Distinct Population Segment - Relationship To Evolutionarily Significant Units (ESU's)

Relationship To Evolutionarily Significant Units (ESU's)

In consideration of Pacific salmon for listing under the Act, NMFS has relied on the evolutionarily significant unit (ESU) concept and previous developed a policy on the definition of species under the 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. The 1996 joint policy considers the 1991 NMFS policy on Pacific salmon to be consistent with the joint policy, being a detailed extension of it. The joint policy further states that NMFS will continue to exercise the 1991 policy with respect to Pacific salmonids.

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