm and 
maximum weight in excess of 225 kg (Beckvar, 1981; Rosewater, 1965). 
The shell of T. gigas is thick and heavy, equivalve (having valves of 
the same size), and equilateral (symmetrical front-to-back) (Hernawan, 
2012). The shell exterior is off-white, and is often covered with 
marine growths (e.g., vermetids, annelid tubes, coral, etc.) (Kinch & 
Teitelbaum, 2010; Rosewater, 1965). For the most part, the shell lacks 
scales except near the byssal orifice where small scales may be 
present. The shell interior is porcellaneous white, dull in the area 
within the pallial line, and shiny above the pallial line to the dorsal 
end of the shell (Rosewater, 1965). Often, the mantle is yellowish-
brown to olive-green and is a darker shade along the mantle's edge and 
around the clam's siphons (Rosewater, 1965). Numerous, small, brilliant 
blue-green rings are dispersed across the mantle, each enclosing one or 
several hyaline organs. These rings are especially prevalent along the 
lateral edges of the mantle and around the siphonal openings 
(Rosewater, 1965). Smaller specimens (i.e., 150-200 mm) may be more 
uniformly colored, lacking a darker shade along the edge of the mantle 
and with fewer colored rings (Rosewater, 1965).
    T. gigas is readily identified by many characteristics, most 
notably its large

[[Page 60501]]

size. The species can also be identified by four to six unique deep 
radial folds that give way to elongate, triangular projections at the 
upper margins of its shells (Hernawan, 2012; Lucas, 1988), a complete 
outer demibranch (the V-shaped structure of gills common to bivalves; 
Rosewater, 1965), the lack of tentacles on the inhalant siphon 
(Hernawan, 2012), and the lack of byssal attachment (i.e., they are 
free-living; Rosewater, 1965).

Tridacna Mbalavuana

    Before it was formally classified taxonomically, Fijians had long 
referred to T. mbalavuana as `tevoro,' or devil clam, based on its 
thin, sharply-edged valves and warty brownish grey mantle. T. 
mbalavuana has been hypothesized to be a transitional species between 
the Hippopus and Tridacna genera due to overlapping characteristics 
(Lucas et al., 1991; Schneider & Foighil, 1999). It has Hippopus-like 
features including the absence of a byssal gape, a mantle that does not 
extend over the shells, and the absence of hyaline organs (Lucas et 
al., 1991); however, T. mbalavuana looks most like T. derasa in 
appearance (Lewis & Ledua, 1988). It can be distinguished from T. 
derasa by its rugose mantle, prominent guard tentacles on the incurrent 
siphon, thinner valves, and colored patches on the shell ribbing (Neo, 
Eckman, et al., 2015). The shell exterior is off-white, often partly 
encrusted with marine growths. It can grow to just over 50 cm long 
(Lewis & Ledua, 1988; Neo, Eckman, et al., 2015) with the largest 
specimen recorded at 56 cm (Lucas et al., 1991).

Tridacna Squamosa

    Commonly known as the fluted or scaly giant clam due to the 
characteristic leaf-like projections on its valves, T. squamosa is one 
of the most widely distributed species of giant clams. The exterior of 
its shell is greyish white in color, often with various hues of orange, 
yellow, or pink/mauve (Rosewater, 1965). The primary radial sculpture 
consists of 4-12 strongly convex, rib-like folds. The concentric 
sculpture consists of ``undulate lines of growth which produce widely 
spaced, broadly leaf-like, projecting scales on primary folds'' 
(Rosewater, 1965). The prominent scales on the shell commonly feature 
different shades or colors (Kinch & Teitelbaum, 2010). The shell 
interior is porcellaneous white, with an occasional hint of orange 
(Kinch & Teitelbaum, 2010). Rosewater (1965) describes the mantle as 
having a main ground color of greyish purple with a row of light blue 
rhomboidal spots along the outer mantle margin and multicolored 
irregularly-circular spots toward the center. The outer periphery of 
the spots is pale yellow, inside of which is a band of dark yellow, and 
the entire center is nearest to light blue. Generally, T. squamosa 
reaches a maximum shell length of ~40 cm (Neo et al., 2017).

Tridacna Squamosina

    T. squamosina, or the Red Sea giant clam, exhibits a strong 
resemblance to T. squamosa, but can be distinguished by its 
asymmetrical shells, crowded scutes, wider byssal orifice, and five to 
seven deep triangular radial folds (Roa-Quiaoit, 2005; Richter et al., 
2008). Additionally, the mantle is most commonly a subdued brown 
mottled pattern with a green margin that features prominent ``wart-
like'' protrusions and pale markings following the mantle contour 
(Richter et al., 2008). These are the main diagnostic features 
separating T. squamosina from its sympatric congeners and are 
conservatively present even in small clams <10 cm shell length (Richter 
et al., 2008). T. squamosina can reach at least 32 cm in shell length 
(Neo, Eckman, et al., 2015)--the largest specimen recorded was found in 
the southern Red Sea at Kamaran Island, off the coast of Yemen (Huber & 
Eschner, 2011).

Range, Distribution, and Habitat Use

H. Hippopus
    H. hippopus is widely distributed throughout the Indo-Pacific 
(i.e., the tropical and subtropical waters of the Indian Ocean, the 
western and central Pacific Ocean, and the seas connecting the two in 
the general area of Indonesia), occurring from the Andaman and Nicobar 
Islands in the west to the Republic of Kiribati in the east, and from 
New Caledonia in the south to the southern islands of Japan in the 
north (Neo et al., 2017).
    According to Munro (1993a), H. hippopus occurs in the widest range 
of habitat types of all the giant clam species. Most often, it is found 
in shallow, nearshore patches of reef, sandy areas and seagrass beds 
that can be exposed during low tides, but it can also be found on reefs 
as deep as 10 m (S. Andr[eacute]fou[euml]t, pers. obs. cited in Neo et 
al., 2017). Based on a recent survey in New Caledonia, Purcell et al. 
(2020) found that H. hippopus ``strongly preferred'' lagoonal reefs. 
The authors hypothesized that the species may either prefer the siltier 
sediments and more turbid water of lagoon reef flats or alternatively 
may have low tolerance to the wave exposure of barrier reefs.
H. Porcellanus
    H. porcellanus has one of the most restricted geographic ranges of 
the giant clams, centered in the Coral Triangle region. The species is 
mostly known from the Sulu Archipelago and Palawan region in the 
Philippines, but it has also been reported in Palau, the Milne Bay 
Province (Papua New Guinea), Sabah (Malaysia), and Sulawesi and Raja 
Ampat (Indonesia) (S. Wells, 1997; Neo et al., 2017).
    There is very little information specifying the habitat preferences 
of H. porcellanus, but according to Calumpong (1992), the species is 
commonly found in shallow, nearshore sandy areas adjoining coral reefs. 
Juvenile or young H. porcellanus are frequently found byssally attached 
to coral heads, whereas larger mature H. porcellanus can be found on 
sandy bottoms unattached to substrate (Rosewater, 1982; Kinch & 
Teitelbaum, 2010).
T. Derasa
    The geographic range of T. derasa primarily encompasses the Coral 
Triangle region, although it extends east to Tonga and as far west as 
the Cocos (Keeling) Islands in the eastern Indian Ocean (Rosewater, 
1965). Adams et al. (1988) described T. derasa as having a patchy 
distribution, being rare in many places throughout its range and 
abundant in others. Notably, T. derasa has been one of the most widely 
cultured species of giant clam and has been introduced to a number of 
countries and territories throughout the central and western Pacific 
Ocean. This includes the Federated States of Micronesia (FSM), Marshall 
Islands, Tuvalu, Cook Islands, Samoa, and American Samoa.
    T. derasa preferentially inhabits clear offshore waters distant 
from areas of significant freshwater run-off (Munro, 1993a). According 
to Calumpong (1992), the species appears to favor oceanic environments 
(i.e., small islands and atolls) more than fringing reefs adjacent to 
large island masses. The species is known to occur at depths of 4-25 m 
(Lewis et al., 1988; Neo et al., 2017), and is usually found weakly 
attached to the tops and sides of coral outcrops as juveniles, but may 
become detached upon reaching a larger size (Adams, 1988).
T. Gigas
    The natural range of T. gigas spans the shallow waters of the Indo-
Pacific and the Great Barrier Reef, from Myanmar in the west to the 
Republic of Kiribati in the east, and from the Ryukyus Islands

[[Page 60502]]

of southern Japan in the north to Queensland, Australia in the south 
(bin Othman et al., 2010; Neo et al., 2017). Cultured specimens of T. 
gigas have been introduced in American Samoa, the Cook Islands, Hawaii, 
and Samoa (Neo et al., 2017). Like most other giant clam species, T. 
gigas is typically associated with coral reefs and can be found in many 
habitats, including high- and low-islands, atoll lagoons, and fringing 
reefs (Munro, 1993a). In a broad survey of T. gigas distribution 
throughout the Great Barrier Reef, Braley (1987a) found that the 
species was most common on inshore reefs potentially influenced by 
seasonal fluctuations in salinity and turbidity and was rare south of 
19[deg] S. The observed distribution was essentially opposite of that 
for T. derasa, which was found primarily on offshore reefs and was 
common in the Swain Reefs at 21-22[deg] S. These contrasting 
distributions led Braley (1987b) to the conclusion that temperature may 
limit the distribution of young T. gigas, while T. derasa may be more 
sensitive to salinity and/or turbidity. T. gigas is typically found 
between the depths of 2 to 20 m and is often found among Acropora spp. 
or other hard coral communities, hard reef substrata, or on bare sand 
(Braley, 1987b; Kinch & Teitelbaum 2010; Rosewater, 1965).
T. Mbalavuana
    T. mbalavuana has one of the most restricted distributions of all 
the giant clam species. For many years, it had only been observed in 
Fiji and Tonga, but recent reports indicate that this species may be 
found in low numbers outside of these two locations. According to Kinch 
and Teitelbaum (2010), T. mbalavuana had been observed in the Loyalty 
Islands in New Caledonia, a report later supported by Tiavouane and 
Fauvelot (2016), who encountered two individuals on the northeastern 
barrier reef of New Caledonia after ``exhaustive searches'' (Neo et 
al., 2017). Single individuals were also reportedly observed on Lihou 
Reef in the Coral Sea (Ceccarelli et al., 2009) and in the Raja Ampat 
region of West Papua, Indonesia (Wakum et al., 2017), but neither of 
these reports have been further corroborated.
    In Fiji, individuals are most often observed along outer slopes of 
leeward reefs in the eastern Lau Islands, in very clear, oceanic water 
(Ledua et al., 1993). In Tonga, they are found in the northern Vava`u 
and Ha`apai islands. T. mbalavuana has a deeper depth distribution than 
most other giant clam species. In one study on spawning and larval 
culture of T. mbalavuana, individuals were collected from waters of 
Fiji and Tonga (Ledua et al., 1993). The mean depth of clams collected 
in Fiji was 27.4 m, with samples collected from depths ranging from 20 
to 33 m, and all specimens were found on the leeward side of reefs and 
islands. Many of the clams found in Tonga were next to the edge of a 
sand patch and cradled against rocky outcrops, rubble or bare rock with 
steep slopes (Ledua et al., 1993).
T. Squamosa
    T. squamosa is the second-most widely distributed giant clam 
species, with a broad geographic range that extends from the Red Sea 
and eastern Africa in the west to the Pitcairn Islands in the east, and 
from the Great Barrier Reef in the south to southern Japan in the north 
(bin Othman et al., 2010; Neo et al., 2017). The species has also been 
introduced in Hawaii and Guam (CITES, 2004b).
    T. squamosa is usually found on coral reefs or on adjacent sandy 
areas (Neo et al., 2017). Juveniles are often attached to the substrate 
by a ``weak but copious byssus,'' while adults can be found either 
attached or free-living (Neo et al., 2017; Rosewater, 1965). T. 
squamosa occurs across a broad depth range, which includes shallow reef 
flats, patch reefs, and reef slopes, both inside and outside of 
lagoons. Individuals have been observed as deep as 42 m in the Red Sea 
(Jantzen et al., 2008). T. squamosa is typically more common on 
shelving fringing reefs than reef flats (Govan et al., 1988) and seems 
to prefer sheltered environments (Kinch & Teitelbaum, 2010; Munro, 
1993a). Comparing the distribution of T. squamosa and T. maxima in 
Mauritius, Ramah et al. (2017) found that T. squamosa were most often 
attached to flat substrata, such as dead plate corals or rubble. Hardy 
and Hardy (1969) reported that T. squamosa and H. hippopus occupied 
much the same habitat in Palau, both being widely distributed in 
relatively shallow water in the lagoon and on the barrier and fringing 
reefs; although, T. squamosa was reportedly more commonly associated 
with coral areas of Acropora spp. than adjacent sandy areas. In New 
Caledonia, Purcell et al. (2020) interpreted the relatively high 
abundance of T. squamosa on barrier reef sites compared to lagoonal 
reefs as indication that the species may prefer cleaner waters, as 
opposed to the siltier sediments and more turbid seawater of lagoon 
reef flats. However, Lewis et al. (1988) note that the species is more 
tolerant of turbid water than T. derasa. Paulay (1987) reported that 
all observations of T. squamosa in the Cook Islands were from the outer 
reef slope, occasionally to depths of 30 m or more.
T. Squamosina
    T. squamosina is endemic to the Red Sea, with its past and present 
distribution including the northeastern Gulf of Aqaba, the Sinai coast, 
and eastern coast of the Red Sea down to Yemen (Huber & Eschner, 2011; 
Lim et al., 2021; Richter et al., 2008; Rossbach et al., 2021). There 
have also been several anecdotal accounts of the species in Mozambique; 
however, later evidence of genetic divergence between specimens in the 
Red Sea and Mozambique (Moreels, 2018), as well as the significant 
geographic distance from its central range, suggests that the reported 
sightings may be of its recently-resurrected sister species, T. 
elongatissima, with which it shares a close phylogenetic history 
(Fauvelot et al., 2020; Tan et al., 2021). For this reason, without 
more information to verify these anecdotal sightings, we do not include 
the Western Indian Ocean in the natural range of T. squamosina.
    In a survey of giant clams in the Red Sea, Richter et al. (2008) 
noted that live specimens of T. squamosina were found exclusively in 
very shallow water habitats (e.g., reef flats, rocky and sandy-rubble 
flats, seagrass beds, or under branching corals or coral heads 
shallower than 2m). Thus, unlike the other two Red Sea species (T. 
maxima and T. squamosa), which have broad depth distributions, T. 
squamosina is restricted to the reef top and is usually weakly attached 
to the substrate (Richter et al., 2008).

Diet and Feeding

    During the earliest stages of larval development, giant clams 
initially rely on nutrients stored in the egg yolk. Upon formation of 
the velum and hollow intestines within the first 2-3 days after 
fertilization, veliger larvae transition to planktivory and are able to 
actively ingest flagellates (~5 [mu]m in diameter), zooxanthellae and 
dissolved organic nutrients from the seawater via the mouth (Fitt et 
al., 1984; Soo & Todd, 2014). Like most bivalves, giant clams retain 
the ability to filter feed into adulthood by pumping water into their 
mantle cavities via an inhalant siphon, filtering plankton through 
ciliated gills, and passing the filtered water back out via an 
excurrent siphon (Hardy & Hardy, 1969).
    However, a defining characteristic of giant clams is their 
mutualistic relationship with dinoflagellates of the family 
Symbiodiniaceae, known commonly as zooxanthellae, which

[[Page 60503]]

provide the primary source of nutrition to adult clams. Giant clams 
strictly acquire symbiotic algae from the seawater during larval 
development and therefore do not inherit symbionts via parental oocytes 
(Fitt & Trench, 1981; Hartmann et al., 2017). Furthermore, 
zooxanthellae are housed extracellularly within a diverticular 
extension of the digestive tract (Norton et al., 1992). This `tubular 
system' extends throughout the upper levels of the mantle and is 
arranged as a dense network of tertiary canals branching off of 
secondary structures with no direct connection to the haemolymph of the 
clam (Norton et al., 1992). Detailed scanning electron microscope 
images have shown that zooxanthellae are often stacked in pillars 
within these canals and are co-located with light-scattering iridocyte 
cells that enhance photosynthesis (L. Rehm, unpub.) and protect the 
algal cells from damaging UV radiation (Rossbach, Overmans, et al., 
2020; Rossbach, Subedi, et al., 2020).
    Symbiosis is thought to be established during metamorphosis from 
pediveliger to the juvenile clam. At this point, zooxanthellae can be 
observed migrating from the stomach to the tubular system (Fitt et al., 
1986; Norton et al., 1992). Although, more recent studies have shown 
that genes known to be associated with symbiosis and glycerol synthesis 
are expressed in giant clam larvae, suggesting that symbiotic activity 
may be initiated earlier during larval development (Mies et al., 2016; 
Mies, Voolstra, et al., 2017).
    Giant clams receive the majority of their metabolic carbon 
requirements via symbiotic autotrophy. They provide dissolved inorganic 
nutrients to support photosynthesis (e.g., NH4\+\, 
NO3-, PO4\+\) via direct absorption 
from the seawater and as an excretory byproduct of respiration (Hawkins 
& Klumpp, 1995; Toonen et al., 2011). In return, zooxanthellae transfer 
photosynthetic carbon to the host in the form of glucose, glycerol, 
oligosaccharides and amino acids (Griffiths & Streamer, 1988; Ishikura 
et al., 1999; Mies et al., 2016).
    Under natural conditions, the contribution of autotrophy to giant 
clam nutrition tends to increase with body size and has been shown to 
vary between species (Klumpp & Griffiths, 1994; Klumpp & Lucas, 1994; 
Hawkins & Klumpp, 1995). This may in part be related to differences in 
their characteristic habitats. For example, T. derasa and T. 
mbalavuana, two species which occur predominantly in clear, oceanic 
environments, derive most (T. mbalavuana: 70 percent at 28 m, 105 
percent at 15 m), if not all (T. derasa), of the carbon required for 
growth and respiration from autotrophy (Klumpp & Lucas, 1994). Notably, 
only T. mbalavuana, which is the deepest-occurring species of giant 
clam, increased its photosynthetic efficiency in the lowest light 
conditions (Klumpp & Lucas, 1994). H. hippopus and T. gigas exhibit a 
different strategy altogether, reflecting their natural occurrence in 
shallower intertidal and subtidal habitats, where there is often a 
higher concentration of suspended organics in the water column. Klumpp 
et al. (1992) showed that T. gigas is an efficient filter-feeder and 
that heterotrophic carbon supplied significant amounts of the total 
carbon necessary for its respiration and growth (65 percent in ~43 mm 
individuals and 34 percent in ~167 mm individuals). In a follow-up 
study, Klumpp and Griffiths (1994) similarly found that ingested carbon 
provided 61 to 113 percent of total needs in 40 to 80 mm T. gigas and 
36 to 44 percent in H. hippopus. Some have hypothesized that 
differences in energy acquisition and expenditure may in part explain 
the growth and size differences among giant clam species, and in 
particular the enormous size of T. gigas. At this point, however, no 
clear nutritional basis for these differences has been resolved (Klumpp 
& Griffiths, 1994).
    Giant clams associate with several Symbiodiniaceae genera, which 
can vary by geographic location (Fitt et al., 1986). In the central Red 
Sea, for example, all sampled species (T. maxima, T. squamosa, T. 
squamosina) were found to exclusively harbor strains of Symbiodinium 
(formerly known as clade A) (Pappas et al., 2017). In Okinawa, Japan, 
T. squamosa hosted varying communities of Symbiodinium, Cladocopium 
(formerly clade C), and Durusdinium (formerly clade D) (Ikeda et al., 
2017). Similarly, populations of T. squamosa, T. maxima, and T. crocea 
in eastern Indonesia were found to associate with mixed communities of 
these three genera (DeBoer et al., 2012). While certain symbiont genera 
have been shown to confer physiological benefits to coral hosts (e.g., 
greater tolerance to thermal stress or enhanced growth rate), there is 
no consistent evidence that these patterns translate directly to giant 
clams (reviewed in DeBoer et al., 2012).

Growth and Reproduction

    Giant clams are protandrous hermaphrodites, meaning they mature 
first as males and later develop ovaries to function as both male and 
female simultaneously (Wada, 1952; Rosewater, 1965). Size and age at 
maturity vary by species and geographic location, but generally, giant 
clams are known to reach male phase maturity at around 2-3 years of age 
(Heslinga et al., 1984; Shelley, 1989) and female phase maturity as 
early as 3-5 years (Heslinga et al., 1984; Isamu, 2008). In larger 
species, such as T. gigas, female maturity typically occurs later at 
around 8-9 years of age (Gomez & Mingoa-Licuanan, 2006). Giant clams 
reproduce via broadcast spawning, in which sperm and eggs are released 
into the water column where external fertilization takes place (Wada, 
1954). Sperm is released first, followed by eggs after a short interval 
(Munro, 1993a).
    Giant clams are exceptionally fecund, with individuals producing by 
many estimates tens to hundreds of millions of eggs during a single 
spawning event (Lucas, 1988). This number varies by species; for 
example, estimates suggest that H. porcellanus can release around 5 
million eggs (Alc[aacute]zar et al., 1987), H. hippopus can release 25-
60 million eggs (Jameson, 1976; Alcala et al., 1986), and T. gigas can 
release up to 500 million eggs (Crawford et al. 1986). However, despite 
their high fecundity, giant clams experience very high rates of 
mortality during early development (Jameson, 1976; Beckvar, 1981), 
resulting in very low levels of natural recruitment (Munro, 1993a). 
Reports suggest that less than 1 percent of all giant clam fertilized 
eggs survive larval development and progress to the juvenile phase in 
the wild (Jameson, 1976; Fitt et al., 1984; Crawford et al., 1986). As 
Lucas (1994) describes, ``the extreme example is T. gigas, which being 
at or near the pinnacle of fecundity, must have near the lowest level 
of survival of potential recruits in the animal kingdom.''
    Many have described giant clam recruitment as ``erratic'' (McKoy et 
al., 1980; Adams et al., 1988; Lucas, 1994; Guest et al., 2008). For 
example, Braley (1988) observed ``extremely low'' average recruitment 
on the Great Barrier Reef, punctuated by a major recruitment event in 
1987, which yielded the largest population of T. gigas that had been 
recorded at the time. This pattern aligns with the concept of 
`sweepstakes' reproduction, which is the chance matching of 
reproductive activity with oceanographic conditions conducive to 
spawning, fertilization, dispersal, and successful recruitment 
(Hedgecock, 1994). This can lead to sporadic waves of recruitment 
depending on the prevailing oceanographic conditions facilitating 
fertilization and carrying a successful cohort of `sweepstakes' larvae 
to a suitable settlement location. Importantly, for broadcast spawning 
organisms like giant clams, which

[[Page 60504]]

primarily rely on the mixing of gametes with neighboring individuals, 
this reproductive strategy can be especially sensitive to changes in 
population density. In particular, low abundance and low population 
density severely reduces the likelihood of such sweepstakes success by 
minimizing the chance of fertilization.
    There is considerable variation in the frequency and seasonality of 
spawning events among giant clam species. There is no evidence of 
reproductive seasonality in the central tropics, with some populations 
possessing ripe gametes year-round (Heslinga et al., 1984; Munro, 
1993a; Lindsay et al., 2004). At higher latitudes, spawning is most 
often associated with late spring and summer months and can occur once 
per year (Shelley & Southgate, 1988) or in some cases periodically over 
the course of several months (Fitt & Trench, 1981; Heslinga et al., 
1984; Roa-Quiaoit, 2005). The environmental cues that initiate gamete 
release are not fully understood, but there is evidence that the lunar 
cycle may play a critical role. In Palau, for example, 76 percent and 
24 percent of 55 observed spawning events by T. gigas occurred during 
the second and fourth quarter of the lunar cycle, respectively 
(Heslinga et al., 1984). Unlike many other broadcast spawning 
organisms, there is little evidence that temperature is important for 
the induction of spawning (Wada, 1954; Fitt & Trench, 1981).
    Once one or more clams have begun to spawn, chemical cues 
associated with egg release have been shown to play a role in 
triggering the spawning of nearby individuals, which then release sperm 
for fertilization (Munro, 1993a). While a maximum distance between 
spawning individuals has not been quantified (Neo et al., 2015), in 
situ observations by Braley (1984) showed that 70 percent of the 
nearest spawning neighbors were within 9 m of one another, while only 
13 percent were between 20-30 m of one another. Through laboratory 
trials, Neo et al. (2015) found that gametes of T. squamosa remained 
viable for up to 8 hours, but that viability decreased significantly 
with time. Because of these factors, maintaining sufficient population 
densities to facilitate fertilization among neighboring individuals is 
vital to the persistence of giant clam populations.
    Importantly, there is also some evidence that giant clams are able 
to self-fertilize with varying fitness consequences among different 
species. After observing that the end of sperm release occasionally 
overlaps with the beginning of egg release in certain giant clam 
species (see also Kurihara et al. (2010)), Murakoshi and Hirata (1993) 
experimentally induced self-fertilization in four species of giant 
clams (H. hippopus, T. crocea, T. maxima, and T. squamosa) by removing 
the gonads and mixing gametes. They found that all four species are 
capable of self-fertilization, but that larval development of H. 
hippopus was significantly altered, and no T. maxima juveniles 
metamorphosed completely to the normal pediveliger stage. Juvenile T. 
crocea and T. squamosa survived up to a year post-fertilization, but 
the study was not long enough to evaluate possible effects on 
reproductive maturity or later-phase development. More recently, Zhang 
et al. (2020) evaluated the fitness effects of self-fertilization in 
three species of giant clams (T. crocea, T. derasa, and T. squamosa) 
after 1 year of development. They found that there was no effect of 
self-fertilization on the fertilization rate or zygotic fertility in 
any species. Larval survival and growth rate was significantly reduced 
in T. crocea and T. squamosa, but not T. derasa. However, while self-
fertilization may be possible in some species, numerous accounts of 
spawning in culture and in situ suggest that sperm and eggs are 
released successively without an overlap in timing in the vast majority 
of spawning events (LaBarbera, 1975; McKoy, 1980; Wada, 1954). It is 
likely that this limits the occurrence of self-fertilization in nature 
and minimizes its role in giant clam productivity.
    Once an egg is fertilized, the life cycle of giant clams is typical 
of bivalve molluscs (Lucas, 1994; Soo & Todd, 2014). Fertilized eggs 
are approximately 90-130 [mu]m in diameter (Jameson, 1976) and have a 
slight negative buoyancy. They usually develop into swimming 
trochophores within 12-24 hours, at which time they are able to alter 
their depth distribution and begin searching for an eventual settlement 
site (Ellis, 1997; Neo et al., 2015). Shell production in molluscs 
begins at this early phase of development, following a thickening of 
epithelial cells that will define the future shell field (Gazeau et 
al., 2013). Within 36-48 hours after fertilization, larvae develop into 
shelled, swimming veligers, which use a ciliated velum for locomotion 
and feeding (Soo & Todd, 2014). The veligers are highly motile and 
begin feeding on microalgae of up to 10 [mu]m in diameter (Munro, 
1993a). Over the course of several days, the velum begins to degenerate 
and a foot develops as the larvae transition into the pediveliger stage 
(Soo & Todd, 2014). At this point, larvae alternate between swimming 
and crawling on the substrate, using their foot for sensing and feeding 
(Lucas, 1988; Soo & Todd, 2014). Pediveligers generally develop 6-14 
days post-fertilization; however, Fitt and Trench (1981) noted 
considerable variation in the timing of this transition, where most 
took place by day 10 but others were observed up to 29 days post-
fertilization.
    Larvae metamorphose into juvenile clams at an approximate size of 
200 [mu]m (LaBarbera, 1975; Lucas, 1988; Soo & Todd, 2014). Juvenile 
clams remain mobile and are able to crawl both horizontally and 
vertically using their foot as they search for a settlement location 
(Soo & Todd, 2014). Giant clam larvae tend to settle on substrates that 
offer shelter in the form of grooves and crevices, highlighting the 
importance of habitat rugosity during this stage of development (Soo & 
Todd, 2014). Additionally, juveniles have been observed to move non-
randomly and clump towards conspecifics, which some hypothesize may be 
a behavioral adaptation to enhance reproduction and predator defense 
(Huang et al., 2007; Neo, 2020). Juvenile clams eventually attach 
themselves to the substrate by use of byssal threads, which in some 
species will remain in place throughout their lifetime. Larger species 
typically lose the byssal threads after reaching adulthood and are held 
in place by their size and weight (Lucas, 1988).
    Growth rates vary among species, with larger species exhibiting 
more rapid growth than smaller species (Munro & Heslinga, 1983; Lucas, 
1988). Growth rates after settlement generally follow a sigmoid (``S'' 
shaped) curve, beginning slowly, then accelerating after approximately 
1 year and slowing again as the animals approach sexual maturity 
(Lucas, 1988; Ellis, 1997). Lucas (1994) provides examples of maximum 
rates of monthly shell growth for several species as recorded under 
culture conditions in the Philippines: H. hippopus--5.3 mm, T. 
squamosa--4.5 mm, T. derasa--5.6 mm, and T. gigas--9.1 mm (Calumpong, 
1992; Gomez & Mingoa, 1993). Shell growth continues throughout the 
clam's lifespan (Lucas, 1994).
    The maximum lifespan of giant clams is not known, but the oldest 
reliably aged individual was a large T. gigas determined to be 63 years 
old (Lucas, 1994). Similar aging studies based on the analysis of 
growth rings in the shell estimated a 43 cm-long T. squamosa to be 
around 22 years old (Basker, 1991), a ~20 cm-long T. maxima to be 
around 28 years old (Romanek et al., 1987), and a 93 cm-long T. gigas 
to be around 60 years old (Watanabe et al., 2004). Using growth and 
mortality estimates, Dolorosa et al. (2014) predicted a

[[Page 60505]]

lifespan of more than 20 years for H. porcellanus.

Population Structure

    Current literature indicates several consistent features of giant 
clam population genetics throughout their range. The first is 
significant genetic differentiation between giant clam populations of 
the central Pacific region, including Kiribati, Marshall Islands, 
Tuvalu and Cook Islands, and the western Pacific region, including the 
Great Barrier Reef, Philippines, Solomon Islands and Fiji (Benzie & 
Williams, 1995, 1997). The pattern is consistent across T. gigas and T. 
maxima, although there is some variability in the inferred level of 
connectivity between the Great Barrier Reef and Philippines in T. 
derasa (Macaranas et al., 1992). Interestingly, the patterns of genetic 
connectivity do not reflect oceanic currents as would be expected for a 
passively-dispersing organism like giant clams. Hence, Benzie and 
Williams (1997) hypothesize that ``other mechanisms dominate present-
day dispersal, or that [the observed patterns] reflect past 
connectivity which present-day dispersal along major surface currents 
has not altered over thousands of years.''
    Other studies describe a relatively consistent pattern of genetic 
structure within the Indo-Pacific region, often highlighting four or 
five genetic clusters distinguishing populations of the Red Sea, 
Western Indian Ocean, Eastern Indian Ocean, Indo-Malay Archipelago, and 
Western Pacific. In every case, populations of T. squamosa and T. 
maxima in the Red Sea are found to be highly divergent from all other 
populations in their range (Nuryanto & Kochzius, 2009; Huelsken et al., 
2013; Hui et al., 2016; Pappas et al., 2017; Lim et al., 2018). The 
same is true of Western Indian Ocean populations, though to a slightly 
lesser extent (Hui et al., 2016; Lim et al., 2018). Additionally, there 
is a uniform pattern of differentiation between giant clam populations 
in the Indo-Malay Archipelago and those in the eastern Indian Ocean and 
Java Sea (Kochzius & Nuryanto, 2008; Nuryanto & Kochzius, 2009; 
Huelsken et al., 2013; Hui et al., 2016). This pattern is largely 
consistent across T. squamosa, T. maxima, and T. crocea, although some 
studies note variability between species with respect to certain 
genetic breaks identified in the Java Sea and in Chendewasih Bay 
(Nuryanto & Kochzius, 2009; Huelsken et al., 2013). Population genetic 
data from T. maxima and T. crocea (species which are not subject to 
this rulemaking) suggest that there may also be genetic breaks between 
the western Pacific islands and Indo-Malay Archipelago (Nuryanto & 
Kochzius, 2009; Huelsken et al., 2013; Hui et al., 2016). However, 
similar data are not available for any of the seven species considered 
here.
    On a smaller scale, giant clam populations within the northern and 
central Great Barrier Reef exhibit high genetic connectivity (Benzie & 
Williams, 1992, 1995, 1997). Evans and Jerry (2006) found tenuous 
evidence of isolation-by-distance in this region, which would suggest 
that populations may be connected by the prevailing southward flow of 
the East Australian Current. In contrast, Kittiwattanawong et al. 
(2001) found that T. squamosa in the Andaman Sea are genetically 
distinct from those in the Gulf of Thailand, likely due to the physical 
barrier of the Malay Peninsula minimizing dispersal between these 
populations.

Current and Historical Distribution and Population Abundance

    There are no current or historical estimates of global abundance 
for any of the seven giant clam species considered here. Therefore, we 
rely on the best available scientific and commercial data, including 
formal and informal survey data, qualitative descriptions of abundance 
or population trends, and anecdotal reports from specific sites, to 
evaluate the status of each species in each country, territory, or 
region throughout its range.
    Much of the information used to determine the status of each 
species is derived from Table 4 of Neo et al. (2017), which we have 
supplemented or revised based on more recent survey data or reports. We 
have also adjusted the criteria used to define each qualitative 
abundance category, which Neo et al. (2017) had previously defined as 
follows: Abundant: >100 individuals (ind) ha-1, Frequent: 1-
10 ind ha-1, Rare: <0.1 ind ha-1. In doing so, we 
considered the reproductive ecology of giant clams, and in particular, 
the observations of Braley (1984) regarding the distance between 
nearest-spawning T. gigas during a natural spawning event. Braley 
(1984) measured that 70 percent of nearest-spawning individuals were 
within 9 m of one another, while only 13 percent were between 20-30 m 
of one another, suggesting that spawning synchrony decreases with 
distance. As broadcast spawning organisms, giant clams rely on 
sufficient population density in order to facilitate successful 
external fertilization of their gametes. Based on the distances above, 
we determined the minimum population density in a 1-hectare (10,000 
m\2\) square grid in which individuals could be evenly spaced at 9 and 
30 m apart. Respectively, these distances represent populations that we 
consider to be ``Abundant,'' where we expect relatively high 
reproductive success, and ``Frequent,'' where we expect lower but 
moderate reproductive success. A ``Rare'' population in which 
individuals are spaced farther than 30 m apart on average is likely to 
have infrequent, sporadic reproductive success. This approach led to 
the following criteria: Abundant: >100 ind ha-1 (9-m 
distance), Frequent: 10-100 ind ha-1 (30-m distance), and 
Rare: <10 ind ha-1 (>30-m distance).
    Importantly, precise quantitative assessments of abundance are not 
possible in most instances, as many regions lack current or 
comprehensive survey data (see the accompanying Status Review Report 
for all reported estimates of population density from specific 
surveys). Thus, where survey data are limited to only a few sites or 
where recent survey data are not available, we also take into account 
other available information, including qualitative descriptions of 
abundance or population trends, to reach a determination on the likely 
status of the species throughout each country, territory, or region in 
its entirety. In other words, although survey data from a single site 
may indicate a relatively abundant population, if the species is 
considered absent from all other areas, the species may be considered 
``frequent'' or ``rare'' on average in that location. This methodology 
generally follows the approach used by Neo et al. (2017).
    Additionally, it is important to note that, in the interest of 
simplicity, these qualitative abundance categories are based on an 
assumption of uniform spacing between individuals. However, a number of 
studies report that giant clams often occur in a clumped distribution, 
where individuals are concentrated in a number of small, distantly-
separated groups. In these cases, the abundance categories may 
underestimate the productivity of the respective population. In other 
words, if survey data indicate that a species occurs in some location 
at low abundance on average, reproductive success is more likely if the 
individuals are clustered in a few small groups, minimizing the 
distance between neighboring individuals, than if they are spread 
uniformly across the seafloor.
    In table 1 below, we summarize the status of each species in each 
of the locations where it has been observed. Full narrative 
descriptions of the data

[[Page 60506]]

and scientific studies that informed the following abundance 
assessments can be found in the accompanying Status Review Report 
(Rippe et al., 2023).

