[Federal Register Volume 80, Number 206 (Monday, October 26, 2015)]
[Proposed Rules]
[Pages 65183-65194]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2015-27148]



National Oceanic and Atmospheric Administration

50 CFR Part 224

[Docket No. 150209121-5941-02]
RIN 0648-XD760

Endangered and Threatened Wildlife; 12-Month Finding on a 
Petition To Identify and Delist a Saint John River Distinct Population 
Segment of Shortnose Sturgeon Under the Endangered Species Act

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

[[Page 65184]]

ACTION: Notice of 12-month petition finding.


SUMMARY: We, NMFS, announce a 12-month finding on a petition to 
identify and ``delist'' shortnose sturgeon (Acipenser brevirostrum) 
within the Saint John River in New Brunswick, Canada under the 
Endangered Species Act (ESA). The shortnose sturgeon is currently 
listed as an endangered species, at the species level, under the ESA. 
Based on our review of the best scientific and commercial data 
available, we have determined that the population of shortnose sturgeon 
from the Saint John River does not qualify as a distinct population 
segment. Therefore, we did not consider the petition further, and we do 
not propose to delist this population.

DATES: This finding was made on October 26, 2015.

ADDRESSES: Information used to make this finding is available for 
public inspection by appointment during normal business hours at NMFS, 
Office of Protected Resources, 1315 East-West Highway, Silver Spring, 
MD 20910. The petition and the list of the references used in making 
this finding are also available on the NMFS Web site at: 

FOR FURTHER INFORMATION CONTACT: Lisa Manning, Office of Protected 
Resources, 301-427-8466; Stephania Bolden, Southeast Regional Office, 
727-824-5312; Julie Crocker, Greater Atlantic Regional Office, 978-282-



    On September 24, 2014, we received a petition from Dr. Michael J. 
Dadswell, Dr. Matthew K. Litvak, and Mr. Jonathan Barry regarding the 
population of shortnose sturgeon (Acipenser brevirostrum) native to the 
Saint John River in New Brunswick, Canada. The petition requests that 
we identify the Saint John River population of shortnose sturgeon as a 
distinct population segment (DPS) and contemporaneously ``delist'' this 
DPS by removing it from the species-wide listing under the Endangered 
Species Act. On April 6, 2015, we published a positive finding 
indicating that the petitioned action may be warranted and that we were 
initiating a status review to consider the petition further (80 FR 
    The shortnose sturgeon was originally listed as an endangered 
species throughout its range by the U.S. Fish and Wildlife Service 
(USFWS) on March 11, 1967, under the Endangered Species Preservation 
Act (ESPA, 32 FR 4001). Shortnose sturgeon remained on the endangered 
species list when the U.S. Congress replaced the ESPA by enacting the 
Endangered Species Conservation Act of 1969, which was in turn replaced 
by the Endangered Species Act of 1973 (ESA, 16 U.S.C. 1531 et seq.). We 
subsequently assumed jurisdiction for shortnose sturgeon under a 1974 
government reorganization plan (39 FR 41370, November 27, 1974). In 
Canada, the shortnose sturgeon falls under the jurisdiction of the 
Department of Fisheries and Oceans (DFO) and was first assessed by the 
Committee on the Status of Endangered Wildlife in Canada (COSEWIC) as 
``Special Concern'' in 1980. This status was reconfirmed in 2005, and 
the species was listed as Special Concern under the Canadian federal 
Species at Risk Act (SARA) in 2009. The Special Concern status was 
reconfirmed again in 2015 (COSEWIC, In Press). Shortnose sturgeon is 
also listed under Appendix I of the Convention on International Trade 
in Endangered Species of Wild Fauna (CITES).

Statutory, Regulatory and Policy Provisions

    We are responsible for determining whether species are threatened 
or endangered under the ESA (16 U.S.C. 1531 et seq.). To make this 
determination, we first consider whether a group of organisms 
constitutes a ``species'' under section 3 of the ESA, and then we 
consider whether the status of the species qualifies it for listing as 
either threatened or endangered. Section 3 of the ESA defines a 
``species'' to include ``any subspecies of fish or wildlife or plants, 
and any distinct population segment of any species of vertebrate fish 
or wildlife which interbreeds when mature'' (16 U.S.C. 1532(16)). A 
joint policy issued by NMFS and the U.S. Fish and Wildlife Service 
(USFWS; collectively referred to as ``the Services'') clarifies the 
interpretation of the phrase ``distinct population segment'' (DPS) for 
the purposes of listing, delisting, and reclassifying a species under 
the ESA (``DPS Policy,'' 61 FR 4722, February 7, 1996). The DPS Policy 
identifies two criteria for determining whether a population is a DPS: 
(1) The population must be ``discrete'' in relation to the remainder of 
the taxon (species or subspecies) to which it belongs; and (2) the 
population must be ``significant'' to the remainder of the taxon to 
which it belongs.
    Congress has instructed the Secretary to exercise the authority to 
recognize DPS's ``sparingly and only when the biological evidence 
indicates that such action is warranted'' (S. Rep. 96-151 (1979)). The 
law is not settled as to the extent of the Services' discretion to 
modify a species-level listing to recognize a DPS having a status that 
differs from the original listing. In a recent decision, the United 
States District Court for the District of Columbia held that the ESA 
does not permit identification of a DPS solely for purposes of 
delisting. Humane Soc'y v. Jewell, 76 F. Supp. 3d 69 (D.D.C. Dec. 19, 
2014), appeal docketed, No. 15-5041 (D.C. Cir. Feb. 19, 2015) (Western 
Great Lakes gray wolves) (consolidated with Nos. 15-5043, 15-5060, and 
    A species, subspecies, or DPS is ``endangered'' if it is in danger 
of extinction throughout all or a significant portion of its range, and 
``threatened'' if it is likely to become endangered within the 
foreseeable future throughout all or a significant portion of its range 
(ESA sections 3(6) and 3(20), respectively, 16 U.S.C. 1532(6) and 
(20)). 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 in the foreseeable future. In other words, the primary 
statutory difference between a threatened and endangered species is the 
timing of when a species may be in danger of extinction, either 
presently (endangered) or in the foreseeable future (threatened). In 
addition, we interpret ``foreseeable future'' as the horizon over which 
predictions about the conservation status of the species can be 
reasonably relied upon.
    Pursuant to the ESA and our implementing regulations, the 
determination of whether a species is threatened or endangered shall be 
based on any one or a combination of the following five section 4(a)(1) 
factors: The present or threatened destruction, modification, or 
curtailment of habitat or range; overutilization for commercial, 
recreational, scientific, or educational purposes; disease or 
predation; inadequacy of existing regulatory mechanisms; and any other 
natural or manmade factors affecting the species' existence. 16 U.S.C. 
1533(a)(1); 50 CFR 424.11(c). Listing determinations must be based 
solely on the best scientific and commercial data available, after 
conducting a review of the species' status and after taking into 
account any efforts being made by any state or foreign nation (or any 
political subdivision of such state or foreign nation) to protect the 
species. 16 U.S.C. 1532(b)(1)(A).

[[Page 65185]]

    Under section 4(a)(1) of the ESA and the implementing regulations 
at 50 CFR 424.11(d), a species shall be removed from the list if the 
Secretary of Commerce determines, based on the best scientific and 
commercial data available after conducting a review of the species' 
status, that the species is no longer threatened or endangered because 
of one or a combination of the section 4(a)(1) factors. The regulations 
provide that a species listed under the ESA may be delisted only if 
such data substantiate that it is neither endangered nor threatened for 
one or more of the following reasons:

    (1) Extinction. Unless all individuals of the listed species had 
been previously identified and located, and were later found to be 
extirpated from their previous range, a sufficient period of time 
must be allowed before delisting to indicate clearly that the 
species is extinct.
    (2) Recovery. The principal goal of the USFWS and NMFS is to 
return listed species to a point at which protection under the ESA 
is no longer required. A species may be delisted on the basis of 
recovery only if the best scientific and commercial data available 
indicate that it is no longer endangered or threatened.
    (3) Original data for classification in error. Subsequent 
investigations may show that the best scientific or commercial data 
available when the species was listed, or the interpretation of such 
data, were in error.

