[Federal Register Volume 61, Number 26 (Wednesday, February 7, 1996)]
[Pages 4722-4725]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-2639]

[[Page 4721]]


Part IV

Department of the Interior
Fish and Wildlife Service

Department of Commerce
National Oceanic and Atmospheric Administration

Policy Regarding the Recognition of District Vertebrate Population; 

Federal Register / Vol. 61, No. 26 / Wednesday, February 7, 1996 / 

[[Page 4722]]


Fish and Wildlife Service


National Oceanic and Atmospheric Administration

Policy Regarding the Recognition of Distinct Vertebrate 
Population Segments Under the Endangered Species Act

AGENCIES: Fish and Wildlife Service, Interior; National Marine 
Fisheries Service, NOAA, Commerce.

ACTION: Notice of policy.


SUMMARY: The Fish and Wildlife Service and the National Marine 
Fisheries Service (Services) have adopted a policy to clarify their 
interpretation of the phrase ``distinct population segment of any 
species of vertebrate fish or wildlife'' for the purposes of listing, 
delisting, and reclassifying species under the Endangered Species Act 
of 1973, as amended (16 U.S.C. 1531 et. seq.) (Act).

ADDRESSES: The complete record pertaining to this action is available 
for inspection, by appointment, during normal business hours at the 
Division of Endangered Species, U.S. Fish and Wildlife Service, in Room 
452, Arlington Square Building, 4401 North Fairfax Drive, Arlington, 

FOR FURTHER INFORMATION CONTACT: E. LaVerne Smith, Chief, Division of 
Endangered Species, U.S. Fish and Wildlife Service at the above address 
(703/358-2171), or Russell Bellmer, Chief, Endangered Species Division, 
National Marine Fisheries Service, 1335 East-West Highway, Silver 
Spring, Maryland 20910 (301/713-1401).



    The Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et. 
seq.). (Act) requires the Secretary of the Interior or the Secretary of 
Commerce (depending on jurisdiction) to determine whether species are 
endangered or threatened. In defining ``species,'' the Act as 
originally passed included, ``* * * any subspecies of fish or wildlife 
or plants and any other group of fish or wildlife of the same species 
or smaller taxa in common spatial arrangement that interbreed when 
mature.'' In 1978, the Act was amended so that the definition read ``* 
* * 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.'' This change restricted application of this 
portion of the definition to vertebrates. The authority to list a 
``species'' as endangered or threatened is thus not restricted to 
species as recognized in formal taxonomic terms, but extends to 
subspecies, and for vertebrate taxa, to distinct population segments 
    Because the Secretary must ``* * * determine whether any species is 
an endangered species or a threatened species'' (section 4(a)(1)), it 
is important that the term ``distinct population segment'' be 
interpreted in a clear and consistent fashion. Furthermore, Congress 
has instructed the Secretary to exercise this authority with regard to 
DPS's ``* * * sparingly and only when the biological evidence indicates 
that such action is warranted.'' (Senate Report 151, 96th Congress, 1st 
Session). The Services have used this authority relatively rarely; of 
over 300 native vertebrate species listed under the Act, only about 30 
are given separate status as DPS's.
    It is important in light of the Act's requirement to use the best 
available scientific information in determining the status of species 
that this interpretation follows sound biological principles. Any 
interpretation adopted should also be aimed at carrying out the 
purposes of the Act (i.e., ``* * * to provide a means whereby the 
ecosystems upon which endangered species and threatened species depend 
may be conserved, to provide a program for the conservation of such 
endangered species and threatened species, and to take such steps as 
may be appropriate to achieve the purposes of the treaties and 
conventions set forth in subsection (a) of this section'' (section 
    Available scientific information provides little specific 
enlightenment in interpreting the phrase ``distinct population 
segment.'' This term is not commonly used in scientific discourse, 
although ``population'' is an important term in a variety of contexts. 
For instance, a population may be circumscribed by a set of 
experimental conditions, or it may approximate an ideal natural group 
of organisms with approximately equal breeding opportunities among its 
members, or it may refer to a loosely bounded, regionally distributed 
collection of organisms. In all cases, the organisms in a population 
are members of a single species or lesser taxon.
    The National Marine Fisheries Service (NMFS) has developed a Policy 
on the Definition of Species under the Endangered Species Act (56 FR 
58612-58618; November 20, 1991). The policy applies only to species of 
salmonids native to the Pacific. Under this policy, a stock of Pacific 
salmon is considered a DPS if it represents an evolutionarily 
significant unit (ESU) of a biological species. A stock must satisfy 
two criteria to be considered an ESU:
    (1) It must be substantially reproductively isolated from other 
conspecific population units; and
    (2) It must represent an important component in the evolutionary 
legacy of the species.
    This document adopts an interpretation of the term ``distinct 
population segment'' for the purposes of listing, delisting, and 
reclassifying vertebrates by the U.S. Fish and Wildlife Service (FWS) 
and NMFS. The Services believe that the NMFS policy, as described 
above, on Pacific salmon is consistent with the policy outlined in this 
notice. The NMFS policy is a detailed extension of this joint policy. 
Consequently, NMFS will continue to exercise its policy with respect to 
Pacific salmonids
    The Services' draft policy on this subject was published on 
December 21, 1994 (59 FR 65885) and public comment was invited. After 
review of comments and further consideration, the Services adopt the 
policy as issued in draft form.