   Table 1--Summary of the Population Status for Each of the Seven Giant Clam Species in All Countries, Territories, and Regions Where They Have Been
                         Observed (Adapted From Neo et al., 2017 and Supplemented With More Recent Information Where Available)
--------------------------------------------------------------------------------------------------------------------------------------------------------
           Location                 HH \1\            HP \1\            TD \1\            TG \1\           TMB \1\           TS \1\          TSI \1\
--------------------------------------------------------------------------------------------------------------------------------------------------------
Red Sea:
    Djibouti.................  ................  ................  ................  ................  ...............  +..............  ...............
    Egypt....................  ................  ................  ................  ................  ...............  ++.............  +
    Israel...................  ................  ................  ................  ................  ...............  dd.............  ...............
    Jordan...................  ................  ................  ................  ................  ...............  ++.............  +
    Saudi Arabia.............  ................  ................  ................  ................  ...............  +++............  +
    Somalia..................  ................  ................  ................  ................  ...............  +..............  ...............
    Sudan....................  ................  ................  ................  ................  ...............  ++.............  ...............
    Yemen....................  ................  ................  ................  ................  ...............  ++.............  dd
Southeast Africa:
    Cargados Carajos           ................  ................  ................  ................  ...............  +..............  ...............
     Archipelago.
    Comoros..................  ................  ................  ................  ................  ...............  ++.............  ...............
    Kenya....................  ................  ................  ................  ................  ...............  +..............  ...............
    Madagascar...............  ................  ................  ................  ................  ...............  ++.............  ...............
    Mauritius................  ................  ................  ................  ................  ...............  +..............  ...............
    Mayotte..................  ................  ................  ................  ................  ...............  dd.............  ...............
    Mozambique...............  ................  ................  ................  ................  ...............  +..............  dd
    La R[eacute]union........  ................  ................  ................  ................  ...............  dd.............  ...............
    Seychelles...............  ................  ................  ................  ................  ...............  +..............  ...............
    South Africa.............  ................  ................  ................  ................  ...............  dd.............  ...............
    Tanzania.................  ................  ................  ................  ................  ...............  +..............  ...............
Indian Ocean:
    India....................  +...............  ................  ................  +...............  ...............  +..............  ...............
    Australia (NW Islands)...  ++..............  ................  ++..............  +...............  ...............  +..............  ...............
    Christmas Island.........  ................  ................  +...............  -...............  ...............  +..............  ...............
    Cocos (Keeling) Islands..  ................  ................  +...............  -...............  ...............  -..............  ...............
    Chagos...................  ................  ................  ................  ................  ...............  dd.............  ...............
    Maldives.................  ................  ................  ................  ................  ...............  +..............  ...............
    Sri Lanka................  ................  ................  ................  ................  ...............  dd.............  ...............
East Asia:
    Japan....................  +...............  ................  ................  +...............  ...............  +..............  ...............
    Taiwan...................  -...............  ................  -...............  -...............  ...............  +..............  ...............
    China....................  ................  ................  ................  -...............  ...............  +..............  ...............
    South China Sea..........  +...............  ................  +...............  +...............  ...............  ++.............  ...............
South Asia:
    Indonesia................  +...............  +...............  +...............  +...............  ...............  +++............  ...............
    Malaysia.................  +...............  +...............  +...............  +...............  ...............  +++............  ...............
    Myanmar (Burma)..........  dd..............  ................  ................  dd..............  ...............  dd.............  ...............
    Cambodia.................  ................  ................  ................  dd..............  ...............  ++.............  ...............
    Brunei...................  ................  ................  ................  ................  ...............  dd.............  ...............
    Philippines..............  +...............  +...............  +...............  +...............  ...............  ++.............  ...............
    Singapore................  -...............  ................  ................  -...............  ...............  +..............  ...............
    Thailand.................  ................  ................  ................  -...............  ...............  +..............  ...............
    Vietnam..................  ................  ................  ................  dd..............  ...............  ++.............  ...............
    East Timor...............  ................  ................  ................  dd..............  ...............  ...............  ...............
Pacific Ocean:
    Australia (Great Barrier   ++..............  ................  ++..............  ++..............  dd.............  ++.............  ...............
     Reef).
    Fiji.....................  REIN............  ................  +...............  REIN............  +..............  ++.............  ...............
    New Caledonia............  +...............  ................  +...............  -...............  +..............  +..............  ...............
    Papua New Guinea.........  +...............  +...............  +...............  +...............  ...............  +..............  ...............
    Solomon Islands..........  +...............  ................  +...............  +...............  ...............  +++............  ...............
    Vanuatu..................  ++..............  ................  REIN............  REIN............  ...............  +..............  ...............
    FSM......................  +...............  ................  INT.............  REIN............  ...............  +..............  ...............
    Guam.....................  REIN............  ................  REIN............  REIN............  ...............  +..............  ...............
    Republic of Kiribati.....  +...............  ................  ................  +...............  ...............  +..............  ...............
    Marshall Islands.........  ++..............  ................  INT.............  +...............  ...............  ++.............  ...............
    CNMI.....................  REIN............  ................  REIN............  REIN............  ...............  -..............  ...............
    Palau....................  ++..............  +...............  ++..............  +...............  ...............  ++.............  ...............
    American Samoa...........  REIN............  ................  INT.............  INT.............  ...............  +..............  ...............
    Cook Islands.............  ................  ................  INT.............  INT.............  ...............  +..............  ...............
    French Polynesia.........  ................  ................  ................  ................  ...............  +..............  ...............
    Pitcairn Islands.........  ................  ................  ................  ................  ...............  ++.............  ...............
    Niue.....................  ................  ................  ................  ................  ...............  +..............  ...............
    Samoa....................  REIN............  ................  INT.............  INT.............  ...............  +..............  ...............
    Tokelau..................  ................  ................  ................  ................  ...............  +..............  ...............
    Tonga....................  REIN............  ................  +...............  REIN............  +..............  +..............  ...............

[[Page 60507]]

 
    Tuvalu...................  dd..............  ................  INT.............  -...............  ...............  +..............  ...............
    United States (Hawaii)...  ................  ................  ................  INT.............  ...............  INT............  ...............
    United States (Johnston    ................  ................  ................  dd..............  ...............  ...............  ...............
     Atoll).
    United States (Kingman     ................  ................  ................  ................  ...............  +..............  ...............
     Reef).
    United States (Wake        ................  ................  ................  dd..............  ...............  dd.............  ...............
     Atoll).
    Wallis and Futuna Islands  ................  ................  ................  ................  ...............  +++............  ...............
--------------------------------------------------------------------------------------------------------------------------------------------------------
Note: Species abundance categories are as follows. +++: Abundant (>100 ind ha-1), ++: Frequent (10-100 ind ha-1), +: Rare (<10 ind ha-1), -: Locally
  extinct, INT: Introduced to non-native location; REIN: Reintroduced (cultured specimens) to locations where the species had previously been
  extirpated; dd: Data Deficient (i.e., reports of species presence are not confirmed). Empty cells indicate locations where a species has not been
  observed.
\1\ Species names are abbreviated as follows: HH: H. hippopus, HP: H. porcellanus, TD: T. derasa, TG: T. gigas, TMB: T. mbalavuana, TS: T. squamosa,
  TSI: T. squamosina.

Extinction Risk Analysis

Methods

    In determining the extinction risk of each species, it is important 
to consider both the demographic risks facing the species, as well as 
current and potential threats that may affect the species' status. To 
this end, the status review synthesized the best available scientific 
and commercial data regarding the five threat categories listed in 
section 4(a)(1) of the ESA. These are: (1) the present or threatened 
destruction, modification, or curtailment of its habitat or range; (2) 
overutilization for commercial, recreational, scientific, or 
educational purposes; (3) disease or predation; (4) inadequacy of 
existing regulatory mechanisms; or (5) other natural or manmade factors 
affecting its continued existence. Second, we conducted a demographic 
risk analysis following the Viable Population (VP) approach derived 
from McElhany et al. (2000), which addresses four biological 
descriptors of species status: abundance, productivity (i.e., 
population growth rate), spatial distribution, and diversity. The VP 
approach reflects concepts that are well-founded in conservation 
biology and considers demographic factors that individually and 
collectively provide strong indicators of extinction risk. It is 
designed to both capture the biological symptoms of past threats that 
have contributed to the species' current status and provide insight 
into how the species may respond to present and future threats.
    With respect to each threat and each demographic risk factor, we 
assigned a qualitative score from 1 to 5 representing its estimated 
contribution to the species' extinction risk (``very low,'' ``low,'' 
``moderate,'' ``high,'' or ``very high'' risk). Detailed definitions of 
these risk levels can be found in the accompanying Status Review 
Report. We also assigned a confidence rating from 0 to 3, reflecting 
the quantity and quality of information used to assign the score, as 
follows: 0 = No confidence (i.e., no available information); 1 = Low 
confidence (i.e., very limited available information); 2 = Medium 
confidence (i.e., some reliable information available, but reasonable 
inference and extrapolation is required); 3 = High confidence (i.e., 
reliable information with little or no extrapolation or inference 
required).
    Lastly, all information from the threats assessment and demographic 
risk analysis was synthesized to estimate the overall risk of 
extinction for each species. For this analysis, we used three reference 
levels of extinction risk (``low,'' ``moderate,'' and ``high''), which 
are consistent with those used in prior ESA status reviews. ``Low'' 
risk indicates a species that is not at a moderate or high level of 
extinction risk (see ``Moderate'' and ``High'' risk below). A species 
may be at a low risk of extinction if it is not facing threats that 
result in declining trends in abundance, productivity, spatial 
structure, or diversity. A species at low risk of extinction is likely 
to show stable or increasing trends in abundance and productivity with 
connected, diverse populations. ``Moderate'' risk indicates a species 
that is on a trajectory that puts it at a high level of extinction risk 
in the foreseeable future (see ``High'' risk below). A species may be 
at moderate risk of extinction due to projected threats or declining 
trends in abundance, productivity, spatial structure, or diversity. 
``High'' risk indicates a species that is at or near a level of 
abundance, productivity, spatial structure, and/or diversity that 
places its continued persistence in question. The demographics of a 
species at such a high level of risk may be highly uncertain and 
strongly influenced by stochastic or depensatory processes. Similarly, 
a species may be at high risk of extinction if it faces clear and 
present threats (e.g., confinement to a small geographic area; imminent 
destruction, modification, or curtailment of its habitat; or disease 
epidemic) that are likely to create present and substantial demographic 
risks.
    Importantly, these extinction risk categories are not meant to be a 
direct translation of the final listing determination for the species, 
as listing determinations must also consider ongoing conservation 
efforts of any State, foreign nation, or political subdivision thereof 
(16 U.S.C. 1533(b)(1)(A)) to determine whether the species meets the 
ESA's definition of an ``endangered species'' or ``threatened 
species.'' Rather, the extinction risk assessment in the Status Review 
Report represents the scientific conclusion about the overall risk of 
extinction faced by the species under present conditions and in the 
foreseeable future based on an evaluation of the species' demographic 
risks and assessment of threats.

Defining the ``Foreseeable Future''

    The appropriate time horizon for evaluating whether a species is 
more likely than not to be at a high level of risk in the ``foreseeable 
future'' varies on a case-by-case basis. For example, the time horizon 
may reflect certain life history characteristics (e.g., long generation 
time or late age-at-maturity) and the time scale over which identified 
threats are likely to impact the biological status of the species. In 
other words, the foreseeable future represents the period of time over 
which we can reasonably determine that both future threats and the 
species' response to

[[Page 60508]]

those threats are likely. See generally 50 CFR 424.11(d). It does not 
necessarily need to be limited to the period that the species' status 
can be quantitatively modeled or predicted within predetermined limits 
of statistical confidence. Reliable projections may be qualitative in 
nature.
    With these criteria in mind, we determined that the ``foreseeable 
future'' for the following extinction risk analyses spans approximately 
~50-60 years. Based on what is known about the life history traits of 
giant clams, with longevity estimated to be at least 50 years (up to 60 
years for T. gigas), maturity ranges from 3 to 9 years, and exceedingly 
low recruitment, it would likely take at least this amount of time 
(i.e., multiple generations) for the effects of any management actions 
to be realized and reflected in population abundance indices. 
Similarly, the impact of present threats to the species would be 
realized in the form of noticeable population declines within this 
timeframe, as has been demonstrated in the available literature. As the 
primary operative threats to giant clams are overutilization for 
subsistence and commercial harvest, this timeframe would allow for 
reliable predictions regarding the impact of current levels of harvest-
related mortality on the biological status of all the species.
    One important exception to this timeframe is in regard to the 
future impacts and threats related to climate change. Based on the 
current standard for climate projections, under which most available 
models are extended to the end of the century, we use the same 
timeframe (i.e., present day-2100) to define the ``foreseeable future'' 
in assessing the likely future threat of climate-related habitat 
degradation and climate-related impacts to giant clam fitness.

Threats Assessment

    Below, we describe the natural and anthropogenic threats to each of 
the seven giant clam species within the framework of the five threat 
categories outlined in section 4(a)(1) of the ESA. Because a number of 
species occupy overlapping ranges and often co-occur in similar 
habitats, certain threats may apply to more than one species. In each 
section, we highlight the severity of the threat to each of the species 
affected and provide additional species-specific information where 
appropriate. Additional details may be found in the Status Review 
Report (Rippe et al., 2023).

The Present or Threatened Destruction, Modification, or Curtailment of 
Its Habitat or Range

    As is mentioned in the species descriptions above, giant clams are 
often closely associated with coral reefs, inhabiting all types of 
shallow-water reef ecosystems (i.e., fringing, barrier and atoll 
reefs), as well as various reef-adjacent habitats. However, there is no 
conclusive evidence that giant clams directly rely on live, pristine 
corals for their survival. Certain species are habitat generalists 
(e.g., T. squamosa, T. gigas)--they are often observed among live 
corals but can also be found in other habitats, which are not pristine 
coral reef (e.g., sand, rock, dead coral rubble, seagrass beds, 
macroalgae zones). Others are more specialized--T. mbalavuana is found 
exclusively at depth on reef slopes, T. derasa is found predominantly 
in offshore coral reef areas, while H. hippopus, H. porcellanus and T. 
squamosina tend to prefer sandy areas, shallow lagoon flats and 
seagrass beds adjacent to coral reefs.
    Available research on larval settlement preference offers some 
clues as to what may be driving the association with coral reefs. 
Several studies show that T. squamosa larvae prefer to settle on 
substrates of relatively high rugosity and are drawn to crustose 
coralline algae (CCA), but actively avoid settling on live coral 
(Courtois de Vicose, 2000; Calumpong et al., 2003; Neo et al., 2009). 
Additionally, the small giant clam (T. maxima) has shown an ability to 
discriminate between ``favorable'' and ``unfavorable'' habitats, 
preferring to settle near the effluent of conspecifics and near the 
effluent of live coral and CCA, rather than cyanobacteria and sponges 
(Dumas et al., 2014). However, this information is limited to only one 
of the seven species being analyzed in connection with this proposed 
rule, and there are no such data for species that are predominantly 
found in sand flats and seagrass beds, where rugosity is especially low 
and settlement cues might differ.
    Based on the known features of giant clam biology and larval 
development, Lucas et al. (1989) hypothesized that the proximity of 
giant clams to coral reefs is, to some extent, a result of two 
environmental requirements, which are maximized in shallow reef 
habitats: (1) high light conditions to support the photosynthetic 
nutrition that giant clams derive from their algal symbionts, and (2) 
substrate rugosity to provide cryptic settlement locations for 
vulnerable recruits and juveniles. While we cannot conclude that these 
factors are equally important to all species of giant clams, it is 
within the context of these two habitat requirements that we discuss 
the following threats to coral reef ecosystems and their potential 
impacts to giant clams.
Climate Change Impacts to Coral Reefs
    Reef-building corals typically occur in waters that range between 
25 [deg]C-30 [deg]C and are highly sensitive to temperature excursions 
outside of this range (Brainard et al., 2011). Prolonged exposure to 
high temperature anomalies can lead to coral bleaching, where the coral 
host expels its symbiotic zooxanthellae, leaving the tissue translucent 
and revealing its white skeleton underneath. Bleaching-associated 
mortality is quite variable and can depend on the duration and 
intensity of elevated temperatures, geographic location, bleaching 
history, species present, and other factors (Pandolfi et al., 2011; 
Putnam & Edmunds, 2011; van Hooidonk & Huber, 2012). Mild to moderate 
bleaching does not always lead to death; however, repeated and 
prolonged bleaching can cause widespread coral mortality on regional or 
global scales. Extreme summer temperature anomalies associated with 
strong El Ni[ntilde]o events have led to three recognized global 
bleaching events in 1997-98, 2009-10 and 2014-17 (Hughes, Kerry, et 
al., 2017; Lough et al., 2018; Eakin et al., 2019). The latest (2014-
17) was the longest and most severe global bleaching event in recorded 
history. It affected every major coral reef region and led to the 
mortality of one third of the Great Barrier Reef in Australia (Couch et 
al., 2017; Hughes, Kerry, et al., 2017; Hughes, Kerry, et al., 2018). 
In addition, many other regional-scale bleaching events over the last 
several decades have caused widespread coral mortality in reef 
communities throughout the Indo-Pacific (Brainard et al., 2011; Hughes, 
Anderson, et al., 2018).
    While coral bleaching patterns can be complex, there is a general 
consensus that rising global ocean temperatures have led to more 
frequent and severe coral bleaching and mortality events (Hughes, 
Anderson, et al., 2018; Lough et al., 2018). Without drastic action to 
curb greenhouse gas emissions, this trend is projected to continue 
throughout this century (van Hooidonk et al., 2016). Additionally, 
several studies have shown that warming can significantly increase 
coral susceptibility to disease (Bruno et al., 2007; Sokolow, 2009; 
Brainard et al., 2011; Howells et al., 2020). The combination of these 
warming-related impacts has already caused dramatic

[[Page 60509]]

declines in many coral species and changes to the composition and 
structure of coral reefs around the world (Brainard et al., 2011; 
Hughes, Barnes, et al., 2017; Hughes, Kerry, et al., 2018). During the 
major 2016 coral bleaching event on the Great Barrier Reef, for 
example, the fast-growing, structurally complex tabular and branching 
species suffered disproportionately (>75 percent mortality on heavily 
bleached reefs), shifting reef communities towards taxa with simpler 
morphological characteristics and slower growth rates (Hughes, Kerry, 
et al., 2018). Other studies similarly suggest that coral reef 
ecosystems, rather than disappear entirely as a result of warming, will 
likely persist, but with unpredictable changes to their community 
composition and ecological function (Pandolfi et al., 2011; Hughes et 
al., 2012).
    Coral reefs are also facing increasing risk from ocean 
acidification, the process by which atmospheric carbon dioxide 
(CO2) is absorbed into the surface ocean, resulting in 
reduced seawater pH and reduced availability of carbonate ions. Due to 
anthropogenic CO2 emissions, average surface ocean pH (total 
scale, pHt) has already decreased by more than 0.1 pHt units below the 
pre-industrial average of 8.17, and is expected to fall up to an 
additional 0.42 pHt units by 2100 under the worst-case emissions 
scenario from the Intergovernmental Panel on Climate Change (IPCC) (RCP 
8.5) (P[ouml]rtner et al., 2014).
    Such reductions in ocean pH could lead to drastic changes to the 
net calcification balance in many coral reef ecosystems. Numerous 
laboratory and mesocosm experiments have demonstrated a correlation 
between lower pH (or elevated partial pressure of CO2, 
pCO2) and decreased coral calcification rates (Anthony et 
al., 2008; Ries et al., 2009; Anthony et al., 2011; Gazeau et al., 
2013; Albright et al., 2018). Brainard et al. (2011) provide a table 
summarizing the existing literature on the topic (table 3.2.2 of the 
report), and for every species studied, net calcification rate either 
declines, or in very few, there is no significant effect. In a pair of 
controlled mesocosm experiments, net community calcification of a small 
enclosed coral reef was found to increase under enhanced alkalinity and 
decrease after the addition of CO2 (Albright et al., 2016; 
Albright et al., 2018), indicating that current levels of acidification 
are already impairing ecosystem-level calcification and will likely 
exacerbate this effect in the future. Coupled with dwindling coral 
cover due to warming-associated bleaching and mortality, continued 
acidification could transition many reef systems from net overall 
accretion to net erosion within this century (Eyre et al., 2018; 
Cornwall et al., 2021).
    Others anticipate that ocean acidification will also weaken the 
structural integrity of coral reefs, both by promoting the efficiency 
of bioeroding organisms and by reducing reef cementation (i.e., 
secondary processes of carbonate precipitation that bind the reef 
framework). Observations from coral reefs of the eastern Pacific, which 
occur in naturally low-pH upwelling zones reveal some of the highest 
rates of bioerosion documented globally, as well as poorly cemented, 
fragile, and unstable reef frameworks (Glynn, 1988; Eakin, 1996, 2001; 
Manzello et al., 2008). Crustose coralline algae (CCA) contribute 
significantly to reef cementation by consolidating loose rubble and 
sealing porous dead coral skeletons (Adey, 1998; Littler & Littler, 
2013). There is major concern that CCA may be among the most sensitive 
taxa to declines in seawater pH, because they build their skeletons 
with magnesium-rich calcite, a highly soluble form of carbonate 
(Andersson et al., 2008). Although some argue that the risk to CCA may 
be over-estimated, as certain aspects of their skeletal structure and 
biology have proven resilient to projected future conditions (Nash et 
al., 2013; Nash et al., 2015; Nash et al., 2016). At this point, the 
potential impacts of ocean acidification on CCA are not fully resolved.
    Given the documented and projected impacts of ocean warming and 
acidification on coral reef ecosystems, we assessed the direct 
implications of these impacts on the extinction risk of the seven giant 
clam species. In our previous status review for 82 species of corals, 
Brainard et al. (2011) concluded that ``the combined direct and 
indirect effects of rising temperature, including increased incidence 
of disease, and ocean acidification [. . .] are likely to represent the 
greatest risks of extinction to all or most of the candidate coral 
species over the next century.'' They assessed the threat of continued 
ocean warming to be ``highly certain'' and graded the threat as 
``high'' for most regions where the candidate corals are known to 
occur. Based on this assessment, we find it likely that live coral 
cover in general will continue to decline due to more frequent and 
severe bleaching events, and that ecosystem-scale calcification rates 
will decline as a result. Critically for giant clams, the negative 
impacts of warming are most pronounced in the fast-growing branching 
and tabular coral species, which are the primary contributors to the 
three-dimensional complexity of reef habitats. Thus, continued loss of 
live coral cover and of these coral species in particular will likely 
severely reduce the rugosity of future reef ecosystems. There is also 
evidence that ocean acidification will further inhibit calcification 
rates of living corals and weaken the structural integrity of the reef 
framework, although the magnitude of these effects is not clear. As 
with ocean warming, the primary implication of these effects for giant 
clams will be reduced habitat rugosity.
    Nevertheless, there are two important layers of uncertainty 
associated with these predictions, and especially their potential 
impacts to giant clam habitat. First, with respect to ocean 
acidification, carbonate chemistry is notoriously difficult to model 
precisely in open systems, as it relies on many physical and biological 
factors, including seawater temperature, proximity to land-based runoff 
and CO2 seeps, proximity to sources of oceanic 
CO2, salinity, nutrients, as well as ecosystem-level 
photosynthesis and respiration rates. The last factor, in particular, 
means that in many cases, daily fluctuations in pH or carbonate 
chemistry can significantly outweigh projected long-term changes to the 
average (Manzello et al., 2012; Johnson et al., 2019). Secondly, as 
mentioned above, there is very little research establishing the degree 
to which giant clams rely on coral reef rugosity and thus might be 
impacted by any reduction thereof. The few larval choice experiments to 
date suggest that T. squamosa prefers rough to smooth surfaces and is 
attracted to CCA. However, most giant clam species can be found in an 
array of habitat types, and some even seem to prefer areas of low 
rugosity, such as sand flats and seagrass beds (e.g., H. hippopus, H. 
porcellanus, and T. squamosina). No studies have quantified how or if 
giant clams might be affected under varying levels of coral reef 
complexity.
    If giant clams are sensitive to reductions in net ecosystem 
calcification and reef rugosity, the projected climate change-related 
impacts to coral reefs would likely pose a significant threat to T. 
derasa, T. gigas, T. mbalavuana, and T. squamosa within the foreseeable 
future, as these species are known to inhabit coral reef environments. 
We would expect decreased larval recruitment and juvenile survival 
across broad portions of their range. These early life stages are 
already known to suffer exceptionally

[[Page 60510]]

high mortality rates naturally, and any further reduction in 
productivity would greatly threaten the viability of remaining giant 
clam populations.
    However, without more information on the direct association between 
substrate rugosity and giant clam survival and productivity, it is 
difficult to estimate with any confidence the degree to which reef 
rugosity must decline to threaten the persistence of these species. 
Likewise, given the lingering uncertainty in the dynamics and effects 
of ocean acidification, it is not possible to estimate a timespan over 
which such a risk can be expected. Thus, while it is likely that 
continued ocean warming and acidification will drastically alter coral 
reef communities and reduce the rugosity of many reef habitats, we 
concluded that the potential effect on the quality or suitability of 
giant clam habitat cannot be confidently assessed.
Coastal Development
    The physical degradation of nearshore habitats due to coastal 
development poses an additional threat to giant clams throughout much 
of their range. Sedimentation associated with the construction and 
maintenance of coastal infrastructure can reduce the amount of suitable 
substrate available for larval settlement. There is extensive evidence 
for such an effect in corals--increased sediment load has been shown to 
deter larval recruitment (Babcock & Davies, 1991), reduce settlement 
success and survival (Hodgson, 1990; Babcock & Smith, 2002), and 
decrease the effectiveness of CCA to induce settlement (Ricardo et al., 
2017). We could not find any research directly investigating this 
effect in giant clams; however, similarities in the biology and 
behavior of giant clam larvae would suggest that comparable results can 
reasonably be expected. Like coral larvae, giant clam larvae prefer 
rough settlement surfaces and are likely deterred by unconsolidated, 
fine-grained silt that is typical of anthropogenic sedimentation. 
Moreover, CCA provide a similarly important settlement cue for giant 
clams (Courtois de Vicose, 2000; Neo et al., 2009; Neo et al., 2015), 
and a reduction in effectiveness would likely decrease larval 
recruitment and settlement success.
    Importantly, compared to habitat degradation due to climate change, 
coastal development poses a more localized threat to giant clam 
populations in specific regions. In the Red Sea, for example, Roa-
Quiaoit (2005) notes intense modification to the Jordanian coastline 
over ``four decades of rampant development of ports, industrial and 
tourism areas, as well as extreme events such as oil spills.'' Surveys 
of giant clam density in the area revealed an inverse relationship 
between the population density of T. squamosa and metrics of human 
impact and coastal use. The author argues that the observed 12-fold 
reduction of giant clam density in Jordan over three decades is in 
major part due to this intense habitat modification. Similar examples 
of anthropogenic impacts to the coastal environment have also been 
documented in many areas of the Indo-Pacific region, although this is 
often discussed in relation to the health of coral reef ecosystems. In 
Singapore, approximately 60 percent coral reef area was lost during the 
20th century due to land reclamation and associated sedimentation 
(Chou, 2006; Guest et al., 2008). On three specific Singapore reefs--
Tanjong Teritip, Pulau Seringat, and Terumbu Bayan--Neo and Todd (2012) 
note that giant clams were once found, but the areas have since been 
reclaimed (covered over) in their entirety. In addition, more than 20 
percent of coral reefs in Indonesia, 35 percent of reefs in Malaysia, 
25 percent of reefs in Papua New Guinea, and 60 percent of reefs in the 
Philippines are threatened by the impacts of coastal development, 
including runoff from construction and waste from coastal communities 
(Burke et al., 2012).
    In addition to undergoing intense coastal development activities 
over the past several decades, many of these areas are not well 
regulated with respect to coastal runoff and often do not prioritize 
sustainable management of the coastal environment (e.g., Gladstone et 
al., 1999; O. A. Lee, 2010). In contrast, the Great Barrier Reef in 
Australia and island nations of the central and western Pacific, two 
other important areas of giant clam distribution, likely do not suffer 
the same effects of coastal development. Australia strictly enforces an 
integrated management plan to protect the Great Barrier Reef from the 
effects of coastal land use change via numerous national and State 
regulations, and the relatively small populations of most Pacific 
island nations minimize the impact of coastal development on 
surrounding waters.
    Because T. mbalavuana and T. derasa reside preferentially in 
offshore coral reef areas, we conclude that habitat degradation of the 
nearshore environment related to coastal development likely does not 
pose a significant threat to these two species. With respect to H. 
hippopus, T. gigas, and T. squamosa, considering the relatively 
localized impacts of coastal development (e.g., near heavily urbanized 
areas) compared to the size of the species' ranges, we conclude that 
the threat of habitat destruction, modification, or curtailment related 
to nearshore impacts of coastal development likely poses a low risk to 
H. hippopus and T. gigas, and a very low risk to T. squamosa. 
Specifically, we find the risk to be lower for T. squamosa due to the 
species' expansive geographic range as well as its current abundance 
and distribution, compared to H. hippopus and T. gigas.
    Because the restricted range of H. porcellanus is centered in a 
region of intense urban development (i.e., within the densely populated 
Indo-Malay Archipelago), we conclude that habitat destruction and 
modification of the nearshore environment poses a moderate risk to the 
species. In other words, it likely contributes significantly to the 
species' long-term extinction risk, but given the localized nature of 
these impacts, does not in itself constitute a danger of extinction in 
the near future. H. porcellanus is also faced with an acute threat of 
habitat destruction in the northern portion of its range, where 
fishermen primarily from Tanmen, China have been razing shallow reef 
areas of the South China Sea in a search for giant clam shells (see 
Tanmen Destructive Shell Harvesting below). The damage from these 
operations is extensive and has likely eliminated any H. porcellanus 
that may have previously occurred in the islands of the South China 
Sea.
    With respect to T. squamosina, we considered reports indicating 
specific areas of the Red Sea coastline which have been targeted for 
development of tourist activities and infrastructure, including 
Hurghada and the Gulf of Aqaba coastline from Sharm el-Sheikh to 
Nuweiba (Egypt), Eilat (Israel), and Aqaba (Jordan). These areas are 
significant, as they directly overlap with the majority of recent T. 
squamosina observations. As is mentioned above, Roa-Quiaoit (2005) 
estimated that 70 percent of the Jordanian coastline has been developed 
into ports, industrial centers, and tourism areas over the past several 
decades. Additionally, near Hurghada, Mekawy and Madkour (2012) 
observed dredging activities associated with a newly-constructed harbor 
and offshore trash disposal from boats. The authors also described 
industrial and tourist activities in several other areas along the 
coast of mainland Egypt (e.g., oil drilling in El-Esh, dense industrial 
and tourism-related development near Safaga Harbor, high human activity 
in Quesir), which they argue have likely been the principal factors 
driving the

[[Page 60511]]

declining abundance of giant clams (primarily T. maxima) in these 
areas. Similarly, Hassan et al. (2002) reported ``major decreases in 
giant clam populations between 1997 and 2002, with many small clams 
seen in 1997 not surviving through to 2002.'' The authors attributed 
this population loss directly to sedimentation from major construction 
activities in South Sinai. While these studies address impacts to giant 
clams broadly, it is likely that T. squamosina experiences a similar 
threat in these areas. Lastly, Pappas et al. (2017) suggest that 
coastal development may, in combination with overutilization, explain 
the apparent absence of T. squamosina in the central Red Sea, but do 
not provide any data to support this claim.
    Thus, while we do not have any data specifically linking habitat 
destruction, modification, or curtailment with the abundance of T. 
squamosina, based on the species' distribution in nearshore habitats, 
documented evidence of the impact of coastal development on giant clam 
abundance generally, and ongoing regional development goals, we 
conclude that this threat poses a high risk to T. squamosina. In other 
words, we find that it contributes significantly to the species' long-
term extinction risk and is likely to contribute to its short-term 
extinction risk in the near future.
Tanmen Destructive Shell Harvesting
    Despite a relatively small geographic scope, giant clam shell 
harvesting in the South China Sea has caused severe destruction of 
shallow water habitats. In the last decade, the small fishing village 
of Tanmen in China's Hainan province became a regional epicenter for 
giant clam shell handicraft and trade (Hongzhou, 2016; Larson, 2016; 
Lyons et al., 2018). From 2012 to 2015, the number of retailers of 
giant clam shell handicraft increased from 15 to more than 460, the 
number of shell carving workshops increased from a dozen to more than 
100, and by the end of this period, it was estimated that this industry 
supported the livelihood of nearly 100,000 Tanmen residents (Hongzhou, 
2016; Bale, 2017; Wildlife Justice Commission, 2021).
    As the industry grew, many Tanmen fishermen increasingly abandoned 
the traditional fishing industry and shifted focus to giant clam shells 
as their primary livelihood. With local stocks of giant clams having 
been depleted by a long history of overharvesting, many fleets resorted 
to destructive methods of digging out large portions of coral reef 
using their boat propellers to access the shells of long-dead clams 
that had been buried under the reef substrate (Wildlife Justice 
Commission, 2021). As reported by V. R. Lee (2016), harvesting boats 
are anchored with a long rope or chain against which the propeller 
holds tension as it carves an arc-shaped scar in the reef (see also 
Wingfield-Hayes, 2015). The majority of this activity has occurred the 
South China Sea, and an analysis of satellite imagery revealed 
extensive damage in the Spratly Islands and Paracels, with an estimated 
160 km\2\ of coral reef in these areas completely destroyed by the 
combination of clam dredging and island-building activities (McManus, 
2017).
    In response to international pressures and following a 2016 
arbitral tribunal ruling that China was aware of and responsible for 
``severe harm to the coral reef environment'' in the South China Sea 
due in part to these activities (Permanent Court of Arbitration, 2016), 
steps were taken to halt destructive clam shell harvesting operations. 
China began to enforce anti-corruption measures aimed at undermining 
demand for the expensive jewelry and statues carved from giant clam 
shells (Bale, 2017), and in January 2017 the Hainan Province People's 
Congress passed new regulations that effectively banned the commercial 
trade of all giant clam species in Hainan (Wildlife Justice Commission, 
2021). However, while giant clam shell harvesting operations were found 
to decline significantly between 2016 and 2018, the Wildlife Justice 
Commission (2021) reports several lines of evidence to suggest that 
``illegal giant clam shell trade persists in China in a covert manner 
with one clear supply area'' (Hainan Province), and that a new influx 
of clam harvesting boats have returned since 2018. Thus, while the 
extensive damage to the habitat in this region would likely take 
several decades or more to undo if the ecosystems were allowed to 
recover, the ongoing threat of illegal harvesting is likely to prevent 
any substantial habitat recovery in the foreseeable future.
    This threat of habitat loss is relevant to the species that are 
known to occur in this region and that are typically found in reef flat 
environments where the harvesting operations primarily occur. This 
includes T. gigas, T. squamosa, H. hippopus, and most critically H. 
porcellanus, which has a highly restricted range centered in the 
Sulawesi region of Indonesia but that extends northward into the 
Philippines and portions of the South China Sea (Wells, 1997; bin 
Othman et al., 2010; Neo et al., 2017). As is mentioned above, the 
damage from these operations has likely eliminated any H. porcellanus 
that may have previously occurred in the islands of the South China 
Sea.