50 CFR 424.11(d).

    To complete the required finding in response to the current 
delisting petition, we first evaluated whether the petitioned entity 
meets the criteria of the DPS Policy. As we noted in our initial 
petition finding, a determination whether to revise a species-level 
listing to recognize one or more DPSs in place of a species-level 
listing involves, first, determining whether particular DPS(s) exist(s) 
(based on meeting the criteria of the DPS Policy) and, if that finding 
is affirmative, complex evaluation as to the most appropriate approach 
for managing the species in light of the purposes and authorities under 
the ESA.

Species Description

    Below, we summarize basic life history information for shortnose 
sturgeon. A more thorough discussion of all life stages, reproductive 
biology, habitat use, abundance estimates and threats are provided in 
the Shortnose Sturgeon Biological Assessment completed by the Shortnose 
Sturgeon Status Review Team in 2010 (SSRT 2010; http://www.fisheries.noaa.gov/pr/species/fish/shortnose-sturgeon.html).
    There are 25 species and four recognized genera of sturgeons 
(family Acipenseridae), which comprise an ancient and distinctive 
assemblage with fossils dating to at least the Upper Cretaceous period, 
more than 66 million years ago (Findeis 1997). The shortnose sturgeon, 
Acipenser brevirostrum, is the smallest of the three extant sturgeon 
species in eastern North America. Many primitive physical 
characteristics that reflect the shortnose sturgeon's ancient lineage 
have been retained, including a protective armor of bony plates called 
``scutes''; a subterminal, protractile tube-like mouth; and 
chemosensory barbels. The general body shape is cylindrical, tapering 
at the head and caudal peduncle, and the upper lobe of the tail is 
longer than the lower lobe. Shortnose sturgeon vary in color but are 
generally dark brown to olive or black on the dorsal surface, lighter 
along the row of lateral scutes, and nearly white on the ventral 
surface. Adults have no teeth but possess bony plates in the esophagus 
that are used to crush hard prey items (Vladykov and Greeley 1963; 
Gilbert 1989). The skeleton is almost entirely cartilaginous with the 
exception of some bones in the skull, jaw and pectoral girdle.
    Shortnose sturgeon occur along the East Coast of North America in 
rivers, estuaries, and marine waters. Historically, they were present 
in most major rivers systems along the Atlantic coast (Kynard 1997). 
Their current riverine distribution extends from the Saint John River, 
New Brunswick, Canada, to possibly as far south as the St. Johns River, 
Florida (Figure 1; Kynard 1997; Gorham and McAllister 1974). Recently 
available information indicates that their marine range extends farther 
northward than previously thought and includes the Minas Basin, Nova 
Scotia (Dadswell et al. 2013). The distribution of shortnose sturgeon 
across their range, however, is disjunct, with no known reproducing 
populations occurring within the roughly 400 km of coast between the 
Chesapeake Bay and the southern boundary of North Carolina. Shortnose 
sturgeon live in close proximity with Atlantic sturgeon (Acipenser 
oxyrinchus oxyrinchus) throughout much of their range. However, 
Atlantic sturgeon spend more of their life cycle in the open ocean 
compared to shortnose sturgeon. Within rivers, shortnose sturgeon and 
Atlantic sturgeon may share foraging habitat and resources, but 
shortnose sturgeon generally spawn farther upriver and earlier than 
Atlantic sturgeon (Kynard 1997, Bain 1997).

[[Page 65186]]


    Shortnose sturgeon typically migrate seasonally between upstream 
freshwater spawning habitats and downstream foraging mesohaline (i.e., 
salinities of 5 to 18 parts per thousand) habitat based on water 
temperature, flow, and salinity cues. Based on their varied and complex 
use of freshwater, estuarine, and marine waters, shortnose sturgeon 
have been characterized in the literature as ``anadromous'' or 
``amphidromous'' (Bain 1977; Kieffer and Kynard 1993). An anadromous 
species is defined as one that spawns in freshwater and spends much of 
its life cycle in marine waters, whereas a freshwater amphidromous 
species is one that spawns and remains in freshwater for most of its 
life cycle but spends some time in saline water. Because shortnose 
sturgeon had historically rarely been detected far from their natal 
estuary, they were once considered to be largely confined to their 
natal rivers and estuaries (NMFS 1998). However, more recent research 
has demonstrated that shortnose sturgeon leave their natal estuaries, 
undergo coastal migrations, and use other river systems to a greater 
extent than previously thought (Kynard 1997; Savoy 2004; Fernandes 
2010; Zydlewski et al. 2011; Dionne et al. 2013). The reasons for 
inter-riverine movements are not yet clear, and the degree to which 
this behavior occurs appears to vary among river systems.
    Shortnose sturgeon are benthic feeders, and their diet typically 
consists of small insects, crustaceans, mollusks, polychaetes, and 
small benthic fishes (McCleave et al. 1977; Dadswell 1979;

[[Page 65187]]

