The relationship between the dispersion of salmon fishing vessels and their catch

Abstract

Commercial salmon trollers (hook and line fishermen) aggregate in well-defined patterns on the fishing grounds off southwestern Vancouver Island. The pattern is persistent when the fleet is concentrating on a particular species of salmon, but alters when the species being harvested changes. In this study we analysed catch rate in relation to local density of vessels for May and June, when chinook salmon was the only species open for harvest, and 1–15 July, when coho salmon dominated the harvest. The model that we used was Fretwell's (1972) ideal free distribution model which predicts that average catch rate should be independent of local vessel density. If the fishermen are not ideal (i.e. they have imperfect information on the distribution of fish) then catch rate should decline with increasing vessel density. If the fishermen are not free (i.e. less competitive fishermen can be excluded from good fishing patches) then catch rate should increase with increasing vessel density. Catch rate was found to be independent of local vessel density during all fishing periods analysed over 2 years, suggesting that the fishermen are behaving like ideal free predators.