Summary of Comments and Recommendations

    The Services received 31 letters from individuals and organizations 
commenting on the draft policy. In addition, since publication of the 
draft policy, the National Academy of Sciences, National Research 
Council (NRC), has published a report titled ``Science and the 
Endangered Species Act,'' prepared by a committee appointed by the 
Academy at the request of several members of Congress. This report in 
part examines the definition of ``species'' under the Act, and endorses 
the recognition of scientifically identified evolutionary units for 
conservation purposes. It discusses the recognition of DPS's in terms 
of ``distinctiveness,'' which is consistent with the concept of 
``discreteness'' as presented in the draft policy except that it would 
not recognize an international political boundary to delimit a DPS. The 
committee noted that: ``Although there can be good policy reasons for 
such delineations, there are not sound scientific reasons to delineate 
species only in accordance with political boundaries.'' The Services 
agree that the inclusion of international boundaries in determining 
whether a population segment is discrete is sometimes undertaken as a 
matter of policy rather than science. Although the committee 

[[Page 4723]]
expressed the belief that application of a distinctiveness test 
(analogous to the standard of discreteness in the policy) would 
adequately carry out the congressional instruction that the authority 
to address DPS's be exercised sparingly, the Services continue to 
believe that a judgement regarding the significance of any unit found 
to be discrete is necessary to comply with congressional intent.
    Respondents presented a wide range of opinion regarding the 
recognition of DPS's. Some argued that the draft policy would be too 
restrictive and make it difficult or impossible to protect important 
elements of biodiversity; others maintained that the draft was not 
restrictive enough and would allow the Services to extend protection to 
entities never intended to be eligible for protection under the Act. A 
few respondents questioned the need for any policy framework and 
advocated case-by-case determinations of the eligibility of entities 
for listing under the DPS provision. The Services continue to believe 
that the Act will be best administered if there is a general policy 
framework governing the recognition of DPS's that can be disseminated 
and understood by the affected public.
    Several respondents questioned the relationship of the draft policy 
to the NMFS policy regarding salmonids. The Services believe that the 
NMFS policy for salmonids is consistent with the general policy 
outlined in this notice, although the salmonid policy is formulated 
specifically to address the biology of this group. Several respondents 
also questioned the use of qualifying words such as ``significant'' or 
``markedly'' in the policy. The Services intended these words to have 
their commonly understood senses. At the time any distinct population 
is recognized or not recognized the reasons for which it is believed to 
satisfy or not satisfy the conditions of the policy will be fully 
    Several respondents maintained that a policy of this nature 
required adoption under rulemaking procedures of the Administrative 
Procedure Act. The Services disagree, and continue to regard the policy 
as non-regulatory in nature. Specific recommendations advanced by 
respondents are paraphrased and responded to below.

Only Full Species are Genetically Distinct From one Another, and 
Listing Should Only be Extended to These Genetically Distinct Entities.

    Restricting listings to full taxonomic species would render the 
Act's definition of species, which explicitly includes subspecies and 
DPS's of vertebrates, superfluous. Clearly, the Act is intended to 
authorize listing of some entities that are not accorded the taxonomic 
rank of species, and the Services are obliged to interpret this 
authority in a clear and reasonable manner.

