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Status Review for Oregon's Illinois River Winter Steelhead
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1993
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[PDF-31.89 MB]
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Description:This report summarizes biological information gathered in conjunction with an Endangered Species Act (ESA) status review for winter steelhead (Oncorhynchus mykiss) from the Illinois River, a tributary of the Rogue River in southern Oregon. The National Marine Fisheries Service (NMFS) received a petition in May 1992 asking that this population be listed as a threatened or endangered species under the ESA. In evaluating the petition, two key questions had to be addressed: Do Illinois River winter steelhead represent a species as defined by the ESA? and, if so, is the species threatened or endangered? With respect to the first question, the ESA allows listing of "distinct population segments" of vertebrates as well as named species and subspecies. NMFS policy on this issue for Pacific salmon and steelhead is that a population will be considered "distinct" for purposes of the ESA if it represents an evolutionarily significant unit (ESU) of the species as a whole. To be considered an ESU, a population or group of populations must 1) be substantially reproductively isolated from other populations, and 2) contribute substantially to ecological/genetic diversity of the biological species. Once an ESU is identified, a variety of factors related to population abundance are considered in determining whether a listing is warranted.
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Rights Information:Public Domain
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