Sorry for the lengthy post below, but there is, within the ESA ESU designation a provision for a Distinct Population Segment (DPS) to allow for management of species within a portion of their overall range. A DPS listing can drive management schemes down to a very small level. In theory, if a DPS within an ESU is never "recovered" the application of 4d take restrictions can be continued on ad infinitum. Personally, I would suggest a strong caution for a DPS listing.

The following is copied from the NOAA website on chum:

"NOAA Fisheries has identified 4 evolutionarily significant units (ESUs) of chum salmon in Washington, Oregon and California. Each ESU is treated as a separate species under the Endangered Species Act. Click the links below to get information about a specific ESU, its status, and other relevant information"

The 4 "distinct" ESUs for chum are the coast (Doc's map) and the Puget Sound/Strait of Georgia, both of which are not currently listed. The other two are the Hood Canal summer chum and the Columbia River chum which are both listed as threatened.,_United_States
Distinct Population Segment policy (1996) under the Endangered Species Act, United States
Published: June 18, 2008, 8:41 pm
Updated: June 18, 2008, 8:41 pm
Lead Author: Tatjana Rosen
Topics: Ecology Environmental Law

This article has been reviewed by the following Topic Editor: Peter Saundry
Under the Endangered Species Act ("ESA" or "Act") as originally enacted, the term species was defined to include "any subspecies of fish or wildlife or plants and any other group of fish or wildlife of the same species or smaller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 and the new definition provides that a species includes “any subspecies of fish or wildlife or plants, and any distinct population segment (DPS) of any species of vertebrate fish or wildlife which interbreeds when mature” (ESA, Section 4). (emphasis added)
In 1990, the U.S. Fish and Wildlife Service and the National Marine Fisheries Service (NMFS) convened a Vertebrate Population Workshop to develop guidelines for interpreting the DPS language in the ESA. The NMFS memorandum provided that a vertebrate population (or group of populations) will be considered "distinct" for purposes of the ESA if it represents “an evolutionarily significant unit (ESU) of the biological species”. An ESU was defined as a population that (1) is substantially “reproductively isolated” from other populations of the same species and (2) represents an “important component of the evolutionary legacy of the species”.
In 1996, U.S. Fish and Wildlife and the NMFS developed a joint policy (1996 Policy) intended to clarify the meaning of Distinct Population Segment (61 Fed. Reg. 4722, Feb. 7, 1996). Three basic principles guided the development of the 1996 Policy: (1) the intent of the framers of the ESA to use it to protect genetic diversity (93rd Congress, 1st session, 1973, H.R. Report 412); (2) the 1979 directive that the government agencies involved list populations “sparingly“; and (3) the stipulation in the ESA (section 4(b)(1)(A)) that listing decisions be based “solely on the basis of the best scientific and commercial data available”.
To constitute a DPS, the policy provides a population must exhibit (i) “discreteness” in relation to the remainder of the species and (ii) “significance” to the species to which it belongs.
As to "discreteness" the 1996 Policy states that: “A population segment of a vertebrate species may be considered discrete if [either]: 1. It is markedly separated from other populations of the same taxon as a consequence of physical, physiological, ecological, or behavioral factors …. [or] 2. It is delimited by international governmental boundaries within which differences in control of explication, management of habitat, conservation status or regulatory mechanisms exist ….” (1996 Policy)
Once discreteness has been established, “the Services will consider available scientific evidence of the discrete population segment’s importance to the taxon to which it belongs.” This “significance” test may be satisfied by: “1. Persistence of the [DPS] in an ecological setting unusual or unique for the taxon. 2. Evidence that loss of the [DPS] would result in a significant gap in the range of a taxon. 3. Evidence that the [DPS] represents the only surviving natural occurrence of a taxon . . . . [and] 4. Evidence that the [DPS] differs markedly from other populations of the species in its genetic characteristics….” (1996 Policy)
Further Reading
• Rosen T. 2007. The Endangered Species Act and the distinct population segment policy. Ursus, 18(1):109-116
• U.S. Fish and Wildlife Service, Endangered Species Program. 1996 Distinct Population Segment Policy (full text).
• Waples R.S. 1991. Pacific salmon, Oncorhynchus spp. and the definition of “species” under the Endangered Species Act. Marine Fisheries Review, 53:11-22
Tatjana Rosen (Lead Author);Peter Saundry (Topic Editor) "Distinct Population Segment policy (1996) under the Endangered Species Act, United States". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth June 18, 2008; Last revised Date June 18, 2008; Retrieved February 1, 2013 <,_United_States>
Distinct Population Segments, 4(d) Rules, and Experimental Populations
There are features built into the Endangered Species Act (ESA) and its implementing regulations that give the U.S. Fish and Wildlife Service (USFWS) flexibility in listing, protecting, managing, and recovering species that need the ESA's protections.
