A distinct population segment (DPS) is the smallest division of a taxonomic species permitted to be protected under the U.S.
These are applied similarly for addition to the lists of endangered and threatened wildlife and plants, reclassification, and removal from the lists: A population segment of a vertebrate species may be considered discrete if it satisfies either one of the following conditions: 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 DPSes be used "...sparingly" while encouraging the conservation of genetic diversity.
In carrying out this examination, the Services [USFWS and NMFS] will consider available scientific evidence of the discrete population segment's importance to the taxon to which it belongs.
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.