Chinook Salmon - Trends in Abundance and Biological Characteristics

Abstract

Chinook salmon, Oncorhynchus tshawytscha, the least abundant but largest in size of the five major Pa - cific salmon species, are widely distributed throughout the North Pacific Rim. Although precise numbers spawning in many rivers are little known, many stocks have only a small percentage of their historic abundance levels, and more than 50 stocks have become extinct. Over the past decade commercial catches have fluctuated between one and two million fish annually with an additional 0.6-0.9 million fish caught in recreational, subsistence, and aboriginal fisheries. About half of all commercial catches are made in the United States, particularly in Alaska and Pacific-Northwest states, with the remainder caught, in descending order, by Canada, Russia, and Japan. Within the U. S., nine fish populations are listed in Pacific-Northwest states as threatened or endangered, according to the Endangered Species Act (ESA). While no formal ESA-type listings occur in other areas, some populations in Canada and Russia are of special concern due to declining trends. Current trends in abundance are reviewed from different regions with a focus on stocks of concern but also including some stocks whose trends are relatively stable. While equivocal in improving the status of many depressed wild stocks, hatcheries are important in help- ing maintain fisheries and general abundance in some areas. Chinook salmon are characterized by high plasticity and life-history variability, as seen in their multiple age groups, diverse temporal migration behavior as they return to natal streams, distinct races with separate freshwater and ocean life-history behavior patterns, and red-fleshed and white-fleshed forms. Long-term declines in the average size and age of Chinook salmon appear to be con - tinuing for some stocks and fisheries. The species may be establishing new populations and expanding its range into higher latitudes, possibly due to global warming and other climatic changes.