A. Status of the Spectacled Eider - U.S. Fish and Wildlife Service

E. Distinct Population Segments
The Endangered Species Act (as amended in 1978) provides protection to “...any distinct
population segment ofany species ofvertebrate fish or wildlife which interbreeds when mature.”
Congress (Senate Report 151, 96th Congress, 1st Session) instructed the Secretary ofthe Interior
to exercise this authority “...sparingly and only when the biological evidence indicates that such
action is warranted.”
In the “Policy Regarding the Recognition ofDistinct Vertebrate Population Segments under the
Endangered Species Act” (USFWS 1996), the Service defined “distinct population segment” forthe
purposes oflisting, delisting and reclassif~,’ing vertebrates. Under the policy, three elements
are to be considered sequentially in determining the status ofa potentially distinct population
segment: 1) the discreteness ofthe population relative to the rest ofthe species; 2) the
significance ofthe population segment to the species; and 3) the population segment’s
conservation status in relation to the Act’s standards for listing (i.e., is the population segment
endangered or threatened when treated as ifit were a species?).
The three breeding populations ofSpectacled Eiders (i.e., YKD, NS, and AR) meet the criteria
for designation as distinct population segments under the policy. The criteria for evaluating each
element are presented below, along with the corresponding analyses ofthe Spectacled Eider
breeding populations.
Element I - Discreteness
Criteria
A population segment ofa vertebrate species may be considered discrete ifit satisfies one ofthe
following criteria:
1. It is markedly separated from other populations ofthe same taxon as a consequence of
physical, physiological, ecological, or behavioral factors.
2. It is delimited by international governmental boundaries within which differences in control
ofexploitation, management ofhabitat, conservation status, or regulatory mechanisms exist
that are significant in light ofsection 4(a)( 1 )(D) ofthe Act.
Analysis
The three main breeding populations are physically separated from one another by several
hundred kilometers, and, on that basis alone, they fulfill the first criterion ofbeing “markedly
separated.” Although perhaps only reflecting facultative responses to the environment, these
populations also exhibit marked ecological and behavioral differences such as different migration
routes and breeding chronologies. No data exist to evaluate the possibility ofphysiological
differences.
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