Fine-scale geographic interactions between Steller sea lion ('Eumetopias jubatus') trends and local fisheries

Abstract

Fine-scale geographic interactions between Steller sea lion ('Eumetopias jubatus') abundance trends and the abundance of local fisheries and commercial fishing efforts from Southeast Alaska to the Aleutian Islands were assessed. Census counts of Steller sea lions from 1976 to 2002 at 53 different trend sites and rookeries were grouped into 33 locales with similar population trends. Localized estimates of commercial groundfish biomass densities for walleye pollock ('Theragra chalcogramma'), Pacific cod ('Gadus macrocephalus'), arrowtooth flounder ('Atheresthes stomias'), and Atka mackerel ('Pleurogrammus monopterygius') from 1983 to 2002 and localized estimates of commercial fishing effort from 1990 to 2002 were matched to the 33 locales. Generalized estimating equations methods found a negative relationship between Steller sea lion abundance trends and walleye pollock density (P < 0.10). However, the 4.8-fold change in walleye pollock density between 1984 and 2001 was estimated to change the rate of population change (λ) by only 0.029. The analysis estimated that elimination of all trawl fishing effort would increase λ by as little as 0.0056. Neither commercial groundfish abundance nor commercial fishing effort could explain the large historical declines in the rate of Steller sea lion population change observed.