Overutilization for Commercial, Recreational, Scientific, or 
Educational Purposes

    The pervasive harvest of giant clams for subsistence and domestic 
sale, and several periods of short-lived but intensive commercial 
harvest have severely depleted giant clam populations throughout their 
respective ranges. Once the center of giant clam diversity in the 
region, the Philippines saw commercial exploitation of giant clams for 
the international shell trade decimate populations of H. hippopus, H. 
porcellanus, T. gigas, and T. squamosa. Similar trends have been 
observed throughout Southeast Asia (i.e., Indonesia, Singapore, 
Thailand, Cambodia, Vietnam, and in the South China Sea), where each of 
these species except T. squamosa is now considered rare or locally 
extinct (Neo et al., 2017). Likewise, illegal harvest of giant clams 
for the international clam meat trade, primarily by Taiwanese fishermen 
or to supply Taiwanese demand, severely reduced giant clam populations 
throughout the western and central Pacific. As a result, as in 
Southeast Asia, nearly all of the species (excluding T. squamosa) are 
now considered rare or extinct throughout most of their Pacific range 
(Wells, 1997; Neo et al., 2017). Although international demand 
(primarily for the aquarium trade) is increasingly met by the growing 
field of giant clam mariculture, wild-sourced clams are still observed 
in international trade, and the potential for laundering wild clams 
with mariculture-produced specimens cannot be discounted (Sant, 1995).
    Ongoing harvest for subsistence or domestic market supply, as well 
as persistent poaching, continues to limit substantial population 
recovery of giant clams throughout much of their range. As broadcast-
spawning organisms with little to no mobility, giant clams are reliant 
on sufficient population density to facilitate gamete fertilization. 
Thus, even if small populations of giant clams have survived the years 
of exploitation, in many cases individuals may be too dispersed to 
successfully reproduce. Furthermore, the largest individuals were often 
targeted for the meat and shell trade, leading to altered size 
structures in remnant giant clam populations. Juveniles and smaller 
adults are known to be more susceptible to predators and to exhibit 
lower reproductive output, which will likely continue to limit 
population recovery in the near future. It is for these reasons that we 
consider overutilization to be the most significant threat to all seven 
giant clam species. Below, we

[[Page 60512]]

summarize the threats posed by overutilization related to subsistence 
fisheries, domestic markets, international trade, and illegal poaching, 
highlighting specific details related to each affected species.
Subsistence Fisheries
    Giant clams have long been, and continue to be, an important 
component of traditional livelihoods and culture throughout their 
geographic range (Craig et al., 2011). As described by Lindsay et al. 
(2004), ``there are few locations within the Pacific where tridacnids 
are not gathered on a daily basis and found in local markets'' (Munro, 
1993a). Archaeological evidence from shell middens (piles of discarded 
shells), which can be found across the Indo-Pacific from as far back as 
2000 years ago (Swadling, 1977), as well as anecdotal accounts and 
local fishing practices all point to the importance of giant clam in 
Indo-Pacific diets (Neo & Loh, 2014). The shells of giant clams are 
also frequently carved for use as tools, containers, and ornaments 
(Copland & Lucas, 1988; Lucas, 1994).
    Because H. hippopus is unattached to the substrate and occupies 
nearshore habitats that are relatively accessible to humans, it is an 
easy target for reef gleaners (i.e., fishers that collect organisms by 
hand from nearshore sand and reef flats). Consequently, it has been a 
popular species for local harvest and consumption throughout its range. 
Many years of subsistence harvest have driven widespread population 
declines and local extirpations from many Pacific island nations and 
territories, including American Samoa, CNMI, and Guam.
    In Fiji, for example, Seeto et al. (2012) discovered H. hippopus 
fossils in shell middens from two Lapita-era settlements (1100-550 
B.C.), and found that shell size increased with midden depth, 
suggesting that human consumption contributed to population reductions 
and to its eventual extirpation. Surveys from Palau in the 1970s 
indicated that H. hippopus populations declined drastically as a direct 
result of overharvest (Bryan & McConnell, 1975). In Singapore, H. 
hippopus was considered rare historically (S. K. Lee, 1966; Dawson & 
Philipson, 1989), but consistent harvest pressure is thought to have 
prevented the species from establishing a sustainable population in the 
area and ultimately led to its extirpation (Neo & Todd, 2012). 
Additionally, H. hippopus continues to be exploited for consumption by 
coastal communities in Indonesia (Naguit et al., 2012), Malaysia (Neo & 
Todd, 2012), New Caledonia (Purcell et al., 2020), the Andaman and 
Nicobar Islands (Nandan et al., 2016), Papua New Guinea (Kinch, 2003), 
and virtually every other country where it occurs, except for Australia 
(Wells, 1997).
    H. hippopus has also been extirpated from American Samoa, CNMI, and 
Guam due to a long history of harvest for subsistence consumption and 
for sale in local markets (Munro and Heslinga, 1983; Sant, 1995; Wells, 
1997; Green and Craig, 1999; Pinca et al., 2010). According to Score 
(2017), giant clams have a ``special significance'' in American Samoa 
culture and are often used as offerings during family and community 
gatherings when available. Moreover, Cunningham (1992) describes the 
cultural significance of giant clams to the Chamorro people, who live 
throughout the Mariana Islands, including CNMI and Guam. The common use 
of H. hippopus as a source of food and to make tools likely led to its 
extirpation in these locations (Wells, 1997).
    Similar to H. hippopus, the tendency of H. porcellanus to occupy 
shallow nearshore areas make the species highly vulnerable to 
harvesting (Dolorosa et al., 2014). Heavy exploitation from both 
subsistence and commercial harvest has led to severe population 
declines throughout its range (Dolorosa et al., 2014; Neo et al., 
2017). Villanoy et al. (1988) determined that H. porcellanus was 
overexploited in the Philippines as early as the 1980s, and more 
recently, Rubec et al. (2001) reported that H. porcellanus has been 
depleted to such an extent that it is no longer commercially viable for 
harvest in the Philippines. Ultimately, while subsistence harvest was 
widespread, heavy fishing pressure on giant clam stocks in the 
Philippines for the commercial shell trade has been the primary cause 
of population decline, and has led to local extinctions throughout the 
region (see International Trade in Giant Clam Shells and Shell-Craft 
below).
    Because of their large size and fast growth rates, T. derasa and T. 
gigas have historically been two of the most widely exploited giant 
clam species for the consumption of their meat. Reports from throughout 
their ranges indicate that both species are harvested for subsistence 
consumption in nearly every location where they occur, with the major 
exception being the Great Barrier Reef and northwestern (NW) islands of 
Australia. There are certain Pacific island communities that attribute 
unique significance to T. gigas as a cultural symbol and place high 
value on the species as a food item for special occasions (Hviding, 
1993). The shell of T. gigas is also valued as a traditional resource 
among many coastal communities for use as basins or as personal or 
religious decorations (Juinio et al., 1987; Hviding, 1993; Lucas, 
1994). Both T. derasa and T. gigas are reported to have been extirpated 
from CNMI and Guam as a result of longstanding subsistence harvest 
(Wells, 1997; Pinca et al., 2010).
    Based on the best available scientific and commercial data, it is 
likely that past and current subsistence harvest has played a 
significant role in the low abundance of T. mbalavuana throughout its 
range. S. Lee et al. (2018) attributes its absence from areas outside 
of the eastern Lau group in Fiji to a combination of ecological factors 
and ``serial overfishing.'' Additionally, Lewis and Ledua (1988) 
reported that in Fiji, T. mbalavuana is occasionally harvested 
unintentionally with T. derasa, due to the similarity in appearance 
between the two species. In Tonga, T. mbalavuana has traditionally been 
harvested for subsistence consumption and to supply domestic markets 
(Ledua et al., 1993), and although its occurrence in deeper areas may 
have offered some protection from harvest historically, the advancement 
of SCUBA and hookah gear has facilitated greater access to previously 
inaccessible stocks (Lewis & Ledua, 1988; Lucas et al., 1991; Neo et 
al., 2017). Interviews with a number of traditional fishermen indicated 
that the abundance of T. mbalavuana in Tonga had declined considerably 
during their lifetimes (Ledua et al., 1993). Harvest of giant clams for 
subsistence consumption and domestic markets is ongoing and largely 
unregulated in Fiji and Tonga.
    Compared to the more common T. maxima and T. crocea (that are not 
themselves subject to this rulemaking), which often co-occur with T. 
squamosa, T. squamosa is typically larger and easier to physically 
remove from the reef, which makes it highly susceptible to harvest, 
particularly in shallow nearshore areas. For this reason, T. squamosa 
is an important resource in subsistence fisheries in nearly every 
location across its range, and in several locations, it is the 
preferred giant clam species for meat consumption (Neo et al., 2017). 
Few exceptions include Australia, where giant clam harvest is strictly 
prohibited, and remote areas where the distance from human settlements 
and infrastructure limits accessibility. However, in most locations 
where the species occurs, longstanding subsistence harvest has 
reportedly driven widespread population declines (Neo et al., 2017).

[[Page 60513]]

    There are several studies that provide some insight as to the 
impact of past and current harvest on the abundance of the T. 
squamosina in the Red Sea. Paleolithic artifacts indicate that modern 
humans have been exploiting mollusks in the Red Sea for at least 
125,000 years (Richter et al., 2008). During this time, Richter et al. 
(2008) found that giant clam communities in the Red Sea have changed 
dramatically from before the last interglacial period (122,000 to 
125,000 years ago), when T. squamosina constituted approximately 80 
percent of the shell remains, to T. squamosina comprising less than 5 
percent of shells in freshly discarded shell middens. While the authors 
acknowledge that variable recruitment rates and mortality among the 
three Red Sea giant clam species may be attributed to natural 
disturbances, a concurrent decline in the size of giant clam shells 
strongly suggests that overutilization has played a significant role 
(Richter et al., 2008). In general, giant clam stocks in the Red Sea 
(including T. maxima, T. squamosa, and T. squamosina) have declined to 
less than 5 percent of their historical abundance in the 1980s and 
1990s, largely due to artisanal reef-top gathering for meat and shells 
(Richter et al., 2008).
    As with H. hippopus and H. porcellanus, the distribution of T. 
squamosina in shallow, nearshore habitats makes it particularly 
accessible to reef-top gatherers and exacerbates the threat of 
overutilization. Bodoy (1984) reported that giant clams had been 
subject to ``heavy exploitation in the vicinity of Jeddah, Saudi 
Arabia, and they [were] often collected on the reef flat, both for food 
and for decorative purposes.'' Additionally, two firsthand accounts 
from Gladstone (2000, 2002) described the harvest of ``a significant 
number of clams'' (primarily T. maxima, which is not subject to this 
rulemaking) from the Kharij As Sailah and Kharij Al Qabr areas of the 
Farasan Islands, noting that ``clams were easily harvested in the 
shallow reef flats.'' Overall, the best available scientific and 
commercial data suggest that giant clams have been harvested 
extensively in the Red Sea for many years, and given their traditional 
importance in the diets of coastal communities, harvest is likely 
ongoing in most areas of the Red Sea.
Domestic Markets (Meat and Shells)
    In areas where giant clams were historically abundant, commercial 
fisheries often developed alongside subsistence harvesting to supply 
the local demand for giant clam meat and shells. In Fiji, T. squamosa 
and T. derasa were harvested by small-scale commercial operations and 
sold in 11 municipal markets or other direct sales outlets (Lewis et 
al., 1988). From 1979-1987, annual sale of giant clam meat in the 
domestic market ranged between 6 and 42 tons (Adams, 1988; Lewis et 
al., 1988; Wells, 1997). With respect to both species, Lewis et al. 
(1988) reported that the commercial harvest had driven once abundant 
populations to low densities, particularly near major urban centers.
    Local markets also exist in a number of other Pacific countries and 
territories, although data on giant clam meat are often not reported at 
the species level. This is because of the difficulty in identifying the 
species once the meat is harvested since the shells are often left in 
the water, or because giant clam meat may have been mixed together or 
recorded collectively with other shellfish products when it was landed. 
Wells (1997) reported varying prices for giant clam meat from markets 
in American Samoa, the Solomon Islands (amounting to about 1 tonne of 
giant clam meat sold per year), the Marshall Islands (H. hippopus and 
T. squamosa), Niue, Vanuatu, Samoa, and FSM, where in 1990, 3.66 tonnes 
of giant clam meat were sold in the main markets of Chuuk. Data 
collected over a 10-week period in Tonga suggested that annual landings 
of giant clam meat for the domestic market might be 639-1,346 kg 
(Tacconi & Tisdell, 1992). Wells (1997) noted that in Jepara, 
Indonesia, giant clam meat was often sold dried, suggesting that the 
lack of fresh meat may be due to local overutilization of stocks. In 
Myanmar, clam meat was often marketed fresh for local consumption 
(Munro, 1989).
    Additional reports indicate that domestic markets have continued in 
many of these localities into at least the early 2000s. In 1998-1999, 
nearly six tonnes of giant clam products were sold at a single market 
in Samoa (Skelton et al., 2000). Giant clam meat was still reported to 
be sold openly at markets in Malaysia as of 2003 (Shau-Hwai & Yasin, 
2003). Until bag limits were established in 2009, the declared 
commercial catch of giant clams in New Caledonia varied between 1.5 and 
9 tonnes per year. This included T. derasa, T. squamosa, and H. 
hippopus, and the authors indicate that it is often the adductor muscle 
that is sold in stalls of local markets. In the decade since the bag 
limits were put in place, commercial catch has fallen below 2 tonnes 
per year (Purcell et al., 2020). Kinch and Teitelbaum (2010) report 
that a high demand for giant clams to supply the local market in Tonga 
``has resulted in the over-exploitation of giant clam stocks in some 
areas.'' In Papua New Guinea, Kinch (2003) attributes sparse 
populations of giant clams to commercial harvest, particularly that of 
Brooker Islanders. From January to September 1999, the author recorded 
the total sales of giant clam adductor muscle from Brooker Islanders to 
a local fishing company, which included 551 kg (or 1,970 clams) of 
specimens under 400 g and 146 kg (or 170 clams) greater than 400 g. 
Notably, nearly one-third of the T. gigas individuals included in these 
sales were not full-grown adults, which likely had an effect on the 
future productivity of those populations. Similarly, harvesting of 
giant clams for sale and subsistence use in Vanuatu has led to severely 
reduced populations that are ``now considered close to collapse in many 
locations despite the presence of suitable habitats for juveniles and 
adults'' (Dumas et al., 2012).
    Domestic markets for giant clam shells are often related to the 
tourism industry. In the Andaman and Nicobar Islands of India, Nandan 
et al. (2016) report that giant clams, including T. squamosa and H. 
hippopus, are fished for the tourism-based ornamental shell industry. 
Additionally, in Thailand, giant clams shells are usually first sold to 
local traders in Phuket, and then sold to tourists as ornamental shells 
or various shell crafts (e.g., ashtrays, soap trays, lamps) 
(Chantrapornsyl et al., 1996). Shells have also been a popular souvenir 
for tourists visiting beach and resort areas of the Philippines and 
Indonesia (Tisdell, 1994). At the Pangandarin and Pasir Putah beach 
resorts in Java, Indonesia, as many as 39 and 35 giant clam shells, 
respectively, were available for sale in 2013, despite a prohibition on 
the harvest and sale of giant clams (except under ``exceptional 
circumstances'') under Indonesian law since 1987 (Nijman et al., 2015).
    Prior to this prohibition, a major industry based on the use of 
giant clam shells for production of floor tiles (a.k.a, `teraso' tiles) 
led to the extensive harvest of giant clams in Indonesian waters. While 
much of the shell material was dead shells of T. derasa and T. gigas 
buried in reef flats, living specimens were known to be taken when 
found (Lucas, 1994). As described by Lucas (1994), there were tile 
production centers at Jakarta, Semarang, Bali, Manado, and likely 
Suabaya in the early 1980s, and clam shell trade routes had developed 
throughout the Indonesian islands to supply the industry. The best 
estimates of giant clam shell import to the Semarang tile production 
center from the nearby Karimun Jawa islands varied between about 20 and 
200 tonnes per month over the period 1978-1983 (Brown & Muskanofola, 
1985). At the

[[Page 60514]]

Jakarta production center, the clam shell trade was estimated to reach 
at least 600 tonnes per month in 1982 (Usher, 1984 cited in Lucas, 
1994). This industry is no longer active in Indonesia as a result of 
the 1987 prohibition; however, it is likely that such intense demand 
contributed significantly to the depletion and current rarity of T. 
derasa and T. gigas in Indonesian waters and limited any potential for 
their recovery. Moreover, despite regulatory protection, all species of 
giant clams remain heavily exploited in Indonesia for their meat and 
shells, and some for the live aquarium trade (Neo et al., 2017). As a 
result of this overutilization, the larger giant clam species are now 
thought to occur in only a few locations archipelago-wide (Hernawan, 
2010).
International Trade of Giant Clam Meat and Poaching
    While giant clam meat is consumed throughout the Indo-Pacific 
region, Taiwan has consistently had the largest market and demand for 
giant clams. Some of the earliest references indicate that giant clams 
around Taiwan were depleted many decades ago (Pearson, 1977; Tisdell & 
Chen, 1994). As local stocks were rapidly exhausted, Taiwanese vessels 
began to range farther from their home ports, and from the 1960s to the 
mid-1980s, a surge of Taiwanese fishing vessels began illegally 
entering the waters of other Pacific nations in search of giant clam 
adductor muscle, particularly from the larger species, T. gigas and T. 
derasa (Munro, 1993a; Kinch & Teitelbaum, 2010). Occasionally, these 
vessels operated under agreements with local communities in exchange 
for resources (Adams, 1988), but in the vast majority of cases, giant 
clams were harvested illegally and to an unsustainable degree (Lucas, 
1994; Kinch, 2002). The clam poachers progressively worked their way 
through the Pacific, typically concentrating their efforts on 
uninhabited islands and reefs where giant clam stocks had been 
virtually untouched and where local surveillance was limited. Reports 
of Taiwanese poaching include areas of the Philippines, FSM, Indonesia, 
Papua New Guinea, the Solomon Islands, Australia (the Great Barrier 
Reef), Palau, Fiji, Kiribati, and the Marshall Islands (Dawson & 
Philipson, 1989; Sant, 1995).
    Data on the landings of giant clam meat in Taiwan are generally 
unavailable due both to their illegal nature and because in the 
records, landings were combined with meat of other marine molluscs and 
collectively referred to as `ganbei' or `compoy' (Lucas, 1994; Tisdell 
& Chen, 1994). Tisdell and Chen (1994) report that imports of ganbei 
ranged from 9 tons in 1977 to 621 tons in 1988. Other estimates of 
giant clam adductor muscle landings in the 1960s and 1970s range 
between 100 and 400 tons per year (Carlton, 1984; Dawson & Philipson, 
1989). Dawson and Philipson (1989) estimated that during the peak of 
the Taiwanese fishery for giant clams, harvest did not likely exceed 
100 tons of adductor muscle per year, though Munro (1989) regarded this 
to be an underestimate. Accounting for the potential harvest of the 
smaller species, T. derasa and H. hippopus, which have an adductor 
muscle about one-third the weight of T. gigas, those landings 
correspond to 300,000 to 450,000 clams per year. According to Dawson 
(1986), ``it seems certain [. . .] that the total illegal harvest of 
giant clams over the twenty-odd years that such activities have 
occurred in the region can safely be measured in the millions.''
    Poaching by long-range Taiwanese vessels peaked in the mid-1970s 
and gradually declined during the 1980s as the extension of exclusive 
economic zones, improved surveillance of reef areas, boat seizures, and 
depleted stocks made the fishery less profitable (Lucas, 1994). In 
addition, growing pressure from many Indo-Pacific nations forced the 
Taiwanese government to take stricter actions against giant clam 
harvesters (Dawson, 1986). The last five `compoy' (i.e., clam and other 
shellfish) fishing licenses were rescinded by the Taiwanese government 
in 1982, mainly due to pressure from the Australian government, and 
beginning in 1986, the Taiwanese government began rejecting all 
requests for approval of Taiwanese involvement in any clam fishing 
activities, regardless of whether foreign agreement or license 
documents were provided. There is evidence, however, that some poaching 
activities continued in remote locations. From 1982 to 1987, at least 
four Taiwanese vessels were apprehended on outlying reefs of the 
Solomon Islands, in each case carrying clam meat from tens of thousands 
of giant clams (Govan et al., 1988). The authors note that the small 
size of the adductor muscles recovered indicates that large clams had 
likely already been harvested from the reef at an earlier date.
    Even as Taiwanese poaching operations declined, the demand for 
giant clam meat in Taiwan persisted, incentivizing the development of 
legal commercial fisheries for export throughout the Indo-Pacific 
(Lewis et al., 1988; Basker, 1991; Lucas, 1994). It was estimated that 
imports of adductor muscle to Taiwan from these newly formed fisheries 
totaled approximately 30-40 tons in 1987 and 1988 (Tisdell & Chen, 
1994). The fisheries, however, rapidly depleted local stocks and were 
in most cases short-lived, typically being shut down by local 
authorities in the span of a few years. In the Maldives, for example, 
commercial harvest of giant clams began in June 1990 and continued 
until early in 1991. Two buyers were operating and collectively 
harvested over 90,000 individuals; one buyer exported 9.8 tons to a 
Taiwanese buyer (Basker, 1991). Concerned over the high exploitation 
rate, the Ministry of Fisheries and Agriculture conducted an assessment 
of the giant clam stocks and fishery, and the resulting report 
recommended closing off high density areas to further fishing and other 
restrictions (Basker, 1991). The commercial fishery was subsequently 
closed, and collection of giant clams remains prohibited in the 
Maldives. Likewise, a commercial fishery in Papua New Guinea reportedly 
removed at least 85 tons of adductor muscle over a 5-year period, 
equivalent to over 750 tons total flesh weight, until it was closed due 
to depleted stocks (Munro, 1993a).
    Adams (1988) described one example of the impact of extreme 
commercial harvesting pressure in Fiji when a ship named `Vaea' 
intensively harvested giant clam stocks in 1985. Teams of two 
harvesters on Hookah gear reportedly caught 50-250 clams per day. At 
one site, harvesters had taken approximately 80 percent of the standing 
stock of T. derasa, or nearly 15,000 individuals, from an area of 25.9 
square miles down to a depth of 20 meters. Adams (1988) estimated that 
harvesting rates averaged 70 percent of the total living stock at each 
reef, less for scattered populations and more for denser ones. From 
1984 to 1987, T. derasa catch rates in Fiji varied between 20 and 40 
tons of flesh per year, half of which was exported (Adams, 1988). The 
Fijian fishery as a whole (including municipal markets, wholesale and 
retail outlets, and exports) landed over 149 tons during this period, 
with the largest annual harvest reaching 49.5 tons in 1984, the year in 
which exports began (Lewis et al., 1988).
    By the early 1990s, pervasive stock depletions across the Indo-
Pacific severely limited Taiwanese imports of giant clam meat (Tisdell 
and Chen, 1994). In the years since, many countries in the region have 
banned commercial export of giant clams, some have imposed size and/or 
bag limits, and many have become signatories to the Convention on 
International Trade in Endangered Species of Wild Flora and Fauna 
(CITES). The regulatory

[[Page 60515]]

implications of CITES participation are discussed more thoroughly below 
in the section on Inadequacy of Existing Regulatory Mechanisms, but one 
of its requirements is that Parties must submit an annual report of 
their trade in CITES-listed species, including the number and type of 
permits and certificates granted, the countries involved, and the 
quantities and types of specimens traded. All species of giant clams 
have been listed under appendix II of CITES since 1985, and we can 
therefore rely to some extent on trade statistics from the CITES 
reporting database to characterize more recent patterns in the 
international market for giant clams.
    In most cases, countries have limited their reporting to the family 
or genus level, and outside of a few instances of trade reported for T. 
derasa, T. gigas, and T. squamosa, no other species were identified 
specifically. Additionally, of all the transactions reported from 1983 
to 2020, 50.4 percent and 39.5 percent were en route to New Zealand and 
the United States, respectively, while Japan, Singapore, and Australia 
comprised the remaining 10.1 percent of imports. Law Enforcement 
Management Information System (LEMIS) trade data provided by USFWS for 
the period 2016-2020 indicate that nearly all of the imports of giant 
clam meat over the past 5 years were classified to be of `Personal' 
nature, likely representing shipments intended for families or friends 
of Pacific islanders (Shang et al., 1994). Prior to 2000, there are 
several years in which countries reported significant export of meat 
from giant clams that had been born or bred in captivity. This includes 
3615 kg and 472 kg of T. gigas and T. derasa meat, respectively, 
exported from Solomon Islands in the 1990s, 1695 kg of T. derasa meat 
exported from Palau in 1990-1991, and 65 kg of T. gigas meat exported 
from Australia.
    A number of other countries have reported significant export of 
giant clam meat (species unknown) since the late 1990s, primarily to 
New Zealand and the United States. Nearly all of these exports are of 
wild-caught specimens, many of which have been seized or confiscated at 
the border due to improper or missing CITES export permits. The major 
exporters of giant clam meat in the last two decades include the Cook 
Islands, Kiribati, Marshall Islands, FSM, and Tonga. At the higher end, 
Tonga has exported an average of 1210 kg giant clam meat per year since 
2005, and at the lower end, the FSM has averaged 58 kg per year during 
the same period.
    Importantly, a number of the key countries in the trade of giant 
clam meat are not CITES contracting parties (e.g., Cook Islands, 
Kiribati, Marshall Islands, FSM) or have only become so relatively 
recently (e.g., Palau in 2004, Solomon Islands in 2007, Tonga in 2016). 
Thus, any trade reported for these countries is based on values 
reported by the CITES party involved, and any trade among two non-
contracting nations is not included in these estimates. Additionally, 
the USFWS Office of Law Enforcement in Honolulu, Hawaii has reported 
that approximately 450 lbs (200 kg) of giant clam meat per year is 
refused (i.e., seized, confiscated, or re-exported) from Tonga, FSM, 
and the Marshall Islands (K. Swindle, USFWS, pers. comm., December, 
2017). This is likely a significant underestimate of the total amount 
of giant clam meat that comes into the United States (as a whole) 
illegally, as many shipments outside of those that pass through 
Honolulu likely make it past enforcement inadvertently (K. Swindle, 
USFWS, pers. comm., December, 2017). For these reasons, the CITES data 
should be viewed as incomplete, and the reported quantities are likely 
an underestimate of the total trade in giant clam meat.
International Trade in Giant Clam Shells and Shell-Craft
    Giant clam shells have been used for a variety of decorative and 
utilitarian purposes, including as beads, vases, lamps, ashtrays, and 
wash basins. H. hippopus and T. squamosa are considered the most 
popular giant clam species for the shell trade (Shang et al., 1994) 
because of their unique physical characteristics (e.g., attractive 
colors, bowl-like shape, etc.), although nearly all of the species have 
been harvested depending on the intended use, cultural preference, or 
geographic availability.
    The Philippines has historically operated as the largest exporter 
of giant clam shells and shell-craft, accounting for over 95 percent of 
the global exports of giant clam shell products from 1983 to 2020. 
During the peak of the shell trade from 1979 to 1992, total exports 
from the Philippines surpassed 4.2 million kg (Juinio et al., 1987; 
Wells, 1997). While all species of giant clam that occur in the 
Philippines have been exploited, the two Hippopus spp. and T. squamosa 
were the most frequently used for ornamental purposes and handicrafts, 
and T. gigas was most frequently used for basins (Lucas, 1994). Juinio 
et al. (1987) noted that T. derasa may have also been harvested but was 
often not distinguished by shell dealers as a separate species; rather, 
it was known as a ``heavier variety'' of T. gigas or H. porcellanus.
    Export records from the Philippines Bureau of Fisheries and Aquatic 
Resources indicate an initial peak in 1979, when 1,003 tonnes of giant 
clam shells were exported, corresponding to 895,000 shell pairs. 
Exports then declined to a minimum of 63 tonnes (or 67,000 shell pairs) 
in 1982, which was thought to reflect saturation of the international 
demand. Juinio et al. (1987) reported that the demand for giant clam 
shells could be met from existing stock piles (except those of H. 
porcellanus, which was still considered to be highly marketable). 
However, exports began to increase again in the late 1980s and peaked 
in 1991 with nearly 1.2 million shells, over 460,000 carvings, and over 
1,186 tonnes of shells (equivalent to about 825,000 shell pairs) 
exported in a single year (Wells, 1997). This occurred despite the 
government of the Philippines instituting a ban on the export of giant 
clams (except T. crocea, not subject to this rulemaking) in 1990. In 
the following year, exports declined to 374,000 shells and 70,000 
carvings, likely due to the issuance of CITES Notification No. 663 (16 
January 1992) urging all CITES Parties to refuse trade permits for 
Tridacninae products from the Philippines, in accordance with 
Philippine legislation (Wells, 1997). In the three decades since 1992, 
reported exports of giant clam shells from the Philippines have been 
considerably lower (but not absent), totaling only 8,528 shells and 
6,359 carvings (CITES Trade Database, accessed 22 Mar 2022).
    Ultimately, widespread subsistence harvest in conjunction with the 
heavy fishing pressure on giant clams to supply the commercial shell 
trade decimated the populations of several giant clam species (e.g., H. 
hippopus, H. porcellanus, T. gigas, and T. squamosa), with local 
extinctions widespread throughout the Philippines (Juinio et al., 
1987). Wells (1997) reported that exports until 1992 were dominated by 
H. hippopus, T. squamosa, and H. porcellanus, with H. hippopus 
comprising 53 percent of shell exports and 94 percent of carvings. Even 
the few remaining locations thought to be the species' last strongholds 
in Philippine waters (e.g., in the Sulu Archipelago and Southern 
Palawan) were overharvested by the mid-1980s (Villanoy et al., 1988). 
Presently, five of the seven giant species considered here (H. 
hippopus, H. porcellanus, T. derasa, T. gigas, and T. squamosa) can 
still be found in the Philippines and they are all protected by 
Philippine law. Native T. gigas populations are restricted to small 
portions of Tubbataha Reefs Natural Park in very low abundances; T. 
derasa,

[[Page 60516]]

H. hippopus, and H. porcellanus are considered rare, and T. squamosa is 
considered frequent (Neo et al., 2017).
    The United States, Japan, Australia and various European countries 
have historically been the largest importers of shells and shell-craft 
from the Philippines (Juinio et al., 1987; Wells, 1997). The United 
States alone has accounted for over 50 percent of shells and over 60 
percent of shell carvings imported between 1983 and 2020. More 
recently, however, dwindling giant clam populations as well as greater 
regulatory protections in many countries have limited the shell trade 
among the traditional major importers of the 1980s. Instead, the 
majority of international trade has shifted increasingly to illegal 
means. From 2016 to 2020, the global trade in giant clam shells based 
on CITES reports totaled 65,129 shells and 221 shells carvings 
(primarily T. gigas), of which over 92 percent originated in Indonesia 
and over 97 percent was imported by China. This has occurred despite a 
prohibition on the harvest and export of giant clams under Indonesian 
law since 1987. While not at the same scale as the Philippines, 
Indonesia has participated in the trade of giant clam shells and shell 
products since the 1980s. Once giant clams were listed as protected 
species in 1987, Tisdell (1992) suggested that unrecorded exports of 
giant clam shells continued to occur from Indonesia to the Philippines. 
Likewise, several reports in the years since indicate that enforcement 
of the harvest and export ban remains grossly insufficient and, as is 
suggested by the CITES reports, substantial export of giant clam shells 
from Indonesia is ongoing (Allen & McKenna, 2001; Nijman et al., 2015; 
Harahap et al., 2018).
    Presently, the largest market for giant clam shells is in the city 
of Tanmen, in the southern Chinese Province of Hainan. As discussed 
previously, a major shell-crafting industry developed in this region 
during the 2000s. During the peak of the Tanmen shell-crafting industry 
in 2013-2014, there were an estimated 150 processing workshops 
supplying 900 craft shops with giant clam shell products in the 
province (Wildlife Justice Commission, 2021). The annual sales revenue 
of giant clam shell handicrafts in 2014 was estimated to be $75 million 
USD (Lyons et al., 2018). In January 2017, the Hainan Province People's 
Congress passed new regulations banning the commercial trade of giant 
clams in Hainan. However, investigations conducted 2 years later by the 
Wildlife Justice Commission (2021) found that there were still more 
than 100 craft shops in Tanmen, although fewer than 20 percent were 
still in business. Giant clam shell products were also being sold 
openly in hundreds of stores in other parts of the Hainan Province, 
such as Haikou, Sanya, Guangdong and Fujian provinces, and could be 
ordered on social media platforms, such as WeChat, for delivery to 
other locations (Wildlife Justice Commission, 2021). This has been 
corroborated by first-hand news reporting from Scarborough Shoal in 
April 2019, which documented ongoing shell harvesting by fishing boats 
flying the Chinese flag (ABS-CBN News, 2019). The ABS-CBN film crew 
captured many large piles of extracted giant clam shells around the 
harvesting area, some even extending above the water surface.
    This industry primarily targets the shells of deceased clams 
embedded in the reef substrate; however, live clams are also taken 
whenever found. Large shells in particular are of the highest value, 
putting the remaining T. gigas populations in the area at the greatest 
risk. According to Lyons et al. (2018), ``the more valuable [T. gigas] 
pieces come with a certificate of origin, specifying, for example, that 
it comes from Scarborough Shoal, Spratlys, or Paracels and, 
occasionally, even the specific reef concerned.'' This suggests that T. 
gigas shells are considered to have different grades or qualities 
depending on where in the South China Sea they were harvested. As a 
result of this intense market demand in combination with the 
destructive shell harvesting methods described above, Gomez (2015) 
noted that T. gigas is now ``virtually extinct'' in the center of the 
South China Sea, including the Paracels, the Macclesfield Banks, and 
the Spratlys.
International Trade of Live Giant Clams for Aquaria
    The largest current market for giant clams is that of live 
specimens for the aquarium trade and, to a lesser extent, to supply 
broodstock for mariculture operations. It can be difficult to 
distinguish the purpose of live specimen transactions from CITES 
reports alone, but Wells (1997) concluded ``that the aquarium trade is 
now the main market for both wild-collected and mariculture clams.'' In 
the 25 years since that report, the market for giant clams as aquarium 
specimens has continued to grow, with giant clams now representing one 
of the most desired groups of invertebrates in the aquarium industry 
(Wabnitz et al., 2003; Teitelbaum & Friedman, 2008; Mies, Dor, et al., 
2017). They are a sought-after commodity and have been described as a 
``must have'' item by collectors and aquarium hobbyists (Lindsay et 
al., 2004). The smaller, more brightly colored species (i.e., T. maxima 
and T. crocea, species not subject to this rulemaking) are by far the 
most popular in the marine ornamental trade, but T. squamosa, T. gigas, 
T. derasa, and H. hippopus are also traded in smaller numbers (Lindsay 
et al., 2004; Kinch & Teitelbaum, 2010).
    CITES records indicate that the primary source countries for the 
seven species considered here include Australia, Palau, Vietnam, 
Solomon Islands, and Marshall Islands, among others. Notably, the vast 
majority of giant clams exported from Australia, Palau and Marshall 
Islands have been bred/born in captivity and thus pose less risk to 
wild populations; however, much of the export volume from Vietnam, 
Solomon Islands, Tonga, and more recently, Cambodia, are of wild-
sourced specimens.
    Of the seven species considered here, T. derasa and T. squamosa 
have been the most popular in the trade of live specimens, according to 
CITES reports. Comparing the two, exports of T. derasa have been higher 
from Pacific island nations, such as Palau, Solomon Islands, Marshall 
Islands, Tonga, and FSM. Nearly all recent trade of this species is of 
captive-bred/born individuals, with wild harvest in these countries 
contributing minimally, if at all, by 2010. T. squamosa, by comparison, 
has been harvested more often by countries in Southeast Asia, such as 
Vietnam, Cambodia and Indonesia, and many of the recent exports from 
Vietnam and Cambodia are of wild-sourced individuals. Exports from 
Vietnam peaked in the 2000s and have declined over the last decade, 
while exports from Cambodia have increased more recently, reaching 
nearly 10,000 T. squamosa specimens in 2019. Neo et al. (2017) notes 
that the decline in exports from Vietnam is related to trade 
restrictions implemented in response to concerns and regulations 
sourcing wild specimens, and it is possible that some giant clams from 
Vietnam have been re-routed for export through Cambodia. In fact, 
according to CITES reports, over 99 percent of the recorded T. squamosa 
exports from Cambodia were imported by Vietnam, implying a close trade 
connection between the two nations. Neither H. hippopus nor T. gigas 
have been harvested consistently for the aquarium trade, although with 
respect to T. gigas, Craig et al. (2011) attributed this to a lack of 
available supply rather than a decline in demand. Because of declining 
populations throughout much of its range, the majority T. gigas

[[Page 60517]]

specimens for the aquarium trade in the late 2000s were being sourced 
from just a few small island nations, primarily Tonga (Craig et al., 
2011). However, according to CITES records, trade of T. gigas from 
Tonga has not occurred since 2011. T. gigas is not considered to be 
native to Tonga, but had reportedly been introduced there as part of 
stock enhancement and aquaculture programs (Munro, 1993a; Wells, 1997). 
According to a CITES assessment in 2004, the introduced populations of 
T. gigas had by that point died out, so it is not clear where the 
exported specimens originated (CITES, 2004a).
    The United States has consistently been one of the top import 
markets for live giant clams, along with Canada, several countries in 
Europe, Japan and Hong Kong (Wabnitz et al., 2003; Craig et al., 2011). 
In 2002, 70 percent of the giant clams exported for the aquarium trade 
went to the United States (Mingoa-Licuanan & Gomez, 2002 cited in Craig 
et al., 2011). According to CITES reports from 1983-2020, the United 
States has accounted for 24.2 percent of the total recorded imports of 
H. hippopus, 53 percent of imports of T. derasa, 56 percent of imports 
of T. gigas, 38.4 percent of imports of T. squamosa, and 12.8 percent 
of imports of Tridacninae specimens that were not identified to the 
species level. Throughout the full record since 1983, 50.6 percent of 
the imports to the United States were recorded as captive-bred/born 
specimens, while 44.7 percent were recorded as wild-sourced; however, 
according to LEMIS data for the period 2016-2020, wild-sourced 
specimens now represent only 4 percent of imports, with captive-bred/
born specimens accounting for the remaining 96 percent.
Summary of Risks to Specific Species Due to Overutilization for 
Commercial Purposes
    After considering the best available scientific and commercial data 
presented above and in the Status Review Report, we reached several 
different conclusions regarding the threat of overutilization for 
various commercial purposes to the seven giant clam species considered 
here. We summarize these conclusions of the risks for this threat 
category for each species below.

H. hippopus

    A long history of subsistence harvest punctuated by two decades of 
intense commercial exploitation for the shell and shell-craft industry 
have led to severe declines of H. hippopus populations throughout its 
range. As is mentioned above, H. hippopus has been one of the most 
popular giant clam species in the international shell trade because of 
its size and physical characteristics (e.g., attractive colors, bowl-
like shape) (Shang et al., 1994). The Philippines operated as the 
largest exporter of giant clam shells in the 1970s and 1980s, with H. 
hippopus being the most frequently traded species during this time. 
According to CITES annual report data, over 277,000 kg, 341,000 shell 
pairs, 2 million ``shells'' (without associated units), and 1.7 million 
shell carvings of H. hippopus were exported from the Philippines from 
1985 to 1993. This period of intense harvest left H. hippopus severely 
depleted throughout the Philippines and much of Southeast Asia, where 
it remains at very low abundance except in a few isolated areas.
    While most countries have imposed prohibitions on the commercial 
exploitation of giant clams and CITES records indicate that recent 
international trade of H. hippopus is minimal, subsistence harvest 
continues to pose a threat to the species in most populated areas where 
it occurs. Without more thorough monitoring from many of these 
locations, it is difficult to determine if this ongoing harvest is 
causing further population declines, but at the very least, it is 
likely preventing any substantial rebound of depleted populations 
throughout its range. An important exception is Australia, where 
anecdotal reports suggest that strictly enforced harvest bans have been 
largely successful in preventing overutilization and protecting 
reportedly healthy stocks of this species. For these reasons, and 
considering the documented effects of past harvest for the 
international shell trade on species abundance, we conclude that 
overutilization of H. hippopus contributes significantly to the 
species' long-term risk of extinction.

