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

摘要

This paper presents information on the movements of white sharks,Carcharodon carcharias, at the South Farallon Islands (SFI), centralCalifornia. Acoustic telemetry techniques provided preliminary data on thediurnal space utilization, movement patterns and swimming depths of fourwhite sharks, ranging from approximately 3.7 to 4.9 m in length. Sharksswam within about 10 m of the bottom to depths of approximately 30 m, butin deeper water they tended to stray more from the bottom. Activity spacesfor time periods tracked ranged from 1.84 to 9.15 km(2). Indications arethat an inverse relationship exists between length and activity space.During the time tracked, larger individuals swam within particular areasaround the islands whereas smaller individuals did not restrict theirmovements in the same manner. Values of a site attachment index wereinversely related to length for all sharks tracked. The site attachmentindices, apparent inverse relationship between total length and activityspace and observations on telemetered and other known individuals supporta hypothesis that larger sharks possess site fidelity in their search forprey at SFI, within and between years. With the high frequency ofpredation by white sharks on juvenile northern elephant seals at SFI inthe fall, the majority of the sharks' movements are probably related totheir search for these pinniped prey. These data provide preliminaryevidence that white sharks at SFI may search for prey by swimming in aparticular area over a number of days or weeks, traversing the area in amanner which maximizes coverage, and swimming close to the bottom or at adistance far enough from the surface to remain cryptic from prey.[References: 26]