Marchette and Smiley 1982; Dadswell et al. 1984; Moser and Ross 1995; 
Kynard et al. 2000; Collins et al. 2002). Both juvenile and adult 
shortnose sturgeon primarily forage over sandy-mud bottoms, which 
support benthic invertebrates (Carlson and Simpson 1987, Kynard 1997). 
Shortnose sturgeon have also been observed feeding off plant surfaces 
(Dadswell et al. 1984). Sturgeon likely use electroreception, 
olfaction, and tactile chemosensory cues to forage, while vision is 
thought to play a minor role (Miller 2004).
    Foraging in the colder rivers in the northern part of their range 
appears to greatly decline or cease during winter months when shortnose 
sturgeon generally become inactive. In mid-Atlantic areas, including 
the Chesapeake Bay, and the Delaware River, foraging is believed to 
occur year-round, though shortnose sturgeon are believed to feed less 
in the winter (J. O'Herron, Amitrone O'Herron, Inc., pers. comm. 2008 
as cited in SSRT 2010). In the southern part of their range, shortnose 
sturgeon are known to forage widely throughout the estuary during the 
winter, fall, and spring (Collins and Smith 1993, Weber et al. 1999). 
During the hotter months of summer, foraging may taper off or cease as 
shortnose sturgeon take refuge from high water temperatures.
    Shortnose sturgeon are relatively small compared to most extant 
sturgeon species and reach a maximum length of about 120 cm total 
length (TL) and weight of about 24 kg (Dadswell 1979; Waldman et al. 
2002); however, both maximum size and growth rate display a pattern of 
gradual variation across the range, with the fastest growth rates and 
smallest maximum sizes occurring in the more southern populations 
(Dadswell et al. 1984). The northernmost populations exhibit the 
slowest growth and largest adult sizes. The largest shortnose sturgeon 
reported in the published literature to date was collected from the 
Saint John River, Canada, and measured 143cm TL (122 cm fork length 
(FL)) and weighed 23.6 kg (Dadswell 1979). In contrast, in their 
review, Dadswell et al. (1984) indicated that the largest adult 
reported from the St. Johns River, Florida, was a 73.5 cm (TL) female. 
Dadswell et al. (1984) compared reported growth parameters across the 
range and showed that the von Bertalanffy growth parameter K and 
estimated asymptotic length ranged from 0.042 and 130.0 cm (FL), 
respectively, for Saint John River fish to 0.149 and 97.0 cm (FL) for 
Altamaha River, Georgia fish. However, the land-locked shortnose 
sturgeon population located upstream of Holyoke Dam at river km 140 of 
the Connecticut River has the slowest adult growth rate of any 
surveyed, which may at least in part reflect food limitations (Taubert 
    Shortnose sturgeon are relatively long-lived and slow to mature. 
The oldest shortnose sturgeon reported was a 67 year-old female from 
the Saint John River, and the oldest male reported was a 32 year-old 
fish, also captured in the Saint John River (Dadswell 1979). In 
general, fish in the northern portion of the species' range live longer 
than individuals in the southern portion of the species' range (Gilbert 
1989). Males and females mature at about the same length, around 45-55 
cm FL, throughout their range (Dadswell et al. 1984). However, age at 
maturity varies by sex and with latitude, with males in the southern 
rivers displaying the youngest ages at maturity (see review in Dadswell 
et al. 1984). For example, age at first maturation in males occurs at 
about 2-3 years of age in Georgia and at about 10-11 years in the Saint 
John River. Females mature by 6 years of age in Georgia and at about 13 
years in the Saint John River (Dadswell et al. 1984).
    Sturgeon are iteroparous, meaning they reproduce more than once 
during their lifetime. In general, male shortnose sturgeon are thought 
to spawn every other year, but they may spawn annually in some rivers 
(Dovel et al. 1992; Kieffer and Kynard 1996). Females appear to spawn 
less frequently--approximately every 3 to 5 years (Dadswell 1979). 
Spawning typically occurs during late winter/early spring (southern 
rivers) and mid-to-late spring (northern rivers) (Dadswell 1979, 
Taubert 1980a and b, Kynard 1997). The onset of spawning may be cued by 
decreasing river discharge following the peak spring freshet, when 
water temperatures range from 8 to 15 [deg]C and bottom water 
velocities range between 25-130 cm/s, although photoperiod (or day-
length) appears to control spawning readiness (Dadswell et al. 1984; 
Kynard et al. 2012). Spawning appears to occur in the sturgeons' natal 
river, often just below the fall line at the farthest accessible 
upstream reach of the river (Dovel 1981; Buckley and Kynard 1985; 
Kieffer and Kynard 1993; O`Herron et al. 1993; Kieffer and Kynard 
1996). Following spawning, adult shortnose sturgeon disperse quickly 
down river and typically remain downstream of their spawning areas 
throughout the rest of the year (Buckley and Kynard 1985, Dadswell et 
al. 1984; Buckley and Kynard 1985; O'Herron et al. 1993).
    In a review by Gilbert (1989), fecundity of shortnose sturgeon was 
reported to range between approximately 30,000-200,000 eggs per female. 
Shortnose sturgeon collected from the Saint John River had a range of 
27,000-208,000 eggs and a mean of 11,568 eggs/kg body weight (Dadswell 
1979). Development of the eggs and transition through the subsequent 
larval, juvenile and sub-adult life stages are discussed in more detail 
in SSRT 2010.
    A total abundance estimate for shortnose sturgeon is not available. 
However, population estimates, using a variety of techniques, have been 
generated for many individual river systems. In general, northern 
shortnose sturgeon population abundances are greater than southern 
populations (Kynard 1997). The Hudson River shortnose sturgeon 
population is currently considered to be the largest extant population 
(61,000 adults, 95 percent CI: 52,898-72,191; Bain et al. 2007; 
however, see discussion of this estimate in SSRT 2010). Available data 
suggest that some populations in northern rivers have increased over 
the past several decades (e.g., Hudson, Kennebec; Bain et al. 2000; 
Squiers 2003) and that others may be stable (e.g., Delaware; Brundage 
and O'Herron 2006). South of Chesapeake Bay, populations are relatively 
small compared to the northern populations. The largest population of 
shortnose sturgeon in the southern part of the range is from the 
Altamaha River, which was most recently estimated at 6,320 fish (95% 
CI: 4387-9249; Devries 2006). Occasional observations of shortnose 
sturgeon have been made in some rivers where shortnose sturgeon are 
considered extirpated (e.g., St. Johns, St. Mary's, Potomac, 
Housatonic, and Neuse rivers); the few fish that have been observed in 
these rivers are generally presumed to be immigrants from neighboring 
    The most recent total population estimate for the Saint John River 
dates to the 1970's. Using tag recapture data from 1973-1977, Dadswell 
(1979) calculated a Jolly-Seber population estimate of 18,000 (30% SE; 95 percent CI: 7,200-28,880, COSEWIC, In Press) adults (> 
50 cm) below the Mactaquac Dam. Several partial population estimates 
are also available for the Kennebecasis River, a tributary in the lower 
reaches of the Saint John River. Litvak (unpublished data) calculated a 
Jolly-Seber estimate of 2,068 fish (95% CI: 801-11,277) in the 
Kennebecasis using mark-recapture data from 1998 to 2004 (COSEWIC, In 
Press). Based on videotaping of overwintering aggregations of shortnose 
sturgeon on the Kennebecasis River at the confluence of the Hammond 
River (rkm 35), Li et al. (2007) used ordinary Kriging to estimate that 
4,836 (95% CI:

[[Page 65188]]

4,701-4,971) adult shortnose sturgeon were overwintering in that area. 
Usvyatsov et al. (2012) repeated this sampling in 2009 and 2011 and, 
using three different modeling techniques, estimated a total of 3,852-
5,222 shortnose sturgeon in the study area, which suggests fairly 
stable abundance and habitat use at this site.
    Threats that contributed to the species' decline and led to the 
listing of shortnose sturgeon under the ESA included pollution, 
overfishing, and bycatch in the shad fishery (USDOI 1973). Shortnose 
sturgeon were also thought to be extirpated, or nearly so, from most of 
the rivers in their historical range (USDOI 1973). In the late 
nineteenth and early twentieth centuries, shortnose sturgeon were 
commonly harvested incidental to Atlantic sturgeon, the larger and more 
commercially valuable of these two sympatric sturgeon species (NMFS 
1998). Although there is currently no legal directed fishing for 
shortnose sturgeon in the United States, poaching is suspected, and 
bycatch still occurs in some areas. In particular, shortnose sturgeon 
are caught incidentally by bass anglers and in the alewife/gaspereau, 
American shad, American eel, and Atlantic sturgeon fisheries in the 
Saint John River; and shad fisheries in the Altamaha River, Santee 
River, Savannah River, and elsewhere (COSEWIC, In Press; SSRT 2010; 
Bahn et al. 2009; COSEWIC 2005). The construction of dams has also 
resulted in substantial loss of historical shortnose sturgeon habitat 
in some areas along the Atlantic seaboard. The construction and 
operation of dams can impede upstream movement to sturgeon spawning 
habitat (e.g., Connecticut River, Santee River). Remediation measures, 
such as dam removal or modification to allow for fish passage have 
improved access in some rivers, and additional similar restoration 
efforts are being considered in other areas (e.g., possible removal of 
the Mactaquac dam in the Saint John River). Other possible and ongoing 
threats include operation of power generating stations, water diversion 
projects, dredging, and other in-water activities that impact habitat.

Distinct Population Segment Analysis

    The following sections provide our analysis of whether the 
petitioned entity--the Saint John River population of shortnose 
sturgeon--qualifies as a DPS of shortnose sturgeon (whether it is both 
``discrete'' and ``significant''). To complete this analysis we relied 
on the best scientific and commercial data available and considered all 
relevant literature and public comments submitted in response to our 
90-day finding (80 FR 18347, April 6, 2015).
    For purposes of this analysis, we defined the Saint John River 
population segment of shortnose sturgeon to consist of shortnose 
sturgeon spawned in the Saint John River downstream of the Mactaquac 
Dam. Prior to construction of Mactaquac Dam in 1968/1969, sturgeon 
occurred upstream of the dam; however, it is unclear whether these were 
shortnose and/or Atlantic sturgeon and whether any sturgeon are still 
present upstream of the dam (COSEWIC, In Press). Lacking this 
information, we cannot consider fish that may be present upstream of 
the dam in our distinct population segment analysis. Throughout our 
discussion below we also use the term ``population'' to refer 
collectively to all shortnose sturgeon that are presumed to be natal to 
a particular river rather than using this term to refer strictly to a 
completely closed reproductive unit.