H. porcellanus

    As is mentioned above, heavy fishing pressure on H. porcellanus in 
the Philippines for the commercial shell trade has been the primary 
cause of population decline, and has led to local extinction of the 
species throughout the region (Juinio et al., 1987). Villanoy et al. 
(1988) documented the export volume of giant clam shells from one major 
shell dealer in the Zamboanga region of the Philippines, San Luis Shell 
Industries. From 1978 to 1985, approximately 413,230 pairs of shells 
were exported by this company, of which about 37 percent (or nearly 
153,000) were H. porcellanus. Based on comparisons to data provided by 
Juinio et al. (1987), the authors estimate that this shell dealer 
accounted for approximately 18.5 percent of the estimated total export 
volume of giant clam shells from the Zamboanga region during this 
period, suggesting that the total harvest of H. porcellanus during this 
period was likely much higher. According to CITES annual reports, from 
1985 to 1992, the Philippines exported an additional 576,298 H. 
porcellanus shells, 145,926 shell pairs, 179,043.5 kg of shell 
material, 293,110 shell carvings, and 38,138 kg of shell carvings. All 
were either reported to be wild-caught or did not include the source of 
harvest. No other nation reported export volumes close to this 
magnitude during this time. Malaysia reported the export of 500 kg of 
shell material in 1985, and Indonesia reported the export of 100 kg of 
shell material in 1986, but there are no other CITES reports relating 
to H. porcellanus from these two countries. CITES reports also indicate 
that 16 H. porcellanus were exported as live specimens from the 
Philippines to Norway and Germany in 1992 and 1997, respectively; there 
have been no exports of live H. porcellanus specimens since. 
Additionally, export of 35 live specimens from the Solomon Islands to 
Germany and the United States was reported in 1997, but this is likely 
a reporting error, as this species has not been observed in the Solomon 
Islands.
    In Indonesia, H. porcellanus is extremely rare. It was 
historically, and still is reportedly, exploited for its meat and 
shells when it is found (Pasaribu, 1988; Neo et al., 2017). 
Consequently, the species is now thought to occur in only a few 
locations in Indonesia (Hernawan, 2010; Wakum et al., 2017). Likewise, 
H. porcellanus abundance is also declining in Malaysia, in part due to 
ongoing harvest of meat and shells (Neo et al., 2017). As they are 
considered rare and are restricted to Sabah and Pulau Bidong on the 
east coast of Peninsular Malaysia, continued harvest likely threatens 
the persistence of these populations. Additionally, international 
poaching continues to pose a threat, as authorities from both Malaysia 
and the Philippines reported an increase in the number of fishing boats 
illegally harvesting giant clams as recently as 2010-2015 (Neo et al., 
2017).
    Overall, it is clear that intense historical commercial demand for 
H. porcellanus led to severe population declines and the current low 
abundance of the species throughout its range. Furthermore, ongoing 
subsistence harvest and poaching of giant clams throughout the South 
Asia region continue to threaten the few

[[Page 60518]]

populations of H. porcellanus that remain. Accordingly, we conclude 
that overutilization is contributing significantly to the long-term 
extinction risk of H. porcellanus and is likely to contribute to short-
term extinction risk in the near future.

T. derasa and T. gigas

    Due to the similarities of the threat to T. derasa and T. gigas, we 
present the conclusions for these two species together. Overall, the 
best available scientific and commercial data indicate that both T. 
derasa and T. gigas have been widely exploited for many years for their 
meat, shells, and as popular aquarium specimens. Many consider T. gigas 
to be the most heavily exploited among all giant clams (Craig et al., 
2011; Mies, Scozzafave, et al., 2017; Neo et al., 2017), noting its 
extensive harvest for its meat and shells in nearly every location 
where it has occurred. Similarly, T. derasa is also highly valued as a 
food source throughout the entirety of its range. For over two decades, 
both species were subject to an intense commercial demand for the meat 
of their adductor muscle, primarily from consumers in Taiwan. 
Widespread harvest and poaching to supply this commercial market caused 
severe, documented population losses throughout the majority of the 
species' ranges. The commercial demand for giant clam meat began to 
decline by the end of the 1980s due to the low abundance of remaining 
populations in conjunction with stricter harvest regulations and 
improved enforcement. However, due to their traditional importance as a 
food source in many cultures, subsistence harvest of T. derasa and T. 
gigas continues in most locations throughout their respective ranges, 
which may lead to further population decline and likely prevents any 
substantial recovery of depleted populations.
    Furthermore, recent CITES records and available reports indicate 
that T. gigas shells continue to be traded in high volumes from 
Indonesia to China despite a prohibition on the harvest and export of 
giant clams that has been in place under Indonesian law since 1987 
(Allen & McKenna, 2001; Nijman et al., 2015; Harahap et al., 2018).
    The Great Barrier Reef and outlying islands of NW Australia are, 
for the most part, an exception to the range-wide trends for these 
species. Northern areas of the Great Barrier Reef were subjected to 
widespread poaching of T. derasa and T. gigas in the 1970s and 1980s, 
but improved surveillance of Australian fishing grounds and stronger 
enforcement of harvest bans reduced the poaching pressure considerably. 
As a result, harvest of the two species in Australian waters since the 
1980s has likely been minimal. Recent quantitative estimates of 
abundance are scarce, but based on past surveys and the strong 
protective measures in place, most experts consider the Great Barrier 
Reef to have relatively large, stable populations of giant clams, 
including T. derasa and T. gigas (Neo et al., 2017; Wells, 1997).
    Overall, we consider the severe impact of past harvest on species 
abundance range-wide alongside reports of ongoing subsistence and 
commercial use in most locations except Australia. Based on this 
information, we conclude that overutilization of T. derasa and T. gigas 
contributes significantly to the species' long-term extinction risk. 
However, because the threat is minimal in Australia, which represents a 
substantial proportion of suitable habitat within these species' 
respective ranges, and where populations are reportedly healthy, this 
factor likely does not constitute a danger of extinction to the two 
species in the near future.

T. mbalavuana

    As is discussed above, harvest of giant clams for subsistence 
consumption and domestic markets is ongoing and largely unregulated in 
Fiji and Tonga. Thus, given the highly restricted range and general 
scarcity of T. mbalavuana, we conclude that the threat of 
overutilization for commercial purposes contributes significantly to 
the species' long-term extinction risk and is likely to contribute to 
the short-term risk of extinction in the near future.

T. squamosa

    T. squamosa has been harvested extensively for both subsistence and 
commercial purposes for several decades, which has led to documented 
population declines in many areas of its range (Neo et al., 2017). 
While most countries have imposed prohibitions on the commercial 
exploitation of giant clams, the demand for T. squamosa in the 
ornamental aquarium market continues to pose a threat to wild 
populations in Cambodia and Vietnam. Additionally, subsistence harvest 
is ongoing in most populated areas where the species occurs. Without 
more thorough monitoring from many of these locations, it is difficult 
to determine if this ongoing harvest is causing further population 
declines, but at the very least, it is likely preventing any 
substantial rebound of depleted populations throughout its range. As 
with other species, an important exception is Australia, where 
anecdotal reports suggest that strictly enforced harvest bans have been 
largely successful in preventing overutilization and protecting 
reportedly healthy stocks of giant clams. For these reasons, and 
considering the documented effects of past harvest on species 
abundance, we conclude that overutilization of T. squamosa contributes 
significantly to the species' long-term risk of extinction, but does 
not in itself constitute a danger of extinction in the near future.

T. squamosina

    The best available scientific and commercial data suggest that 
giant clams (including T. squamosina) have been harvested extensively 
in the Red Sea for many years. Given their traditional importance in 
the diets of coastal communities, harvest is likely ongoing in most 
areas of the Red Sea. In combination with the natural accessibility of 
T. squamosina in shallow nearshore areas, this past and ongoing harvest 
pressure has likely contributed significantly to the exceptionally low 
abundance of this species throughout the region. We are aware of 30 
documented observations of T. squamosina since its re-discovery in 
2008. This includes 17 specimens from the Gulf of Aqaba and northern 
Red Sea (Roa-Quiaoit, 2005; Richter et al., 2008; Huber & Eschner, 
2011; Fauvelot et al., 2020), seven individuals from the Farasan 
Islands in southern Saudi Arabia (Fauvelot et al., 2020; K.K. Lim et 
al., 2021), and six individuals from an unnamed site in the southern 
Red Sea (Rossbach et al., 2021). As an indication of its exceptionally 
low abundance at present, Rossbach et al. (2021) surveyed 58 sites 
along the entire eastern coast of the Red Sea, from the Gulf of Aqaba 
down to southern Saudi Arabia, and observed six T. squamosina at only 
one survey site in the southern Red Sea. Similarly, Pappas et al. 
(2017) did not encounter any T. squamosina at nine survey sites in the 
central Red Sea. With so few T. squamosina remaining, we conclude that 
this factor is likely to contribute to short-term extinction risk in 
the near future.

Disease or Predation

    There are a number of infectious diseases and parasites that have 
been reported in giant clams, most often either bacterial or protozoan 
in origin (Braley, 1992; Mies, Scozzafave, et al., 2017). Bacterial 
infections are most often caused by Rickettsia sp., which infect the 
ctenidia (gill-like respiratory organ) and the digestive lining of the 
clam (Norton et al., 1993; Mies, Scozzafave, et al., 2017). Protozoan

[[Page 60519]]

infections are often caused by either Marteilia sp. or Perkinsus spp. 
Giant clams with Marteilia infections show no external symptoms, but 
the infection will eventually cause superficial lesions on the kidney 
(Mies, Scozzafave, et al., 2017).
    Perkinosis, also known as pinched mantle syndrome, is caused by 
Perkinsus spp. Giant clams typically do not exhibit any symptoms of the 
infection until they become immunosuppressed due to some other 
environmental stress. At that point, the protozoan population is able 
to proliferate, and in some cases causes mortality of the host clam. 
Once the clam dies, trophozoites of Perkinsus spp. become waterborne 
and can infect nearby individuals (Mies, Scozzafave, et al., 2017). A 
significant rate of infection by Perkinsus spp. was previously observed 
at several sites on the Great Barrier Reef, with 38 of 104 sampled 
individuals (including T. gigas and H. hippopus) being infected (Goggin 
& Lester, 1987). Additionally, several Perkinsus infections were 
observed in association with a mass mortality of giant clams at Lizard 
Island in Australia in 1985; however, the cause of the death was never 
determined and the infections may have been coincidental (Alder & 
Braley, 1989).
    Giant clams are also affected by external parasites, including 
snails, sponges, and algae. Pyramidellid snails are particularly 
invasive, exploiting the clams by inserting their proboscises (i.e., 
feeding appendage) into the clam tissue and consuming the hemolymph 
within the siphonal mantle (Braley, 1992). On rare occasions, the 
snails may prove fatal to juvenile clams, but they are unlikely to 
cause mortality in adult clams (Mies, Scozzafave, et al., 2017). Other 
external parasites (i.e., sponges and algae) are typically more of a 
nuisance to giant clams rather than fatal infestations. For instance, 
boring sponges (e.g., Cliona) may drill holes into the clam's shells, 
and algae (e.g., Gracilaria sp.) may overcrowd the shell and prevent 
the mantle from extending, but neither of these parasites typically 
cause mortality (Mies, Scozzafave, et al., 2017).
    When disease is present, giant clams exhibit physical symptoms that 
are usually quite obvious, including a retracted mantle (typically the 
initial symptom), a gaping incurrent siphon (indicative of more 
advanced disease), and discarding of the byssal gland (Mies, 
Scozzafave, et al., 2017). While some diseases may respond to 
antibiotics, concentrations and dosages for giant clams have not been 
well studied. Overall, the prevalence and severity of disease likely 
vary across the extensive range of giant clams, but there is no 
information to indicate that disease is an operative threat to giant 
clams to the extent that it is significantly increasing the extinction 
risk of the species addressed here.
    Much of what is known regarding predation of giant clams has been 
learned from the ocean nursery phase of mariculture activities, when 
juveniles are outplanted to their natural environment (Govan, 1992). 
Giant clams are widely exploited as a food source on coral reefs, with 
75 known predators that employ a variety of attack methods (see table 3 
in Neo, Eckman, et al. (2015) for a comprehensive list). These 
predators are largely benthic organisms, including balistid fishes, 
octopods, xanthid crabs, and muricid gastropods (Govan, 1992). The 
fishes (e.g., wrasse, triggerfish, and pufferfish) prey on both 
juvenile and adult giant clams by biting the mantle edge, the exposed 
byssus, or extended foot. Other predators (e.g., crabs, snails, and 
mantis shrimp) have been observed chipping, drilling holes into, and/or 
crushing the shells of smaller individuals (see review in Neo et al. 
2015). Heslinga et al. (1984) observed several instances of predation 
firsthand in association with giant clam culturing operations in Palau. 
Large muricid snails (Chicoreus ramosus) were found to attack, kill, 
and eat T. squamosa specimens up to at least 300 mm shell length, and a 
single hermit crab was able to crush 26 T. gigas juveniles (20-30 mm) 
when inadvertently left in the culture tank. The authors also noted 
circumstantial evidence of predation by Octopus spp. in Palau based on 
the characteristically chipped shells of giant clams often observed 
outside of octopus dens.
    Giant clams employ a suite of defense mechanisms, both 
morphological and behavioral, to resist predatory attacks (Soo & Todd, 
2014). For example, their large body size, small byssal orifice, and 
strong shells create physical barriers to predation. In addition, T. 
squamosa is equipped with hard, scaly projections on its shell known as 
scutes that have been shown to provide protection from crushing 
predators (Han et al., 2008). Giant clams also exhibit behavioral 
defense mechanisms, such as aggregation, camouflage, rapid mantle 
withdrawal (Todd et al., 2009) and squirting water from siphons (Neo & 
Todd, 2010). While the ability of giant clams to endure intense 
predation pressure and acclimate to repeated disturbance can have 
implications on their survival, these attributes have not been studied 
extensively (Soo & Todd 2014). Similar to disease, we find no evidence 
to indicate that predation presents a significant threat to the 
extinction risk of the giant clam species addressed here.

The Inadequacy of Existing Regulatory Mechanisms

    Giant clams are protected from overutilization to varying degrees 
by a patchwork of regulatory mechanisms implemented by the many 
countries, territories, and Tribal entities within their range. These 
local-scale measures are also supplemented by CITES international trade 
regulation, and in some areas, by multi-national initiatives aimed at 
supporting sustainable regional giant clam fisheries. We address each 
of these regulatory mechanisms in the following section and also 
include a brief discussion of international climate change regulations 
in the context of their potential effects on the extinction risk of 
giant clams. More detailed information on these management measures can 
be found in the accompanying Status Review Report (Rippe et al., 2023).
Local Regulations
    There is national legislation in place in more than 30 countries 
and territories specifically related to the conservation of giant 
clams. Many also provide indirect protection via marine parks and 
preserves or ecosystem-level management plans. In general, management 
of giant clam populations has been most effective in Australia, where 
early harvest prohibitions and strict enforcement have been largely 
successful in stabilizing giant clam population declines and limiting 
illegal poaching (Wells et al., 1983; Dawson, 1986; Lucas, 1994). Many 
Pacific island nations have also implemented strict measures to 
mitigate fishing pressure on giant clams. These include total bans on 
commercial harvest and export of giant clams (e.g., Fiji, Papua New 
Guinea, Solomon Islands, Vanuatu, FSM, Guam, Republic of Kiribati and 
Palau), minimum size limits for harvest (e.g., French Polynesia, Niue, 
Samoa, American Samoa, Guam, and Tonga), harvest quotas or bag limits 
(e.g., New Caledonia, the Cook Islands, and Guam), and gear 
restrictions on the use of SCUBA or certain fishing equipment 
(Andr[eacute]fou[euml]t et al., 2013; Kinch & Teitelbaum, 2010; Neo et 
al., 2017). We are not aware of any local regulations in place 
restricting the harvest of giant clams in CNMI, although the harvest of 
all coral reef-associated organisms in Guam and CNMI is managed under 
the 2009 Fishery Ecosystem Management Plan for the Mariana Archipelago.

[[Page 60520]]

    In many Pacific islands, national legislation is also supplemented 
or enforced by way of customary fishing rights and marine tenure 
systems. This is the case in parts of Fiji, Samoa, Solomon Islands, 
Cook Islands, Papua New Guinea, and Vanuatu, where indigenous village 
groups hold fishing rights and regulate access to adjacent reef and 
lagoon areas (Govan et al., 1988; Fairbairn, 1992a, 1992b, 1992c; 
Wells, 1997; Foale & Manele, 2004; Chambers, 2007; UNEP-WCMC, 2012). 
The rights of each Tribal group over its recognized fishing area 
include the right to carry out and regulate subsistence fishing 
activities. In certain circumstances, a local village or villages may 
impose temporary area closures to reduce harvesting pressure and allow 
giant clam stocks to recover (Foale & Manele, 2004; Chambers, 2007).
    The effectiveness of these measures to address overutilization, 
however, is variable, and with limited capacity for long-term 
monitoring programs in the region, it can be difficult to properly 
assess. In general, anecdotal reports indicate that giant clam 
populations throughout the Indo-Pacific region continue to face severe 
stress (Neo et al., 2017).
    In the Philippines, for example, numerous reports following the 
giant clam export ban in 1990 suggested problems with enforcement, 
particularly within Badjao communities. The Badjao people live a 
predominantly seaborne lifestyle and are spread across the coastal 
areas of the southern Philippines, Indonesia, and Malaysia, with a 
total population estimated to be around one million (Government of the 
Philippines National Statistics Office, 2013; Rincon, 2018). Many in 
these communities were encouraged by buyers to collect and stockpile 
giant clam shells in the hope that the ban on giant clam export would 
eventually be lifted (Salamanca & Pajaro, 1996; Wells, 1997). Middlemen 
would reportedly advance money and provisions to fishermen on the 
condition that the shells be sold to them exclusively. The Badjaos 
would then harvest clams, consume or discard the meat and stockpile the 
shells (Salamanca & Pajaro, 1996). The non-compliance was exacerbated 
by varying interpretations of the law by Philippine authorities, who 
issued numerous CITES export permits in 1991-1992 under the presumption 
that the law excluded `pre-ban stock' (Wells, 1997). The ban was 
ultimately never lifted, and CITES reports indicate that the legal 
export of giant clams has ended in the Philippines. However, a recent 
report by the Wildlife Justice Commission (2021) found that authorities 
have continued to find stockpiles of giant clam shells throughout the 
country. Authorities have made 14 seizures from 2016 to 2021, including 
of a 132,000-ton stockpile in the southern Philippines in October 2019 
and several stockpiles in the Palawan area, one of the centers of giant 
clam abundance in the region. It is unclear how many of the shells were 
collected prior to the ban in 1990 versus how many were collected 
illegally in the years since, but it suggests that the market for giant 
clam shells remains active more than 30 years after the ban was 
instituted. In an interview with ABS-CBN News (2021), Teodoro Jose 
Matta, executive director of Palawan Council for Sustainable 
Development, claimed that the clams are being smuggled to Southeast 
Asia and Europe and attributed the activities to a criminal syndicate 
operating across the Philippines, not just in Palawan. To our 
knowledge, these claims have not been corroborated by authorities.
    Similar confusion over giant clam harvesting regulations has 
impeded the effectiveness of regulations to address overutilization in 
Papua New Guinea. An initial ban on the purchase and export of wild-
caught giant clams was put in place in 1988 by the Department of 
Environment and Conservation (DEC) (Kinch, 2002; UNEP-WCMC, 2011). It 
was lifted in 1995 following the development of a management plan for 
sustainable harvest; however, Kinch (2002) noted that although the 
Milne Bay Province Giant Clam Fishery Management Plan had been drawn up 
by the National Fisheries Authority (NFA)--the CITES Scientific 
Authority for Papua New Guinea--it was never officially adopted ``owing 
to confusion between the NFA and the DEC over responsibility for the 
enforcement of the plan and because of opposition from commercial and 
political interests.'' The ban was reinstated in 2000 following reports 
that a local fishing company was exporting wild-caught specimens as 
captive-bred. Kinch (2002) suggested that further ``conflict and 
confusion between the fisheries and environmental legislation'' ensued 
and recommended that it be addressed to ensure success of the 
regulation. Unfortunately, the last known monitoring survey in Papua 
New Guinea was conducted in 1996 in the Engineer and Conflict Island 
Groups. Based on survey findings, it was estimated that the overall 
density of giant clams (all local species) had declined by over 82 
percent since the early 1980s, while the density of T. gigas had 
declined by over 98 percent (Ledua et al., 1996). Without more recent 
data, we cannot determine whether the regulatory actions have had any 
effect on this trajectory.
    Furthermore, despite various levels of harvest and export 
prohibitions among many of the Pacific island nations, Kinch and 
Teitelbaum (2010) highlight a number of common challenges to ensuring 
sustainable giant clam management in these communities. This includes a 
lack of capacity for conducting stock assessments, promoting giant clam 
mariculture, enforcing harvesting regulations, and monitoring and 
actively managing giant clam harvest. The list also includes a lack of 
education and awareness among community members about sustainable giant 
clam harvest, uncoordinated legislative structure, and a lack of 
international collaboration to promote a sustainable and scalable 
market for captive-bred giant clams. According to the assessment by 
Kinch and Teitelbaum (2010), each of the countries experiences these 
challenges to a different degree, but overall it highlights the 
difficulties in effectively managing giant clam populations for smaller 
island nations that may lack enforcement resources or expertise. This 
is compounded, in many cases, by the traditional importance of giant 
clams as a coastal resource, which may limit the willingness among 
indigenous communities to adopt the recommended practices (Neo et al., 
2017).
    In addition to the two examples above, there are a number of other 
reports highlighting the inadequacy of local regulations to address the 
threat of overutilization throughout Indo-Pacific region. In Malaysia, 
and particularly in Borneo, illegal collection of giant clams was 
reported to occur despite a national prohibition on the collection of 
giant clams (Ibrahim & Ilias, 2006). In the Solomon Islands, commercial 
harvest and export was banned in 1998, but CITES records indicate that 
export of wild-sourced clams and shells from the Solomon Islands has 
continued to occur throughout the 2000s and as recently as 2015. Yusuf 
and Moore (2020) note that despite being fully protected under 
Indonesian law and widespread public awareness of associated harvest 
prohibitions, giant clams are still harvested regularly in the Sulawesi 
region of Indonesia, including mass collections for traditional 
festivals. When asked about enforcement of legal protections, locals 
explained that surveillance in certain areas was generally absent (or 
at best sporadic and ineffective), and throughout the region was 
``minimal, often perceived as misdirected and/or unfair, and mostly

[[Page 60521]]

ineffective.'' Due in part to the ineffectiveness of the existing 
regulations, Yusuf and Moore (2020) have documented progressive 
declines in giant clam populations from 1999 to 2002, 2007, and 2015, 
with ``some larger species (T. gigas, T. derasa, T. squamosa, and H. 
porcellanus) no longer found at many sites.'' Low abundance of T. 
squamosa, T. derasa, T. gigas, and H. hippopus has also been observed 
in the Anambas Islands of Indonesia, where Harahap et al. (2018) report 
ongoing harvesting and habitat destruction. In Mauritius, giant clams 
are protected under the Fisheries and Marine Resources Act of 2007, but 
a recent study shows continued population declines even within marine 
protected areas (Ramah et al., 2018). There are few studies 
highlighting success of local regulations, but Rossbach et al. (2021) 
report based on interviews with local fishermen that giant clams are no 
longer targeted in Saudi Arabia since a harvest prohibition was imposed 
in the early 2000s. Although we note that giant clams were listed as 
``Taxa of High Conservation Priority'' in Saudi Arabia's First National 
Report to the Convention on Biological Diversity in 2004 (AbuZinada et 
al., 2004), we could not find any national regulations associated with 
this designation.
    The general lack of long-term monitoring data makes it difficult to 
evaluate the effectiveness of local regulatory mechanisms to address 
threats from overutilization for commercial purposes beyond relying on 
anecdotal reports. In many areas, for example, harvest prohibitions 
have been instituted within the last decade or two, but there have been 
few, if any, follow-up surveys conducted in the time since. However, 
using what survey data are available, we can infer that existing 
regulations have been inadequate to protect any of the seven giant clam 
species from overutilization. Despite widespread commercial export 
bans, the capacity for enforcing existing regulations is often limited, 
existing regulations do not restrict continued subsistence harvest in 
many locations, and illegal harvest and trade of giant clams 
(particularly for the shell trade) continues to occur (Kinch & 
Teitelbaum, 2010; Yusuf & Moore, 2020; Wildlife Justice Commission, 
2021). For these reasons, we conclude that the inadequacy of local 
harvest regulations to address overutilization associated with 
subsistence fisheries and illegal harvest in all locations outside of 
Australia contributes significantly to the long-term extinction risk of 
H. hippopus, T. derasa, T. gigas, and T. squamosa. Moreover, 
considering the exceptionally low abundance and restricted ranges of H. 
porcellanus and T. mbalavuana, we conclude that the inadequacy of local 
harvest regulations to address overutilization associated with 
subsistence fisheries likely also poses a short-term risk of extinction 
for these species in the near future.
    With respect to T. squamosina, we also considered the likely effect 
of marine protected areas (MPAs), which are the principal regulatory 
mechanism relevant to the protection of giant clams from 
overutilization in the Red Sea. Based on the known distribution of T. 
squamosina, there are three MPAs that are most relevant to the species: 
Ras Mohammed National Park in South Sinai, Aqaba Marine Park in Jordan, 
and the Farasan Islands Protected Area in southern Saudi Arabia. These 
are three areas where T. squamosina has previously been observed, and 
remaining populations likely benefit from the prohibitions against 
hunting or collecting wildlife within the boundaries of the MPAs. 
According to Gladstone (2000), a prohibition on the collection of giant 
clams in the Farasan Islands appeared to be effective, with harvest-
related mortality falling to 1.7 percent, compared to an estimated 
11.1-47.8 percent mortality rate prior to the regulation. Ras Mohammed 
National Park is also regarded as effective in the protection of 345 
km\2\ of marine area, which includes important fringing reef habitats 
in the southern portion of the Gulf of Aqaba.
    Collectively, however, these three protected areas encompass only a 
small fraction (5,756 km\2\) of the coastal marine area in the Red Sea. 
Throughout most of the region, harvest of giant clams remains largely 
unregulated. As is described above, historical harvest of giant clams 
has likely led to the exceptionally low abundance of T. squamosina in 
the Red Sea, and there are reports that harvest is ongoing in most 
locations. Thus, given the lack of national regulations pertaining to 
the harvest of giant clams in the Red Sea, we find that an inadequacy 
of existing regulatory mechanisms to address the threat of 
overutilization contributes significantly to the long-term extinction 
risk for T. squamosina. However, because several MPAs have been 
established in key areas where the species has been recently observed, 
we conclude that this factor does not in itself constitute a danger of 
extinction in the near future.
Regulations for International Trade
    Giant clams are listed under appendix II of CITES, which consists 
of species that ``are not necessarily now threatened with extinction, 
but may become so unless trade is closely monitored.'' This designation 
does not necessarily limit trade of the species, but instead requires 
that any species in trade has been legally acquired and a finding that 
trade is not detrimental to the survival of the species by the 
exporting Party's Scientific Authority. CITES regulates all 
international trade in giant clams (including living, dead, and 
captive-bred specimens) and requires the issuance of export permits and 
re-export certificates. For each listing, a Party may take a 
reservation to that listing, meaning the Party will not be bound by the 
provisions of the Convention relating to trade in that species. While 
the reservation is in effect, the Party is treated as a non-Party 
regarding trade in the particular species. Currently, Palau has 
reservations on all of the giant clam listings. Parties with 
reservations or other non-Parties that trade with a CITES Party are 
required to have documentation comparable to CITES permits. It is up to 
the Party State receiving the export whether to accept this 
documentation in lieu of CITES permits.
    Effective enforcement of CITES is largely dependent on whether the 
countries involved are signatories to the Treaty, as well as the 
accuracy of trade data supplied by the Parties (Wells, 1997). Of the 60 
countries and territories where the seven giant clam species considered 
here naturally occur, 52 are signatories to the Treaty. This includes 
the United States and all of its Pacific island territories. A number 
of countries that have historically played a significant role in the 
trade of giant clam products are not CITES contracting parties (e.g., 
Cook Islands, Kiribati, Marshall Islands, FSM) or have only become so 
relatively recently (e.g., Palau in 2004, Solomon Islands in 2007, 
Maldives in 2012, Tonga in 2016). However, all CITES Parties trading in 
CITES listed species with countries that are not members of CITES, or 
with CITES Parties that have taken a reservation on the species, must 
still seek comparable documentation from the competent authorities of 
the reserving Party or the non-member country, which substantially 
conforms with the usual requirements of CITES for trade in the species. 
Importantly, even in instances where exporting countries are Parties to 
CITES, the trade data must be interpreted cautiously for reasons that 
may include frequent

[[Page 60522]]

discrepancies in recorded import and export quantities, inconsistencies 
in the terms or units used to describe the trade, occasional omissions 
of seized or confiscated specimens, erroneous data entry, and delays or 
failure to submit trade statistics to the Secretariat (UNEP-WCMC, 2012; 
CITES, 2013; Neo et al., 2017).
    Overall, the threat of inadequate regulations related to the 
international trade of giant clam products is relevant only to the 
species that are traded in significant quantities. This does not 
include T. mbalavuana or T. squamosina, as we could not find any 
information to indicate that there has ever been an international 
commercial export market for these species. With respect to H. 
hippopus, T. derasa, and T. squamosa, CITES annual report data indicate 
that the large majority of recent international trade of these species 
is of culture-raised specimens and products. Since 2010, only 2,756 H. 
hippopus shells and 7,302 live H. hippopus specimens have been recorded 
in trade. Approximately 51.2 percent of traded shells during this 
period were of wild-caught origin, primarily from the Solomon Islands 
in 2014, while 34.1 percent were reportedly culture-raised. Of the live 
specimens, only 2.6 percent were wild-caught, while 96.2 percent were 
reportedly culture-raised.
    Similarly, since 2010, 154,245 of the 158,319 live T. derasa 
specimens recorded in trade were culture-raised (97.4 percent), while 
only 3,514 were reportedly wild-caught (2.2 percent). A smaller 
proportion of shells and shell products recorded in trade since 2010 
were of cultured T. derasa, but the total trade volume is significantly 
lower. In total, 3,775 of the 11,100 T. derasa shells and shell 
products were of culture-raised specimens (34 percent), while 7,312 
were wild caught (65.9 percent).
    The primary market for T. squamosa in international trade is of 
live clams for the ornamental aquarium industry, and it appears that 
most major exporters have transitioned their supply to cultured 
specimens. The major exceptions are Cambodia and Vietnam, which 
together have exported over 50,000 wild-caught T. squamosa since 2010. 
The government of Vietnam instituted a quota system to regulate the 
commercial harvest of wild giant clams after concerns were raised in 
the early 2010s about the level of exploitation. However, the 
subsequent rise in the export of live T. squamosa from Cambodia to 
Vietnam suggests that this regulation simply diverted the harvest to 
neighboring waters. While this harvest pressure likely threatens the 
persistence of T. squamosa populations in Cambodia in the long term, 
available reports suggest that the species is still frequent in both 
countries.
    Based on these data, we conclude CITES regulations have been 
effective at transitioning much of the international supply of H. 
hippopus, T. derasa, and T. squamosa products away from wild harvest 
and towards mariculture operations and therefore, minimizing the risks 
to these three species from overutilization associated with 
international trade. In other words, it is unlikely that this factor 
contributes significantly to the extinction risk for these species.
    With respect to H. porcellanus, only five shells have been recorded 
in international trade since 2010--two exported from Malaysia to the 
Netherlands in 2013, and three exported from the Philippines and seized 
in the United States in 2011 and 2016. However, it is likely that the 
low trade levels are as much a reflection of the species' low abundance 
as they are of the effectiveness of international regulation. 
Regardless, although commercial trade of this species significantly 
reduced its abundance in the past, there is little evidence to suggest 
that international trade is a threat currently operating on this 
species, and given the available information to suggest otherwise, the 
regulations appear to be adequate to address that threat.
    With respect to T. gigas, unlike H. hippopus and T. derasa, CITES 
records indicate that the majority of the reported trade since 2010 is 
of wild-caught specimens, suggesting that mariculture has not played a 
significant role in diverting harvest away from wild populations. As 
recently as 2018, Indonesia exported 59,000 wild-harvested T. gigas 
shells to China despite the reportedly low abundance of T. gigas 
throughout the region and despite both nations being CITES contracting 
Parties. While most countries and territories within the range of T. 
gigas are regulated under the provisions of CITES, the associated 
protections were clearly not adequate to prevent widespread population 
loss and local extirpations of the species from many of the same 
locations (Neo et al., 2017). Thus, we conclude that inadequate 
regulation of international trade to address the threat of 
overutilization contributes significantly to the long-term extinction 
risk of T. gigas.
Regulations on Climate Change
    In the final rule to list 20 reef-building corals under the ESA (79 
FR 53851), we assessed the adequacy of existing regulatory mechanisms 
to reduce global greenhouse gas (GHG) emissions and thereby prevent 
widespread impacts to corals and coral reefs. We concluded that 
existing regulatory mechanisms were insufficient to effectively address 
this threat. Since the publication of that final rule in 2014, 197 
countries and the European Union (EU) adopted the Paris Agreement on 
climate change, which set a goal of limiting the global temperature 
increase to below 2 [deg]C and optimally keeping it to 1.5 [deg]C. 
Since the Agreement was entered into force on November 4, 2016, 191 
countries and the EU have ratified or acceded to its provisions, and 
each Party has made pledges to decrease GHG emissions to achieve its 
goals (UNFCC, 2018). The United States, which currently accounts for 
one-fifth of the world's emissions, pledged to cut its emissions by 26-
28% percent. However, according to the 2023 Synthesis Report for the 
IPCC's Sixth Assessment Report, there remains a ``substantial emissions 
gap'' between the projected emissions trajectory associated with the 
climate actions currently proposed by the Parties to the Paris 
Agreement and the trajectories associated with mitigation pathways that 
limit warming to 1.5 [deg]C or 2 [deg]C by 2100 (IPCC 2023). The IPCC 
reported with high confidence that current limited progress towards GHG 
emissions reduction make it likely that warming exceeds 1.5 [deg]C by 
2100 and make it considerably harder to limit warming to less than 2 
[deg]C. In addition, the IPCC projected with medium confidence that the 
current emissions trajectory without strengthening of policies will 
lead to an estimated global temperature increase of 3.2 [deg]C by 2100, 
with a range of 2.2 [deg]C to 3.5 [deg]C (IPCC, 2023).
    At this rate, unless average emissions reduction goals are 
significantly strengthened, van Hooidonk et al. (2016) project that 
over 75 percent of reefs will experience annual recurrence of severe 
bleaching events before 2070. In a similar analysis, Hoegh-Guldberg et 
al. (2007) investigated four emissions reduction pathways that are used 
by the Intergovernmental Panel on Climate Change and found that only 
the most aggressive scenario would allow the current downward trend in 
coral reefs to stabilize. The study predicts that even moderate 
emission reductions will still lead to the loss of more than 50 percent 
of coral reefs by 2040-2050. Thus, regardless of whether the goals of 
the Paris Agreement are met, impacts to coral reefs are expected to be 
widespread and severe. However, as is

[[Page 60523]]

discussed above, while there is clear evidence that coral reefs will 
undergo substantial changes as a result of ocean warming and 
acidification, it is unclear whether and to what degree the changes in 
coral reef composition and ecological function will threaten the 
survival and productivity of giant clams. Furthermore, as is discussed 
below in Other Natural or Man-Made Factors, there is substantial 
evidence to suggest that giant clams may experience significant 
physiological changes under projected ocean warming scenarios. The 
precise magnitude of these impacts is unknown, but any significant 
changes in metabolic demand, reproductive success, and the possibility 
of bleaching due to warming summer temperatures, will likely increase 
the risk of extinction. For this reason, we find with respect to all 
seven species that the inadequacy of regulations to address climate 
change may, in combination with the aforementioned impacts, contribute 
significantly to the long-term or near future risk of extinction, but 
is unlikely a significant threat on its own.
Inadequacy of Regulations in the South China Sea
    As is discussed above, H. hippopus, H. porcellanus, T. gigas, and 
T. squamosa also face the threat of habitat destruction in portions of 
the South China Sea where fishermen, primarily from the Hainan Province 
of China, have been razing shallow reef areas in a search for giant 
clam shells (see Present or Threatened Destruction, Modification, or 
Curtailment of Its Habitat or Range). In an effort to curtail this 
destructive activity, the Hainan Province People's Congress passed 
regulations in January 2017 to prohibit the commercial trade of all 
giant clam species in the province. However, a recent report from the 
Wildlife Justice Commission (2021) suggests that the illegal harvest 
and trade of giant clam shells continues to occur in the region, with 
new harvesting boats returning to the Hainan Province since 2018. For 
this reason, we conclude that the inadequacy of existing regulations to 
address the threat of habitat destruction in the South China Sea due to 
giant clam shell harvesting operations contributes significantly to the 
long-term extinction risk of H. hippopus, T. gigas, and T. squamosa. In 
addition, due to the exceptionally low abundance and highly restricted 
range of H. porcellanus, which includes the southern portion of the 
South China Sea, the combination of these threats likely also 
contributes to the near future extinction risk for H. porcellanus.

