Space utilization and swimming depth of white sharks, Carcharodon carcharias, at the South Farallon Islands, central California

This paper presents information on the movements of white sharks, Carcharod on carcharias, at the South Farallon Islands (SFI), central California. Aco ustic telemetry techniques provided preliminary data on the diurnal space u tilization, movement patterns and swimming depths of four white sharks, ran ging from approximately 3.7 to 4.9 m in length. Sharks swam within about 10 m of the bottom to depths of approximately 30 m, but in deeper water they tended to stray more from the bottom. Activity spaces for time periods trac ked ranged from 1.84 to 9.15 km(2). Indications are that an inverse relatio nship exists between length and activity space. During the time tracked, la rger individuals swam within particular areas around the islands whereas sm aller individuals did not restrict their movements in the same manner. Valu es of a site attachment index were inversely related to length for all shar ks tracked. The site attachment indices, apparent inverse relationship betw een total length and activity space and observations on telemetered and oth er known individuals support a hypothesis that larger sharks possess site f idelity in their search for prey at SFI, within and between years. With the high frequency of predation by white sharks on juvenile northern elephant seals at SFI in the fall, the majority of the sharks' movements are probabl y related to their search for these pinniped prey. These data provide preli minary evidence that white sharks at SFI may search for prey by swimming in a particular area over a number of days or weeks, traversing the area in a manner which maximizes coverage, and swimming close to the bottom or at a distance far enough from the surface to remain cryptic from prey.