Discreteness Criterion

    The Services' joint DPS Policy states that a population segment of 
a vertebrate species may be considered discrete if it satisfies either 
one of the following conditions:
    (1) It is markedly separated from other populations of the same 
taxon as a consequence of physical, physiological, ecological, or 
behavioral factors. Quantitative measures of genetic or morphological 
discontinuity may provide evidence of this separation.
    (2) It is delimited by international governmental boundaries within 
which differences in control of exploitation, management of habitat, 
conservation status, or regulatory mechanisms exist that are 
significant in light of section 4(a)(1)(D) of the ESA (61 FR 4722, 
February 7, 1996).
    There are no physical barriers preventing the movement of Saint 
John River shortnose sturgeon outside of the Saint John River estuary 
or along the coast. The Mactaquac Dam, located about 140 km upstream 
and at the head of tide (Canadian Rivers Institute 2011), is the first 
upstream physical barrier on the Saint John River. This and other dams 
on the Saint John River block shortnose sturgeon from accessing 
upstream habitats, but there are no dams or other physical barriers 
separating Saint John River sturgeon from other shortnose sturgeon 
    As mentioned previously, shortnose sturgeon have been documented to 
leave their natal river/estuary and move to other rivers to varying 
extents across their range. For example, telemetry data generated by 
Zydlewski et al. (2011) during 2008-2010 indicate that inter-riverine 
movements of adult shortnose sturgeon occur fairly frequently among 
rivers in Maine. Seventy percent of tagged adults (25 of 41 fish) moved 
between the Penobscot and Kennebec rivers (about 150 km away), and up 
to 52% of the coastal migrants (13 of 25 fish) also used other, smaller 
river systems (i.e., Damariscotta, Medomak, St. George) between the 
Penobscot and Kennebec rivers (Zydlewski et al. 2011). Shortnose 
sturgeon are also known to move between rivers in Maine and (e.g., 
Kennebec, Saco) and the Merrimack River estuary in Massachusetts, 
traveling distances of up to about 250 km (as measured by a 
conservative, direct path distance; Little et al. 2013; Wippelhauser et 
al. 2015). At the other end of the range, in the Southeast United 
States, inter-riverine movements appear fairly common and include 
movements between the Savannah River and Winyah Bay and between the 
Altamaha and Ogeechee rivers (Peterson and Farrae 2011; Post et al. 
    Many inter-riverine movements have been observed elsewhere within 
the species' range, but patterns are not yet well resolved. For 
example, some shortnose sturgeon captured and/or tagged in the 
Connecticut River have been recaptured, detected, or were previously 
tagged in the Housatonic River (T. Savoy, CT DEP, pers. comm. 2015), 
the Hudson River (Savoy 2004), and the Merrimack River (M. Kieffer, 
USGS, pers. comm. 2015). At this time, the available tagging and 
tracking information is too limited to determine if Hudson River and 
Connecticut River shortnose sturgeon are making regular movements 
outside of their natal rivers and whether movement as far as the 
Merrimack River is a normal behavior. Movement data from the Chesapeake 
Bay is also relatively limited, but existing data indicate that 
shortnose sturgeon do move from the Chesapeake Bay through the 
Chesapeake and Delaware Canal into the Delaware River (Welsh et al. 
    The distances of the reported marine migrations vary widely from 
very short distances--such as between the Santee River and Winyah Bay, 
which are only about 15 km apart--to fairly long--as in the case of 
movements between the Merrimack and the Penobscot rivers, which are 
about 339 km apart at their mouths.\1\ In general, the available data

[[Page 65189]]

suggest that movements between geographically proximate rivers are more 
common, while movements between more distant rivers do not, or only 
rarely, occur. A detailed discussion of the physical movements of 
shortnose sturgeon is provided in SSRT 2010.

    \1\ Distances between rivers mouths reported here were measured 
in GIS using the NOAA Medium Resolution Vector Shoreline, 20m 
bathymetry contour, and a fixed scale of 1:250,000. Estimated 
distances reported are the average of three, independently drawn and 
measured paths for each river pair. The assumed travel path between 
river mouths was the shortest possible distance that followed the 
general outline of the coast and was constrained by the 20m 
bathymetry contour, except where the shortest travel path across a 
deep, narrow inlet or bay crossed the 20m bathymetry contour.

    The extent of coastal movements of shortnose sturgeon from the 
Saint John River is currently unknown (COSEWIC, In Press); however, 
some limited data are available and provide some insight into whether 
these fish may be geographically isolated from other populations. Any 
movement between Saint John River sturgeon and the nearest population 
in the Penobscot River would require a marine migration of about 362 
km, a similar travel distance as between the Merrimack and the 
Penobscot rivers (340 km) and between the Connecticut and Merrimack 
rivers (348 km).\2\ Dadswell (1979) reported that of 121 marked Saint 
John River shortnose sturgeon recaptured by commercial fisherman, 13 
fish (11 percent) were recaptured in the Bay of Fundy, indicating that 
a portion of the population migrated into the marine environment. In 
addition, a confirmed shortnose sturgeon was caught in a fishing weir 
in the Minas Basin, off the coast of Nova Scotia about 165 km north of 
the mouth of the Saint John River (Dadswell et al. 2013). Fishermen in 
the Minas Basin also claim to catch about one to two shortnose sturgeon 
per year in their weirs (Dadswell et al. 2013). While it is plausible 
that the shortnose sturgeon captured in the Minas Bay originated from 
the Saint John River, data to confirm this are not available. In 
contrast, limited telemetry data suggest that movements outside of the 
Saint John River are not common. Of 64 shortnose sturgeon tagged in the 
Saint John River over the course of about 16 years from 1999 to 2015, 
none have been detected moving past the farthest downriver acoustic 
receiver located near the Saint John Harbor Bridge (M. Litvak, pers. 
comm. July 31, 2015).

    \2\ Distances reported here were measured following the same 
methods described in the previous footnote. The distance reported 
between the Connecticut and Merrimack River assumes a travel path 
via the Cape Cod Canal. A travel path around Cape Cod would instead 
result in a marine migration of about 560 km.

