Gear-Related Mortality in Selective Fisheries for Ocean Salmon

Abstract

In ocean fisheries for Pacific salmon Oncorhynchus spp., there can be several forms of gear-related mortality. Much research effort has been directed at estimating mortality rates for salmon that are hooked and then released. Also potentially important but not easily measured is mortality of fish that escape from the hook before being brought to the boat or fish that are removed from the hook by predators, so-called “drop offs.” In selective fisheries in which some hatchery-bred fish are marked for retention and unmarked fish legally must be released, the actual mortality rate suffered by unmarked fish depends on the harvest rate for the marked fish, the accuracy of mark recognition, and the proportion of marked and unmarked fish when fishing begins. This paper develops a model for evaluating gear-related mortality in selective fisheries and explores the potential importance of several sources of mortality. Mortality rates for unmarked fish are generally lower than the apparent harvest rates but increase rapidly as harvest rates increase. In the overall mortality of unmarked fish, drop-off mortality could be as important as hook-and-release mortality.