Other Natural or Man-Made Factors

    There are several other natural or manmade factors that impact 
giant clams, such as ocean warming and acidification, coastal pollution 
and sedimentation, and stochastic mortality events. Below, we summarize 
each of these factors, and where sufficient information is available, 
evaluate the severity of the associated threat to each of the seven 
giant clam species.
Ocean Warming
    As is mentioned above, giant clams associate symbiotically with a 
diverse group of dinoflagellates of the family Symbiodiniaceae which 
reside within a network of narrow tubules that branch off the primary 
digestive tract and spread throughout the upper layers of the mantle 
(Norton et al., 1992). Giant clams provide dissolved inorganic 
nutrients to the zooxanthellae via direct absorption from the seawater 
or as an excretory byproduct of respiration, and in return, receive 
photosynthetic carbon in the form of glucose, glycerol, 
oligosaccharides and amino acids, comprising the majority of their 
metabolic carbon requirements (Klumpp et al., 1992; Hawkins & Klumpp, 
1995). Exposure to stressful environmental conditions, however, can 
cause dysfunction in the symbiosis and, in extreme cases, can lead to a 
bleaching response wherein the zooxanthellae is expelled from the 
mantle tissue. When they bleach, giant clams lose a critical source of 
nutrition and experience drastic changes to their physiology, including 
decreased glucose and pH in the hemolymph, an increased concentration 
of inorganic carbon (e.g., CO2 and 
HCO3-), and a reduced capacity for ammonium 
assimilation (Leggat et al., 2003).
    Elevated temperatures, in particular, are known to induce bleaching 
in giant clams. Widespread bleaching of giant clams was observed in the 
central Great Barrier Reef, Australia in 1997-1998, when elevated water 
temperatures in conjunction with low salinity caused 8,000 of 9,000 
surveyed T. gigas to experience varying levels of bleaching (Leggat, 
pers. comm., cited in Buck et al., 2002; Leggat et al., 2003). Some 
individuals suffered a complete loss of symbionts, while others were 
only affected in the central part or at the margins of the mantle 
tissue (Grice, 1999). A follow-up experiment designed to replicate the 
environmental conditions during this event demonstrated that elevated 
temperatures combined with high solar irradiance induced a consistent 
bleaching response in T. gigas (Buck et al., 2002). Populations of T. 
squamosa around Mannai Island, Thailand also suffered extensive 
bleaching in mid-2010 due to prolonged exposure to temperatures 
averaging 32.6 [deg]C (Junchompoo et al., 2013). Bleaching was recorded 
in every T. squamosa specimen observed (n = 12), of which only four 
individuals recovered while the remaining two-thirds died (Junchompoo 
et al., 2013).
    While the appearance is similar to the bleaching response observed 
in corals, bleaching of giant clams is unique in two important ways. 
First, the mechanics differ on account of the zooxanthellae residing 
extracellularly in giant clams. Rather than being expelled from host 
cells, as is the case with corals, zooxanthellae are thought to be 
driven out of the giant clam tubular system via long cilia and expelled 
through the digestive tract (Norton & Jones, 1992; Norton et al., 
1995). The expulsion of algal cells is associated with atrophy of the 
tertiary zooxanthellae tubes, which is thought to inhibit the return of 
the zooxanthellae to the host clam (Norton et al., 1995). According to 
one account, some adult T. gigas have remained partially bleached for 
more than a year (R. Braley, pers. comm., cited in Norton et al., 
1995). Second, there is evidence that giant clams are more resilient to 
bleaching than corals and can tolerate temperature stress for longer 
(Grice, 1999; Buck et al., 2002; Leggat et al., 2003). According to 
Leggat et al. (2003), of 6,300 T. gigas that bleached at Orpheus 
Island, Australia in 1998, over 95 percent completely recovered after 8 
months. Moreover, during the three global-scale coral bleaching events 
when anomalous warming caused widespread mortality of stony corals 
(1998, 2010, and 2014-2017), reports of giant clam bleaching have been 
sparse and variable across species and geography. Neo et al. (2017) 
reported that in 2016, ``Tridacna maxima [which is not subject to this 
rulemaking] did not bleach in Mauritius (R. Bhagooli, pers. comm., 
cited in Neo et al., 2017), but those in Singapore (M. L. Neo, pers. 
obs.), Guam (A. Miller, pers. comm., cited in Neo et al., 2017), and 
East Tuamoto (S. Andr[eacute]fou[euml]t, pers. comm., cited in Neo et 
al., 2017) were bleached severely.'' At Lizard Island, Australia, T. 
gigas reportedly suffered ``much lower'' mortality than T. derasa and 
T. squamosa during the 2016 event (A.D. Lewis, pers. comm., cited in 
Neo et al., 2017). Actual mortality rates were not provided.
    Even in the absence of bleaching, warming-related stress can 
profoundly impact the growth and reproduction of giant clams. Growth 
rates in giant clams

[[Page 60524]]

tend to follow a standard thermal performance curve whereby growth is 
positively correlated with temperature up to a thermal optimum (Pearson 
& Munro, 1991; Hart et al., 1998; Schwartzmann et al., 2011; Van 
Wynsberge et al., 2017). Beyond this point, further warming can cause 
shell growth to become erratic and slow down significantly 
(Schwartzmann et al., 2011; Syazili et al., 2020). Excessive warming 
has also been shown to lower fitness by reducing photosynthetic yield 
(Brahmi et al., 2021), altering the photosynthesis-respiration ratio 
(Braley et al., 1992; Blidberg et al., 2000; Elfwing et al., 2001), 
reducing the strength and carbonate content of the shells (Syazili et 
al., 2020), and reducing fertilization success (Armstrong et al., 
2020). Early life stages are thought to be particularly sensitive to 
these impacts, as warming has been shown to speed up the progression 
through early development, leading to abnormal development, reduced 
settlement, and lower overall juvenile survival (Watson et al., 2012; 
Neo et al., 2013; Enricuso et al., 2019).
    In assessing the contribution of ocean warming to the extinction 
risk of the seven species considered in this rulemaking, we relied on 
the best available scientific and commercial data relating to each 
species specifically. With respect to H. hippopus, results from a 
laboratory experiment in the Philippines showed that H. hippopus 
experienced a significant increase in respiration under elevated 
temperatures and was more sensitive to warming than the two other 
species tested (T. gigas and T. derasa). After 24 hours of exposure to 
elevated temperatures (3 [deg]C above ambient), no bleaching was 
observed (Blidberg et al., 2000). Additionally, Schwartzmann et al. 
(2011) documented the in situ response of H. hippopus to elevated 
temperatures in New Caledonia. At the end of the summer, the 
combination of high temperatures and high irradiance altered the growth 
and gaping behavior of H. hippopus. At the solar maximum, daily growth 
increments and gaping behavior became erratic, indicating some degree 
of physiological distress. The effect was pronounced when temperatures 
stayed above 27 [deg]C, which is near the current summer maximum in 
this region.
    The few studies available with respect to T. derasa found that 
juveniles suffered reduced photosynthetic production and respiration 
when exposed to warming of 3 [deg]C, but neither bleaching nor 
mortality were reported (Blidberg et al., 2000). Neo et al. (2017) also 
noted significant mortality of T. derasa at Lizard Island, Australia 
following anomalous warming in 2016 that led to widespread coral 
bleaching and following three successive years of cyclones, but did not 
provide evidence directly tying the mortality to one cause or the 
other.
    The best available scientific and commercial data suggest that T. 
gigas is sensitive to ocean warming at multiple life stages. For 
example, Enricuso et al. (2019) found that higher water temperatures 
(33 [deg]C, compared to 28 [deg]C and 30 [deg]C) promote rapid 
progression through early development, but result in lower overall 
survival as a consequence of abnormal development and reduced post-
settlement survival. Lucas et al. (1989) found that juvenile growth 
rate increased during summer months as temperatures rose to 30 [deg]C, 
but noted that higher temperatures (33-35 [deg]C) can lead to bleaching 
(Estacion & Braley, 1988). As is discussed above, widespread bleaching 
of T. gigas was observed in the central Great Barrier Reef, Australia 
in 1997-1998 (Leggat, pers. comm., cited in Buck et al., 2002; Leggat 
et al., 2003), later attributed to the combination of elevated 
temperatures with high solar irradiance (Buck et al., 2002). Notably, 
according to Leggat et al. (2003), over 95 percent of the T. gigas that 
were observed to have bleached in 1998 completely recovered after 8 
months, indicating that T. gigas can withstand the acute stress of 
bleaching if anomalous conditions are not prolonged.
    With respect to T. squamosa, two similar studies used a cross-
factorial experimental design to examine the synergistic effects of 
elevated temperature and pCO2 on the survival and growth 
rate of juveniles. Watson et al. (2012) found that juvenile survival 
decreased with increasing temperature, with the lowest survival 
occurring at the moderate and highest seawater temperatures (30.0[deg] 
and 31.5 [deg]C, versus 28.5 [deg]C) combined with the highest 
acidification treatment (1019 ppm pCO2, versus 416 and 622 
ppm). Likewise, Syazili et al. (2020) found that elevated warming 
significantly reduced juvenile growth rate, as well as the strength and 
carbonate content of the shell, based on temperature treatments of 30, 
32, and 34 [deg]C. However, a separate study by Armstrong et al. (2022) 
yielded conflicting results indicating that the growth rate of juvenile 
T. squamosa was unaffected by an increase in temperature. These 
findings were based on temperature treatments of 28.5 [deg] and 30.5 
[deg]C, meant to simulate present-day and end-of-century conditions. 
Elfwing et al. (2001) found that experimental warming enhanced 
respiration rate in T. squamosa juveniles and, in effect, reduced the 
photosynthesis-respiration ratio. Elevated temperatures have also been 
shown to enhance fertilization success in T. squamosa but significantly 
reduce trochophore survival (Neo et al., 2013). Only 3.6-13.9% of 
trochophores survived 24 hours of exposure to 29.5 [deg]C compared to 
32.5-46.8% survival at 22.5 [deg]C.
    Based on this information, we find it likely that ocean warming 
will negatively impact the fitness of H. hippopus, T. derasa, T. gigas, 
and T. squamosa in various ways and that it may, in combination with 
other threats and demographic risk factors, contribute to the long-term 
extinction risk for these species. However, given the limited 
information available and the variability in the reported impacts of 
ocean warming among studies and species, we cannot conclude with 
confidence that ocean warming on its own constitutes a significant 
long-term or near future extinction risk to H. hippopus, T. derasa, T. 
gigas, and T. squamosa.
    With respect to H. porcellanus, T. mbalavuana, and T. squamosina, 
we could not find any specific information addressing the potential 
impacts of ocean warming beyond what is discussed above in regard to 
other giant clam species. Based on the information that is available 
for other species, we find that ocean warming may, in combination with 
other threats and demographic risk factors, contribute to the long-term 
extinction risk for H. porcellanus, T. mbalavuana, and T. squamosina. 
However, while we can broadly infer that ocean warming may negatively 
impact the fitness of these species in some respect, we are reluctant 
to make extrapolations from these studies about the specific nature or 
magnitude of the impact, as it is possible that susceptibility may vary 
significantly among species. For example, species like H. porcellanus 
or T. squamosina, which reside preferentially in shallow habitats where 
temperature fluctuations can be quite extreme, may have adapted a 
higher tolerance to such conditions. Given this uncertainty, we do not 
have sufficient information to conclude that ocean warming is a 
significant threat to H. porcellanus, T. mbalavuana, and T. squamosina 
on its own.
Ocean Acidification
    There is concern that ocean acidification may also pose a 
significant risk to giant clams, based primarily on experimental 
evidence from other shelled mollusks. In two comprehensive literature 
reviews, both Parker et al. (2013) and Gazeau et al. (2013)

[[Page 60525]]

concluded that the consequences of ocean acidification for calcifying 
marine organisms (and mollusks in particular) are likely to be severe, 
as they rely on the uptake of calcium and carbonate ions for shell 
growth and calcification. Yet, while many studies have demonstrated a 
negative effect on the growth of marine mollusks, some species have 
shown no response or even a positive growth response to ocean 
acidification (Ries et al., 2009; Gazeau et al., 2013; Parker et al., 
2013).
    With respect to giant clams specifically, experimental data on the 
effects of ocean acidification are limited and similarly inconclusive. 
Syazili et al. (2020) found that juvenile T. squamosa exhibited 
decreased growth and weaker shell structure under elevated 
pCO2; however, Armstrong et al. (2022) found the opposite, 
that growth rates of juvenile T. squamosa were enhanced under 
acidification treatments. Watson et al. (2012) found that juvenile T. 
squamosa suffered greater mortality when exposed to elevated 
pCO2 (see also Syazili et al., 2020), and fertilization 
success of T. maxima was found to be unaffected (Armstrong et al., 
2020). Lastly, in comparing the growth and survival of four giant clam 
species in conditions approximating future ocean acidification 
scenarios, Toonen et al. (2011) found the responses to vary among 
species. T. maxima and T. squamosa had significantly lower growth rates 
in low pH, T. derasa had a significantly higher growth rate, and T. 
crocea was not significantly different between low pH and ambient 
seawater. The authors concluded that ``such strong species-specific 
differences and interactions among treatment variables [. . .] caution 
against broad generalizations being made on community effects of ocean 
acidification from single-species laboratory studies'' (Toonen et al., 
2011).
    Furthermore, as is mentioned above, ocean acidification will likely 
not affect all regions uniformly, as seawater carbonate dynamics are 
highly dependent on many local-scale factors, such as temperature, 
proximity to land-based runoff, proximity to sources of oceanic 
CO2, salinity, nutrients, as well as ecosystem-level 
photosynthesis and respiration rates. This makes it difficult to assess 
how ocean acidification is impacting giant clams currently or may 
impact them in the future. For this reason, and given the existing 
uncertainty regarding the effects of ocean acidification on giant 
clams, there is not sufficient information to further consider this 
potential threat in the extinction risk assessments for each species.
Land-Based Sources of Pollution
    Giant clams are also susceptible to land-based sources of 
pollution, including sedimentation, elevated nutrients, salinity 
changes, and exposure to heavy metals. Together, these factors 
represent environmental conditions that giant clams may experience 
following heavy rains, particularly near coastlines that have been 
altered by human development. In its Sixth Assessment Report, the IPCC 
found that the frequency and intensity of heavy rainfall events has 
likely increased globally since the pre-industrial era and projected 
that this trend is ``virtually certain'' to continue with additional 
global warming (Seneviratne et al., 2021). The IPCC also found it 
``likely'' that annual precipitation will increase over the equatorial 
Pacific and monsoon regions under a business-as-usual scenario, and 
projected with ``medium confidence'' that flooding and associated 
runoff will increase over parts of South and Southeast Asia by 2100 
(Douville et al., 2021). Thus, it is likely that giant clams will face 
an increasing occurrence of heavy rain events, runoff, and associated 
changes to water quality throughout much of their range.
    Available evidence suggests that the impacts of sedimentation may 
vary between species. Reduced light levels associated with 
sedimentation have been shown to significantly decrease the growth rate 
of T. squamosa (Beckvar, 1981; Foyle et al., 1997; Guest et al., 2008), 
likely by limiting the photosynthetic potential of the symbiotic algae 
(Jantzen et al., 2008; Przeslawski et al., 2008). However, in situ 
observations from Pioneer Bay, Australia revealed that T. gigas 
actually grows faster in more turbid conditions compared to two 
offshore sites (Lucas et al., 1989). These contrasting results may be 
indicative of differences in nutritional strategy between species 
(Klumpp et al., 1992), suggesting that certain species are able to 
compensate for the reduction in photosynthetic yield by increasing the 
relative contribution of heterotrophy.
    Giant clams are also sensitive to variations in salinity, 
nutrients, and heavy metal concentrations. Blidberg (2004) showed that 
a reduction in salinity significantly decreased the survival rates of 
T. gigas larvae. Only 1.1 percent and 2.2 percent of larvae survived 
when exposed to salinities of 20 parts per thousand (ppt) and 25 ppt, 
respectively, compared to a survival rate of 4.2 percent in the 32 ppt 
control. Maboloc et al. (2014) also found that lower salinity (18 ppt 
and 25 ppt vs. 35 ppt) reduced the feeding capacity of juvenile T. 
gigas due to alteration of the digestive membrane. The same effects, 
however, were not observed for T. squamosa, as a milder salinity 
reduction (27 ppt vs. 30 ppt) led to an increase in survival of T. 
squamosa trochophores and no significant effect on the survival T. 
squamosa embryos (Neo et al., 2013).
    Extreme reductions in salinity have been shown to alter the 
behavior of early life stages. T. squamosa trochophores and veligers 
stopped swimming and sank to the bottom of an experimental tank when 
exposed to salinities of 9 ppt and 12 ppt; although, once conditions 
returned to normal, the larvae resumed normal swimming functions within 
an hour (Eckman et al., 2014). These results provide some evidence that 
giant clams may be able to withstand temporary salinity fluctuations. 
However, it is unlikely that they would experience such extreme 
conditions in situ. For example, in October 2010, immediately after a 
week-long heavy rainfall in the Bolinao region of the Philippines 
brought by Typhoon Megi, salinity at a coastal giant clam nursery was 
measured to be 25 ppt (Maboloc et al., 2014).
    With respect to dissolved nutrients, there is consistent evidence 
that nitrogen enrichment increases the density of zooxanthellae in the 
clam tissue (Braley et al., 1992; Belda, Lucas, et al., 1993; Belda-
Baillie et al., 1999) and, in most cases, enhances the growth rate of 
giant clams. The addition of inorganic nitrogen led to a near doubling 
of the growth rate of young juvenile T. derasa (<1 cm) and a 20 percent 
increase in shell length in older juveniles over controls (Heslinga et 
al., 1990). Similarly, H. hippopus juveniles exhibited a 110 percent 
increase in growth per month when exposed to elevated nitrogen (Solis 
et al., 1988). Nitrogen enrichment has also been shown to enhance the 
shell and tissue growth of T. gigas (Belda, Cuff, et al., 1993; Belda, 
Lucas, et al., 1993).
    Elevated heavy metals contribute to the environmental stress 
factors in contaminated waters near human development. For instance, in 
the Cook Islands, giant clams collected from the populated Pukapuka 
Atoll had significantly higher concentrations of iron, manganese, zinc, 
and lead than clams from the unpopulated Suvorov Atoll (Khristoforova & 
Bogdanova, 1981). Three related studies demonstrated that exposing T. 
gigas, H. hippopus, and T. squamosa to sub-lethal levels of copper (T. 
gigas and H. hippopus: 5 [mu]g l-1; T. squamosa: 50 [mu]g 
l-1) reduces photosynthetic activity and, in effect, 
significantly lowers the

[[Page 60526]]

production-respiration ratio (Elfwing et al., 2001; Elfwing et al., 
2002; Elfwing et al., 2003). This aligns with previous work showing 
that copper acts as an inhibitor in photosynthesis (Cid et al., 1995 
cited in Elfwing et al., 2001).
    In most circumstances, however, it is unlikely that giant clams 
would experience only one of the aforementioned issues associated with 
land-based sources of pollution independent of the others. River 
outflows and runoff from heavy rain events will necessarily alter the 
salinity, and in most cases will also carry suspended sediments, 
dissolved nutrients, heavy metals, or a combination of the three to the 
nearshore environment. Blidberg (2004) suggests that synergistic 
effects of elevated heavy metal concentrations in combination with low 
salinity may be more detrimental to giant clams than either factor 
alone. At a relatively low dose of copper (2.5 [mu]g l-1), 
T. gigas larvae survival was not significantly altered, but combined 
with a moderate reduction in salinity (25 ppt vs. 32 ppt), larval 
survival rate was decreased by nearly 75 percent. From these results, 
Blidberg (2004) hypothesized that chronically high copper 
concentrations and low salinity may explain the absence of giant clams 
near human settlements and river mouths.
    Overall, the best available scientific and commercial data provide 
some indication that sedimentation, salinity changes, nutrient 
enrichment, and elevated heavy metal concentrations may impact the 
physiology and fitness of giant clams in certain respects. However, the 
effects are often not consistent between species and, in some cases, 
the experimental treatments do not reflect conditions that giant clams 
may realistically experience in the natural environment. Given this 
uncertainty and the likely localized nature of these impacts near areas 
of high runoff, we conclude that the threat of land-based sources of 
pollution is unlikely to contribute significantly to the extinction 
risk of any of the seven giant clam species considered here, either 
itself or in combination with other threats and demographic risks.
Stochastic Mortality Events
    There have been several reports of mass mortalities of giant clams 
without a definitive cause. For example, reports from Lizard Island, 
Great Barrier Reef indicated that 25 percent of T. gigas and T. derasa 
died in a 6-week period in mid-1985, and over the following 18 months, 
total mortality rates were 55-58 percent (Alder & Braley, 1988). The 
authors ruled out toxins, predators, environmental conditions, and old 
age as possible causes, and hypothesized that two pathogens that were 
observed (Perkinsus and an unknown protozoan) may be to blame. However, 
the findings were inconclusive, and the hypothesis was never confirmed. 
Extensive mortality was also reported in the early 1990s in the Solomon 
Islands, where T. gigas and H. hippopus were the main species affected 
(Gervis, 1992).
    Mass mortality events represent a complex, unpredictable issue that 
can cause acute damage to giant clam populations with little 
forewarning. In each case, only certain giant clam species and certain 
areas were impacted by the mortality events, while other species, other 
bivalve mollusks, and other regions remained apparently unaffected 
(Lucas, 1994). For this reason, the extinction risk associated with 
these stochastic events is likely most significant for species with a 
restricted range or with few remaining populations, such as H. 
porcellanus, T. mbalavuana, and T. squamosina. However, the inherent 
unpredictability of these events affords little confidence in any 
assessment regarding the time scale of this threat. Overall, we 
conclude that the threat of stochastic mortality events may, in 
combination with low abundance, contribute significantly to the long-
term extinction risk of H. hippopus, H. porcellanus, T. derasa, T. 
gigas, T. mbalavuana, and T. squamosina. Considering the expansive 
range of T. squamosa, including several regions of relatively high 
abundance, we find it unlikely that this threat contributes 
significantly to the long-term or near future extinction risk of T. 
squamosa by itself or in combination with other threats or demographic 
risks.

Demographic Risk Analysis

Abundance

    Because there are no global abundance estimates for the seven 
species considered here, we rely on the qualitative estimates of 
population status summarized in table 1, which are based on the best 
available survey data from all countries or territories where each 
species has been recorded.

H. hippopus

    Available data indicate that H. hippopus has suffered significant 
population declines to the extent that the species is rare, extirpated, 
has been reintroduced after extirpation, or is data deficient (likely 
exceptionally rare or extinct) in 21 of 26 locations throughout its 
range. For broadcast spawning organisms like H. hippopus, which rely on 
the external fertilization of gametes, the implications of such sparse 
distribution on reproduction can be significant. As is discussed above, 
Braley (1984) observed that 70 percent of nearest spawning giant clams 
(T. gigas) were found within 9 m of one another, while only 13 percent 
were between 20-30 m of one another. These findings suggest that 
individuals in rare populations are less likely to spawn in synchrony 
and as a result are likely to experience infrequent, sporadic 
reproductive success. This negative relationship between population 
density and productivity, known as the Allee effect, can cause further 
reductions in population abundance and put rare populations of H. 
hippopus at greater risk of extinction.
    In 5 of the 26 locations where H. hippopus has been recorded, the 
species is considered frequent, indicating population density estimates 
that are between 10 and 100 ind ha-1. This includes the 
Great Barrier Reef, outlying islands of NW Australia, the Marshall 
Islands, Vanuatu, and Palau. Of these locations, only Australia has in 
place a total ban on the harvest of H. hippopus. The other countries 
have instituted a ban on the commercial export of giant clams, but 
subsistence harvest is still ongoing. In Vanuatu, H. hippopus is 
considered a prized subsistence food and is harvested regularly for 
household consumption and special occasions. Zann and Ayling (1988) 
reported that H. hippopus was overharvested on inhabited islands in 
Vanuatu and secure on only two reefs; it is unknown if these remote 
populations have been subjected to harvest in the three decades since 
the observations were published. Similarly, in the Marshall Islands, 
available reports suggest that giant clams are heavily exploited near 
population centers, and H. hippopus was reported to be abundant only on 
three remote atolls. Thus, in Vanuatu and Marshall Islands, 
overutilization remains a significant threat to H. hippopus 
populations. In Palau, the most recent survey from Helen Reef, a remote 
uninhabited atoll in the Western Caroline Islands was conducted in 
1976, when the standing stock of H. hippopus was estimated to be over 
70,500 (or 40.1 ind ha-1) (Hirschberger, 1980). However, due 
to its remoteness from the inhabited islands of Palau and the 
difficulty of surveilling the area, Helen Reef was historically 
targeted by giant clam poachers in the 1970s. While we are not aware of 
any more recent poaching in the area, it is possible that such 
activities have gone undetected. Thus, the current status of H. 
hippopus at Helen Reef is unknown. A recent survey

[[Page 60527]]

from the main island group in Palau (Rehm et al., 2022) recorded an 
average population density of 51.5 ind ha-1, but the authors 
note that harvest of H. hippopus in this area is still ``very common.'' 
In Australia, there are very limited survey data on the abundance of H. 
hippopus on the Great Barrier Reef; however, anecdotal reports commonly 
suggest that populations of giant clams in general are healthy relative 
to other areas of the Indo-Pacific. Additionally, there is evidence 
that existing regulations have been effective at preventing illegal 
harvest and minimizing the risk of overutilization of giant clams in 
Australian waters. Several reports have suggested significant 
population declines from 1999 to 2009 at Ashmore and Cartier Reefs, two 
islands in NW Australia that have historically had abundant H. hippopus 
populations. The cause of the decline and current status of these 
populations is unknown.
    Thus, while we consider H. hippopus to be frequent in 5 of the 26 
locations where it occurs naturally (i.e., where it has not been 
artificially introduced), in 2 of these locations (Vanuatu and the 
Marshall Islands), available reports indicate only a few remote sites 
have relatively abundant populations. The abundance of H. hippopus 
outside of these remote sites, particularly near human population 
centers, is considerably lower and is subject to the ongoing threat of 
unregulated domestic harvest. Populations of H. hippopus in Palau, NW 
Australia, and on the Great Barrier Reef appear to be healthy, despite 
ongoing harvest in Palau. Considering these locations alongside the 21 
other locations in the species' range where overutilization has driven 
H. hippopus to low abundance, we find that this factor likely 
contributes significantly to the species' long-term risk of extinction, 
but does not in itself constitute a danger of extinction in the near 
future.

H. porcellanus

    Although quantitative abundance estimates are limited, the best 
available scientific and commercial data suggest that H. porcellanus 
has suffered significant population declines since the 1970s, leading 
to low abundance and very few remaining populations throughout its 
historical range. Only 55 individuals have been observed and recorded 
in published surveys since 1989, and recent reports suggest that the 
species has disappeared from most areas of the Philippines and 
Indonesia, which were once the core of this species' distribution. Only 
two sites, Tubbataha Reefs Natural Park in the Philippines and Raja 
Ampat in Indonesia, are thought to have substantial populations of H. 
porcellanus. However, while there is some evidence that H. porcellanus 
may have recovered to an extent in Tubbataha Reefs after two decades of 
protection from harvest (Dolorosa & Jontila, 2012), the most recent 
survey data available are from 2008 and cover only 0.42 ha of the 
96,828 ha in the park. Given the history of intense exploitation of 
this species in the Philippines and recent evidence of ongoing giant 
clam poaching in the region, we cannot conclude that this population 
has recovered to a sustainable level.
    With so few remaining populations reduced to such a small fraction 
of the species' historical range, H. porcellanus is highly susceptible 
to the ongoing and future threats described above, including coastal 
development, ongoing harvest, the inadequacy of existing regulations, 
potential physiological impacts of ocean warming, and stochastic 
mortality events. Continued population reductions due to these factors 
threatens the persistence of remaining populations, and in effect, 
significantly elevates the extinction risk of H. porcellanus. For this 
reason, we find that the species' low abundance puts it in danger of 
extinction in the near future.

T. derasa

    The best available scientific and commercial data indicate that T. 
derasa has suffered significant population declines to the extent that 
the species is considered rare, extirpated, or has been reintroduced 
after extirpation in 15 of the 18 locations throughout its range. As is 
discussed with respect to H. hippopus, such sparse distribution can 
significantly reduce reproductive success by disrupting spawning 
synchrony and minimizing fertilization rates. In every location where 
T. derasa is considered rare, subsistence harvest is still permitted or 
existing harvest bans, such as in Indonesia and the Philippines, have 
largely been ineffective at eliminating illegal harvest. In these 
locations, the low abundance of T. derasa exacerbates the extinction 
risk associated with continued harvest pressure.
    Of the 18 locations where T. derasa occurs naturally (i.e., where 
it has not been artificially introduced), there are only 3 locations 
where reports indicate that the species is likely frequent--these are 
the Great Barrier Reef, outlying islands of NW Australia, and Palau. 
Both locations in Australia are subject to a total ban on the harvest 
of T. derasa. As is discussed with respect to H. hippopus, while there 
are very limited recent survey data on the abundance of T. derasa on 
the Great Barrier Reef, anecdotal reports consistently suggest that 
populations of giant clams (including T. derasa) in Australia are 
healthy relative to other areas of the Indo-Pacific.
    In NW Australia, population estimates of T. derasa are variable, 
ranging from 1.3 ind ha-1 at Ashmore Reef to 77.7 ind 
ha-1 at N Scott Reef (Skewes et al., 1999). In Palau, there 
is a ban on the commercial export of giant clams, but harvesting for 
subsistence and domestic sale is still reportedly very common, and T. 
derasa remains a highly desired food item, leaving these populations at 
risk of overutilization.
    Overall, the abundance of T. derasa is greatly reduced from 
historical levels throughout its range, leaving only three locations 
where the species is not considered rare or extirpated. The species is 
at continued risk of overutilization in all locations where it is 
found, except for Australia, due to ongoing subsistence harvest and 
inadequate regulation. Based on this information, we find that the 
abundance of remaining populations contributes significantly to the 
species' long-term risk of extinction, but does not in itself 
constitute a danger of extinction in the near future.

T. gigas

    The best available scientific and commercial data indicate that T. 
gigas has suffered significant population declines to the extent that 
the species is considered rare, extirpated, has been reintroduced after 
extirpation, or is data deficient (likely exceptionally rare or 
extinct) in 32 of the 33 locations where it occurs naturally (i.e., 
where it has not been artificially introduced). As is discussed above, 
such sparse distribution can significantly reduce reproductive success 
by disrupting spawning synchrony and minimizing fertilization rates. In 
every location where T. gigas is considered rare, except for NW 
Australia, subsistence harvest is still permitted or existing harvest 
bans, such as in Indonesia and the Philippines, have largely been 
ineffective at eliminating illegal harvest. In these locations, the low 
abundance of T. gigas exacerbates the extinction risk associated with 
continued harvest pressure.
    Of the 33 locations where T. gigas occurs naturally, the only 
location where the species is considered ``frequent'' is the Great 
Barrier Reef in Australia. Populations on the Great Barrier Reef are 
protected by a total ban on the harvest of giant clams. As is

[[Page 60528]]

mentioned above, while there are very limited recent survey data on the 
abundance of T. gigas on the Great Barrier Reef, the data that are 
available, as well as anecdotal reports, consistently suggest that 
populations of giant clams (including T. gigas) in Australia are 
healthy relative to other areas of the Indo-Pacific.
    Overall, the abundance of T. gigas is greatly reduced from 
historical levels throughout its range, leaving only one location where 
the species is not considered rare or locally extinct. Importantly, 
however, while we refer to the Great Barrier Reef as only one location, 
it covers an expansive geographic area that comprises a significant 
proportion of the suitable habitat within the species' range. 
Nonetheless, in all locations of its range outside of the Great Barrier 
Reef, T. gigas is at continued risk of overutilization due to ongoing 
subsistence harvest and inadequate regulation. Based on this 
information, we find that the abundance of remaining populations 
contributes significantly to the species' long-term risk of extinction, 
but does not in itself constitute a danger of extinction in the near 
future.

T. mbalavuana

    Although quantitative abundance estimates are lacking, the best 
available scientific and commercial data suggest that T. mbalavuana 
occurs at exceptionally low abundance and is sparsely distributed 
``with single individuals being found at most locations'' (Ledua et 
al., 1993). As part of a concentrated effort to collect broodstock 
specimens of T. mbalavuana for attempted spawning and larval culture, 
Ledua et al. (1993) estimated the number of clams found per man-hour of 
search on SCUBA. The data showed that an average of about one clam per 
man-hour was collected in Tonga, while about 0.26 clams per man-hour 
were collected in Fiji. There were only three sites where more than six 
clams were found, and all were around Ha'apai, Tonga, which the authors 
suggested may be the center of distribution for T. mbalavuana with the 
``largest repository of the species.'' In total, 76 T. mbalavuana were 
observed and collected in Fiji and Tonga between 1986 and 1992 in more 
than 277 hours of searching.
    Given its exceptionally low abundance, sparse distribution, and 
highly restricted range, T. mbalavuana is highly susceptible to the 
ongoing and future threats described previously, including continued 
domestic harvest, the inadequacy of existing regulations, and the 
possibility of future climate change-related impacts to coral reef 
habitats. Potential population reductions due to these factors 
threatens the persistence of remaining populations, and in effect, 
significantly elevates the extinction risk of T. mbalavuana. For this 
reason, we find that the species' low abundance puts it in danger of 
extinction in the near future.

T. squamosa

    Based on the best available scientific and commercial data, 
historical demand for T. squamosa meat and shells, ongoing demand for 
live specimens for the ornamental aquarium industry, and longstanding 
subsistence harvest has depleted T. squamosa populations in many areas 
of its range. Yet, despite the widespread exploitation, the global 
abundance of T. squamosa is relatively high compared to other giant 
clam species, with several locations where populations are likely 
frequent or abundant. This includes Australia (Great Barrier Reef), 
Indonesia, and the Philippines, which are the three locations with the 
most estimated coral reef area (and likely suitable habitat for T. 
squamosa) of all locations within the species' range. Of the 63 
locations where T. squamosa occurs naturally, it is likely abundant in 
5 locations, frequent in 14, rare in 32, and extirpated in 2 locations, 
with the other locations characterized as data deficient. Available 
reports suggest that abundance is particularly high in the Red Sea and 
in the South Asia regions, despite these areas being subject to 
widespread subsistence harvest and, in the case of South Asia, being at 
the center of the commercial shell and shell craft industry of the 
1980s. Given the significant harvest pressure, this pattern suggests 
that T. squamosa populations in these regions are somewhat resilient to 
population declines, perhaps due to a large historical population size 
or due to high demographic connectivity facilitating larval exchange 
among connected populations within each region. Such a scenario would 
align with the genetic connectivity observed throughout the Indo-Malay 
Archipelago, discussed further in regard to the Spatial Structure/
Connectivity risk below.
    Overall, because the species occurs at relatively high abundance in 
a number of locations throughout its range, and especially in locations 
where the total area of coral reefs (and likely T. squamosa habitat) is 
relatively high, we find it unlikely that its abundance contributes 
significantly to the long-term or near-future risk of extinction by 
itself. However, its reportedly low abundance at many locations in the 
Pacific islands and southeast Africa, where population growth may be 
hindered by the relative isolation of these populations from the 
closest regions of abundance, suggests that this factor may, in 
combination with other VP descriptors or threats, contribute to the 
species' extinction risk.

T. squamosina

    There have been 30 documented observations of T. squamosina since 
its re-discovery in 2008, including 17 specimens from the Gulf of Aqaba 
and northern Red Sea, 7 individuals from the Farasan Islands in 
southern Saudi Arabia, and 6 individuals from an unnamed site in the 
southern Red Sea. The species was absent from all but 1 of the 58 
survey sites visited by Rossbach et al. (2021) along the eastern Red 
Sea coast, including all sites in central and northern Saudi Arabia.
    Given its exceptionally low abundance, sparse distribution, and 
highly restricted range, T. squamosina is highly susceptible to the 
ongoing and future threats described above, including habitat 
destruction and modification, continued artisanal harvest, and the 
inadequacy of existing regulations. Potential population reductions due 
to these factors threatens the persistence of remaining populations, 
and in effect, significantly elevates the extinction risk of T. 
squamosina. For this reason, we find that the species' low abundance 
puts it in danger of extinction in the near future.

Productivity

    Despite exceptionally high fecundity, there is substantial evidence 
that low recruitment success and high mortality rates during early 
development lead to low productivity in most species of giant clams 
(Jameson, 1976; Beckvar, 1981; Fitt et al., 1984; Crawford et al., 
1986; Munro, 1993a). Thus, as is discussed in relation to the Abundance 
risk factor above, we find it likely that all seven species are 
experiencing an Allee effect in locations where each species is 
considered rare, such that low productivity is directly correlated with 
low population abundance. As broadcast spawning organisms, giant clams 
rely on sufficient population density in order to respond to spawning 
cues of nearby individuals and to facilitate successful external 
fertilization of their gametes. The best available evidence suggests 
that spawning synchrony in T. gigas drops significantly at population 
densities lower than 10 ind ha-1 (Braley, 1984), and while 
gametes have been found to

[[Page 60529]]

remain viable for up to 8 hours in T. squamosa, viability decreases 
significantly with time (Neo et al., 2015). It is possible that the 
exact distance and duration of viability may vary among species, but 
because reproductive success is so closely tied to population density, 
we find it likely that the overall effect of low abundance in reducing 
productivity is applicable to all seven species considered here.
    For these reasons, we conclude that the low natural productivity of 
giant clams as well as decreased productivity due to low abundance 
contribute significantly to the long-term risk of extinction of all 
seven species. Additionally, with respect to H. porcellanus, T. 
mbalavuana, and T. squamosina, which are exceptionally rare throughout 
their ranges, we find that this factor is likely to contribute to the 
short-term risk of extinction in the near future.

