Nutrients in Salmonid Ecosystems: Sustaining Production and Biodiversity
Past and Present Pacific Salmon Abundance: Bioregional Estimates for Key Life History Stages
Peter K. Schoonmaker, Ted Gresh, Jim Lichatowich, and Hans D. Radtke
Abstract.—Pacific salmon Oncorhynchus spp. are important components of numerous food webs throughout their life history, yet we know very little about the historic and current abundance of these life history stages. We used past cannery records, recent harvest and hatchery records, and salmon life history information drawn from the literature to construct a simple bioregional model of historic and recent salmon abundance at egg, fry, smolt, ocean adult, and spawning stages for five species of Pacific salmon from Alaska to California. We found a historic-to-recent bioregional decline in salmon biomass in all life history stages. Recent salmon egg, fry, smolt, ocean-going adult, and escapement biomass estimates for northwestern North America are 74%, 55%, 59%, 86%, and 35%, respectively, of historic levels. Recent high productivity in Alaskan waters, however, masks a precipitous decline south of Alaska, where recent egg, fry, smolt, ocean-going adult, and escapement biomass levels are 34%, 23%, 50%, 40%, and 15% that of historic levels. Adult production and harvest levels are no longer sufficient measures of salmon management success. Researchers need to quantify and elucidate the ecosystem effects of historic biomass changes in life history stages of Pacific salmon on a watershed basis. Fisheries managers must set and meet specific targets for salmon life history stage abundance—from egg to spawning adult—to restore and maintain ecosystem function.