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

The composition of Juan Fernandez fur seal (Arctocephalus philippii) p rey was assessed through analysis of 437 seats collected during five r eproductive seasons (1987-1991). In total, 14 collections were analyze d and, based on 4172 fish otoliths and cephalopod beaks, 13 prey speci es were identified. The occurrences of fish families were as follows: Myctophidae (80.3%), Scomberesocidae (10%), Carangidae (9.5%), Engraul idae (1.0%), and Bathylagidae (0.7%). Cephalopod families included Ony choteuthidae (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 se ats (P < 0.004). Female seats contained larger numbers of the squid On ychoteuthis banksi than did subadult male and juvenile seats (P < 0.00 01). When collections made in early December were compared, the occurr ence of O. banksi in subadult male and juvenile seats differed signifi cantly between years (P < 0.0001). Within-year variations in occurrenc e were significant only for O. banksi in 1989. The data suggest that t he narrow range of species preyed upon by Juan Fernandez fur seals is unlikely to represent specialization, but is probably related to overa ll prey availability in the pelagic environment. Although information on marine communities in this area is limited, it is possible to relat e observed prey shifts to variations in sea-surface temperature.