Abundance, food habits, and annual fish consumption of California sea lion (Zalophus californianus) and its impact on salmonid fisheries in Monterey Bay, California

Abstract

To assess competition between commercial fisheries and California sea lion (Zalophus californianus) in Monterey Bay, California I estimated sea lion seasonal abundance, seasonal food habits, annual fish consumption, and percentages of hooked fish taken by sea lions in commercial and recreational salmon fisheries during 1997 and 1998. Aerial and ground surveys indicated that peak numbers of sea lions occurred during their spring and fall migration. While sahnon occurred in the sea lion diet year-round, sea lions primarily consumed schooling prey such as market squid (Loligo opalescens), Pacific sardine (Sardinops sagax), and northern anchovy (Engraulis mordax). Increased depredation of the salmon catch by sea lions in 1998 was most likely the result of the large 1997-1998 El Nino event. Hooked salmon from the fisheries were likely the majority of salmon in the sea lion diet. Assessing the impact of sea lions and other natural predators on prey populations is difficult, but necessary for effective fisheries management.