The Services Should Focus on Genetic Distinctness in Recognizing a 
Distinct Population Segment. Conversely, Some Respondents Believed 
There Should be No Requirement That a DPS be Genetically Differentiated 
or Recognizable for it to be Protected Under the Act

    There appears to be a diversity of understanding regarding the 
purposes of the Act, with some individuals viewing it as directed 
almost exclusively toward the conservation of unique genetic resources 
while other individuals emphasize its stated intention of conserving 
ecosystems. This diversity of viewpoints is reflected in comments 
addressing the role to be played by genetic information in the draft 
policy. The Services understand the Act to support interrelated goals 
of conserving genetic resources and maintaining natural systems and 
biodiversity over a representative portion of their historic 
occurrence. The draft policy was intended to recognize both these 
intentions, but without focusing on either to the exclusion of the 
other. Thus, evidence of genetic distinctness or of the presence of 
genetically determined traits may be important in recognizing some 
DPS's, but the draft policy was not intended to always specifically 
require this kind of evidence in order for a DPS to be recognized. The 
ESU policy of NMFS also does not require genetic data before an ESU can 
be identified. Thus in determining whether the test for discreteness 
has been met under the policy, the Services allow but do not require 
genetic evidence to be used. At least one respondent evidently 
understood the draft policy to require that genetic distinctness be 
demonstrated before a DPS could be recognized, and criticized the draft 
on that basis. As explained above, this was never intended.

The Elements Describing Reasons for Considering a Population Segment 
Significant Should be Laid Out Comprehensively, Rather Than Presented 
as an Open-Ended Set of Examples as in the Draft Policy

    The Services appreciate the need to make a policy on this subject 
as complete and comprehensive as possible, but continue to believe that 
it is not possible to describe in advance all the potential attributes 
that could be considered to support a conclusion that a particular 
population segment is ``significant'' in terms of the policy. When a 
distinct population is accepted or rejected for review pursuant to a 
petition or proposed for listing or delisting, the Services intend to 
explain in detail why it is considered to satisfy both the discreteness 
and significance tests of the policy.

In Assessing the Significance of a Potential Distinct Population 
Segment, the Services Should Focus on its Importance to the Status of 
the Species to Which it Belongs. Alternatively, the Services Should 
Emphasize the Importance of a Potential DPS to the Environment in Which 
it Occurs

    Despite its orientation toward conservation of ecosystems, the 
Services do not believe the Act provides authority to recognize a 
potential DPS as significant on the basis of the importance of its role 
in the ecosystem in which it occurs. In addition, it may be assumed 
that most, if not all, populations play roles of some significance in 
the environments to which they are native, so that this importance 
might not afford a meaningful way to differentiate among populations. 
On the other hand, populations commonly differ in their importance to 
the overall welfare of the species they represent, and it is this 
importance that the policy attempts to reflect in the consideration of 

International Boundaries are not Appropriate in Determining That a 
Population is Discrete in the Draft Policy; Political Boundaries Other 
Than Those Between Nations may be Appropriate in Some Cases to Delimit 

    The Services recognize that the use of international boundaries as 
a measure of discreteness may introduce an artificial and non-
biological element to the recognition of DPS's. Nevertheless, it 
appears to be reasonable for national legislation, which has its 
principal effects on a national scale, to recognize units delimited by 
international boundaries when these coincide with differences in the 
management, status, or exploitation of a species. Recognition of 
international boundaries in this way is also consistent with practice 
under the Convention on International Trade in Endangered Species of 
Wild Fauna and Flora, which is implemented in the United States by the 
Act. Recognition of other political boundaries, such as State lines 
within the United States, would appear to lead to the recognition of 

[[Page 4724]]
entities that are primarily of conservation interest at the State and 
local level, and inappropriate as a focus for a national program. The 
Services recognize, as suggested in some comments, that infra-national 
political boundaries offer opportunities to provide incentives for the 
favorable management of species if they were used as a basis for 
recognizing discrete entities for delisting or for exclusion from a 
listing. Particularly when applied to the delisting or reclassification 
of a relatively widespread species for which a recovery program is 
being successfully carried out in some States, recognition of State 
boundaries would offer attractive possibilities. Nevertheless, the Act 
provides no basis for applying different standards for delisting than 
those adopted for listing. If the Services do not consider entities for 
listing that are not primarily of conservation interest at a national 
level, they must also refrain from delisting or reclassifying units at 
this level.