Spatial Structure/Connectivity

    As is discussed above, the best available scientific and commercial 
data indicate that T. gigas populations in the central Pacific region 
(i.e., Kiribati, Marshall Islands, Tuvalu, and Cook Islands) are 
genetically differentiated from populations in the western Pacific 
(i.e., Great Barrier Reef, Philippines, Solomon Islands, and Fiji). The 
same pattern is largely consistent for T. derasa, although there is 
some variability in the inferred level of connectivity between the 
Great Barrier Reef and the Philippines.
    There is strong evidence indicating four (possibly five) 
genetically isolated clades (i.e., groups of individuals that share 
similar ancestry) of T. squamosa in the Indo-Malay Archipelago, the 
northeastern Indo-Pacific (i.e., northern Philippines and Cenderwasih 
Bay), Red Sea, and western Indian Ocean. There may be a fifth clade in 
the eastern Indian Ocean, but more data are needed to corroborate this 
finding. We could not find any data pertaining to the genetic signature 
of T. squamosa populations in the Pacific islands or on the Great 
Barrier Reef and therefore cannot infer the degree of connectivity to 
these areas.
    We could not find any data regarding the genetic structure or 
connectivity among populations of H. hippopus, H. porcellanus, T. 
mbalavuana, or T. squamosina.
    Based on the relatively short duration of the pelagic larval phase 
of giant clams (~6-14 days), we would expect that long-range dispersal 
between distant locations is likely highly infrequent for each of these 
species, and perhaps particularly so among the regions highlighted 
above (i.e., the central Pacific, western Pacific, Indo-Malay 
Archipelago, eastern Indian Ocean, western Indian Ocean, and the Red 
Sea).
    With respect to T. derasa and T. gigas, based on the spatial 
structure suggested by the available genetic data, it is unlikely that 
populations on the Great Barrier Reef provide significant larval 
subsidy to other locations of the species' ranges. Because the Great 
Barrier Reef represents one of the few remaining locations supporting 
relatively healthy populations of these species, any barrier to 
dispersal from this region reduces its capacity as a larval source and 
limits the species' rebound potential range-wide. Likewise, according 
to the limited genetic data, populations in Palau may function as a 
significant larval source only to nearby locations in the western 
Pacific, such as the Philippines. For this reason, based on the best 
available population genetic data and considering the abundance 
distribution of T. derasa and T. gigas, we conclude that limited 
connectivity, particularly between the Great Barrier Reef and other 
locations within the species' ranges, likely contributes significantly 
to the long-term extinction risk for these species, but does not in 
itself constitute a danger of extinction in the near future.
    With respect to T. squamosa, the available data regarding spatial 
structure suggest that the relatively abundant populations in the Indo-
Malay and Red Sea region likely do not provide significant larval 
subsidy to less abundant populations in the western Pacific and western 
Indian Oceans. Therefore, it is likely that the status of the 
populations in these regions is primarily dependent on local 
demographics. Reported declines of many T. squamosa populations in 
these regions due to longstanding harvest for subsistence and 
commercial purposes suggest that the lack of connectivity may be 
limiting the species' potential for population growth in these regions 
and exacerbating the species' extinction risk range-wide. However, 
because the abundance of T. squamosa remains relatively high in major 
portions of its range (e.g., the Indo-Malay Archipelago, Red Sea, and 
Great Barrier Reef), we find it unlikely that the observed spatial 
structure contributes significantly to long-term or near-term risk of 
extinction by itself, but it may in combination with other VP 
descriptors or threats.
    Without further information on the spatial structure and 
connectivity of H. hippopus, H. porcellanus, T. mbalavuana, and T. 
squamosina, we cannot assess the contribution of this factor to the 
extinction risk for these four species.

Diversity

    Overall, we could find very little information regarding the 
genetic diversity of the seven species considered here. With respect to 
T. derasa and T. gigas, the best available scientific and commercial 
data indicate regional differences in the degree of genetic variation. 
Macaranas et al. (1992) found that mean heterozygosity of T. derasa 
based on allozyme variation was highest on the Great Barrier Reef (h = 
0.35-0.46), intermediate in the Philippines (h = 0.29), and lowest in 
Fiji (h = 0.14). Similarly, Gomez et al. (1994) found low mean 
heterozygosity in both Fiji and Tonga (h = 0.17-0.19). While it is 
difficult to know the exact cause, the relatively low genetic diversity 
in the small island populations may be reflective of smaller 
populations and low rates of immigration due to their geographic 
remoteness. Macaranas et al. (1992) also note that samples from Fiji 
were collected from the Makogai Island hatchery, where genetic 
diversity may be artificially reduced. Similarly, comparing across 
several locations in the Indo-Pacific, Benzie and Williams (1995) found 
that genetic diversity of T. gigas, based on the percentage of 
polymorphic loci and mean number of alleles per locus (Na), 
was lowest in the Philippines (57.1 percent; Na = 2), 
Marshall Islands (71.4 percent; Na = 2.3), and Kiribati 
(57.1 percent; Na = 2.3), and highest in the Solomon Islands 
(85.7 percent; Na = 2.4-2.7) and the Great Barrier Reef (100 
percent; Na = 2.9). Overall, while these data highlight 
geographic differences in the magnitude of genetic diversity in both T. 
derasa and T. gigas, we find no evidence to suggest that this factor 
contributes significantly to the extinction risk for these species by 
itself or in combination with other factors.
    Likewise, with respect to T. squamosa, the best available 
scientific and commercial data suggest that genetic diversity in the 
Indo-Malay region is low relative to T. maxima and T. crocea, two other 
giant clam species with similarly broad distributions but which are not 
subject to this rulemaking. However, we find no evidence to suggest 
that this factor contributes significantly to the extinction risk for 
T. squamosa by itself or in combination with other factors.
    With respect to T. squamosina, K.K. Lim et al. (2021) measured very 
low diversity of the mitochondrial DNA (i.e., 16S haplotype diversity) 
and very few polymorphic loci, indicating that genetic diversity is 
very low. The authors hypothesized that the low diversity may be the 
result of a

[[Page 60530]]

population bottleneck, but cautioned that it may also reflect low 
natural diversity or a small sample size. In general, low genetic 
diversity may limit adaptive potential, and effectively lower the 
resilience of populations to environmental change. Thus, we have some 
concern that this factor may, in combination with the low abundance of 
the species, contribute to the long-term or near future extinction risk 
for T. squamosina.
    We could not find any information regarding the genetic diversity 
of H. hippopus, H. porcellanus, or T. mbalavuana. Given these species' 
declining population trends, and the exceptionally low abundance of H. 
porcellanus and T. mbalavuana overall, it is possible that genetic 
diversity may be significantly reduced as a result of a population 
bottleneck. However, without any genetic testing on these species to 
determine diversity or effective population size, we are unable to 
conclude whether this is a relevant threat contributing to the species' 
risk of extinction.

Overall Risk Summary

    Guided by the results of the demographic risk analysis and threats 
assessment above, we considered the best available scientific and 
commercial data to analyze the overall risk of extinction for each of 
the seven giant clam species throughout their respective ranges. We 
outline the conclusions and supporting rationale for each species 
below.

H. hippopus

    Considering the best available scientific and commercial data 
regarding H. hippopus from all locations of the species' range, we 
determined that the most critical demographic risks to the species 
include the low abundance and negative trajectory of populations 
throughout the majority of its range, compounded by low natural 
productivity. Additionally, our threats assessment revealed that the 
past and present overutilization and associated inadequacy of existing 
regulatory mechanisms to address overutilization (e.g., subsistence 
fisheries, domestic markets, and international trade in giant clam 
shells and shell-craft) contribute most significantly to the extinction 
risk of this species. Continued harvest of H. hippopus primarily for 
subsistence purposes, combined with the species' low productivity will 
likely drive further population declines and prevent any substantial 
population increases.
    The best available scientific and commercial data indicate that 
very few abundant populations of H. hippopus remain, and that in almost 
every location outside of Australia, domestic harvest of H. hippopus is 
ongoing. In Palau, Vanuatu, and the Marshall Islands, which are three 
of the five locations where we consider H. hippopus to be frequent, 
anecdotal reports indicate that harvest for subsistence and for sale in 
domestic markets is still very common. In Vanuatu and the Marshall 
Islands, there is evidence that this has significantly reduced H. 
hippopus abundance in the areas around human population centers, 
leaving very few remote areas with relatively healthy populations. 
There is very little quantitative information regarding the abundance 
of H. hippopus on the Great Barrier Reef, but anecdotal reports 
commonly suggest that populations of giant clams in general are 
healthy. There is also quantitative evidence that H. hippopus occurs in 
significant numbers in the outlying islands of NW Australia (Richards 
et al., 2009; Skewes et al., 1999), likely benefitting from the strong 
regulatory protections within Australian waters. Additionally, in 
Palau, although subsistence harvest of giant clams is permitted and is 
reported to occur commonly, a recent survey indicated relatively large 
populations of H. hippopus (Rehm et al., 2022). As is discussed below 
in the Protective Efforts section, it is possible that the significant 
output of cultured giant clams from the Palau Mariculture Demonstration 
Center (PMDC) mariculture facility and reported efforts to use a 
portion of H. hippopus seedstock to enhance depleted populations in 
certain conservation areas may be offsetting the harvest pressure in 
Palau. However, without further information, we are not able to assess 
with confidence whether populations in Palau are stable, or whether 
they may be increasing or decreasing significantly due to one factor 
outweighing the other.
    In contrast to these 5 locations where H. hippopus populations are 
relatively healthy (i.e., the Great Barrier Reef, NW Australia, Palau, 
and remote areas of Vanuatu and the Marshall Islands), the best 
available scientific and commercial data indicate that, at the 21 other 
locations across the range with documented occurrences of this species, 
extensive exploitation for past commercial harvest for the shell and 
shell-craft industry and ongoing subsistence harvest have driven H. 
hippopus to low abundance, and in some cases, extirpation. The 
continued threat of overutilization and the demographic risks outlined 
above likely put the species at a high level of extinction risk in 
these locations in the foreseeable future. However, because H. hippopus 
populations in Australia and Palau, and certain areas of Vanuatu and 
the Marshall Islands are relatively abundant, and the enforcement of 
strict harvest bans have effectively minimized the threat of 
overutilization in Australian waters, we cannot conclude that the 
species is at moderate or high risk of extinction throughout its entire 
range.
Significant Portion of Its Range (SPR) Analysis: H. hippopus
    Under the ESA and our implementing regulations, a species may 
warrant listing if it is in danger of extinction or likely to become so 
within the foreseeable future throughout all or a significant portion 
of its range. Thus, a species may be endangered or threatened 
throughout all of its range, or a species may be endangered or 
threatened throughout only a significant portion of its range. Having 
determined that H. hippopus is not at moderate or high risk of 
extinction throughout all of its range, in order to inform the listing 
determination, we conducted an additional analysis to assess whether 
the species is at higher risk of extinction in a ``significant portion 
of its range''--that is, we assessed whether there is any portion of 
the species' range for which it is true that both (1) the portion is 
significant and (2) the species, in that portion, is in danger of 
extinction or likely to become so in the foreseeable future. A joint 
USFWS-NMFS policy, finalized in 2014, provided the agencies' 
interpretation of this phrase (``SPR Policy,'' 79 FR 37578, July 1, 
2014) and explains that, depending on the case, it might be more 
efficient for us to address the ``significance'' question or the 
``status'' question first. (Certain aspects of the SPR Policy have been 
invalidated by courts; we describe below where those decisions affect 
the SPR analysis.) Regardless of which question we choose to address 
first, if we reach a negative answer with respect to the first 
question, we do not need to evaluate the other question for that 
portion of the species' range.
    Because there are infinite ways in which a range could be 
theoretically divided for purposes of this analysis, we first evaluated 
whether there are portions of the range of H. hippopus that have a 
reasonable likelihood of being both in danger of extinction or likely 
to become so in the foreseeable future, and biologically significant to 
the species. In other words, unless portions met both of these 
conditions, they were not further considered in this analysis. As 
discussed in the SPR Policy, as a

[[Page 60531]]

practical matter, a key part of this analysis is considering whether 
threats are geographically concentrated in some way. In this case, 
because we determined that the most significant threats to the species 
are overutilization and inadequacy of regulatory mechanisms to address 
overutilization, we focused our analysis on the portion of the range 
where these threats are most severe.
    As has been discussed previously, several sources indicate that the 
early adoption of strict harvest prohibitions in Australia has been 
largely effective at preventing illegal harvest and minimizing the risk 
of overutilization of giant clams in Australian waters. This differs 
considerably from reports from every other location throughout the 
species' range, which consistently indicate that the threat of 
overutilization in combination with inadequate regulatory mechanisms to 
address this overutilization poses a significant extinction risk to H. 
hippopus. Thus, for the purpose of this SPR analysis, we distinguish 
locations in Australia (i.e., the Great Barrier Reef and NW Australia) 
from all other locations where H. hippopus occurs and consider them as 
two separate portions of the species' range.
    The portion of the range outside of Australia includes 24 countries 
and territories where the primary threat to the species is 
overutilization. In 21 of these locations (Andaman and Nicobar Islands 
(India), Japan, Taiwan, South China Sea, Indonesia, Malaysia, Myanmar, 
Philippines, Singapore, Fiji, New Caledonia, Papua New Guinea, Solomon 
Islands, FSM, Guam, Republic of Kiribati, CNMI, American Samoa, Samoa, 
Tonga, and Tuvalu), the best available scientific and commercial data, 
consisting of surveys as well as qualitative descriptions of abundance, 
suggest that past commercial harvest for the shell and shell-craft 
trade (primarily in the South Asia region), as well as past and ongoing 
subsistence harvest throughout this entire portion of the species' 
range has driven H. hippopus to low abundance, and in several cases, 
extirpation.
    There are three main exceptions to this trend--Vanuatu, the 
Marshall Islands, and Palau. In Vanuatu, a single survey in 1988 
spanning 13 islands reported that H. hippopus was ``overfished on 
inhabited islands but secure on two remote reefs'' (Zann & Ayling, 
1988). We are not aware of any follow-up surveys, and the current 
status of these remote reef populations is unknown. Available reports 
from the Marshall Islands suggest that H. hippopus is relatively 
abundant at three less-populated atolls, reporting ``huge undisturbed'' 
populations in Bok-ak and Pikaar Atolls in particular, but do not 
provide any quantitative data (Maragos, 1994; Beger et al., 2008). 
Lastly, in Palau, a recent survey of the main island group and past 
surveys of a remote uninhabited atoll indicate that abundance of H. 
hippopus is relatively high (Rehm et al., 2022). It is also important 
to note that, while we consider the overall abundance of H. hippopus in 
the Philippines and Indonesia to be ``rare,'' there are a number of 
studies reporting small areas within each country where H. hippopus 
still occurs at relatively high frequency. This includes, for example, 
Carbin Reef and Tubbataha Reefs Natural Park in the Philippines, and 
Raja Ampat and Kei Islands in Indonesia, where recently estimated 
population densities are over 20 ind ha-1 (Dolorosa, 2010; 
Lebata-Ramos et al., 2010; Wakum et al., 2017; Triandiza et al., 2019).
    However, in each of Vanuatu, the Marshall Islands, and Palau, 
existing regulations do not prohibit the domestic harvest of giant 
clams for subsistence purposes or for sale in local markets. According 
to Neo et al. (2017), giant clams, and especially H. hippopus, are 
still a prized subsistence food on most islands in Vanuatu. The same is 
true in Palau, where the harvest of H. hippopus is still very common 
near populated areas (L. Rehm, pers. comm., May 26, 2022), and in the 
Marshall Islands, where available information indicates that H. 
hippopus has historically been sold in local markets (S. Wells, 1997). 
Thus, while the current status of H. hippopus in these locations may be 
healthier than many other locations throughout the species' range, the 
threat of domestic harvest and inadequate regulatory mechanisms to 
address overutilization continues to expose the species to an elevated 
extinction risk in the foreseeable future. It seems that the principal 
factor protecting H. hippopus in Vanuatu and the Marshall Islands is 
simply the remoteness of the populations rather than any formal 
regulatory mechanism.
    Theoretically, mariculture operations in Palau could potentially 
prevent the species from going extinct in the foreseeable future. As 
noted above, however, we are not able to assess whether populations in 
Palau are stable or are increasing or decreasing significantly due to 
the output of cultured giant clams compared to ongoing harvest. We did 
not base our assessment on the past success of mariculture operations, 
because of its reliance on a number of unpredictable factors (e.g., 
funding, management priorities, natural disasters, etc.). Thus, it is 
difficult to extrapolate the effect of mariculture beyond the next few 
years.
    Basing our assessment on the demographic risks of low abundance and 
low productivity in 21 of 24 locations where the species naturally 
occurs, and the ongoing threats of overutilization and inadequate 
regulatory mechanisms to address it in all 24 locations, we conclude 
that in the portion of the species' range defined as all locations 
outside of Australia, H. hippopus is at moderate risk of extinction. 
Because the species still occurs in 24 locations within this portion of 
its range, which encompass a broad geographic area and variety of 
environmental conditions, and relatively healthy populations can still 
be found in the Marshall Islands, Palau, Vanuatu, and a number of small 
areas within the Philippines and Indonesia, we do not find that H. 
hippopus is at or near a level of abundance that places its continued 
persistence in question. However, given the ongoing threats of 
overutilization and inadequate regulatory mechanisms to address it, as 
well as documented populations declines that have been attributed to 
these threats, we find that the species is on a trajectory that puts it 
at a high level of extinction risk within the foreseeable future in the 
portion consisting of 24 countries and territories outside of 
Australia.
    Having reached a positive answer with respect to the ``status'' 
question, we move on to determine whether this portion of the range is 
``significant.'' The definition of ``significant'' in the SPR Policy 
has been invalidated in two District Court cases that addressed listing 
decisions made by the USFWS. The SPR Policy set out a biologically-
based definition that examined the contributions of the members in the 
portion to the species as a whole, and established a specific threshold 
(i.e., when the loss of the members in the portion would cause the 
overall species to become threatened or endangered). The courts 
invalidated the threshold component of the definition because it set 
too high a standard. Specifically, the courts held that, under the 
threshold in the policy, a species would never be listed based on the 
status of the species in the portion, because in order for a portion to 
meet the threshold, the species would be threatened or endangered 
range-wide. See Center for Biological Diversity v. Jewell, 248 F. Supp. 
3d 946, 958 (D. Ariz. 2017); Desert Survivors v. DOI, 321 F. Supp. 3d 
1011 (N.D. Cal. 2018). However, those courts did not take issue with 
the fundamental approach of evaluating

[[Page 60532]]

significance in terms of the biological significance of a particular 
portion of the range to the overall species. NMFS did not rely on the 
definition of ``significant'' in the policy here. Rather, to assess 
whether a portion of a species' range is ``significant,'' we consider 
relevant biological information, such as whether the portion was 
historically highly abundant, potentially functioning as a source 
population for other areas of the range, whether there is evidence that 
it was historically highly productive with potential to contribute to 
the population growth of this species as a whole, whether the portion 
encompasses a substantial area relative to the species' current range, 
whether the portion historically facilitated gene flow between 
populations, and whether the portion contains genetic or phenotypic 
diversity that is important to species viability. The contribution or 
role of that portion to the viability of the species as a whole is also 
considered from a historical, current, and future perspective to the 
extent possible.
    With respect to H. hippopus, there is strong evidence that the 
portion of the species' range defined as all locations outside of 
Australia qualifies as a ``significant portion.'' Based on historical 
trade statistics, as well as the countless reports describing major 
population losses resulting from years of domestic harvest and intense 
commercial harvest, primarily for the international shell and shell-
craft industry (e.g., see Villanoy et al., 1988; Kinch, 2003; Dolorosa 
& Schoppe, 2005; Harahap et al., 2018; Purcell et al., 2020), it is 
clear that H. hippopus was historically highly abundant in this portion 
of its range.
    Furthermore, prior to these losses, it is likely that populations 
in this portion, which includes 24 of 26 locations comprising the 
species' range (i.e., all locations except for the Great Barrier Reef 
and NW islands in Australia), played a critical role in maintaining 
genetic connectivity throughout the species' range. For many marine 
organisms, and particularly sedentary taxa such as giant clams, long-
range dispersal (e.g., between islands and other distant locations) is 
likely highly stochastic and infrequent (see Cowen et al., 2003; Siegel 
et al., 2008). As is discussed above in Growth and Reproduction, it 
relies on a process known as `sweepstakes' reproduction, in which 
spawning and fertilization coincidentally align with oceanographic 
conditions that facilitate successful long-distance dispersal and 
recruitment to a suitable habitat. The relatively short pelagic larval 
duration of giant clams (~6-14 days) further limits the probability of 
long-distance dispersal. Thus, it is likely that H. hippopus was 
dependent on serial migration between nearby locations (i.e., `stepping 
stones') to maintain genetic connectivity throughout its range. 
Historically, this portion would have once facilitated this 
connectivity between populations.
    Given its geographic size, this portion of the species' range 
encompasses a wide variety of habitats and environmental conditions. 
Therefore, we expect that, to some extent, past populations were likely 
genetically adapted to their local setting, as has been demonstrated 
with respect to numerous other marine organisms across similar 
geographic scales (e.g., see Sanford & Kelly, 2011 for comprehensive 
review). Such genetic diversity can function as an important foundation 
to enhance the resilience of the species and facilitate future 
adaptation to environmental change. Furthermore, given the geographic 
extent of this portion of this range and the varied habitats it 
encompasses, the populations of H. hippopus within this portion would 
have provided an important demographic reserve, which could facilitate 
recovery following stochastic mortality events or other localized 
population declines.
    Based on the rationale described above, we find that the portion of 
the species' range defined as all locations outside of Australia is 
``significant,'' and serves a biologically important role in 
maintaining the long-term viability of H. hippopus.

H. porcellanus

    Despite a lack of formal, comprehensive abundance estimates, the 
best available scientific and commercial data suggest that H. 
porcellanus has suffered significant population declines since the 
1970s, leading to low abundance and very few remaining populations 
throughout its historical range. The inherent risks of such low 
abundance are compounded by low natural productivity, which likely 
prevents any substantial short-term rebound. Additionally, our threats 
assessment revealed that past and present overutilization in 
subsistence fisheries, domestic markets, and the international trade of 
giant clam shells and shell-craft, as well as the inadequacy of 
existing regulatory mechanisms to address this overutilization 
contribute most significantly to the extinction risk of this species. 
H. porcellanus has historically been highly desired commercially for 
the aesthetic of its shell and once comprised a substantial portion of 
the giant clam shell export volume from the Philippines, reaching a 
total export of nearly a million H. porcellanus shells and shell pairs 
between 1978 and 1992. While H. porcellanus is no longer legally 
exported from the Philippines, reports of ongoing subsistence harvest 
throughout its range and illegal poaching to supply a continued demand 
for giant clam shells and shell-craft throughout East Asia suggest that 
the species will likely continue to experience declining trends in its 
abundance and productivity in the foreseeable future. Based on our 
assessment of these threats and demographic risk factors, we conclude 
that H. porcellanus is at a high risk of extinction throughout its 
range.

T. derasa

    Considering the best available scientific and commercial data 
regarding T. derasa from all locations of the species' range, we 
determined that the most critical demographic risks to T. derasa are 
the low abundance and negative trajectory of populations throughout the 
majority of its range, compounded by low natural productivity and the 
likelihood of the Allee effect. Additionally, our threats assessment 
revealed that the past and present overutilization due to subsistence 
fisheries, domestic markets, and the international trade of giant clam 
meat and poaching, as well as the inadequacy of existing regulatory 
mechanisms to address this overutilization contribute most 
significantly to the extinction risk of this species. Continued harvest 
of T. derasa primarily for subsistence purposes, combined with the 
species' low productivity will likely drive further population declines 
and prevent any substantial population rebound. We also consider that 
the close association of T. derasa with coral reefs may make the 
species more susceptible to the projected impacts of ocean warming and 
acidification on coral reef habitats.
    As with H. hippopus, the best available scientific and commercial 
data indicate that very few abundant populations of T. derasa remain 
and occur primarily in the waters of Australia. Extensive surveys of T. 
derasa on the Great Barrier Reef from the 1980s (Braley, 1987a, 1987b) 
found that the species' distribution was patchy with several sites of 
relatively high density (>10 ind ha-1) interspersed among 
many other sites of low abundance or where the species was completely 
absent. The Swain Reefs in particular, a group of approximately 350 
offshore reefs in the southern region of

[[Page 60533]]

the Great Barrier Reef, was one area described as having especially 
high abundance of T. derasa, with densities ranging from 12 to 172 ind 
ha-1 (Pearson, 1977). Based on the species' patchy 
distribution and the observed pattern of recruitment, Braley (1988) 
found it likely that the relatively few reefs with abundant populations 
of clams (mostly in the south) may dominate recruit production for the 
rest of the Great Barrier Reef.
    According to Pearson (1977), during the 1960s and early 1970s, 
Taiwanese vessels poached giant clams (primarily T. gigas and T. 
derasa) from the entire length of the Great Barrier Reef. As 
surveillance and enforcement efforts by Australian authorities 
increased in the 1970s, poachers began to concentrate their activities 
to offshore areas, such as the Swain Reefs, but this likely only lasted 
at significant scale for a few years, as Dawson (1986) claimed that 
during the lead up to the declaration of the Australian Fishing Zone 
(AFZ) in 1979, Taiwanese authorities were warned that continued illegal 
poaching of giant clams would jeopardize Taiwan's position in gaining 
access rights to the AFZ. This forced the Taiwanese government to 
enhance inspection of suspected boats upon departure and return to 
port. According to Dawson (1986), ``the combined effect of these two 
components, almost certain apprehension by the coastal State and 
effective sanctions by the flag State, combined to result in the 
virtual cessation of illegal giant clam activities in the AFZ.'' Based 
on this assessment and because subsistence demand for giant clams in 
Australia is minimal, we find it likely that the population density 
estimates provided by Braley (1987a, 1987b) generally represent the 
current status of T. derasa on the Great Barrier Reef. This is further 
supported by more recent reviews and reports (bin Othman et al., 2010; 
Braley, 2023; Neo et al., 2017; S. Wells, 1997) suggesting that T. 
derasa is still relatively abundant on much of the Great Barrier Reef.
    There is also quantitative evidence that T. derasa occurs in 
significant numbers in the outlying islands of NW Australia (Richards 
et al., 2009; Skewes et al., 1999), likely benefitting from the strong 
regulatory protections within Australian waters. Additionally, in 
Palau, although subsistence harvest of giant clams is permitted and is 
reported to occur commonly, a recent survey indicated relatively large 
populations of T. derasa (Rehm et al., 2022). As with H. hippopus, it 
is possible that the significant output from the PMDC mariculture 
facility and reported efforts to use a portion of T. derasa seedstock 
to enhance depleted populations in certain conservation areas may be 
balancing the harvest pressure in Palau. However, without further 
information, we are not able to assess with confidence whether T. 
derasa abundance in this location is stable, or whether it may be 
increasing or decreasing significantly due to one factor outweighing 
the other.
    In contrast to these 3 locations where T. derasa populations are 
relatively healthy (i.e., the Great Barrier Reef, NW Australia, Palau), 
the best available data indicate that, at the 15 other locations across 
the range where this species naturally occurs, extensive exploitation 
for past commercial trade, ongoing subsistence use, and illegal harvest 
have driven T. derasa to exceptionally low abundance, and in some 
cases, extirpation. The continued threat of overutilization, the 
inadequacy of existing regulatory mechanisms to address 
overutilization, the possible future threat of habitat degradation due 
to climate change impacts on coral reefs, and the demographic risks 
outlined above, likely put the species at a high level of extinction 
risk in these locations. However, because T. derasa populations in 
Australia and Palau are relatively abundant, and the enforcement of 
strict harvest bans have effectively minimized the threat of 
overutilization in Australian waters, we cannot conclude that the 
species is at moderate or high risk of extinction throughout its entire 
range.
    It is worth highlighting that, although we refer to the Great 
Barrier Reef as only one location for the purpose of this analysis, it 
covers an expansive geographic area that comprises a substantial 
proportion of the suitable habitat within the species' range. 
Additionally, while the future threat of habitat degradation due to 
climate change impacts on coral reefs may be relevant to these 
populations, we do not have sufficient information to confidently 
assess the extent to which the survival or productivity of giant clams 
(even those species closely associated with coral reefs, such as T. 
derasa) may be impacted by projected changes to coral reef communities.

SPR Analysis: T. derasa

    Having determined that T. derasa is not at moderate or high risk of 
extinction throughout all of its range, in order to inform the listing 
determination, we conducted an additional analysis to assess whether 
the species is at higher risk of extinction in a ``significant portion 
of its range''--that is, we assessed whether there is any portion of 
the species' range for which it is true that both (1) the portion is 
significant and (2) the species, in that portion, is in danger of 
extinction or likely to become so in the foreseeable future.
    Because we determined that the most significant threats to T. 
derasa are overutilization and the inadequacy of regulatory mechanisms 
to address overutilization, we focused our analysis on the portion of 
the range where these threats are most severe, consistent with the 
approach used in the SPR analysis for H. hippopus. As discussed above, 
several sources indicate that the early adoption of strict harvest 
prohibitions in Australia has been largely effective at preventing 
illegal harvest and minimizing the risk of overutilization of giant 
clams in Australian waters. This differs considerably from reports from 
every other location throughout the species' range, which consistently 
indicate that the threat of overutilization in combination with 
inadequate regulation and enforcement poses a significant extinction 
risk to T. derasa. Thus, for the purpose of this SPR analysis, we 
distinguish locations in Australia (i.e., the Great Barrier Reef and NW 
Australia) from all other locations where T. derasa occurs and consider 
them as two separate portions of the species' range.
    In this case, the portion outside of Australia that was further 
considered includes 16 countries and territories (Christmas Island, 
Cocos (Keeling) Islands, Taiwan, South China Sea, Indonesia, Malaysia, 
Philippines, Fiji, New Caledonia, Papua New Guinea, Solomon Islands, 
Vanuatu, Guam, CNMI, Palau, and Tonga) where the primary threat to the 
species is overutilization. In 15 of these locations, the best 
available scientific and commercial data, consisting of surveys as well 
as qualitative descriptions of abundance, suggest that past commercial 
harvest for the giant clam meat trade, past and ongoing subsistence 
harvest, and widespread illegal poaching have driven T. derasa to 
exceptionally low abundance, and in several cases, extirpation. The one 
exception is Palau, where a recent survey of the main island group and 
past surveys of a remote uninhabited atoll indicate that abundance of 
T. derasa is likely relatively high. However, as is discussed above, 
while commercial export of wild-caught giant clams is prohibited in 
Palau, harvest for subsistence purposes and for sale in domestic 
markets is reportedly very common, and T. derasa is one species that is 
specifically targeted by locals.
    As with H. hippopus, the success of mariculture operations in Palau 
could

[[Page 60534]]

theoretically prevent the species from going extinct in the foreseeable 
future. For example, since 1990, the PMDC alone has cultured over 
150,000 T. derasa for export internationally, and likely many more that 
were traded or distributed domestically, or were otherwise not included 
in CITES reports. It is possible that the threat of overutilization in 
Palau has been somewhat offset in the short term by documented efforts 
to reseed depleted populations (see Protective Efforts). However, as we 
discussed previously with respect to H. hippopus, we are not basing our 
assessment on the past success of mariculture operations; its reliance 
on a number of unpredictable factors (e.g., funding, management 
priorities, natural disasters, etc.) makes it difficult to extrapolate 
the effect of mariculture beyond the next few years. Thus, we based our 
assessment on the demographic risks of low abundance and low 
productivity that exist in 15 of 16 locations in this portion where the 
species naturally occurs, and the ongoing threats of overutilization 
and inadequate regulatory mechanisms to address it in all 16 locations.
    Similar to H. hippopus, we considered the geographic range of the 
remaining populations, noting that the species still occurs in 16 
locations within this portion of its range, which encompass a broad 
geographic area and a variety of environmental conditions within the 
Indo-Pacific region. However, Palau is the only location in this 
portion where T. derasa is considered frequent (although, we note that 
two recent surveys have found relatively abundant populations in the 
Anambas Islands and Raja Ampat region of Indonesia). Because of its 
large size, T. derasa is often the most highly desired species for 
subsistence consumption and to sell for its meat in local markets. This 
continued demand at the local level, combined with the widespread and 
lasting impact of the Taiwanese poaching effort, has driven the species 
to exceptionally low abundance on average in this portion of its range. 
Among the many low estimates of population density, T. derasa has been 
described as ``virtually extinct from most of [the Philippines] due to 
overexploitation'' (Gomez & Alcala, 1988), ``likely functionally 
extinct'' from Karimun Jawa, Indonesia (Brown & Muskanofola, 1985), and 
``at risk of extirpation'' in New Caledonia (Purcell et al., 2020). For 
these reasons, despite the geographic scope of the remaining T. derasa 
populations, given the desirability and ongoing demand for T. derasa 
for consumption and sale in local markets, we find that the species is 
at or near a level of abundance that places its continued persistence 
in this portion in question (high extinction risk).
    Having reached a positive answer with respect to the ``status'' 
question, we next considered whether this portion of the range is 
``significant.'' Similar to the SPR analysis for H. hippopus, we 
considered the historically high abundance of T. derasa in this portion 
of the range, as evidenced by trade statistics and the many reports of 
major population losses resulting from years of subsistence and 
commercial harvest. Additionally, as was described with respect to H. 
hippopus, it is likely that populations in this portion played an 
important role in maintaining genetic connectivity throughout the 
species' range. Given the relatively short pelagic larval phase of 
giant clams (~6-14 days), there is a diminishing likelihood of larval 
dispersal between locations at progressively greater distances. 
Therefore, genetic exchange between distant populations likely relied 
on many smaller dispersal events across the network of more closely 
spaced islands or habitat areas that comprise this portion of the 
species' range. Lastly, considering the geographic extent of this 
portion and the diverse habitats that it encompasses, the populations 
of T. derasa within this portion likely served as an important 
demographic and genetic reserve, which could facilitate recovery 
following localized population declines. Based on this rationale, we 
find that the portion of the species' range defined as all locations 
outside of Australia is ``significant,'' or in other words serves a 
biologically important role in maintaining the long-term viability of 
T. derasa.

T. gigas

    Considering the best available scientific and commercial data 
regarding T. gigas from all locations of the species' range, we 
determined that the most critical demographic risks to T. gigas are the 
low abundance and negative trajectory of populations throughout the 
majority of its range, compounded by low natural productivity and 
likely Allee effect. Additionally, our threats assessment revealed that 
the past and present overutilization due to subsistence fisheries, 
domestic markets, the international trade of giant clam meat and 
poaching, and the international trade of giant clam shells and shell-
craft, as well as the inadequacy of existing regulatory mechanisms to 
address this overutilization contribute most significantly to the 
extinction risk of this species. Continued harvest of T. gigas 
primarily for subsistence purposes and illegally by poachers, combined 
with the species' low productivity will likely drive further population 
declines and prevent any substantial population recovery in locations 
where it is rare.
    The best available scientific and commercial data indicate that 
very few abundant populations of T. gigas remain and occur exclusively 
on the Great Barrier Reef in Australia. Extensive surveys of T. gigas 
on the Great Barrier Reef from the 1980s (Braley, 1987a, 1987b) 
recorded population densities as high as 56 ind ha-1, with 
numerous sites hosting populations of T. gigas at densities greater 
than 10 ind ha-1 interspersed among other sites of low 
abundance or where the species was completely absent. Braley (1987a) 
noted that T. gigas was present on 36 of 57 (63 percent) randomly 
chosen survey sites, and 17 of 19 (89 percent) sites chosen 
specifically because of known giant clam populations. High population 
densities were found in the Cairns, Cooktown, and Escape Reefs 
transects, while no living T. gigas were observed south of 19[deg] S. 
Based on the species' patchy distribution and the observed pattern of 
recruitment, Braley (1988) found it likely that the scattered reefs 
hosting abundant populations of clams (mostly in the south) may 
dominate recruit production for the rest of the Great Barrier Reef.
    As was discussed in the extinction risk analysis for T. derasa, 
Taiwanese vessels poached giant clams (primarily T. derasa and T. 
gigas) from the Great Barrier Reef during the 1960s and 1970s. However, 
strict enforcement of a harvest ban on giant clams resulted in the 
virtual cessation of illegal giant clam activities in Australia by the 
mid-1980s. Based on this information and because giant clams are not 
harvested for subsistence in Australia, we find it likely that the 
population density estimates provided by Braley (1987a, 1987b) 
generally represent the current status of T. gigas on the Great Barrier 
Reef. This is further supported by more recent reviews and reports (bin 
Othman et al., 2010; Braley, 2023; Neo et al., 2017; S. Wells, 1997) 
suggesting that T. gigas is still relatively abundant on much of the 
Great Barrier Reef. According to R.D. Braley (pers. comm., October 19, 
2022) and Neo et al. (2017), the distribution of T. gigas on the Great 
Barrier Reef represents a ``natural'' and ``virtually undisturbed'' 
state for the species.
    In contrast to the Great Barrier Reef, where T. gigas populations 
are relatively healthy, the best available data indicate that, at the 
other 32 of 33

[[Page 60535]]

locations across the range with documented natural occurrence of this 
species, extensive exploitation for past commercial trade, ongoing 
subsistence use, and illegal harvest have driven T. gigas to 
exceptionally low abundance, and in many cases, extirpation (this 
applies to all locations except NW Australia, where the low abundance 
cannot be attributed to harvest). The continued threat of 
overutilization, the possible future threat of habitat degradation due 
to climate change impacts on coral reefs, and the demographic risks 
outlined above, places the continued persistence of T. gigas in these 
locations in question. However, because T. gigas populations on the 
Great Barrier Reef are relatively abundant, even described as 
``virtually untouched,'' and the enforcement of strict harvest bans 
have effectively minimized the threat of overutilization in Australian 
waters, we cannot conclude that the species is at moderate or high risk 
of extinction throughout its entire range.
    It is worth highlighting that, although we refer to the Great 
Barrier Reef as only one location for the purpose of this analysis, it 
covers an expansive geographic area that comprises a substantial 
proportion of the suitable habitat within the species' range. 
Additionally, as is mentioned in regard to T. derasa, while the future 
threat of habitat degradation due to climate change impacts on coral 
reefs may be relevant to T. gigas populations, including those on the 
Great Barrier Reef, we do not have sufficient information to 
confidently assess the extent to which the survival or productivity of 
giant clams may be impacted by projected changes to coral reef 
communities.

