SPRING AND SUMMER PREY OF THE JUAN-FERNANDEZ FUR-SEAL, ARCTOCEPHALUS-PHILIPPII

The composition of Juan Fernandez fur seal (Arctocephalus philippii) prey was assessed through analysis of 437 seats collected during five reproductive seasons (1987-1991). In total, 14 collections were analyzed and, based on 4172 fish otoliths and cephalopod beaks, 13 prey species were identified. The occurrences of fish families were as follows: Myctophidae (80.3%), Scomberesocidae (10%), Carangidae (9.5%), Engraulidae (1.0%), and Bathylagidae (0.7%). Cephalopod families included Onychoteuthidae (27.1%), Ommastrephidae (3.7%), and Tremoctopodidae (0.7%). In one year when data were available, Symbolophorus sp. B was found more frequently in subadult male and juvenile seats than in female seats (P < 0.004). Female seats contained larger numbers of the squid Onychoteuthis banksi than did subadult male and juvenile seats (P < 0.0001). When collections made in early December were compared, the occurrence of O. banksi in subadult male and juvenile seats differed significantly between years (P < 0.0001). Within-year variations in occurrence were significant only for O. banksi in 1989. The data suggest that the narrow range of species preyed upon by Juan Fernandez fur seals is unlikely to represent specialization, but is probably related to overall prey availability in the pelagic environment. Although information on marine communities in this area is limited, it is possible to relate observed prey shifts to variations in sea-surface temperature.