    Overall, while there is unambiguous evidence that shortnose 
sturgeon from the Saint John River leave the estuary--at least 
occasionally--and use the marine environment, and that shortnose 
sturgeon are capable of making long distance movements between river 
systems, there are no available data on coastal migrations of Saint 
John River shortnose sturgeon. To date, there are also no reported 
observations or detections of shortnose sturgeon from the Gulf of Maine 
rivers moving into the Saint John River. Thus, while it is possible 
that the Saint John River shortnose sturgeon come in contact with 
shortnose sturgeon from elsewhere, it is also likely that some degree 
of geographical isolation by distance is occurring.
    Although acoustic telemetry studies have revealed that shortnose 
sturgeon leave their natal river systems to a much greater extent than 
previously thought, such movements do not necessarily constitute 
permanent emigration or indicate interbreeding of populations. Tagging 
and telemetry studies within several river systems have provided 
evidence that shortnose sturgeon in those particular systems tend to 
spawn in their natal river (e.g., Dovel 1981; Buckley and Kynard 1985; 
Kieffer and Kynard 1993; O`Herron et al. 1993; Kieffer and Kynard 
1996). Tag return data for shortnose sturgeon in the Saint John River 
over the course of a 4-year study completed by Dadswell (1979) suggests 
there is little emigration from this system as well, and that spawning 
takes place in the freshwater sections of the upper estuary. The high 
site fidelity to natal rivers suggested by this and other studies 
indicates a there is a possible behavioral mechanism for the marked 
separation of the Saint John River population of shortnose sturgeon 
from other populations of the species.
    A substantial amount of genetic data has become available since the 
``Final Recovery Plan for Shortnose Sturgeon'' was developed in 1998. 
Below, we summarize the best available genetic data and information, 
which informed our evaluation of the ``discreteness'' of the Saint John 
River population segment. A more in-depth presentation of genetic data, 
including discussions of types of analyses and assumptions, is 
available in the Biological Assessment (SSRT 2010).
    Much of the published information on population structure for 
shortnose sturgeon has been based on the genetic analysis of the 
maternally inherited mitochondrial DNA (mtDNA) due in part to the 
difficulties of analyzing data from the polyploid nuclear genome 
(Waldman et al. 2008). The analyses have focused on a moderately 
polymorphic 440 base pair portion of the mtDNA control region--a 
relatively rapidly evolving region of mtDNA and thus a good indicator 
of population-level differentiation. Haplotype frequencies and sequence 
divergence data have consistently indicated an overall isolation-by-
distance pattern of genetic population structure across the species' 
range, meaning that populations of shortnose sturgeon inhabiting rivers 
and embayments that are geographically more distant tend to be less 
related than those that are geographically closer (e.g., Walsh et al. 
2001, Grunwald et al. 2002, Waldman et al. 2002, and Wirgin et al. 
2005; Wirgin et al. 2009). The haplotypes observed are typically shared 
across two to four or more adjacent sampled rivers but with little 
sharing of haplotypes between northern and southern populations 
(Waldman et al. 2002; Wirgin et al. 2009). Results for the Saint John 
River are compatible with these general patterns. For example, in the 
largest study to date, Wirgin et al. (2009) observed eight haplotypes 
within the Saint John River sample (n=42); and of the eight observed 
haplotypes, one was exclusive (or ``private'') to the Saint John River 
(and observed in 1 of 42 fish), and the remaining haplotypes were 
shared with two to six other rivers. None of the shared haplotypes were 
observed in samples south of the Chesapeake Bay. A previously 
unreported haplotype was recently observed in 2 of 15 shortnose caught 
from the Kennebecasis River, a tributary of the Saint John (Kerr, 2015; 
P. Wilson, public comment, May 2015). This new haplotype could indicate 
an even greater degree of differentiation of the Saint John River fish; 
however, no other rivers were sampled or analyzed as part of this 
    Despite the localized sharing of haplotypes, frequencies of the 
observed haplotypes are significantly different in most pairwise 
comparisons of the rivers sampled (i.e., comparisons of haplotype 
frequencies from samples from two rivers), including many adjacent 
rivers (Wirgin et al. 2009). Such pairwise comparisons for the Saint 
John River in particular have indicated that this population is 
genetically distinct from the geographically closest sampled 
populations, including the Penobscot, Kennebec, and Androscoggin rivers 
(Grunwald et al. 2002; Waldman et al. 2002; Wirgin et al. 2005; Wirgin 
et al. 2009). For example, Wirgin et al. (2009) reported significant 
differences (p<0.0005) in haplotype frequencies between Saint John 
River shortnose sturgeon (n=42) and Penobscot (n=44, Chi-square=37.22), 
Kennebec (n=54, Chi-square=54.85), and Androscoggin (n=48, Chi-
square=37.91) river samples. The level of genetic differentiation 
between the Saint John River population and the Penobscot, Kennebec, 

[[Page 65190]]

Androscoggin rivers also appears substantial, with Phi ST 
values ranging from 0.213 to 0.291 (where Phi ST ranges from 
0 to 1, with 1 indicating complete isolation; Wirgin et al. 2009).
    Estimates of female-mediated gene flow between the Saint John River 
and the Gulf of Maine rivers are fairly low. Wirgin et al. (2009) 
estimated female-mediated gene flow between the Saint John River and 
other Gulf of Maine rivers as 1.90-2.85 female migrants per generation 
based on Phi ST values, and as 1.5-1.9 females per 
generation in a separate, coalescent-based analysis. This result 
suggests that (if model assumptions are true) no more than three female 
shortnose sturgeon from the Saint John River are likely to spawn in the 
other Gulf of Maine rivers (or vice versa) per generation. These 
results provide additional evidence that the degree of female-based 
reproductive exchange between the Saint John River population and other 
nearby shortnose river populations has been relatively limited over 
many generations.
    More recently, King et al. (2014) completed a series of analyses 
using nuclear DNA (nDNA) samples from 17 extant shortnose sturgeon 
populations across the species range. In contrast to the maternally 
inherited mtDNA, nDNA reflects the genetic inheritance from both the 
male and female parents. King et al. (2014) surveyed the samples at 11 
polysomic microsatellite DNA loci and then evaluated the 181 observed 
alleles as presence/absence data using a variety of analytical 
techniques. The population structuring revealed by these analyses is 
consistent with the previous mtDNA analyses in that they also indicate 
a regional scale isolation-by-distance pattern of genetic 
differentiation. Analysis of genetic distances among individual fish 
(using principle coordinate analysis, PCO) revealed that the sampled 
fish grouped into one of three major geographic units: (1) Northeast, 
which included samples from the Saint John, Penobscot, Kennebec, 
Androscoggin, and Merrimack rivers; (2) Mid-Atlantic, which included 
samples from the Connecticut, Hudson, and Delaware rivers, as well as 
the Chesapeake Bay proper; and (3) Southeast, which included samples 
from the Cape Fear River, Winyah Bay, the Santee-Cooper, Edisto, 
Savannah, Ogeechee, and Altamaha rivers, and Lake Marion (King et al. 
    Subsequent analyses revealed that each of the three regions has a 
different pattern of sub-structuring. Within the Northeast group, two 
separate analyses (PCO and STRUCTURE) indicated a high degree of 
relatedness and possible panmixia (i.e., random mating of individuals) 
among the Penobscot, Kennebec, and Androscoggin rivers; whereas, the 
Saint John and Merrimack rivers appeared more differentiated from each 
other as well as from the other Gulf of Maine rivers (King et al. 
2014). Pairwise comparisons at the population level showed that, within 
the Northeast region, estimates of genetic differentiation were 
greatest between the Saint John and Merrimack rivers (Phi PT 
= 0.100, p <0.0004), the two most distant rivers within this region. 
Pairwise comparisons of the Saint John River to the remaining rivers 
within the Northeast region revealed lower but still statistically 
significant levels of genetic differentiation (Phi PT = 
0.068-0.077; King et al. 2014). Relatively low levels of 
differentiation were observed in pairwise comparisons for all other 
rivers within the Northeast region (Phi PT = 0.013-0.087), 
half of which were not statistically significant (King et al. 2014). In 
comparison, within the Mid-Atlantic group, pairwise comparisons among 
rivers showed moderate levels of genetic differentiation among most 
river populations (average Phi PT = 0.077, range = 0.018-
0.118); whereas, estimates of population level genetic differentiation 
were very low among samples populations in the Southeast group (average 
Phi PT = 0.047, range = 0.005 to 0.095; King et al. 2014), 
suggesting a more genetically similar set of populations.
    Theoretical estimates of gene flow (derived from Phi PT 
values) between the Saint John River and the other Northeast rivers 
ranged from 2.25 to 3.43 migrants per generation (King et al. 2014). 
Gene flow estimates for the Merrimack River were similarly low, ranging 
from 2.25 to 4.06 (King et al. 2014). In contrast, the effective number 
of migrants per generation estimated to occur between the remaining 
rivers within the Northeast region was much higher and ranged from 
16.42 to 83.08 (King et al. 2014).
    Overall, the analyses completed by King et al. (2014) indicate that 
differentiation among Northeast populations is less than that observed 
among the Mid-Atlantic populations and greater than that observed among 
Southeast populations. However, within the Northeast region, both the 
Saint John and Merrimack River sample populations are genetically 
distinct from the other sample populations. Although the estimates of 
gene flow suggest some connectivity between the Saint John and other 
rivers within the Northeast, the significantly different allele and 
haplotype frequencies shown consistently in the nDNA and mtDNA studies 
provide indirect evidence that the Saint John River population is 
relatively reproductively isolated.
    As highlighted in the DPS Policy, quantitative measures of 
morphological discontinuity or differentiation can serve as evidence of 
marked separation of populations. We examined whether the morphological 
data for shortnose sturgeon across its range provide evidence of marked 
separation of the Saint John River population. As noted previously, 
maximum adult size (length and weight) varies across the range, with 
the largest maximum sizes occurring in the Saint John River at the 
northernmost end of the range, and the smallest sizes occurring in 
rivers at the southern end of the range (Dadswell et al. 1984). The 
largest individual reported in the literature (122 cm FL, 23.6 kg) was 
captured in the Saint John River, although there is also a report of a 
specimen measuring 124.6 cm FL (M. Litvak, unpublished data, as cited 
in COSEWIC, In Press). Lengths of shortnose sturgeon captured in 
surveys of the Saint John River in 1974-1975 ranged from 60 to 120 cm 
FL (n=1,621). The majority of these fish, however, were smaller than 
100 cm FL (1,476 fish), and only six fish were longer than 111 cm FL 
(Dadswell 1979). To the south, in the Kennebec River, Maine shortnose 
sturgeon captured during 1980 and 1981 had lengths ranging from 58.5 to 
103.0 cm FL, and averaging 80.8 cm FL (n=24; Walsh et al. 2001). 
Smaller size ranges are reported for rivers in the southernmost portion 
of the range with some occasional captures of larger specimens. For 
example, adult shortnose sturgeon captured in the Altamaha River, 
Georgia, in 2010-2013 ranged from 57.4-83.0 cm FL and averaged 70.1 cm 
long (FL, n=40; Peterson 2014), but a shortnose sturgeon measuring 
104.5 cm FL and weighing 8.94 kg was captured in the Altamaha River in 
summer, 2004 (D. Peterson, UGA, unpubl. data). Overall, the attribute 
of size appears to display clinal variation, meaning there is a gradual 
change with geographic location (Huxley 1938). The fact that the Saint 
John River population segment, which lies at the northernmost end of 
the range, exhibits the largest sizes does not in itself constitute a 
morphological discontinuity. Given the apparent gradual nature of the 
variation in size with latitude, we find that there is no marked 
separation of the Saint John River population segment on the basis of a 
quantitative discontinuity in size.
    In addition to body size, other attributes such as snout length, 
head length, and mouth width can provide evidence of a morphological