Distinct Population Segments
In addition to the listing and delisting of species and subspecies, the ESA allows the listing/delisting of Distinct Population Segments of vertebrate species (i.e., animals with backbones, mammals, birds, fish, reptiles, and amphibians). A Distinct Population Segment is a portion of a species' or subspecies' population or range. The Distinct Population Segment is described geographically instead of biologically, such as "all members of XYZ that occur north of 40 north latitude."
The use of Distinct Population Segments is a benefit to species conservation and a benefit to people whose activities may be affected by the ESA's prohibitions. Conservation efforts are more effective and less costly if they are started early and a Distinct Population Segment listing makes earlier listings possible. By listing a Distinct Population Segment, we apply the ESA's protections only to the deteriorating portion of a species' range. Threats can then be addressed in that specific (and smaller) area instead of waiting until the entire species has declined to the point that listing the entire species throughout its range is necessary.
Also, the USFWS uses Distinct Population Segment listings to customize application of the ESA across the range of listed vertebrate species. For listed species with improving populations, we can delist or reclassify (from endangered to threatened) a Distinct Population Segment. By doing this we remove or reduce the ESA's protections from part of the listed species' range (where it is doing well) while keeping full ESA protection for the Distinct Population Segment of that species that has not yet experienced recovery.
The USFWS's policy for designating Distinct Population Segments is sometimes called the Vertebrate Population Policy. This policy contains the criteria that must be met for a portion of a species' population to be designated as a Distinct Population Segment. Those criteria include the requirements that a Distinct Population Segment must be discrete and significant. This policy was published in the Federal Register (61 FR 4722-4725; February 7, 1996) and can be found on the Web at .
Examples of currently listed Distinct Population Segments:
the northern population of the copperbelly water snake
the interior population of the least tern
the northern population of the bog turtle
Section 4(d) Special Rules
Section 4(d) of the ESA allows the USFWS to establish special regulations for threatened (not endangered) species, subspecies, and Distinct Population Segments. These "4(d) rules" take the place of the normal protections of the ESA and may either increase or decrease the ESA's normal protections. The ESA specifies that 4(d) rules must be "necessary and advisable to provide for the conservation of such species."
One use of 4(d) rules is to relax the normal ESA restrictions to reduce conflicts between people and the protections provided to the threatened species by the ESA. A 4(d) rule can be used in such a situation if those conflicts would adversely affect recovery and if the reduced protection would not slow the species' recovery. This type of 4(d) rule is already in effect for gray wolves. Under authority of a 4(d) rule, Minnesota wolves that have preyed on domestic animals can be trapped and killed by designated government agents. This 4(d) rule was developed to avoid even larger numbers of wolves being killed by private citizens who might otherwise take wolf control into their own hands. (For more details on this example of a section 4(d) special rule, refer to Title 50 Code of Federal Regulations 17.40(d).)
Experimental Populations
Re-establishing a threatened or endangered species in areas of its former range is often necessary for recovery. However, residents and businesses frequently oppose such reintroductions because they fear the presence of the species will also bring severe restrictions on the use of private and public land in the area. To overcome this serious obstacle to species reintroductions, Congress added the concept of experimental populations to the ESA. Experimental population designations are sometimes referred to as section 10(j) rules.
An experimental population is a geographically described group of reintroduced plants or animals that is isolated from other existing populations of the species. Members of the experimental population are considered to be threatened under the ESA, and thus can have special regulations written for them under section 4(d). In addition, if the experimental population is determined to be "nonessential" to the survival of the species, for some activities the experimental population is treated like a species that is proposed for listing as threatened or endangered. In other words, the nonessential experimental population is not given the full protections of the ESA.
Among numerous examples of experimental populations are the Colorado pikeminnow, the southern sea otter, the gray wolf, and the black-footed ferret.
These three aspects of the ESA all can promote the recovery of declining species by fine-tuning the protections of the ESA. This fine-tuning minimizes adverse impacts on people and society while maximizing the likelihood of eventual recovery and delisting of the species. Thus, humans and rare species both benefit from their careful use.
Salmon Populations