Complete Reproductive Isolation Should be Required as a Prerequisite to 
the Recognition of a Distinct Population Segment

    The Services do not consider it appropriate to require absolute 
reproductive isolation as a prerequisite to recognizing a distinct 
population segment. This would be an impracticably stringent standard, 
and one that would not be satisfied even by some recognized species 
that are known to sustain a low frequency of interbreeding with related 
    The Services Should Emphasize Congress' Instruction to use Their 
Authority to Dddress DPS's ``Sparingly''
    The Services believe that application of the policy framework 
announced in this document will lead to consistent and sparing exercise 
of the authority to address DPS's, in accord with congressional 

The Occurrence of a Population Segment in an Unusual Setting Should not 
be Used as Evidence for its Significance

    The Services continue to believe that occurrence in an unusual 
ecological setting is potentially an indication that a population 
segment represents a significant resource of the kind sought to be 
conserved by the Act. In any actual case of a DPS recognized in part on 
this basis, the Services will describe in detail the nature of this 
significance when accepting a petition or proposing a rule.

The Authority to Address DPS's Should be Extended to Plant and 
Invertebrate Species

    The Services recognize the inconsistency of allowing only 
vertebrate species to be addressed at the level of DPS's, and the 
findings of the NRC committee also noted that such recognition would be 
appropriate for other species. Nevertheless, the Act is perfectly clear 
and unambiguous in limiting this authority. This policy acknowledges 
the specific limitations imposed by the Act on the definition of 

The Services Should Stress Uniqueness and Irreplaceability of 
Ecological Functions in Recognizing DPS's

    The Services consider the Act to be directed at maintenance of 
species and populations as elements of natural diversity. Consequently, 
the principal significance to be considered in a potential DPS will be 
the significance to the taxon to which it belongs. The respondent 
appears to be recommending that the Services consider the significance 
of a potential DPS to the community or ecosystem in which it occurs and 
the likelihood of another species filling its niche if it should be 
extirpated from a particular portion of its range. These are important 
considerations in general for the maintenance of healthy ecosystems, 
and they often coincide with conservation programs supported by the 
Act. Nevertheless, the Act is not intended to establish a comprehensive 
biodiversity conservation program, and it would be improper for the 
Services to recognize a potential DPS as significant and afford it the 
Act's substantive protections solely or primarily on these grounds.

Congress did not Intend to Require That DPS's be Discrete. In a Similar 
Vein, Congress did not Require That a Potential DPS be Significant to 
be Considered Under the Act

    With regard to the discreteness standard, the Services believe that 
logic demands a distinct population recognized under the Act be 
circumscribed in some way that distinguishes it from other 
representatives of its species. The standard established for 
discreteness is simply an attempt to allow an entity given DPS status 
under the Act to be adequately defined and described. If some level of 
discreteness were not required, it is difficult to imagine how the Act 
could be effectively administered or enforced. At the same time, the 
standard adopted does not require absolute separation of a DPS from 
other members of its species, because this can rarely be demonstrated 
in nature for any population of organisms. The standard adopted is 
believed to allow entities recognized under the Act to be identified 
without requiring an unreasonably rigid test for distinctness. The 
requirement that a DPS be significant is intended to carry out the 
expressed congressional intent that this authority be exercised 
sparingly as well as to concentrate conservation efforts undertaken 
under the Act on avoiding important losses of genetic diversity.

A Population Should Only be Required to be Discrete or Significant, but 
not Both, to be Recognized as a Distinct Population Segment

    The measures of discreteness and significance serve decidedly 
different purposes in the policy, as explained above. The Services 
believe that both are necessary for a policy that is workable and that 
carries out congressional intent. The interests of conserving genetic 
diversity would not be well served by efforts directed at either well-
defined but insignificant units or entities believed to be significant 
but around which boundaries cannot be recognized.

Requiring That a DPS be Discrete Effectively Prevents the Loss of Such 
a Segment From Resulting in a Gap in the Distribution of a Species. 
Essentially, if Distinct Populations are Entirely Separate, the Loss of 
One Has Little Significance to the Others

    If the standard for discreteness were very rigid or absolute, this 
could very well be true. However, the standard adopted allows for some 
limited interchange among population segments considered to be 
discrete, so that loss of an interstitial population could well have 
consequences for gene flow and demographic stability of a species as a 
whole. On the other hand, not only population segments whose loss would 
produce a gap in the range of a species can be recognized as 
significant, so that a nearly or completely isolated population segment 
could well be judged significant on other grounds and recognized as a 
distinct population segment.

