PI: Le Boeuf 9603633 The aim of this project is to elucidate the foraging strategy of white sharks (Carcharodon carcharias) on their preferred prey, northern elephant seals (Mirounga angustirostris), and reciprocally, to determine the evasive tactics of elephant seals in the high risk zone of shark attack. White sharks will be tagged with acoustic beacons when they surface to feed on tethered decoys or seal carcasses in the waters around Ano Nuevo Island in central California. Ultrasonic tags and diving instruments will be attached to elephant seals on the rookery before they depart on biannual migrations and recovered on their return. We will tag sharks externally with location transmitters and internally with depth and temperature sensing transmitters, placed in bait, to obtain records of three dimensional movements, diving pattern, and feeding behavior (inferred from a rise in stomach temperature). Movements of predators and prey, as well as fluctuations in the diving depth and stomach temperature of the sharks, will be determined for up to 10 tagged animals (sharks or seals) simultaneously to distances of 1.2 to 3.2 km drom the rookery by an array of three radio-acoustic positioning buoys that receive and relay the data to a land base station on the mainland 250 m away. We will determine the presence or absence of tagged sharks near the rookery, the length of time individuals remain in the vicinity, evidence for territorial defense, fluctuations in abundance with time of the year, movements within area, preferred stations where sharks concentrate to capture seals, and the temporal pattern feeding and behavior between kills. Concomitantly, we will determine the corridors of egress and ingress near the rookery taken by migrating and translocated seals and their diving behavior in the high risk zone of shark attack. This study will provide fundamental information on white shark life history and foraging tactics and will elucidate the evasive s trategies of northern elephant seals to its principal predator. This information is vital for understanding this apex predator and its relationship to prey and humans in nearshore waters in this area. A better understanding of the hunting strategy of white sharks will elucidate the importance of predator pressure on elephant seal life history, juvenile survivorship and colony growth, and diving behavior and pattern of rookery us. This will provide a deeper understanding of the predator- prey relationship between white sharks and elephants seals than exists for any other large vertebrate in marine environment.