SPR Analysis: T. gigas

    Having determined that T. gigas is not at moderate or high risk of 
extinction throughout all of its range, in order to inform the listing 
determination, we conducted an additional analysis to assess whether 
the species is at higher risk of extinction in a ``significant portion 
of its range''--that is, we assessed whether there is any portion of 
the species' range for which it is true that both (1) the portion is 
significant and (2) the species, in that portion, is in danger of 
extinction or likely to become so in the foreseeable future.
    Because we determined that the most significant threats to T. gigas 
are overutilization and the inadequacy of regulatory mechanisms to 
address overutilization, we focused our analysis on the portion of the 
range where these threats are most severe, consistent with the approach 
used for both H. hippopus and T. derasa. As has been discussed, several 
sources indicate that the early adoption of strict harvest prohibitions 
in Australia has been largely effective at preventing illegal harvest 
and minimizing the risk of overutilization of giant clams in Australian 
waters. This differs considerably from reports from every other 
location throughout the species' range, which consistently indicate 
that the threat of overutilization in combination with inadequate 
regulatory mechanisms to address that threat pose a significant 
extinction risk to T. gigas. Thus, for the purpose of this SPR 
analysis, we distinguish locations in Australia (i.e., the Great 
Barrier Reef and NW Australia) from all other locations where T. gigas 
occurs and consider them as two separate portions of the species' 
range.
    In this case, the portion of the range outside of Australia that we 
considered further includes 29 countries and territories (Andaman and 
Nicobar Islands (India), Christmas Island, Cocos (Keeling) Islands, 
Japan, Taiwan, China, South China Sea, Indonesia, Malaysia, Myanmar, 
Cambodia, Philippines, Singapore, Thailand, Vietnam, East Timor, Fiji, 
New Caledonia, Papua New Guinea, Solomon Islands, Vanuatu, FSM, Guam, 
Republic of Kiribati, Marshall Islands, CNMI, Palau, Tonga, and Tuvalu) 
where the primary threat to the species is overutilization. In all of 
these locations, the best available scientific and commercial data, 
consisting of survey data as well as qualitative descriptions of 
abundance, suggest that past commercial harvest for the giant clam meat 
trade, past and ongoing subsistence harvest, and widespread illegal 
poaching have driven T. gigas to exceptionally low abundance, and in 
many cases, extirpation. Based on the demographic risks of low 
abundance and low productivity in this portion, and the ongoing threats 
of overutilization and inadequate regulatory mechanisms to address 
overutilization in all 29 locations, we conclude that in the portion of 
the species' range defined as all locations outside of Australia, T. 
gigas is at or near a level of abundance that places it at high risk of 
extinction.
    To evaluate whether this portion is ``significant,'' we applied 
similar rationale as was used with respect to the SPR analyses for H. 
hippopus and T. derasa. We considered the historically high abundance 
of T. gigas in this portion of the range, as evidenced by trade 
statistics and the many reports of major population losses resulting 
from years of subsistence and commercial harvest. Additionally, as was 
described in relation to H. hippopus and T. derasa, it is likely that 
populations of T. gigas in this portion played an important role in 
maintaining genetic connectivity throughout the species' range. Given 
the relatively short pelagic larval phase of giant clams (~6-14 days), 
there is a diminishing likelihood of larval dispersal between locations 
at progressively greater distances. Therefore, genetic exchange between 
distant populations likely relied on many smaller dispersal events 
across the network of more closely spaced islands or habitat areas that 
comprise this portion of the species' range. Lastly, considering the 
geographic extent of this portion and the diverse habitats that it 
encompasses, the populations of T. gigas within this portion likely 
served as an important demographic and genetic reserve, which could 
facilitate recovery following localized population declines. Based on 
this rationale, we find that the portion of the species' range defined 
as all locations outside of Australia is ``significant,'' or in other 
words serves a biologically important role in maintaining the long-term 
viability of T. gigas.

T. mbalavuana

    Despite a lack of formal, comprehensive abundance estimates, the 
best available scientific and commercial data suggest that T. 
mbalavuana occurs at exceptionally low abundance and is sparsely 
distributed throughout its highly restricted range. Anecdotal accounts 
from traditional fishermen in Tonga indicate that the species has 
experienced significant population loss since the 1940s, which has been 
attributed at least in part to longstanding harvest of giant clams in 
both Fiji and Tonga, where the species primarily occurs. The inherent 
risks of such low abundance are compounded by low natural productivity 
and the likelihood of the Allee effect, which likely prevents any 
substantial short-term recovery. Additionally, our threats assessment 
revealed that past and present overutilization and associated 
inadequacy of existing regulatory mechanisms at the local level 
contribute most significantly to the extinction risk of this species. 
T. mbalavuana has historically been and continues to be collected for 
subsistence consumption and for sale in domestic markets, occasionally 
being mistaken for T. derasa by local fishermen. While commercial 
export of giant clams has been prohibited in both Fiji and Tonga, 
existing regulations afford little protection to the species from the 
ongoing domestic harvest. Based on our assessment of these threats and

[[Page 60536]]

demographic risk factors, we conclude that T. mbalavuana is at a high 
risk of extinction throughout its range.

T. squamosa

    Considering the best available scientific and commercial data 
regarding T. squamosa from all locations of the species' range, we 
determined that the most critical demographic risk to the species is 
the low natural productivity of giant clams generally, reflected by 
reports of little to no T. squamosa recruitment in several recently 
published surveys from Malaysia, Singapore, and Palau. Additionally, 
our threats assessment revealed that past and present overutilization 
due to subsistence fisheries, domestic markets, the international trade 
of giant clam shells and shell-craft, and the international trade of 
live giant clams for aquaria, as well as the inadequacy of existing 
regulatory mechanisms to address overutilization contribute most 
significantly to the extinction risk of this species. Continued harvest 
of T. squamosa primarily for subsistence purposes, combined with the 
species' low productivity may drive further population declines and 
prevent substantial recovery in locations where the species is already 
rare, including much of southeast Africa and the Pacific islands.
    However, the best available scientific and commercial data indicate 
that there are a number of locations where T. squamosa still occurs at 
relatively high abundance. This includes significant portions of South 
Asia and the Red Sea, two regions which notably have been subjected to 
a long history of subsistence harvest, and in the case of South Asia, 
intense commercial trade of T. squamosa shells throughout the 1980s. 
Yet, based on available reports, we consider T. squamosa to be 
``frequent'' (10-100 ind ha-1) or ``abundant'' (>100 ind 
ha-1) in locations such as Indonesia, the Philippines, 
Malaysia, Australia (Great Barrier Reef), the Solomon Islands, and 
Saudi Arabia, all of which host substantial coral reef habitat, and 
likely also suitable habitat for T. squamosa based on the species' 
known habitat preferences. Furthermore, of the 63 locations where T. 
squamosa has been observed, it has been reported as likely extirpated 
in only 2 of them. Thus, its current distribution encompasses an 
expansive geographic range and broad array of environmental conditions. 
Together, these factors suggest that, despite the many reports of 
population decline in most locations throughout its range, T. squamosa 
may be somewhat resilient to the threat of subsistence harvest at its 
current level, particularly in the Indo-Malay and Red Sea regions.
    The general lack of information regarding T. squamosa productivity 
(e.g., natural reproductive and recruitment success) and long-term 
abundance trends limits our understanding of the factors that may 
underlie this apparent resilience. One important factor may be that, 
although T. squamosa was harvested extensively for the commercial shell 
trade in the 1980s, it was not targeted for its meat by commercial 
entities and illegal poachers with the same intensity as T. gigas and 
T. derasa, which severely depleted these species in the South Asia 
region. It is also possible that the global abundance of T. squamosa 
was historically larger than other giant clam species, or that high 
demographic connectivity within the Indo-Pacific and Red Sea regions, 
as is suggested by the available population genetic data, may 
facilitate significant larval exchange and recovery of depleted 
populations.
    Regardless, given the relatively high abundance of T. squamosa in 
major portions of its range and its expansive distribution, we conclude 
that the species is at low risk of extinction throughout its entire 
range. In other words, based on the best available scientific and 
commercial data, we find it unlikely that the current and projected 
threats to the species, namely ongoing subsistence harvest and 
inadequate regulatory mechanisms to address overutilization, place the 
continued existence of T. squamosa in question presently or within the 
foreseeable future.

SPR Analysis: T. squamosa

    Having determined that T. squamosa is at low risk of extinction 
throughout all of its range, in order to inform the listing 
determination, we conducted an additional analysis to assess whether 
the species is at higher risk of extinction in a ``significant portion 
of its range''--that is, we assessed whether there is any portion of 
the species' range for which it is true that both (1) the portion is 
significant and (2) the species, in that portion, is in danger of 
extinction or likely to become so in the foreseeable future. We 
analyzed two different configurations of portions (e.g., Australia and 
all areas where T. squamosa currently is known to occur outside of 
Australia; and Red Sea, southeast Africa, Indo-Malay Archipelago, and 
Cenderwasih Bay), both of which had a reasonable likelihood of meeting 
these conditions, as described in more detail below.
    As with the SPR analyses for H. hippopus, T. derasa, and T. gigas, 
because we determined that the most significant threats to T. squamosa 
are overutilization and inadequacy of regulatory mechanisms to address 
that threat, we base our analysis here on the portion of the range 
where these threats are most severe. Using the same rationale as was 
used for H. hippopus, T. derasa, and T. gigas, we distinguish locations 
in Australia (i.e., the Great Barrier Reef and NW Australia) from all 
other locations where T. squamosa occurs and consider them as two 
separate portions of the species' range.
    The portion outside of Australia that we further considered 
includes 59 countries and territories (see table 1) where the primary 
threat to the species is overutilization due to subsistence fisheries, 
domestic markets, the international trade of giant clam shells and 
shell-craft, and the international trade of live giant clams for 
aquaria. Unlike the SPR analyses for H. hippopus, T. derasa, and T. 
gigas, however, there are a number of locations, including the 
Philippines, Indonesia, Malaysia, and much of the Red Sea, where the 
best available scientific and commercial data suggest that T. squamosa 
abundance is quite high and where there is substantial coral reef area, 
and likely suitable habitat for T. squamosa based on the species' known 
habitat preferences.
    While it is clear that T. squamosa has suffered significant 
population declines throughout much of this portion of its range, 
available reports suggest that a major fraction of the loss can be 
attributed to the intense commercial demand for its shell and shell 
products in the 1980s, particularly in the South Asia region. Since the 
early 1990s, when the commercial shell industry in the Philippines 
began to dwindle, harvest of T. squamosa has primarily been limited to 
a smaller scale, mostly for subsistence consumption or for sale in 
local markets. As is discussed above, harvest for subsistence purposes 
continues to occur in all locations outside of Australia, constituting 
the most significant present and future threat to T. squamosa within 
this portion of its range.
    Without the benefit of long-term monitoring data, we are not able 
to assess population trends over the last few decades to quantitatively 
evaluate the effect of the ongoing subsistence harvest. However, given 
the reports of relatively high abundance in locations such as the 
Philippines, Indonesia, and Malaysia, where T. squamosa has been 
subjected to both commercial harvest and longstanding subsistence 
harvest,

[[Page 60537]]

and much of the Red Sea, where subsistence harvest is common, we find 
that T. squamosa is at low risk of extinction in this portion of its 
range.
    Having determined that T. squamosa is at low risk of extinction in 
the portion of its range including all locations outside of Australia, 
we also considered population genetics as a means of delineating 
alternative portions of the species' range. As is discussed above, the 
best available population genetic data indicate at least four (possibly 
five) discrete metapopulations, located in the Red Sea, southeast 
Africa, Indo-Malay Archipelago, and Cenderwasih Bay in northern Papua 
(and a possible fifth population in the eastern Indian Ocean). Studies 
of other broadly distributed species (e.g., T. maxima and T. crocea) 
suggest that there may also be genetic breaks between the central and 
western Pacific islands, and also between the western Pacific and Indo-
Malay Archipelago (Nuryanto & Kochzius, 2009; Huelsken et al., 2013; 
Hui et al., 2016). However, we were not able to find any studies 
including data from T. squamosa populations in the Pacific islands to 
confirm these patterns in this species. Because population genetic 
patterns are often variable between species, we cannot rely on these 
inferences for the purposes of this analysis.
    Therefore, we consider the populations of T. squamosa in the Red 
Sea, southeast Africa, Indo-Malay Archipelago, and Cenderwasih Bay as 
four distinct portions of the species' range. As has been addressed 
above, the relatively high abundance of T. squamosa within the Red Sea 
and Indo-Malay regions leads us to conclude that the species is likely 
at low risk of extinction in these portions of its range. With respect 
to the portions in southeast Africa and in Cenderwasih Bay, given their 
genetic and likely demographic isolation from the majority of the 
species' range, as well as the relatively small geographic area they 
occupy, we do not find that these two portions can be considered 
``significant,'' or that they likely serve a biologically important 
role in maintaining the long-term viability of this species. Thus, as a 
result of this SPR analysis, we do not find any portions within the 
range of T. squamosa for which it is true that both the portion is 
significant and that the species in the portion is at moderate or high 
risk of extinction.

T. squamosina

    The best available scientific and commercial data suggest that T. 
squamosina occurs at exceptionally low abundance and is sparsely 
distributed throughout its highly restricted range. Since the re-
discovery of the species in 2008, there have been only 30 recorded 
observations of T. squamosina, which are divided between the Gulf of 
Aqaba in the northern Red Sea and two sites including the Farasan 
Islands in the south. The inherent risks of such low abundance are 
compounded by low natural productivity, which likely prevents any 
substantial recovery of the species in the near future. Additionally, 
our threats assessment revealed that past and present overutilization 
and associated inadequacy of existing regulatory mechanisms at the 
local level contribute most significantly to the extinction risk of 
this species. T. squamosina has historically been and continues to be 
collected for subsistence consumption and for sale in domestic markets, 
and the existing regulatory mechanisms are limited to the management of 
a few protected areas, affording little protection to the species in 
the remainder of its range. Based on our assessment of these threats 
and demographic risk factors, we conclude that T. squamosina is at a 
high risk of extinction throughout its range.

Protective Efforts

    Section 4(b)(1)(A) of the ESA requires that NMFS make listing 
determinations based solely on the best available scientific and 
commercial data after conducting a review of the status of the species 
and taking into account those efforts, if any, being made by any State 
or foreign nation, or political subdivisions thereof, to protect and 
conserve the species. Above, we identified local and international 
regulatory mechanisms that have been adopted in some parts of these 
species' ranges, and determined that these mechanisms were generally 
inadequate to address threats arising from overutilization outside of 
Australia. In reaction to dwindling giant clam stocks throughout the 
Indo-Pacific, several nations have supported efforts exploring the use 
of mariculture to replenish and/or re-establish populations in local 
waters. As of 2016, there were an estimated 20 giant clam mariculture 
facilities in operation, primarily in the Pacific islands, as well as 
in Indonesia, Malaysia, the Philippines, and Australia (Mies, Dor, et 
al., 2017). Here, we specifically examine whether mariculture efforts 
may be contributing to the protection and conservation of the seven 
giant clam species at issue in this proposed rulemaking.
    There is extensive literature highlighting the challenges of giant 
clam mariculture generally, and particularly for the purpose of stock 
replenishment (Munro, 1993a; Gomez & Mingoa-Licuanan, 2006; Teitelbaum 
& Friedman, 2008; Mies, Scozzafave, et al., 2017). The primary barrier 
to these efforts is the exceptionally low survival rate of giant clam 
larvae post-fertilization compounded by the time and resources required 
to protect juveniles once they have been outplanted and before they 
reach a size at which they are sufficiently protected from predation. 
Despite the numerous restocking and translocation programs known to 
exist throughout the Indo-Pacific, most are reported to still be 
operating on a small or pilot scale with only partial success, and 
further intensification of giant clam mariculture for the purpose of 
stock replenishment or reintroduction is in most cases considered 
economically unviable (Teitelbaum & Friedman, 2008; UNEP-WCMC, 2012).
    One possible exception is in Palau, where the PMDC has pioneered 
many of the methods for giant clam mariculture and has successfully 
cultured large numbers of giant clams, particularly T. derasa. 
Following receipt of funding from the United States in 1982, the PMDC 
expanded production of giant clams substantially, and the facility 
began exporting significant quantities of ``seed'' clams (i.e., small 
juveniles) and broodstock to many other Indo-Pacific countries and 
territories (Shang et al., 1994). It is difficult in most cases to 
determine the exact purpose of the shipments--some were intended to be 
used exclusively for conservation-related stock enhancement, while 
others were used to establish local hatcheries for the purpose of 
subsistence or commercial harvest. Additionally, there are reports that 
a portion of the H. hippopus and T. derasa culture stock is being used 
to enhance giant clam populations in 23 conservation areas around Palau 
(Kinch & Teitelbaum, 2010; L. Rehm, pers. comm., May 26, 2022). We 
could not find any follow-up surveys specifically documenting the 
success of these efforts (or lack thereof). According to L. Rehm (pers. 
comm., May 26, 2022), authorities in Palau struggle to enforce the 
regulations of conservation areas, particularly those on offshore 
reefs, because they lack sufficient personnel and equipment, 
potentially negating any benefit of reseeding.
    In regard to the individual species addressed here, several 
countries are known to have imported H. hippopus broodstock for the 
purposes of stock enhancement or reintroduction, but there is very 
little information regarding the success of these efforts in 
establishing sustainable populations of

[[Page 60538]]

H. hippopus in the wild. An unpublished report by Braley (n.d.) 
describes the outcome of translocating a single cohort of H. hippopus 
(~70,000 specimens) from Australia to Fiji, Tonga, and the Cook Islands 
in 1991. According to the report, survival to mid-1997 averaged 1.79 
percent across all the countries, and was considerably higher in Tonga 
(5.2 percent) compared to Fiji (0.04 percent) and the Cook Islands 
(0.13 percent). In Fiji and the Cook Islands, only 9 and 27 clams, 
respectively, remained in 1997 from the original 25,000 and 20,000 
clams delivered to the countries in 1991. In Tonga, 1,300 of the 25,000 
original clams survived to 1997, but many of these were still being 
actively managed in protective cages on the sand flat.
    There have also been a number of countries and territories which 
have cultured or imported T. derasa and T. gigas for the purpose of 
restocking depleted populations or to introduce the species to 
locations outside of its natural range. Because of its relatively fast 
growth rate, T. derasa has been a priority for mariculture throughout 
the Indo-Pacific for many years. There are at least 17 countries and 
territories with hatchery and/or growout facilities that have cultured 
T. derasa for the purpose of enhancing depleted populations (Lindsay et 
al., 2004; Mies, Dor, et al., 2017), and several others that have 
initiated T. derasa restocking programs without domestic hatcheries 
(Teitelbaum & Friedman, 2008).
    There are also numerous mariculture facilities where T. squamosa 
has been cultured successfully, but most are focused primarily on 
commercial production for the ornamental aquarium industry. We are 
aware of facilities in Fiji, Tonga, Cook Islands, Marshall Islands, 
Palau, Papua New Guinea, American Samoa, Samoa, FSM, Solomon Islands, 
Tuvalu, Vanuatu, Japan, Philippines, Malaysia, Indonesia, Thailand, 
Australia, and Hawaii (USA), which produce T. squamosa currently or did 
so in the past (Kittiwattanawong et al., 2001; Lindsay et al., 2004; 
Gomez & Mingoa-Licuanan, 2006; Teitelbaum & Friedman, 2008; Mies, Dor, 
et al., 2017; Neo et al., 2019). While many have experimented with 
outplanting cultured clams with the purpose of restocking natural 
populations, it seems that success of these efforts has been limited in 
most cases for reasons that have been discussed above (e.g., 
difficulties in sustaining funding, monitoring, and protection). For 
example, the Marine Science Institute at the University of the 
Philippines produced 23,020 T. squamosa juveniles in October 2002 and 
distributed the clams throughout the Mindanao region to restock natural 
populations (Gomez & Mingoa-Licuanan, 2006). The fate of this specific 
restocking effort has not been publicly reported, but other species 
that had been outplanted during the same period (primarily T. gigas) 
experienced high mortality in part due to a loss of institutional 
support, which limited the resources and personnel available to 
maintain and monitor the outplants (Gomez & Mingoa-Licuanan, 2006). 
Thus, it is likely that the T. squamosa suffered similarly low 
survivorship.
    We are aware of two examples that have reported some measure of 
success in establishing sustainable populations of T. derasa in the 
wild. In Tonga, village-based nurseries of T. squamosa and T. derasa 
led to a notable increase in juvenile recruitment according to local 
accounts (Chesher, 1993). Villagers of Vava'u conveyed to the author 
that they had never seen so many young clams in surrounding reefs and 
that the children had collected and eaten ``baskets'' of them. This 
account, however, highlights the primary motivation of this effort, 
which was to replenish the natural giant clam stocks to support 
subsistence harvest, not to establish and conserve a sustainable 
population of the species. The most recent published survey of giant 
clams in the Vava'u area found that abundance of T. squamosa was very 
low, likely as a result of the ongoing harvest. Only 3 T. derasa and 10 
T. squamosa were recorded in total across 27 survey sites in the area 
(Atherton et al., 2014). Similarly, with significant financial support 
from the United States, FSM imported approximately 25,000 T. derasa 
from Palau in 1984-90 with the goal of establishing naturally 
reproducing populations on Yap and several of its outer atolls 
(Lindsay, 1995). Because the species is not endemic to FSM, researchers 
were able to easily monitor whether the introduced populations did 
indeed reproduce and recruit successfully. However, a number of 
challenges, including theft, neglect, limited aquaculture skills, and 
storm damage, led to large losses of introduced clams (Lindsay, 1995). 
At the time of the report in 1995, a small percentage (approximately 8 
percent) of introduced T. derasa remained, but there was evidence of 
successful reproduction and recruitment of offspring on surrounding 
reefs. Surveys conducted by the Secretariat of the Pacific Community 
(PROC-Fish/C-CoFish programmes) noted the continued presence of T. 
derasa in Yap in low numbers in mid-2006 (Teitelbaum & Friedman, 2008). 
We were not able to find any more recent monitoring data to indicate 
the current status of this introduced population, but with subsistence 
harvest of giant clams prevalent in FSM (Lindsay, 1995), it is unlikely 
to have grown significantly.
    Beyond these examples, we could not find any other records 
documenting successful giant clam restocking initiatives. As is 
explained by Munro (1993b), efforts to replenish populations in areas 
where giant clams are still harvested should more accurately be viewed 
as ``a form of fishery enhancement,'' in that outplanted individuals 
will simply increase harvest volume rather than contribute to the 
conservation and long-term population growth of the species. In order 
to achieve significant conservation success, restocking initiatives 
must be accompanied by effective enforcement of harvest bans or an 
otherwise substantial reduction of harvest pressure on giant clams. 
However, as is discussed above, subsistence fishing for all giant clam 
species is ongoing throughout their respective ranges, and in most 
locations where harvest bans are in place, regulations are often poorly 
enforced.
    There have also been a number of projects funded by the U.S. 
government seeking to explore markets, marketing strategies, and 
production economics for giant clams, with a particular focus on the 
Pacific islands that are subject to U.S. jurisdiction (Shang et al., 
1990, 1992; Leung et al., 1994). As is described by Wells (1997), these 
projects have sponsored workshops on CITES and giant clam mariculture 
(Killelea-Almonte, 1992), funded hatchery development in American 
Samoa, and provided giant clam aquaculture training support for the 
U.S. Pacific Island territories. In American Samoa, T. derasa, T. 
gigas, and H. hippopus have all been cultured at the government 
hatchery with the ``main aim of establishing local farms to produce 
meat for local market'' (Wells, 1997). Wells (1997) reported that there 
were 6 lagoon nursery sites and 25 small-scale farms in operation in 
1995, but the current status of each of these operations is not clear. 
According to Marra-Biggs et al. (2022), the ``stocks were harvested 
prior to reproduction and appear to be functionally extirpated.'' Samoa 
gifted approximately 650 T. derasa juveniles to American Samoa at the 
end of 2023, but similar to past giant clam nurseries, it appears that 
the primary ambition for this initiative is to establish a sustainable 
food source for the local community (American Samoa Department of 
Marine and Wildlife Resources Agency Report

[[Page 60539]]

2024). In Guam, a giant clam hatchery was established at the Guam 
Aquaculture Development and Training Center and in the past has 
received a number of shipments of T. derasa broodstock from the PMDC 
(Wells, 1997). However, many were lost due to damage from a cyclone in 
1992, leaving approximately 100 specimens alive by 1994 (Wells, 1997). 
The current status of this initiative is not clear, but similar to 
American Samoa, many sources indicate that past attempts at giant clam 
mariculture in Guam have been plagued by persistent poaching. Heslinga 
et al. (1984) also noted that PMDC had shipped 500 T. gigas and 500 T. 
squamosa to the University of Guam Marine Laboratory ``to explore the 
possibility of reintroducing giant clams to areas where they are now 
extinct or very rare.'' However, we could not find any information 
indicating the outcome of these reintroductions, and later reports 
consistently consider T. gigas to be extinct in Guam (Munro, 1994; 
Pinca et al., 2010; Neo et al., 2017). Lastly, there is a report that 
T. gigas and T. squamosa were introduced to Keahole Point, Hawaii as 
part of a 5-year research project by Indo-Pacific Sea Farms to explore 
aquaculture of ornamental marine invertebrates for the aquarium trade 
(Heslinga, 1996). However, we are not aware of any efforts to outplant 
giant clams in Hawaii specifically for the purpose of establishing 
sustainable populations in the wild.
    Thus, while there are many known mariculture facilities throughout 
the Indo-Pacific that have successfully bred and raised giant clams ex 
situ, there is little evidence that these initiatives further the 
protection or conservation of the seven species considered here. 
Without further information or survey data demonstrating such success, 
we consider the impact of these initiatives to be negligible with 
respect to the status of the species.

Proposed Listing Determinations

    We have independently reviewed the best available scientific and 
commercial data, including the petition, public comments submitted in 
response to the 90-day finding (82 FR 28946, June 26, 2017), the Status 
Review Report, and other published and unpublished information. We 
considered each of the statutory factors to determine whether they 
contributed significantly to the extinction risk of each of the seven 
giant clam species considered here, alone or in combination with one 
another. As required by section 4(b)(1)(A) of the ESA, we also took 
into account efforts to protect the species by States, foreign nations, 
or political subdivisions thereof, and evaluated whether those efforts 
provide a conservation benefit to the species.
    Having considered this information in its entirety, we have 
determined that H. porcellanus, T. mbalavuana, and T. squamosina are 
presently in danger of extinction throughout the entirety of their 
respective ranges, T. derasa and T. gigas are in danger of extinction 
in a significant portion of their respective ranges, and H. hippopus is 
likely to become an endangered species within the foreseeable future in 
a significant portion of its range. Therefore, we propose to list H. 
porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. squamosina as 
endangered species and H. hippopus as a threatened species under the 
ESA. We have determined that the fluted clam (T. squamosa) is not 
currently in danger of extinction throughout all or a significant 
portion of its range and is not likely to become so within the 
foreseeable future. Therefore, we find that T. squamosa does not meet 
the definition of a threatened or an endangered species under section 
4(a)(1) of the ESA.
    This finding is consistent with the statute's requirement to base 
our findings on the best scientific and commercial data available, 
which is summarized and analyzed above, and discussed in more detail in 
Rippe et al. (2023).

Similarity of Appearance

    As discussed in the section titled Overutilization for Commercial, 
Recreational, Scientific, or Educational Purposes, giant clams and 
their derivative products (e.g., meat, shells, and shell carvings) are 
traded extensively in international markets and are commonly imported 
into the United States. Beginning in 2009, U.S. customs officials began 
encountering regular shipments of giant clam meat from Pacific island 
nations, chiefly from the Marshall Islands and FSM, but also from Fiji, 
Tonga, Palau, Samoa, Kiribati, and French Polynesia. Law enforcement 
personnel report that the meat is typically frozen in plastic bags or 
bottles and is often shipped in coolers mixed together with various 
other seafood products. The shipments are very rarely accompanied by 
valid CITES permits and are therefore nearly always seized or refused 
entry at the border when discovered.
    LEMIS trade data provided by USFWS indicate that an average of 127 
shipments of giant clam meat originating from the Marshall Islands and 
FSM were seized or refused entry at U.S. ports of entry per year from 
2016 to 2020. These shipments equated to approximately 233 kg and 4,504 
specimens per year, reflecting shipments recorded by weight and by 
number of specimens, respectively. Furthermore, over the past two 
years, U.S. law enforcement has documented an additional 250 cases of 
giant clam meat violations and seizures between December 2021 and 
October 2023 (S. Valentin, USFWS Office of Law Enforcement, pers. 
comm., November 8, 2023). The LEMIS trade data also reveal an average 
of 9 shipments of shell carvings, jewelry, and other worked shell 
products into the United States per year from 2016 to 2020. These 
shipments comprise approximately 152 specimens per year on average, in 
most cases without record of the location or species of origin.
    Critically, for derivative giant clam parts and products, such as 
meat that has been removed from the shell and worked shell items (i.e., 
carvings and jewelry), law enforcement personnel are not able to 
visually determine or verify the species from which the product is 
derived. Therefore, it is possible that these shipments may have 
contained any of the six giant clam species that are proposed for 
listing based on their extinction risk (i.e., H. hippopus, H. 
porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. squamosina).
    Section 4(e) of the ESA authorizes the treatment of a species, 
subspecies, or population segment as endangered or threatened if: ``(a) 
such species so closely resembles in appearance, at the point in 
question, a species which has been listed pursuant to such section that 
enforcement personnel would have substantial difficulty in attempting 
to differentiate between the listed and unlisted species; (b) the 
effect of this substantial difficulty is an additional threat to an 
endangered or threatened species; and (c) such treatment of an unlisted 
species will substantially facilitate the enforcement and further the 
policy of this Act.''
    The aforementioned reports from U.S. law enforcement personnel make 
it clear that the similarity of appearance between worked products 
derived from the species that are proposed for listing (i.e., H. 
hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, T. 
squamosina) and those from the species that are not proposed for 
listing (i.e., T. crocea, T. maxima, T. noae, and T. squamosa) causes 
substantial difficulty for law enforcement personnel in attempting to 
differentiate between the six species proposed for listing and the 
other four species that are not. Law enforcement personnel have 
expressed confidence in distinguishing the meat of

[[Page 60540]]

giant clams from that of other marine fauna based on visual 
characteristics, but note that visual differentiation between giant 
clam species is not possible.
    Furthermore, the difficulty in distinguishing the species from 
which worked products are derived is an additional threat to the six 
species proposed to be listed under section 4(a)(1) of the Act. Due to 
the inadequacy of existing regulations, lack of enforcement capacity, 
and typical harvesting practices in most Pacific island nations (see 
sections titled Overutilization for Commercial, Recreational, 
Scientific, or Educational Purposes and The Inadequacy of Existing 
Regulatory Mechanisms), it is possible, if not likely, that giant clam 
specimens reaching U.S. ports are harvested opportunistically with 
little regard for the species collected. Moreover, neither the Marshall 
Islands nor FSM are signatories to CITES and have not demonstrated the 
capacity to assess and regulate the trade of protected species. Because 
of these regulatory inadequacies and the aforementioned U.S. 
enforcement challenges, it is feasible that persons engaging in 
commerce involving derivative products from one of the six species 
proposed to be listed could misrepresent, either accidentally or 
purposefully, that such products are derived from a species that has 
not been proposed for listing. For example, a recent forensic 
investigation revealed that several recent seizures of giant clam meat 
contained specimens that were identified genetically as H. hippopus, T. 
gigas, and T. maxima, a combination of species that are and are not 
proposed to be listed. The meat of the three species was otherwise 
indistinguishable by law enforcement personnel, highlighting the 
substantial difficulty in differentiating the species visually and the 
potential for those species that are proposed to be listed as 
threatened or endangered to be misrepresented as species that are not 
proposed to be listed in shipments to the United States. In addition, 
given the significant volume of giant clam meat and shell products 
intercepted by law enforcement personnel on a regular basis, it is not 
always possible to conduct detailed forensic analyses due to a limited 
capacity to store and process the samples on site.
    In order for the ESA's import and export restrictions to be 
effective, enforcement personnel must be able to quickly determine 
whether derivative parts or products are from a listed species at U.S. 
ports of entry and take appropriate enforcement action to suppress 
illegal trade. Misrepresentation of the species of giant clam would 
prevent effective enforcement of the import and export restrictions on 
the species proposed to be listed, because enforcement personnel will 
not be able to visually determine which species derivative parts or 
products are from. The high risk of misrepresentation, coupled with the 
visual similarity of certain derivative part or products of giant clams 
species, creates a loophole that would undermine the effectiveness of 
import and export restrictions imposed under section 9(a)(1)(A) of the 
ESA. The effect of this loophole--the weakened deterrent value of the 
Act in protecting the species proposed to be listed due to the 
substantial difficulty in visually distinguishing derivative parts or 
products among different species of giant clams--is an additional 
threat to the species that we propose to list under section 4(a)(1).
    The similarity of appearance regulation proposed by NMFS in this 
action would substantially facilitate enforcement of the ESA's import 
and export restrictions, because it would allow enforcement personnel 
to easily identify and take enforcement action when they identify 
derivative parts or product from giant clams at U.S. ports of entry. 
Without a similarity of appearance regulation, derivative parts and 
products from a listed giant clam species could easily be mislabeled 
and imported to or exported from the U.S. This would substantially 
undermine the enforcement of regulations under section 9(a)(1) and 
section 4(d) for the protection of the proposed endangered and 
threatened species, respectively. We therefore propose to list T. 
crocea, T. maxima, T. noae, and T. squamosa as threatened species under 
the authority of section 4(e) of the ESA. These four species have 
ranges that overlap the Pacific region where virtually all of the 
shipments of giant clam meat to the U.S. originate. Taking this action 
would alleviate an enforcement challenge that has the potential to 
contribute to unauthorized commerce of endangered and threatened giant 
clam species in the U.S. and would provide for the conservation of 
these species under the ESA.

Effects of This Rulemaking

    Conservation measures provided for species listed as endangered or 
threatened under the ESA include recovery actions (16 U.S.C. 1533(f)); 
concurrent designation of critical habitat, if prudent and determinable 
(16 U.S.C. 1533(a)(3)(A)); Federal agency requirements to consult with 
NMFS under section 7 of the ESA to ensure their actions are not likely 
to jeopardize the species or result in adverse modification or 
destruction of critical habitat should it be designated (16 U.S.C. 
1536); and, for endangered species, prohibitions on ``taking'' (16 
U.S.C. 1538). Recognition of the species' plight through listing also 
promotes conservation actions by Federal and State agencies, foreign 
entities, private groups, and individuals.

