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.
