To assess the impact of California sea lions (Zalophus californianus) on salmon fisheries in the Monterey Bay region of California, the percentages of hooked fish taken
by sea lions in commercial and recreational salmon fisheries were estimated from 1997 to 1999. Onboard surveys of sea lion interactions with the commercial and recreational f isheries and dockside interviews with fishermen after their return to port were conducted in the ports of Santa Cruz, Moss Landing, and Monterey. Approximately 1745 hours of onboard and dockside surveys were conducted—924 hours in the commercial fishery and 821 hours in the recreational fishery (commercial passenger
fishing vessels [CPFVs] and personal skiffs combined). Adult male California sea lions were responsible for 98.4% of the observed depredations of hooked salmon in the commercial and recreational fisheries in Monterey Bay. Mean annual percentages of hooked salmon taken by sea lions
ranged from 8.5% to 28.6% in the commercial fishery, 2.2% to 18.36% in the CPFVs, and 4.0% to 17.5% in the personal skiff fishery. Depredation levels in the commercial and
recreational salmon fisheries were greatest in 1998—likely a result of the large El Niño Southern Oscillation (ENSO) event that occurred from 1997 to 1998 that reduced natural
prey resources. Commercial fishermen lost an estimated 18,031−60,570 of gear and 225,833−498,076 worth of
salmon as a result of interactions with sea lions. Approximately 1.4−6.2% of the available salmon population was removed from the system as a result of sea lion interactions with the fishery. Assessing the impact of a growing sea lion population on fisheries stocks is
difficult, but may be necessary for effective fisheries management