[[Page 65191]]

discontinuity and were also considered. Walsh et al. (2001) examined 
six morphological and five meristic attributes for shortnose sturgeon 
in the Androscoggin, Kennebec, and Hudson rivers. All morphological 
features measured (i.e., body length, snout length, head length, mouth 
width, and interorbital width) were largest for the Kennebec River fish 
and smallest for fish from the southern-most river in the study, the 
Hudson River (Walsh et al. 2001). Meristic features (e.g., scute 
counts) were similar for the three rivers and were not related to fish 
size (Walsh et al. 2001). Overall, the degree of phenotypic 
differentiation of fish from the two rivers in Maine (Androscoggin and 
Kennebec), which share an estuary mouth, was very low, while a much 
greater degree of differentiation was observed for the fish from the 
Hudson River (Walsh et al. 2001). This result was congruent with 
results of corresponding mtDNA analyses, which indicated that the 
Hudson River had a much greater degree of genetic differentiation from, 
and much lower rate of gene flow with, the two rivers in Maine (Walsh 
et al. 2001). The results of this particular study suggest there could 
be clinal variation in these other phenotypic characteristics, similar 
to the pattern observed for body size. As far as we are aware, however, 
similar studies have not yet been conducted to examine the variation in 
additional sets of morphological attributes across the range of 
shortnose sturgeon and relative to the Saint John River population in 
particular. Therefore, there is no basis to conclude marked separation 
of the Saint John River population segment on the basis of 
morphological discontinuity.
    In conclusion, although the currently available data do not show 
that the Saint John River shortnose sturgeon constitute a completely 
isolated or closed population, we find that available genetic data, 
evidence of site fidelity, and the likelihood of some degree of 
geographical isolation together constitute sufficient information to 
indicate that the Saint John River shortnose sturgeon are markedly 
separated from other populations of shortnose sturgeon. Thus, after 
considering the best available data and all public comments submitted 
in response to our initial petition finding, we conclude that the Saint 
John River population segment of shortnose sturgeon is ``discrete.'' We 
therefore proceeded to evaluate the best available data with respect to 
the second criterion of the DPS Policy, ``significance.''

Significance Criterion

    Under the DPS Policy, if a population segment is found to be 
discrete, then we proceed to the next step of evaluating its biological 
and ecological significance to the taxon to which it belongs. As we 
explained above, a population must be both ``discrete'' (the first 
prong of the DPS Policy) and ``significant'' (the second prong of the 
DPS Policy) to qualify for recognition as a DPS.
    Consideration of significance may include, but is not limited to: 
(1) Persistence of the discrete population segment in an ecological 
setting unusual or unique for the taxon; (2) evidence that the loss of 
the discrete population segment would result in a significant gap in 
the range of a taxon; (3) evidence that the discrete population segment 
represents the only surviving natural occurrence of a taxon that may be 
more abundant elsewhere as an introduced population outside its 
historical range; and (4) evidence that the discrete population segment 
differs markedly from other populations of the species in its genetic 
characteristics (61 FR 4722, February 7, 1996). These four factors are 
non-exclusive; other relevant factors may be considered in the 
``significance'' analysis. Further, significance of the discrete 
population segment is not necessarily determined by existence of one of 
these classes of information standing alone. Rather, information 
analyzed under these and any other applicable considerations is 
evaluated relative to the biological and ecological importance of the 
discrete population to the taxon as a whole. Accordingly, all relevant 
and available biological and ecological information is analyzed to 
determine whether, because of its particular characteristics, the 
population is significant to the conservation of the taxon as a whole.

Persistence in an Ecological Setting Unusual or Unique for the Taxon

    Shortnose sturgeon once occupied most major rivers systems along 
the Atlantic coast of North America (Kynard 1997). Although extirpated 
from some areas due mainly to overharvest, bycatch, pollution, and 
habitat degradation, shortnose sturgeon still occur in at least 25 
rivers systems within their historical range (NMFS 1998). Throughout 
their current range, shortnose sturgeon occur in riverine, estuarine, 
and marine habitats; and, as adults, generally move seasonally between 
freshwater spawning habitat and downstream mesohaline and sometimes 
coastal marine areas in response to cues such as water temperature, 
flow, and salinity. Like other species of sturgeon (e.g. A. 
transmontanus in the Columbia River, Oregon), shortnose sturgeon are 
also capable of adopting a fully freshwater existence, as is the case 
for the population of shortnose sturgeon above the Holyoke Dam in the 
Connecticut River and in Lake Marion, South Carolina. While each river 
system within the shortnose sturgeon's range is similar in terms of its 
most basic features and functions, each river system differs to varying 
degrees in terms of its specific, physical and biological attributes, 
such as hydrologic regime, benthic substrates, water quality, and prey 
communities. A few examples are discussed briefly below.
    The Saint John River begins in northern Maine, United States, 
travels through New Brunswick, Canada, and empties into the Bay of 
Fundy within the northeast Gulf of Maine. The river is approximately 
673 km long, fed by numerous tributaries, and has a large tidal estuary 
and a basin area of over 55,000 km\2\ (Kidd et al. 2011). According to 
the Nature Conservancy's (TNC) ecoregion classification system, the 
Saint John River watershed lies within the New England-Acadian 
(terrestrial), Northeast United States and Southeast Canada Atlantic 
Drainages (freshwater), and the Gulf of Maine/Bay of Fundy (marine) 
ecoregions. The mean annual discharge is approximately 1,100 m\3\/s, 
dissolved oxygen levels average 8.5 to 11 mg/l, and benthic substrates 
downstream of the Mataquac Dam consist largely of shifting sands (Kidd 
et al. 2011). Due to the low slope of the lower reaches and the extreme 
tidal range of the Bay of Fundy, the head of the tide can extend about 
140 km upstream from the river mouth (Kidd et al. 2011). During the 
shortnose sturgeon spring/summer spawning season, water temperatures 
range from about 10 to 15 [deg]C; and within overwintering areas, water 
temperature range between 0 and 13 C (Dadswell 1979; Dadswell et al. 
1984). Shortnose sturgeon in the Saint John River appear to move to 
deeper waters when surface water temperatures exceed 21 [deg]C 
(Dadswell et al. 1984). Further to the south, but still within the same 
terrestrial, freshwater, and marine TNC ecoregions as the Saint John 
River, is the smaller Penobscot River system in Maine. This river is 
175 km long (not including the West and South Branches), has a drainage 
basin of 22,265 km\2\, and an annual average discharge of about 342 
m\3\/s (Lake et al. 2012; USGS 2015). Benthic substrates, consisting of 
bedrock, boulders, cobble and sand deposits are undergoing changes in 
response to the removal of