The Services Lack Authority to Address DPS's of Subspecies

    The Services maintain that the authority to address DPS's extends 
to species in which subspecies are recognized, since anything included 
in the taxon of lower rank is also included in the higher ranking 

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    The following principles will guide the Services' listing, 
delisting and reclassification of DPS's of vertebrate species. Any 
proposed or final rule affecting status determination for a DPS would 
clearly analyze the action in light of these guiding principles.


    Three elements are considered in a decision regarding the status of 
a possible DPS as endangered or threatened under the Act. These are 
applied similarly for addition to the lists of endangered and 
threatened wildlife and plants, reclassification, and removal from the 
    1. Discreteness of the population segment in relation to the 
remainder of the species to which it belongs;
    2. The significance of the population segment to the species to 
which it belongs; and
    3. The population segment's conservation status in relation to the 
Act's standards for listing (i.e., is the population segment, when 
treated as if it were a species, endangered or threatened?).
    Discreteness: A population segment of a vertebrate species may be 
considered discrete if it satisfies either one of the following 
    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 Act.
    Significance: If a population segment is considered discrete under 
one or more of the above conditions, its biological and ecological 
significance will then be considered in light of Congressional guidance 
(see Senate Report 151, 96th Congress, 1st Session) that the authority 
to list DPS's be used `` * * * sparingly'' while encouraging the 
conservation of genetic diversity. In carrying out this examination, 
the Services will consider available scientific evidence of the 
discrete population segment's importance to the taxon to which it 
belongs. This consideration may include, but is not limited to, the 
    1. Persistence of the discrete population segment in an ecological 
setting unusual or unique for the taxon,
    2. Evidence that 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 historic range, or
    4. Evidence that the discrete population segment differs markedly 
from other populations of the species in its genetic characteristics.
    Because precise circumstances are likely to vary considerably from 
case to case, it is not possible to describe prospectively all the 
classes of information that might bear on the biological and ecological 
importance of a discrete population segment.
    Status: If a population segment is discrete and significant (i.e., 
it is a distinct population segment) its evaluation for endangered or 
threatened status will be based on the Act's definitions of those terms 
and a review of the factors enumerated in section 4(a). It may be 
appropriate to assign different classifications to different DPS's of 
the same vertebrate taxon.

Relationship to Other Activities

    The Fish and Wildlife Service's Listing and Recovery Priority 
Guidelines (48 FR 43098; September 21, 1983) generally afford DPS's the 
same consideration as subspecies, but when a subspecies and a DPS have 
the same numerical priority, the subspecies receives higher priority 
for listing. The Services will continue to generally accord subspecies 
higher priority than DPS's.
    Any DPS of a vertebrate taxon that was listed prior to 
implementation of this policy will be reevaluated on a case-by-case 
basis as recommendations are made to change the listing status for that 
distinct population segment. The appropriate application of the policy 
will also be considered in the 5-year reviews of the status of listed 
species required by section 4(c)(2) of the Act.

Effects of Policy

    This guides the evaluation of distinct vertebrate population 
segments for the purposes of listing, delisting, and reclassifying 
under the Act. The only direct effect of the policy is to accept or 
reject population segments for these purposes. More uniform treatment 
of DPS's will allow the Services, various other government agencies, 
private individuals and organizations, and other interested or 
concerned parties to better judge and concentrate their efforts toward 
the conservation of biological resources at risk of extinction.
    Listing, delisting, or reclassifying distinct vertebrate population 
segments may allow the Services to protect and conserve species and the 
ecosystems upon which they depend before large-scale decline occurs 
that would necessitate listing a species or subspecies throughout its 
entire range. This may allow protection and recovery of declining 
organisms in a more timely and less costly manner, and on a smaller 
scale than the more costly and extensive efforts that might be needed 
to recover an entire species or subspecies. The Services' ability to 
address local issues (without the need to list, recover, and consult 
rangewide) will result in a more effective program.

    Author/Editor: The editors of this policy are Dr. John J. Fay of 
the Fish and Wildlife Service's Division of Endangered Species, 452 
ARLSQ, Washington, DC 20240 (703/358-2105) and Marta Nammack of the 
National Marine Fisheries Service's Endangered Species Division, 
1335 East-West Highway, Silver Spring, Maryland 20910 (301/713-

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

    Dated: February 1, 1996.
John G. Rogers,
Acting Director, Fish and Wildlife Service.

    Dated: February 1, 1996.
Nancy Foster,
Deputy Assistant Administrator for Fisheries, National Marine Fisheries 
[FR Doc. 96-2639 Filed 2-6-96; 8:45 am]