Description: These data represent the final delineated population boundaries associated with salmonid Evolutionarily Significant Units (ESU) for the four recovery domains in the Pacific Northwest. These boundaries were designated by federally-mandated Technical Recovery Teams (TRTs) each covering a recovery domain; Puget Sound, Willamette-Lower Columbia, Interior Columbia, and the Oregon/Northern California Coast. The teams were formed for the purpose of assisting in recovery planning for Endangered Species Act (ESA)-listed species of salmon in the Pacific Northwest. Each TRT consisted of regional fisheries scientists and managers meeting over a period of 7 years. The population boundaries were delineated by members and technical staff from each of the TRTs following Ricker's definition of a stock and McElhany's description of a Viable Salmonid population (see below for further explanation). Data attributes were generalized for the purpose of consistency, but the majority of details put forth by the TRTs are maintained in this spatial data set. These metadata include details and methodologies of boundary determinations, which differed by TRT (due to slight differences in delineation methodologies and availability of process documentation), as well as supporting references and attribute definitions. Actual population boundary geometry for three of the four TRTs (with the exception of Oregon Coast Coho) was standardized to 6th field hydrologic unit boundaries from the Regional Ecosystem Office (REO) or 5th and 6th field hydrologic unit boundaries from Idaho Department of Water Resources (IDWR) for this data product, unless edits are noted in Domain-Specific narratives. See Data Quality section for more information. There are currently multiple salmon population boundaries available from various state and federal agencies which may overlap with these boundaries. Therefore, it is important to clarify the definitions used in the creation of these. The definition of a "population" applied in the creation of these spatial population boundaries follows Ricker's (1972) definition of a stock, as "a group of fish of the same species that spawns in a particular lake or stream (or portion thereof) at a particular season and which, to a substantial degree, does not interbreed with fish from any other group spawning in a different place or in the same place at a different season." An independent population, as described in the viable salmonid population (VSP) report (McElhany et al. 2000), is indicated where groups are "isolated to such an extent that exchanges of individuals among populations do not substantially affect the population dynamics or extinction risk of the independent populations over a 100-year time frame." Such populations are "units for which it is biologically meaningful to examine extinction risks that derive from intrinsic factors such as demographic, genetic, or local environmental stochasticity." A viable salmonid population is "an independent population of any Pacific salmonid (Oncorhynchus spp.) that has a negligible risk of extinction over a 100-year time frame" from various threats (McElhany et al. 2000). For more information on domain-specific methods or population viability in each domain, please see citations in the domain-specific metadata narrative section. McElhany, P., M.H. Ruckelshaus, M.J. Ford, T.C.Wainwright, and E.P. Bjorkstedt. 2000. Viable salmonid populations and the recovery of evolutionarily significant units. U.S. Dept. Commerce, NOAA Tech. Memo. NMFS-NWFSC-42,156 p. Ricker, W. E. 1972. Hereditary and environmental factors affecting certain salmonid populations. In R. C. Simon and P. A. Larkin (eds.), The Stock Concept in Pacific Salmon, p. 27-160. University of British Columbia, Vancouver, B. C.