[[Page 65192]]

two dams--Great Works Dam at rkm 60 and Veazie Dam at rkm 48--within 
the past three years (FERC 2010; Cox et al. 2014). The Veazie Dam was 
located close to the head of the tide, and although conditions have 
since changed, Haefner (1967, as cited in Fernandes et al. 2010) stated 
that, during peak springtime flows, freshwater extends to rkm 17, and 
that the salt wedge intrudes as far as about rkm 42 when river 
discharges decrease in summer. Water temperatures in shortnose sturgeon 
overwintering areas in the Penobscot River range from about 0 [deg]C to 
13.3 [deg]C, and the fish appear to move out of overwintering areas 
when water temperatures reach about 2.4 [deg]C (Fernandes et al. 2010). 
Towards the southern end of the range and occurring within a very 
different set of ecoregions is the Altamaha River, which is formed by 
the confluence of the Ocmulgee and Oconee rivers in Georgia. One of the 
longest free-flowing systems on the Atlantic Coast, the Atlamaha River 
is just over 220 km long, has a watershed area of about 37,300 km\2\, 
and flows mainly eastward before emptying into the Atlantic Ocean (TNC 
2005). Tidal influence extends up to about rkm 40 (DeVries 2006). The 
average annual discharge is 381 m\3\/s, and benthic substrates consist 
mostly of sands with very few rocky outcrops (Heidt and Gilbert 1979; 
DeVries 2006). Water temperatures during the winter/spring spawning 
period have averaged about 10.5 [deg]C (Heidt and Gilbert 1979), which 
is consistent with DeVries' (2006) observation that spawning runs 
appeared to commence when water temperatures reach 10.2 [deg]C. When 
water temperatures exceed 27 [deg]C, shortnose sturgeon typically move 
above the salt-fresh water interface and aggregate in deeper areas of 
the river (DeVries 2006); however, shortnose sturgeon have also been 
observed to use lower portions of the river throughout the summer, even 
when water temperatures averaged 34 [deg]C (Heidt and Gilbert 1979; 
DeVries 2006).
    Overall, the variation in habitat characteristics across the range 
of shortnose sturgeon indicates that there is no single type or typical 
river system. Despite a suite of existing threats, shortnose sturgeon 
continue to occupy many river systems across their historical range. 
The fact that the Saint John River lies at one end of the species' 
range, and among other attributes, experiences different temperature 
and flow regimes, does not mean that this particular river is unusual 
or unique given the variability in habitat conditions observed across 
the range. Therefore, we conclude that the Saint John River is not an 
unusual or unique ecological setting when viewed against the range of 
the taxon as a whole. Furthermore, though not relied up on for our 
finding, we note that COSEWIC (In Press) recently concluded that 
shortnose sturgeon from other river systems would probably be able to 
survive in Canada.

Significant Gap in the Range of the Taxon

    The second consideration under the DPS Policy in determining 
whether a population may be ``significant'' to its taxon is whether the 
``loss of the discrete population segment would result in a significant 
gap in the range of a taxon'' (61 FR 4722, February 7, 1996). Shortnose 
sturgeon are distributed along the Atlantic coast of North America from 
the Minas Basin, Nova Scotia to the St. Johns River, Florida, 
representing a coastal range of roughly 3,700 km. The Saint John River, 
located at the northern end of the range, represents a small portion of 
the species' currently occupied geographic range. In addition, although 
the Saint John River is presumed to contain a relatively large 
population of shortnose sturgeon, that populaiton is not considered the 
largest, and it represents one of at least 10 spawning populations 
(SSRT 2010). Furthermore, relatively recent field data indicate 
shortnose sturgeon make coastal migrations to a greater extent than 
previously thought (e.g., Dionne et al. 2013) and are capable of making 
marine migrations of over 300 km (e.g., between Penobscot and Merrimack 
rivers; M. Kieffer, USGS, pers. comm. 2010). Such data suggest the 
potential for recolonization of the Saint John River by shortnose 
sturgeon migrating from populations to the south. Further indirect 
evidence in support of this possibility comes from the existing genetic 
data, which indicate some level of gene flow among rivers in the 
Northeast, including the Saint John River (Wirgin et al. 2005; Wirgin 
et al. 2009; King et al. 2014). Thus, in light of the potential for 
recolonization and the fact that the Saint John River population of 
shortnose sturgeon does not constitute a substantial proportion of the 
species' range, we conclude that the loss of the Saint John River would 
not constitute a significant gap in the range of the species.

Only Natural Occurrence of the Taxon

    Under the DPS Policy, a discrete population segment that represents 
the ``only surviving natural occurrence of a taxon that may be more 
abundant elsewhere as an introduced population outside its historical 
range'' may be significant to the taxon as whole (61 FR 4722, February 
7, 1996). This consideration is not relevant in this particular case, 
because shortnose sturgeon are present in many river systems throughout 
their historical range (SSRT 2010).

Genetic Characteristics

    As stated in the DPS Policy, in assessing the ``significance'' of a 
``discrete'' population, we consider whether the discrete population 
segment differs markedly from other populations of the species in its 
genetic characteristics (61 FR 4722, February 7, 1996). Therefore, we 
examined the available data to determine whether the Saint John River 
shortnose sturgeon differ markedly in their genetic characteristics 
when compared to other populations. In conducting this evaluation under 
the second criterion of the DPS policy, we looked beyond whether the 
genetic data allow for discrimination of the Saint John population 
segment from other populations (a topic of evaluation in connection 
with the first criterion of ``discreteness''), and instead focused on 
whether the data indicate marked genetic differences that appear to be 
significant to the taxon as a whole. In this sense, we give independent 
meaning to the ``genetic discontinuity'' of the discreteness criterion 
of the DPS Policy and the ``markedly differing genetic 
characteristics'' of the significance criterion.
    Genetic analyses indicate fairly moderate to high levels of genetic 
diversity of shortnose sturgeon in most river systems across the 
geographic range (Grunwald et al. 2002, Quattro et al. 2002; Wirgin et 
al. 2009). Based on the 11 nDNA loci examined in samples from 17 
locations, King et al. (2014) reported that the number of observed 
alleles (i.e., versions of a gene at a particular locus; here with 
overall frequencies >1%) ranged from a low of 55 in the Cape Fear River 
(n= 3 fish) to a high of 152 in the Hudson River (n= 45 fish); 118 
alleles were observed in the Saint John River sample (n=25 fish). 
Estimated heterozygosity was not reported by river sample, but King et 
al. (2014) noted that it was lowest for the southern rivers relative to 
the mid-Atlantic and northern river samples. Wirgin et al. (2009) 
reported that haplotypic diversity ranged from 0.500 (Santee River, 
n=4) to 0.862 (Altamaha River, n= 69) across 15 sample populations, 
with the Saint John River population having a haplotype diversity index 
of 0.696 (n=42). The number of individual haplotypes observed in any

