Trends in Abundance and Size of Coho Salmon in the Pacific Rim

摘要

In the early 1960s, average Pacific-wide landings of coho salmon reached a stable level of over 12 million fish that persisted for 3 decades, followed by a sharp decrease to under 6 million fish in 1997-2003 as a result of reduced marine survival and fishery restrictions in the Pacific Northwest and British Columbia. Spawning escapement increased in most streams after 1999 in response to restricted fishing and improved marine survival for some stocks. Marine survival has been spatially and temporally variable, accounting for an average of 54% (range 41-68%) of variation in wild adult returns to twelve systems from Washington to southeast Alaska. Average survival rates have been highest (> 12%) in southeast Alaska and Puget Sound, and lowest (4-6%) for the Washington coast, with British Columbia being intermediate (6-10%). Marine survival was highly variable over a limited spatial scale, indicating that localized marine environments are critically important to overall ocean survival. The average weight of coho salmon harvested in Alaskan fisheries has changed little since the 1960s, but indicators of average weight in southern British Columbia to the Columbia River declined from the 1950s to early 1990s, followed by a rapid rebound from 1993 through 2004.