Identification of Those Activities That Would Constitute a Violation of 
Section 9 of the ESA

    All of the prohibitions of section 9(a)(1) of the ESA will apply to 
the five species of giant clams that are proposed to be listed as 
endangered (i.e., H. porcellanus, T. derasa, T. gigas, T. mbalavuana, 
and T. squamosina), should the proposed rule be adopted. We are also 
proposing to extend the section 9(a)(1) prohibitions to H. hippopus. 
Section 9(a)(1) prohibits import; export; delivery, receipt, carriage, 
transport, or shipment in interstate or foreign commerce of the 
species, by any means whatsoever and in the course of commercial 
activity; or sale or offer for sale in interstate or foreign commerce. 
Section 9(a)(1) also prohibits take within the United States or on the 
high seas; or to possess, sell, deliver, carry, transport, or ship a 
species that has been taken in violation of the ESA.
    On July 1, 1994, NMFS and USFWS published a policy (59 FR 34272) 
that requires us to identify, to the maximum extent practicable at the 
time a species is listed, those activities that would or would not 
constitute a violation of section 9 of the ESA. The intent of this 
policy is to increase public awareness of the effect of a listing on 
proposed and ongoing activities within a species' range. Based on 
available information, we believe that the following categories of 
activities are most likely to result in a violation of the ESA section 
9 prohibitions should the proposed rule be adopted. We emphasize that 
whether a violation results from a particular activity is dependent on 
the facts and circumstances of each incident. The mere fact that an 
activity may fall within one of the categories does not mean that the 
specific activity will cause a violation; due to such factors as 
location and scope, specific actions may not result in direct or 
indirect adverse effects on a species. Further, an activity not listed 
may in fact result in a violation. However, based on currently 
available information, we believe the following types of activities 
that could result in a violation of section 9 prohibitions include, but 
are not limited to, the following:

[[Page 60541]]

    (1) Take of any listed species within the U.S. or its territorial 
sea, or upon the high seas. Take is defined in section 3 of the ESA as 
``to harass, harm, pursue, hunt, shoot, wound, kill, trap, capture, or 
collect, or to attempt to engage in any such conduct'';
    (2) Possessing, delivering, transporting, or shipping any 
individual or part of listed species (dead or alive) taken in violation 
of section 9(a)(1)(B) or 9(a)(1)(C);
    (3) Delivering, receiving, carrying, transporting, or shipping in 
interstate or foreign commerce any individual or part of listed 
species, in the course of a commercial activity, even if the original 
taking was legal;
    (4) Selling or offering for sale in interstate or foreign commerce 
any part of listed species, except antique articles at least 100 years 
old;
    (5) Exporting or importing any individual or part of listed species 
to or from any country;
    (6) Releasing captive or cultured specimens of listed species into 
the wild. Although specimens held non-commercially in captivity at the 
time of listing are exempt from certain prohibitions, the individual 
animals are considered listed and afforded most of the protections of 
the ESA, including most importantly the prohibitions against injuring 
or killing of endangered species. Release of a captive animal has the 
potential to injure or kill the animal. Of an even greater conservation 
concern, the release of a captive animal has the potential to affect 
wild populations through introduction of diseases or inappropriate 
genetic mixing. Depending on the circumstances of the case, NMFS may 
authorize the release of a captive animal through a section 10(a)(1)(A) 
permit;
    (7) Altering the habitat of listed species in such a way that 
results in injury or death of the species, such as removing or altering 
substrate or other physical structures, activities resulting in 
elevated water temperatures that lead to bleaching or other degradation 
of the physiological functions of listed species, and activities 
resulting in altered water chemistry and/or water acidification that 
lead to reduced calcification rates, reproductive impairment, or other 
degradation of physiological functions of listed species; and
    (8) Discharging pollutants or organic nutrient-laden water, 
including sewage water, into the habitat of listed species to an extent 
that harms or kills listed species.
    This list provides examples of the types of activities that are 
likely to cause a violation, but it is not exhaustive. Persons or 
entities concluding that their activity is likely to violate the ESA 
are encouraged to immediately adjust that activity to avoid violations 
and to seek authorization under: (a) an ESA section 10(a)(1)(B) 
incidental take permit; (b) an ESA section 10(a)(1)(A) research and 
enhancement permit; or (c) an ESA section 7 consultation. The public is 
encouraged to contact us (see FOR FURTHER INFORMATION CONTACT) for 
assistance in determining whether circumstances at a particular 
location, involving these activities or any others, might constitute a 
violation of the ESA. Furthermore, the scientific research community is 
encouraged to submit applications for research to be conducted on H. 
hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. 
squamosina so that the research can continue uninterrupted should this 
proposed rule be adopted.

Identification of Those Activities That Would Not Constitute a 
Violation of Section 9 of the ESA

    We have also identified, based on information available at this 
time, categories of activities that are not considered likely to result 
in a violation of section 9 should the proposed rule be adopted. As 
noted above, whether a violation results from a particular activity is 
entirely dependent on the facts and circumstances of each incident, and 
it is possible that specific actions taken on this list may in fact 
result in a violation. However, although not binding, we consider the 
following actions as not likely to result in violations of ESA section 
9:
    (1) Take authorized by, and carried out in accordance with the 
terms and conditions of, an ESA section 10(a)(1)(A) permit issued by 
NMFS for purposes of scientific research or the enhancement of the 
propagation or survival of the listed species;
    (2) Incidental take of a listed species resulting from Federally 
authorized, funded, or conducted projects for which consultation under 
section 7 of the ESA has been completed, and when the otherwise lawful 
activity is conducted in accordance with any terms and conditions 
granted by NMFS in an incidental take statement of a biological opinion 
pursuant to section 7 of the ESA;
    (3) Continued possession of listed species that were in captivity 
at the time of listing, including any progeny produced from captive 
specimens after the rule is finalized, so long as the prohibitions of 
ESA section 9(a)(1) are not violated. Specimens are considered to be in 
captivity if they are maintained in a controlled environment (e.g., 
land-based aquaria) or under human care in open-water nurseries (i.e., 
protected nearshore enclosures under the active management of humans). 
Specimens are not considered to be in captivity if they have been 
outplanted to a natural habitat or restoration site. Individuals or 
organizations should be able to provide evidence that specimens or 
parts of listed species were in captivity prior to their listing. 
Captive specimens may be non-commercially exported or imported; 
however, the importer or exporter must be able to provide evidence to 
show that the parts meet the criteria of ESA section 9(b)(1) (i.e., 
held in a controlled environment at the time of listing, in a non-
commercial activity);
    (4) Providing normal care for legally-obtained captive specimens of 
listed species. Normal care includes handling, cleaning, maintaining 
water quality within an acceptable range, extracting tissue samples for 
the purposes of disease diagnosis or genetics, and treating of maladies 
such as disease or parasites using established methods proven to be 
effective;
    (5) Interstate transportation of legally-obtained captive specimens 
or parts of listed species, provided it is not in the course of a 
commercial activity. If captive specimens of listed species are to be 
moved to a different holding location, records documenting the transfer 
should be maintained;
    (6) Use of captive specimens of listed species for scientific 
studies under the authorization of an ESA section 10(a)(1)(A) permit 
issued by NMFS;
    (7) Import or export of live specimens or parts of listed species 
with all accompanying CITES export permits and an ESA section 
10(a)(1)(A) permit for purposes of scientific research or the 
enhancement of the propagation or survival of the species.

Protective Regulations for Threatened Species Under Section 4(d) of the 
ESA

    We are proposing to list H. hippopus as a threatened species under 
section 4(a)(1). The ESA does not specify particular prohibitions for 
threatened species. For species listed as threatened, the second 
sentence in section 4(d) of the ESA authorizes the Secretary to extend 
any or all of the prohibitions identified in section 9(a)(1) for 
endangered species to threatened species. We therefore propose to 
extend the section 9(a)(1) prohibitions in protective regulations 
issued under the second sentence of section 4(d) to H. hippopus. No 
special findings are required to support extending section 9 
prohibitions for the protection of threatened species. See In re Polar 
Bear Endangered Species Act Listing and 4(d) Rule Litigation, 818 
F.Supp.2d 214, 228

[[Page 60542]]

(D.D.C. 2011); Sweet Home Chapter of Cmties. for a Great Oregon v. 
Babbitt, 1 F.3d 1, 8 (D.C. Cir. 1993), modified on other grounds on 
reh'g, 17 F.3d 1463 (D.C. Cir. 1994), rev'd on other grounds, 515 U.S. 
687 (1995).
    We are also proposing to list T. crocea, T. maxima, T. noae, and T. 
squamosa as threatened species under section 4(e) of the ESA. Because 
these listings are being proposed on the basis of similarity of 
appearance rather than the extinction risk of these four species, we 
are not proposing to extend the section 9(a)(1) prohibitions to these 
species in a blanket fashion. Rather, we aim to facilitate the 
protection of H. hippopus, H. porcellanus, T. derasa, T. gigas, T. 
mbalavuana, and T. squamosina by mitigating the challenge that law 
enforcement personnel face in determining the species of origin for 
derivative parts and products of giant clams, such as meat and shell 
carvings, in imports and exports into and from the United States and 
its territories.
    To do so, we are proposing to apply the ESA section 9(a)(1)(A) 
prohibition of import into and export from the United States and its 
territories to T. crocea, T. maxima, T. noae, and T. squamosa, but 
limit the prohibition to derivative parts and products for which the 
species of origin cannot be visually determined. For the purpose of 
this regulation, ``derivative parts and products'' are defined as: (a) 
any tissue part that has been removed from the shell, including mantle 
tissue, adductor muscle, portions thereof, or the whole flesh of the 
animal comprising both the mantle and adductor muscle; (b) any worked 
shell product, including handicrafts, sculptures, jewelry, tableware, 
decorative ornaments, and other carvings, but not raw, unworked shells; 
and (c) pearls or any product derived from a pearl. This prohibition 
would apply to commercial and non-commercial shipments of any such 
products of T. crocea, T. maxima, T. noae, and T. squamosa and would 
make it unlawful for any person subject to the jurisdiction of the 
United States to import such products into or export such products from 
the United States or its territories.
    No other prohibitions under section 9 of the ESA are proposed to be 
extended to these four species. A person would continue to be able to 
possess, deliver, carry, transport, ship, sell, or offer to sell T. 
crocea, T. maxima, T. noae, and T. squamosa, and their parts and 
products, domestically and in interstate and foreign commerce. We have 
information indicating that all four of these species occur within the 
waters of at least one U.S. Pacific Island territory. T. maxima, in 
particular, is the target of several mariculture initiatives intended 
to establish a sustainable source of food and income for communities in 
American Samoa, Guam, and CNMI. The best available scientific and 
commercial information indicates that none of the other six species 
that we are proposing to list as endangered or threatened based on 
their extinction risk are still extant within U.S. waters. Therefore, 
it is unlikely that domestic activities and interstate commerce 
involving T. crocea, T. maxima, T. noae, or T. squamosa would threaten 
the status or recovery of H. hippopus, H. porcellanus, T. derasa, T. 
gigas, T. mbalavuana, and T. squamosina throughout their current range. 
For this reason, we are not proposing to prohibit these activities.
    We are also not proposing to prohibit the import or export of live 
or intact specimens or raw, unworked shells of T. crocea, T. maxima, T. 
noae, T. squamosa into or from the United States and its territories. 
As mentioned above, there are several initiatives within the United 
States focused on culturing one or more of T. crocea, T. maxima, T. 
noae, and T. squamosa for the purpose of providing food and income to 
local communities. These operations often rely on the international 
trade of live broodstock or juveniles between mariculture facilities to 
initiate or supplement a culture stock. We have no information to 
suggest that live or intact specimens or raw, unworked shells of giant 
clams are being misrepresented as incorrect species in imports or 
exports into or from the United States, nor that law enforcement 
personnel have substantial difficulties visually differentiating the 
species of origin for such shipments. Thus, there is little risk that 
imports or exports of live or intact T. crocea, T. maxima, T. noae, and 
T. squamosa or raw, unworked shells of these species into or from the 
United States or its territories would threaten the status or recovery 
of H. hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and 
T. squamosina in the wild. We are therefore not proposing to prohibit 
those activities.

Identifying Section 7 Conference and Consultation Requirements

    Section 7(a)(4) (16 U.S.C. 1536(a)(4)) of the ESA and NMFS/USFWS 
regulations (50 CFR 402.10) require Federal agencies to confer with 
NMFS on actions likely to jeopardize the continued existence of species 
proposed for listing, or that are likely to result in the destruction 
or adverse modification of proposed critical habitat of those species. 
If a proposed species is ultimately listed, under section 7(a)(2) (16 
U.S.C. 1536(a)(2)) of the ESA and the NMFS/USFWS regulations (50 CFR 
part 402), Federal agencies must consult on any action they authorize, 
fund, or carry out if those actions may affect the listed species or 
its critical habitat to ensure that such actions are not likely to 
jeopardize the continued existence of the species or result in adverse 
modification or destruction of critical habitat should it be 
designated. Examples of Federal actions that may affect giant clams 
include, but are not limited to: alternative energy projects, discharge 
of pollution from point sources, non-point source pollution, 
contaminated waste disposal, dredging, pile-driving, development of 
water quality standards, and military activities.

Critical Habitat

    Critical habitat is defined in section 3 of the ESA (16 U.S.C. 
1532(3)) as: (1) the specific areas within the geographical area 
occupied by a species, at the time it is listed in accordance with the 
ESA, on which are found those physical or biological features (a) 
essential to the conservation of the species and (b) that may require 
special management considerations or protection; and (2) specific areas 
outside the geographical area occupied by a species at the time it is 
listed upon a determination that such areas are essential for the 
conservation of the species. ``Conservation'' means the use of all 
methods and procedures needed to bring the species to the point at 
which listing under the ESA is no longer necessary. Section 4(a)(3)(A) 
of the ESA (16 U.S.C. 1533(a)(3)(A)) requires that, to the extent 
prudent and determinable, critical habitat be designated concurrently 
with the listing of a species. Designations of critical habitat must be 
based on the best scientific data available and must take into 
consideration the economic, national security, and other relevant 
impacts of specifying any particular area as critical habitat. Critical 
habitat cannot be designated within foreign countries or in other areas 
outside the jurisdiction of the United States (50 CFR 424.12(g)). Thus, 
with respect to H. porcellanus, T. mbalavuana, and T. squamosina, which 
have highly restricted ranges that are entirely outside the 
jurisdiction of the United States, we cannot designate any areas as 
critical habitat within their occupied ranges.
    At this time, critical habitat is not yet determinable for H. 
hippopus, T. derasa, and T. gigas, which are believed to occur in areas 
under U.S. jurisdiction, because data sufficient to perform

[[Page 60543]]

required analyses are lacking. See 50 CFR 424.12(a)(2). Therefore, we 
are not proposing to designate critical habitat for these species at 
this time. However, we invite public comments on physical and 
biological features and areas in U.S. waters that may be essential to 
these species and well as any other information that may inform our 
consideration of designating critical habitat for these three species 
(see Public Comments Solicited).
    Designation of critical habitat would not be applicable to T. 
crocea, T. maxima, T. noae, and T. squamosa, because these species are 
proposed to be listed due to their similarity of appearance to H. 
hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. 
squamosina, rather than on the basis of their extinction risk.

Role of Peer Review

    In December 2004, the Office of Management and Budget (OMB) issued 
a Final Information Quality Bulletin for Peer Review establishing 
minimum peer review standards, a transparent process for public 
disclosure of peer review planning, and opportunities for public 
participation. The OMB Bulletin, implemented under the Information 
Quality Act (Pub. L. 106-554) is intended to enhance the quality and 
credibility of the Federal Government's scientific information, and 
applies to influential or highly influential scientific information 
disseminated on or after June 16, 2005. To satisfy our requirements 
under the OMB Bulletin, we obtained independent peer review of the 
draft Status Review Report. Three independent specialists were selected 
from the academic and scientific community for this review. After 
substantial revision of the Status Review Report following an initial 
round of peer review, one of the reviewers agreed to provide a second 
review of the updated version, and one additional review was received 
from a fourth expert from the scientific community. All peer reviewer 
comments were addressed prior to dissemination of the Status Review 
Report and publication of this document. The peer review report can be 
found online (see ADDRESSES).

Public Comments Solicited

    To ensure that the final action resulting from this proposal will 
be as accurate and effective as possible, we solicit comments and 
suggestions from the public, other governmental agencies, the 
scientific community, industry, environmental groups, territorial 
governments, cultural practitioners, indigenous communities, and any 
other interested parties. Comments are encouraged on this proposal (see 
DATES and ADDRESSES). Specifically, we are interested in information 
regarding: (1) new or updated information regarding the range, 
distribution, and abundance of the six giant clam species proposed for 
listing based on their extinction risk (H. hippopus, H. porcellanus, T. 
derasa, T. gigas, T. mbalavuana, and T. squamosina); (2) new or updated 
information regarding their genetics and population structure; (3) 
habitat within their range that was present in the past but may have 
been lost over time; (4) new or updated biological or other relevant 
data concerning any threats to these giant clams; (5) current or 
planned activities within their range and the possible impact of these 
activities on the relevant species; (6) recent observations or sampling 
of H. hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and 
T. squamosina; and (7) efforts being made to protect or recover natural 
populations of these species, and documented results of such efforts.

Public Comments Solicited on Critical Habitat

    We request information describing the quality and extent of 
habitats for the three giant clam species proposed for listing based on 
their extinction risk and that occur in areas under U.S. jurisdiction 
(i.e., H. hippopus, T. derasa, and T. gigas), as well as information on 
areas that may qualify as critical habitat for these three species in 
U.S. waters. Specific areas that include the physical and biological 
features essential to the conservation of the species, where such 
features may require special management considerations or protection, 
should be identified. Areas outside the occupied geographical area 
should also be identified, if such areas may be essential to the 
conservation of the species. As noted previously, ESA implementing 
regulations at 50 CFR 424.12(g) specify that critical habitat shall not 
be designated within foreign countries or in other areas outside of 
U.S. jurisdiction. Therefore, we request information only on potential 
areas of critical habitat within waters under U.S. jurisdiction.
    Section 4(b)(2) of the ESA requires the Secretary to consider the 
economic impact, impact on national security, and any other relevant 
impact of designating a particular area as critical habitat. Section 
4(b)(2) also authorizes the Secretary to exclude from a critical 
habitat designation those particular areas where the Secretary finds 
that the benefits of exclusion outweigh the benefits of designation, 
unless excluding that area will result in extinction of the species. 
For features and areas potentially qualifying as critical habitat, we 
also request information describing: (1) Activities or other threats to 
the essential features or activities that could be affected by 
designating them as critical habitat; and (2) the positive and negative 
economic, national security and other relevant impacts, including 
benefits to the recovery of the species, likely to result if these 
areas are designated as critical habitat. We seek information regarding 
the conservation benefits of designating areas within waters under U.S. 
jurisdiction as critical habitat. In keeping with the guidance provided 
by OMB (2000; 2003), we seek information that would allow the 
monetization of these effects to the extent possible, as well as 
information on qualitative impacts to economic values.
    Data reviewed may include, but are not limited to: (1) scientific 
or commercial publications; (2) administrative reports, maps or other 
graphic materials; (3) information received from experts; and (4) 
comments from interested parties. Comments and data particularly are 
sought concerning: (1) maps and specific information describing the 
abundance and distribution of H. hippopus, T. derasa, and/or T. gigas, 
as well as any additional information on occupied and unoccupied 
habitat areas; (2) the reasons why any habitat should or should not be 
determined to be critical habitat as provided by sections 3(5)(A) and 
4(b)(2) of the ESA; (3) information regarding the benefits of 
designating particular areas as critical habitat; (4) current or 
planned activities in the areas that might be proposed for designation 
and their possible impacts; and (5) any foreseeable economic or other 
potential impacts resulting from designation, and in particular, any 
impacts on small entities.
    You may submit your comments and supporting information concerning 
this proposal electronically, by mail (see ADDRESSES), or during public 
hearings (see DATES). The proposed rule and supporting documentation 
can be found on the Federal eRulemaking Portal at https://www.regulations.gov by entering NOAA-NMFS-2017-0029 in the Search box.

Public Informational Meetings and Public Hearings

    Section 4(b)(5)(E) of the ESA requires us to promptly hold at least 
one public hearing if any person requests one within 45 days of 
publication of a proposed rule to implement a species listing 
determination. Public hearings provide a forum for accepting formal

[[Page 60544]]

verbal comments on this proposed rule. Prior to each public hearing, we 
will provide an overview of the proposed rule during a public 
informational meeting. In-person and virtual public hearings on this 
proposed rule will be held during the public comment period at dates, 
times, and locations to be announced in a forthcoming Federal Register 
notice. Requests for additional public hearings must be made in writing 
(see ADDRESSES) by September 9, 2024.

References

    A complete list of the references used in this proposed rule is 
available upon request (see FOR FURTHER INFORMATION CONTACT).

Classification

National Environmental Policy Act (NEPA)

    The 1982 amendments to the ESA, in section 4(b)(1)(A), restrict the 
information that may be considered when assessing species for listing. 
Based on this limitation of criteria for a listing decision and the 
opinion in Pacific Legal Foundation v. Andrus, 675 F. 2d 825 (6th Cir. 
1981), we have concluded that ESA listing actions are not subject to 
the environmental assessment requirements of NEPA (see NOAA 
Administrative Order 216-6A (2016) and the companion manual, ``Policy 
and Procedures for Compliance with the National Environmental Policy 
Act and Related Authorities,'' which became effective January 13, 2017 
(``Companion Manual''), at 2).
    Further, we conclude that extension of the ESA section 9(a)(1) 
protections in a blanket or categorical fashion is a form of 
ministerial action taken under the authority of the second sentence of 
ESA section 4(d). Courts have found that it is reasonable to interpret 
the second sentence of section 4(d) as setting out distinct authority 
from that of the first sentence, which is invoked when the agency 
proposes tailored or special protections that go beyond the standard 
section 9 protections. See In re Polar Bear Endangered Species Act 
Listing and 4(d) Rule Litigation, 818 F. Supp. 2d 214, 228 (D.D.C. 
2011); Sweet Home Chapter of Cmties. for a Great Oregon v. Babbitt, 1 
F.3d 1, 8 (D.C. Cir. 1993), modified on other grounds on reh'g, 17 F.3d 
1463 (D.C. Cir. 1994), rev'd on other grounds, 515 U.S. 687 (1995). 
This type of action is covered under the NOAA categorical exclusion G7, 
which applies to ``policy directives, regulations and guidelines of an 
administrative, financial, legal, technical or procedural nature . . 
.'' See Companion Manual, Appx. E. None of the extraordinary 
circumstances identified in Sec.  4.A. of the Companion Manual apply.
    However, the promulgation of ESA section 4(d) protective 
regulations in association with the proposed listing of T. crocea, T. 
maxima, T. noae, and T. squamosa as threatened species is subject to 
the requirements of NEPA and we have prepared a draft Environmental 
Assessment (EA) analyzing the proposed 4(d) regulation for these 
species and alternatives. We are seeking comment on the draft EA, which 
is available on the Federal eRulemaking Portal (https://www.regulations.gov/) or upon request (see DATES and ADDRESSES, above).

Regulatory Flexibility Act

    As noted in the Conference Report on the 1982 amendments to the 
ESA, economic impacts cannot be considered when assessing the status of 
a species. Therefore, the economic analyses required by the Regulatory 
Flexibility Act are not applicable to the listing process nor the 
ministerial extension of the section 9(a) prohibitions to H. hippopus.
    However, the promulgation of ESA section 4(d) protective 
regulations in association with the proposed listing of T. crocea, T. 
maxima, T. noae, and T. squamosa as threatened species is subject to 
the requirements of the Regulatory Flexibility Act. We have prepared an 
initial regulatory impact analysis (IRFA) in accordance with section 
603 of the Regulatory Flexibility Act (5 U.S.C. 601, et seq.). The IRFA 
analyzes the impacts to small entities that may be affected by the 
proposed 4(d) regulations for T. crocea, T. maxima, T. noae, and T. 
squamosa. To review the IRFA, see the ADDRESSES section above. We 
welcome comments on this IRFA, which is summarized below.
    The IRFA first identified the types and approximate number of small 
entities that would be subject to regulation under the proposed rule. 
It then evaluated the potential for the proposed rule to incrementally 
impact small entities (i.e., result in impacts to small entities beyond 
those that would be incurred due to existing regulations but absent the 
proposed rule). The IRFA was informed by data gathered from the Small 
Business Administration (SBA), Dun and Bradstreet, Inc., the CITES 
trade database, and the LEMIS trade database.
    The IRFA examined the potential economic impacts on small entities 
of the proposed prohibition on the import and export of derivative 
parts and products of T. crocea, T. maxima, T. noae, and T. squamosa 
into and from the United States. It focused specifically on products 
that would otherwise be cleared by U.S. Customs and Border Protection 
officials and whose purpose of import or export is either commercial 
trade or non-personal exhibition. The prohibition on import or export 
of products coded as personal property by U.S. Customs and Border 
Protection officials would not impact a small business or other small 
entity, and any imports or exports of parts accompanied by both a valid 
CITES export permit and an ESA section 10(a)(1)(A) permit for purposes 
of scientific research or the enhancement of the propagation or 
survival of the species would be exempted from the proposed 
prohibition.
    The IRFA anticipates that the proposed prohibition on the import 
and export of derivative parts and products of T. crocea, T. maxima, T. 
noae, and T. squamosa would apply to thousands of small entities, but 
that only a small subset of these small entities would be impacted and 
impacts would be minor. Any additional costs associated with 
enforcement of the rule would be incurred by government agencies that 
do not qualify as small entities, and it is unlikely that the proposed 
rule would affect any small governmental jurisdictions.
    The small entities most likely to be directly impacted by the 
proposed rule include those classified under the North American 
Industry Classification System (NAICS) as Jewelry, Watch, Precious 
Stone, and Precious Metal Merchant Wholesalers (NAICS industry code 
423940) and Museums (NAICS industry code 712110). According to data 
gathered from the Dun and Bradstreet Hoovers database, there are 
approximately 25,000 U.S. small entities classified as Jewelry, Watch, 
Precious Stone, and Precious Metal Merchant Wholesalers and 
approximately 47,000 museums in the U.S. that qualify as small 
entities. Under the proposed rule, wholesalers could lose revenue that 
would otherwise be generated through the importation and sale, or 
exportation, of the derivative parts and products for commercial 
purposes. Museums or similar entities that would otherwise import and 
exhibit derivative parts and products could lose revenue if attendance 
declines as a result of an artistic item not being exhibited.
    LEMIS trade data provided by the USFWS for the years 2016-2020 
indicate that there were two imports into and two exports from the 50 
states and the District of Columbia over these years of derivative 
parts or products of giant clams that were cleared by U.S. Customs and 
Border Protection officials

[[Page 60545]]

and whose purpose of import or export was either commercial trade or 
non-personal exhibition. As there is no basis for expecting an increase 
in the rate of U.S. import or export of derivative parts or products of 
giant clams over the foreseeable future, the IRFA assumes that the 
number, type, and dollar value of imports and exports of these products 
over the years 2016-2020 reasonably represents the composition of trade 
of these products that would occur in the future, absent the proposed 
rule. Based on a combined value of $19,000 of U.S. imports and exports 
of derivative parts or products of giant clams from 2016 to 2020 for 
the purpose of commercial trade, this IRFA estimates that the proposed 
rule would result in annualized impacts on wholesalers of $3,700 (2023 
dollars). Revenue losses to museums cannot be quantified with available 
data but are expected to be minor, as there was only one import into 
and one export from the U.S. of a derivative product of giant clams 
between the years 2016-2020 for the purpose of exhibition in a museum. 
The item, a carving valued at $44,000 (2023 dollars), was imported into 
and then exported from the U.S. in 2018. While it is possible that the 
proposed rule could result in a small entity wholesaler or museum with 
low annual revenue bearing impacts that constitute a large percentage 
of their annual revenue, this outcome is highly uncertain. Based on the 
low volume of annual U.S. imports and exports of derivative parts or 
products of giant clams, it is more likely that impacts on small 
entities would be minor and limited to a very small number of small 
entities.
    The RFA requires consideration of any significant alternatives to 
the proposed rule that would accomplish the stated objectives of the 
applicable statutes and would minimize significant economic impacts to 
small entities. We considered the following alternatives when 
developing this proposed rule.
    Alternative 1. No-action Alternative. Under the No-action 
Alternative, NMFS would not apply any protective regulations in 
association with the proposed listing of T. crocea, T. maxima, T. noae, 
and T. squamosa as threatened species under section 4(e) of the ESA, 
and there would be no change from current management policies of these 
four species. Alternative 1 represents the regulatory status quo with 
respect to T. crocea, T. maxima, T. noae, and T. squamosa, but assumes 
that H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. 
squamosina would be listed as endangered and H. hippopus would be 
listed as threatened under the ESA due to their extinction risk.
    Without a prohibition on the import into and export from the U.S. 
of derivative parts and products derived from T. crocea, T. maxima, T. 
noae, and T. squamosa, derivative parts and products derived from any 
of the six species proposed to be listed due to their extinction risk 
could be misidentified by law enforcement officials as deriving from 
these four species. Thus, Alternative 1 would undermine the listing of 
T. crocea, T. maxima, T. noae, and T. squamosa based on the similarity 
of appearance of their derivative products to those of the six species 
proposed to be listed due to their extinction risk, as their listing 
would provide no incremental benefit to the survival and recovery of 
six species proposed to be listed as endangered or threatened. No 
incremental impacts would be borne by small (or large) entities, but H. 
hippopus, H. porcellanus, T. derasa, T. gigas, T. mbalavuana, and T. 
squamosina would continue to be at risk of further declines in 
abundance and increased risk of extinction due to international trade 
of their derivative parts and products. Thus, Alternative 1 is not a 
reasonable alternative.
    Alternative 2. Proposed Alternative. Under the Proposed 
Alternative, the import into and export from the U.S. of derivative 
parts and products from T. crocea, T. maxima, T. noae, and T. squamosa 
would be prohibited. This alternative would allow for import into and 
export from the U.S. of live and intact specimens and raw, unworked 
shells of these species, as well as the delivery, receipt, carry, 
transport, or shipment, and sale or offer for sale of these species and 
their derivative parts and products in interstate commerce. Impacts on 
small entities would be limited to revenue losses borne by small entity 
wholesalers or museums or other non-personal exhibitors of giant clam 
products that, absent the Proposed Alternative, would engage in the 
import and/or export of parts and products derived from these four 
species. Small entities that, absent the Proposed Alternative, would 
engage in the export of parts and products derived from maricultured T. 
crocea, T. maxima, T. noae, and T. squamosa specimens would be impacted 
to the extent that they would otherwise generate revenue from such 
exports. However, no information is available suggesting this type of 
international trade would occur over the foreseeable future in the 
absence of the Proposed Action. Alternative 2 was selected as the 
Proposed Alternative because it would contribute to the survival and 
recovery of six species of giant clams proposed to be listed as 
endangered or threatened due to their extinction risk without 
constraining international trade of live or intact specimens or shells 
of T. crocea, T. maxima, T. noae, and T. squamosa, or domestic 
activities involving these four species.
    Alternative 3. Application of All ESA section 9(a)(1) Prohibitions 
(Full Action Alternative). Alternative 3 would apply all section 
9(a)(1) prohibitions of the ESA to T. crocea, T. maxima, T. noae, and 
T. squamosa. Prohibitions under this alternative would include, but not 
be limited to, the import, export, possession, sale, delivery, 
carrying, transport, or shipping of these species--including live or 
intact specimens and shells--in interstate or foreign commerce or for 
commercial activity. Imports and exports of live specimens would be 
permitted under the Proposed Alternative but prohibited under 
Alternative 3, which, relative to the Proposed Action and No-action 
Alternative, would incrementally impact small entities to the extent 
that they would otherwise generate revenue from sale of these four 
species of giant clams or their derivative products. The total value of 
U.S. imports of live specimens of T. crocea, T. maxima, T. noae, and T. 
squamosa from 2016 to 2020 was approximately $3.12 million (2023 
dollars), while exports had a total value of approximately $113,000. 
Small businesses in the Pet and Supplies Retailers and Other 
Miscellaneous Nondurable Goods Merchant Wholesalers industries (NAICS 
codes 424990 and 459910) would bear the vast majority of these impacts, 
which would likely be concentrated among a small number of companies. 
Incremental impacts of Alternative 3 on small entities could also be 
substantially greater than those that would occur under the Proposed 
Alternative in part because the prohibitions on take and interstate 
commerce would significantly constrain the development of giant clam 
mariculture projects in the U.S., notably those in the U.S. Pacific 
Island territories. Alternative 3 would impact small entities to the 
extent that they would otherwise generate revenue from these 
mariculture projects. Alternative 3 would likely result in 
substantially greater impacts on small entities than the Proposed 
Alternative, without incrementally contributing to the survival or 
recovery of H. hippopus, H. porcellanus, T. derasa, T. gigas T. 
mbalavuana, or T. squamosina.

[[Page 60546]]

Executive Order 12866 and Paperwork Reduction Act

    This rulemaking is exempt from review under Executive Order 12866. 
This proposed rule does not contain a collection-of-information 
requirement for the purposes of the Paperwork Reduction Act.

Executive Order 13132, Federalism

    In accordance with E.O. 13132, we determined that this proposed 
rule does not have significant federalism effects and that a federalism 
assessment is not required. In keeping with the intent of the 
Administration and Congress to provide continuing and meaningful 
dialogue on issues of mutual State and Federal interest, this proposed 
rule will be given to the relevant governmental agencies in the 
countries in which the species occurs, and they will be invited to 
comment. As we proceed, we intend to continue engaging in informal and 
formal contacts with the States, and other affected local, regional, or 
foreign entities, giving careful consideration to all written and oral 
comments received.

List of Subjects in 50 CFR Part 223 and 224

    Endangered and threatened species.

    Dated: July 2, 2024.
Samuel D. Rauch, III,
Deputy Assistant Administrator for Regulatory Programs, National Marine 
Fisheries Service.

    For the reasons set out in the preamble, NMFS proposes to amend 50 
CFR parts 223 and 224 as follows:

PART 223--THREATENED MARINE AND ANADROMOUS SPECIES

0
1. The authority citation for part 223 continues to read as follows:

    Authority: 16 U.S.C. 1531 1543; subpart B, Sec.  223.201-202 
also issued under 16 U.S.C. 1361 et seq.; 16 U.S.C. 5503(d) for 
Sec.  223.206(d)(9).

0
2. In Sec.  223.102, amend the table in paragraph (e) by adding new 
entries for ``Clam, horse's hoof'', ``Giant clam, boring'', ``Giant 
clam, fluted'', ``Giant clam, Noah's'', and ``Giant clam, small'' in 
alphabetical order under ``Molluscs'' to read as follows:


 Sec.  223.102  Enumeration of threatened marine and anadromous 
species.

* * * * *
    (e) * * *

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Species \1\
-----------------------------------------------------------------------------------------     Citation(s) for
                                                                Description  of listed            listing          Critical habitat        ESA rules
          Common  name                 Scientific  name                 entity               determination(s)
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Molluscs
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
Clam, horse's hoof.............  Hippopus hippopus..........  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, boring.............  Tridacna crocea............  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, fluted.............  Tridacna squamosa..........  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, Noah's.............  Tridacna noae..............  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, small..............  Tridacna maxima............  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Species includes taxonomic species, subspecies, distinct population segments (DPSs) (for a policy statement, see 61 FR 4722, February 7, 1996), and
  evolutionarily significant units (ESUs) (for a policy statement, see 56 FR 58612, November 20, 1991).

0
3. Add Sec.  223.217 to subpart B to read as follows:


Sec.  223.217  Horse's hoof clam.

    Prohibitions. The prohibitions of section 9(a)(1)(A) through 
9(a)(1)(G) of the ESA (16 U.S.C. 1538) relating to endangered species 
shall apply to the horse's hoof clam (Hippopus hippopus) listed in 
Sec.  223.102.
0
4. Add Sec.  223.218 to subpart B 223 to read as follows:


Sec.  223.218  Boring giant clam, small giant clam, Noah's giant clam, 
fluted giant clam.

    (a) Prohibitions. It is unlawful for any person subject to the 
jurisdiction of the United States to import into or export from the 
United States or its territories any derivative parts or products of 
the boring giant clam (Tridacna crocea), fluted giant clam (Tridacna 
squamosa), Noah's giant clam (Tridacna noae), and small giant clam 
(Tridacna maxima) listed in Sec.  223.102. The term ``derivative parts 
or products'' is defined in this part as:
    (1) Any tissue part that has been removed from the shell, including 
mantle tissue, adductor muscle, portions thereof, or the whole flesh of 
the animal comprising both the mantle and adductor muscle;
    (2) Any worked shell product, including handicrafts, sculptures, 
jewelry, tableware, decorative ornaments, and other carvings, but not 
raw, uncarved shells; or
    (3) Pearls or any product derived from a pearl.
    (b) [Reserved]

[[Page 60547]]

PART 224--ENDANGERED MARINE AND ANADROMOUS SPECIES

0
5. The authority citation for part 224 continues to read as follows:

    Authority: 16 U.S.C. 1531-1543 and 16 U.S.C. 1361 et seq.

0
6. In Sec.  224.101, amend the table in paragraph (h) by adding new 
entries for ``Clam, China'', ``Clam, devil'', ``Giant clam, Red Sea'', 
``Giant clam, smooth'', and ``Giant clam, true'' in alphabetical order 
under Molluscs'' to read as follows:


 Sec.  224.101  Enumeration of endangered marine and anadromous 
species.

* * * * *
    (h) * * *

--------------------------------------------------------------------------------------------------------------------------------------------------------
                                       Species \1\
-----------------------------------------------------------------------------------------     Citation(s) for
                                                                Description  of listed            listing          Critical habitat        ESA rules
          Common  name                 Scientific  name                 entity               determination(s)
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
                                                                        Molluscs
--------------------------------------------------------------------------------------------------------------------------------------------------------
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
Clam, China....................  Hippopus porcellanus.......  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Clam, devil....................  Tridacna mbalavuana........  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, Red Sea............  Tridacna squamosina........  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, smooth.............  Tridacna derasa............  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
Giant clam, true...............  Tridacna gigas.............  Entire species............  [Federal Register page  NA................  NA
                                                                                           where the document
                                                                                           begins], [date of
                                                                                           publication of final
                                                                                           rule].
 
                                                                      * * * * * * *
--------------------------------------------------------------------------------------------------------------------------------------------------------
\1\ Species includes taxonomic species, subspecies, distinct population segments (DPSs) (for a policy statement, see 61 FR 4722, February 7, 1996), and
  evolutionarily significant units (ESUs) (for a policy statement, see 56 FR 58612, November 20, 1991).


[FR Doc. 2024-14970 Filed 7-24-24; 8:45 am]
BILLING CODE 3510-22-P