REVIEW OF RATE OF GROWTH AND MORTALITY OF PACIFIC SALMON IN SALT-WATER, AND NONCATCH MORTALITY CAUSED BY FISHING

Mortality (other than landed catch) caused by pelagic gillnetting is estimated to be equal to the catch for salmon in their penultimate year of life, and equal to about a quarter of the catch for salmon in their final year of life. Mortality caused by trolling for coho (Oncorhynchus kisutch) and chinook salmon (O. tshawytscha) averages about 1 fish killed (mostly below legal size) for every 2 that are boated. The natural mortality rate for sockeye salmon (O. nerka) in their final year of life averages about 0.015/mo. and is somewhat more in earlier years of pelagic life; the greater part of natural mortality after the smolt stage occurs during the downstream migration and early months of coastal life. For coho and chinook the best natural mortality estimate for the last year of life is 0.013/mo., and that for pink (O. gorbuscha) and chum (O. keta) is of the same order. Growth rates during the final growing season vary from 0.26/mo. for pink and coho salmon to 0.06/mo. for chinook in their 5th ocean year. Gains from ceasing to take immature salmon on the high seas range up to 300% of the catch now being taken in that category, while for fish taken in their final year they range up to about 70%, depending on the time of year at which the fishing is done. Gains from transferring existing pelagic net fisheries to the coastal region would be 76% (North American sockeye) and 86% (Asian sockeye) of the weight of fish now caught pelagically. Gains in total yield of existing salmon fisheries (pelagic and coastal) are estimated as 78% for Asian pink salmon and 72% for Asian sockeye. The increase in weight of the total catch from discontinuing ocean trolling for Columbia River [Washington, Oregon, USA] chinook salmon and increasing river fishing correspondingly is estimated tentatively as 63-98%.