[[Page 65193]]

one river sample ranged from two (Santee River, n=4) to 13 (Winyah Bay, 
n=46), with eight haplotypes observed in the Saint John River sample 
(n=42, Wirgin et al. 2009). The level of genetic diversity based on the 
mtDNA was not correlated with population size, and there was also no 
evidence of population bottlenecks, which may be due to historical 
recency of most population declines (over past ~100 years, Grunwald et 
al. 2002; Wirgin et al. 2009). Overall, the level of genetic diversity 
observed for the Saint John River population segment is not unusual 
relative to that observed in the taxon as a whole. However, Grunwald et 
al. (2002) noted that the lack of reduced haplotypic diversity within 
the northern sample rivers contrasts with findings for other anadromous 
fishes from previously glaciated rivers. Grunwald et al. (2002) 
hypothesized the high degree of haplotypic diversity and large number 
of unique haplotypes in the previously glaciated northern region (i.e., 
Hudson River and northward) may be the result of a northern population 
having survived in one or more northern refugia.
    As discussed previously, at a regional scale, most of the mtDNA 
haplotypes observed are shared across multiple, adjacent rivers 
sampled; however, very little sharing of haplotypes has been documented 
between the northern and southern portions of the range (Quattro et al. 
2002; Grunwald et al. 2002; Wirgin et al. 2009). In the analysis 
conducted by Wirgin et al. (2009), the Saint John River sample had one 
private haplotype (in 1 of 42 fish) and shared the remaining 7 
haplotypes with multiple rivers. Of the seven shared haplotypes, two 
were each shared with two other river systems, including the Hudson and 
Connecticut rivers, and the remaining five haplotypes were shared 
across three to six other rivers within the northeast and mid-Atlantic 
portions of the range (Wirgin et al. 2009). In an earlier study by 
Quattro et al. (2002) in which control region mtDNA was sequenced for 
211 shortnose sturgeon collected from five southeastern U.S. rivers and 
the Saint John River, one haplotype was observed in all river samples. 
This shared haplotype occurred in 1 of 13 fish (7.7%) sampled from the 
Saint John River and 1 of 5 fish (20%) sampled from Winyah Bay; the 
remaining river samples contained this haplotype at higher frequencies 
(36%-79%, Quattro et al. 2002).
    While the shortnose sturgeon from the Saint John River have a 
fairly high degree of genetic diversity and shared haplotypes with 
other rivers, they can be statistically differentiated from other river 
samples based on haplotype frequencies and nDNA distance metrics 
(Wirgin et al. 2009; King et al. 2014). However, the same is also true 
for the majority of rivers across the range of the species. For 
example, using genetic distances (Phi PT), King et al. 
(2014) detected significant differences in all pairwise comparisons 
except for three rivers in the northeast (Penobscot, Androscoggin, and 
Kennebec rivers) and three rivers in the southeast (Edisto, Savannah, 
and Ogeechee rivers). Similarly, significant differences in haplotype 
frequencies have been reported for most river populations sampled. In 
Chi-squared analyses, Grunwald et al. (2002) reported significant 
differences for all but 4 of 82 pairwise comparisons of mtDNA 
nucleotide substitution haplotype frequencies across 10 sample sets 
(two of which were from different sections of the Connecticut River), 
and Wirgin et al. (2009) reported significant differences for all but 9 
of 91 pairwise comparisons of mtDNA haplotype frequencies across 13 
river populations.
    The magnitude of these genetic differences between individual river 
systems varies across the range of the species and indicates a 
hierarchical pattern of differentiation. For example, the mtDNA data 
reveal a deep divergence between rivers in the northern portion of the 
range from rivers in the southern portion of the range. Of the 29 
haplotypes observed by Grunwald et al. (2002), 11 (37.9%) were 
restricted to northern systems, 13 (44.8%) were restricted to the more 
southern systems, and only 5 (17.2%) slightly overlapped the two 
regions. In the later and larger study by Wirgin et al. (2009), the 
observed haplotypes again clustered into regional groupings: 10 of 38 
observed haplotypes (26.3%) only occurred in systems north of the 
Hudson River, 16 of 38 (42.1%) only occurred in systems south of the 
Chesapeake Bay, and just 5 of 38 (13.2%) haplotypes overlapped in the 
mid-Atlantic region. The limited sharing of haplotypes between the 
north and south regions is consistent with strong female homing 
fidelity and limited gene flow between these regions. The break in 
shared haplotypes corresponds with the historical division of the 
species due to Pleistocene glaciation, which Grunwald et al. (2002) 
stated was probably the most significant event affecting population 
structure and patterns of mtDNA diversity in shortnose sturgeon.
    The recent nDNA analyses of King et al. (2014) also indicate an 
unambiguous differentiation of sample populations into one of three 
major geographic groupings--Northeast, Mid-Atlantic, or Southeast. When 
all 17 sample populations were pooled by these three geographic 
regions, correct assignment to each region was 99.1% for the Northeast 
and 100% (i.e., zero mi-assigned fish) for the remaining two regions 
(King et al. 2014). Of the 133 fish included for the Northeast group, 
one was mis-assigned to the Mid-Atlantic. The estimates of effective 
migrants per generation (based on Phi PT) are consistent 
with the regional zones of genetic discontinuity among Northeast, Mid-
Atlantic, and Southeast river systems. The average migrants per 
generation between regions ranged from less than one migrant (i.e., 
0.89) between Northeast and Southeast to nearly two migrants (i.e., 
1.89) between Northeast and Mid-Atlantic. In contrast, the range of 
estimated migrants per generation within regions was 2.25-83.08 for the 
Northeast, 1.87-13.64 for the Mid-Atlantic, and 2.38-49.75 for the 
Southeast (King et al. 2014). The estimated migrants per generation 
between the Saint John River in particular and all other rivers within 
the Northeast ranged from 2.25-3.43 (King et al. 2014). Taken together, 
these data indicate that the degree of genetic differentiation between 
the Saint John River and the rivers within the Gulf of Maine is 
relatively small or ``shallow'', especially relative to the deeper 
divergence observed among the regional groupings of river populations. 
A possible explanation for the relatively low level of differentiation 
within the Northeast is that the those populations are relatively young 
in a geologic sense due to recent glaciations compared to populations 
in the more southern part of the range (SSRT 2010).
    In conclusion, given the patterns of genetic diversity, shared 
haplotypes, and relative magnitudes of genetic divergence at the river 
drainage versus regional scale, we find there is insufficient evidence 
that the Saint John River population of shortnose sturgeon differs 
markedly in its genetic characteristics relative to the taxon as a 
whole so as to meet the test for ``significance'' on this basis. While 
the Saint John River population segment can be genetically 
distinguished from other river populations, available genetic evidence 
places it into a larger evolutionarily meaningful unit, along with 
several other river populations sampled. The degree of differentiation 
among the three larger regional groups is more marked than the 
differences observed among populations from the Saint John and other 
nearest rivers, suggesting that the Saint John River

[[Page 65194]]

population's differentiation is not ``significant'' in the context of 
the whole species. Gene flow estimates are also consistent with the 
observed deeper zones of divergence detected at the regional scale. 
Thus, we conclude that these data do not support delineation of the 
Saint John River population segment as ``significant.'' In so 
interpreting the available genetic data, we are mindful of the 
Congressional guidance to use the DPS designation sparingly.

DPS Conclusion and Petition Finding

    We conclude that the Saint John River population of shortnose 
sturgeon is ``discrete'' based on evidence that it is a relatively 
closed and somewhat geographically isolated population segment. It thus 
satisfies the first prong of the DPS policy. However, we also find that 
the Saint John River population segment is not ``significant'' to the 
taxon as a whole. It thus fails to satisfy the second prong of the DPS 
Policy. As such, based on the best available data, we conclude that the 
Saint John River population of shortnose sturgeon does not constitute a 
DPS and, thus, does not qualify as a ``species'' under the ESA. 
Therefore, we deny the petition to consider this DPS for delisting. Our 
denial of the petition on this ground does not imply any finding as to 
how we should proceed if the situation were otherwise, i.e., where a 
population is found instead to meet the criteria to be a DPS. Even if 
the population had met both criteria of the DPS Policy, and even if the 
population were also found to have a status that differed from the 
listed entity, it would not necessarily be appropriate to propose 
modifications to the current listing, in light of the unsettled legal 
issues surrounding such revisions. Nor do we resolve here what steps 
would need to be followed to propose revisions to the species' listing 
if the facts had been otherwise; such an inquiry would be hypothetical 
in this case. It is clear that because the petition at issue here 
sought identification of a DPS, and because the population at issue is 
not a DPS, this particular petition must be denied. As this is a final 
action, we do not solicit comments on it.

References Cited

    A complete list of references is available upon request to the 
Office of Protected Resources (see ADDRESSES).


    The authority for this action is the Endangered Species Act of 
1973, as amended (16 U.S.C. 1531 et seq.).

    Dated: October 20, 2015.
Samuel D. Rauch III,
Deputy Assistant Administrator for Regulatory Programs, National Marine 
Fisheries Service.
[FR Doc. 2015-27148 Filed 10-23-15; 8:45 am]