Market squid (Loligo opalescens) in the diet of California sea lions (Zalophus californianus) in southern California (1981-1995)

California sea Lion (Zalophus californianus) seat and spewing samples colle cted at three rookeries in southern California during 1981-95 were used to determine how sea lions utilized the market squid (Loligo opalescens) resou rce. The samples revealed that market squid is one of the most important pr ey of sea lions in southern California, occurring in 35% to 44% of scat sam ples from San Nicolas Island (SNI), San Clemente Island (SCI), and Santa Ba rbara Island (SBI). It is eaten by sea Lions throughout the year, but most often during fall and winter, and patterns suggest periods of high and low consumption associated with prevailing oceanographic conditions and, possib ly, with squid abundance and movements. Percent frequency of occurrence val ues for market squid in seat samples collected seasonally from SNI were pos itively correlated with those from SCI (r = 0.78), and samples collected du ring summer at SBI were positively correlated with summer samples front SCI (r = 0.82) and SNI (r = 0.85). Landings of market squid at ports in southe rn California and percent occurrence Values of market squid in seat samples collected seasonally were positively correlated for SNI (r = 0.66) and SCI (r = 0.74), but not for summer samples from SBI (r = 0.25). Sea lions eat squid with dorsal mantle lengths h-om 10 to 235 mm (mean = 227 mm). Signifi cant seasonal, annual, and interisland differences (P < 0.001) were found i n the size of squid consumed by sea lions. Significant differences (P < 0.0 01) were found in size of squid between seats and spewings, and between ind ividual samples.