The hunting strategy of white sharks (Carcharodon carcharias) near a seal colony

The degree to which white sharks, Carcharodon carcharias, are social while hunting is unclear. Our aim was to describe the behavior and interactions a mong white sharks hunting seals near a seal colony. We attached ultrasonic beacons to five adult white sharks, 4.5-5.2 m long, and recorded their move ments and behavior toward each other over a 15-day period in October 1997 a t Ano Nuevo Island, California. This site is home to colonies of four speci es of seals and sea lions. Two additional sharks, females 5.5 and 4.7 m in length, were later tracked intensively during periods of 12 and 3 days duri ng October 1998 and November 1999, respectively. We recorded stomach temper ature (indicative of feeding on warm-bodied seals) and swimming depths fi-o m the 5.5-m female, swimming speed and depth from the 4.7-m female. We moni tored the movements and behavior of these sharks using an array of sonobuoy s moored near the island; the receptive field measured 1 km(2). Our princip al findings were: (1) the sharks spent a mean time of 39.5% of each day pat rolling within the receptive held; (2) no shark ever moved far out of it; ( 3) the sharks spent an equal amount of time and activity in the receptive f ield at all times of the day, daytime, twilight, and nighttime; (4) movemen ts with respect to the island rookery were most often back and forth parall el to the shoreline, (5) tracks of three sharks, tagged at the same time an d place, overlapped more often than those of the other two sharks; and (6) some sharks patrolled certain areas in the field preferentially, but there was no conclusive evidence that they defended these areas as territories. F eeding appeared to be infrequent: only two likely feeding bouts occurred du ring a cumulative 78-day/shark period that individuals were monitored at An o Nuevo Island. The behavior and movements of the sharks were consistent wi th a hunting strategy, in which individuals search for prey independently b ut, at the same time, remain close enough to each other to "sense" and expl oit a kill by any one of them by joining in on the kill to feed.