Dec. 21, 2012: home page story, Small research station provides immense value to scientific advancement and marine exploration
Pacific salmon and steelhead are salmonids, of the scientific family Salmonidae. They are anadromous fish, which means that they migrate up rivers from the ocean to breed in fresh water. Pacific salmon are in the scientific genus Oncorhynchus, which includes pink, sockeye, chum, Chinook and coho salmon, steelhead and rainbow trout.
These fish have a complex life-cycle that spans a variety of fresh and saltwater habitats. Salmon are born in inland streams and rivers, migrate to coastal estuaries, and then disperse into ocean waters to grow. Once mature, they reverse their course, returning through the estuaries, fighting their way back upriver to the very streams where they were born, to reproduce, die and begin the cycle again.
In 1991, NOAA Fisheries received a petition to list Pacific Northwest salmon runs under the Endangered Species Act (ESA). In response, the Northwest Fisheries Science Center and the Southwest Fisheries Science Center launched a proactive, systematic review of all West Coast salmon runs. To do this, however, the agency first had to determine how a “species” of salmon was defined under the ESA.
The ESA allows listing of “distinct population segments” of vertebrates. NOAA Fisheries, through the scientific leadership and expertise of its science centers, developed a technical document to describe how it will apply this definition in evaluating Pacific salmon stocks for listing under the ESA. A policy (PDF 902KB) was then developed that establishes a group of salmon populations to be a distinct population segment if it is an “evolutionarily significant unit,” or ESU. Scientists established two criteria for ESUs: 1) the population must show substantial reproductive isolation; and 2) there must be an important component of the evolutionary legacy of the species as a whole.
From 1994 to 1999, NOAA Fisheries, through biological review teams (BRTs) convened by its science centers, reviewed the ESA status of all anadromous salmon species on the West Coast. (BRTs are groups of federal agency scientists with expertise in the species being reviewed. They solicit and review all pertinent data and assess risks to the viability of the species.) During these reviews the BRTs identified 52 ESUs, and evaluated whether they were at risk of extinction and should be considered for listing as threatened or endangered under the ESA.
The final BRT reports provided a solid scientific foundation for NOAA Fisheries to make ESA listing determinations. Before beginning the coast-wide status review, the agency had listed two salmon populations in the Snake River basin and one in California's Sacramento River. Following the reviews, NOAA Fisheries had listed a total of 26 salmon and steelhead populations; five as endangered and 21 as threatened. In 2005 the agency completed a periodic review and update of the status of the 26 ESA-listed populations. The agency later listed Oregon coast coho and Puget Sound steelhead as threatened, for a total of 28 populations.
NOAA Fisheries' Northwest Region issued the results of another periodic review of listed salmon and steelhead in August 2011. The agency made no changes to the ESA status of any populations.
Chum Salmon
(Oncorhynchus keta)

NOAA Fisheries has identified 4 evolutionarily significant units (ESUs) of chum salmon in Washington, Oregon and California. Each ESU is treated as a separate species under the Endangered Species Act. Click the links below to get information about a specific ESU, its status, and other relevant information.
ESU ESA Listing Status ESA Critical Habitat
Hood Canal Summer-run
6/28/05 (70FR37160) Designated
9/2/05 (70FR52630)
Columbia River
6/28/05 (70FR37160) Designated
9/2/05 (70FR52630)
Puget Sound/Strait of Georgia
Not Warranted NA
Pacific Coast
Not Warranted NA
ESU Maps
Federal Register Notices

Salmon graphics on the Northwest Region ESA Salmon Web pages are used with permission from Nature Discovery, Copyright © 1996.