Fatigue and Mortality in Troll-Caught Pacific Salmon (Oncorhynchus)

Abstract

Capture by trolling subjects feeding coho and Chinook salmon to hyperactivity which may lead to a distressed condition or death, and death cannot be predicted from examination of individual fish at time of capture. Mortality of coho was estimated to be in the 0.95 confidence interval of 34% and 52%. Time of maximum death rate of coho is shown to coincide with the period of maximum blood lactate response. Survival occurred either when blood lactate did not reach critical levels (above 125 mg%) or reached critical levels and subsequently subsided. Holding salmon in a live box for 8-14 hours before release did not improve tag recovery, suggesting additional indiscriminant stress was caused at release. Adult coho in fresh water did not appear capable of lethal hyperactivity. This led to the hypothesis that cessation of feeding during spawning migration has adaptive significance for survival of Pacific salmon.