White Shark Predatory BehaviorBrief Overview
During the winter, white sharks visit Seal Island to predate on Cape fur seals. About 48% of surface attacks on Cape fur seals result in successful kills. Attack frequency is high, averaging 6.68 per day, with as many as 43 recorded in a single day. Sharks attack seals on the surface via a sudden vertical rush, which propels predator and prey out of the water in an awesome display of power and acrobatic prowess. White sharks appear to hunt solitary juvenile Cape fur seals near their primary entry and exit point early in the morning, when light levels are low. Stalking is conducted from near the bottom, from sufficient depth to remain undetected during approach, and the attack launched vertically. This strategy maximizes a shark's chance of catching a seal unaware, resulting in a fatal or incapacitating initial strike. Stealth and ambush are key elements in the white shark's predatory strategy. Further, recognizable individual white sharks display distinct predoatry strategies and some enjoy a predatory success rate of roughly 80%.
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Since predatory events and seal movements at Seal Island are greatest at sunrise, I wondered whether we were seeing the tail end of nocturnal activity. Experiments using infrared video imaging demonstrated that both seals and white sharks can be detected in darkness by their thermal signatures and helped document that seal movement about the Island is greater at night than during the day. Thermal Imaging Video of Great White Shark Breach (232 kb)
Thermal Imaging of Seals Moving at Night (6 mb)
Some 300 individual white sharks have been catalogued to date, including numerous re-sightings over separate days and years. Accumulated data is beginning to show that white sharks at Seal Island stay for short periods of time, many of the same individual sharks return year after year, and that numerous identifiable sharks appear to come and go together in groups of two to six. Group constitution appears to be constant from year-to-year and threat interactions among group members is low (suggesting well-established, stable social hierarchies), but occurs occasionally between members of different groups. Social hierarchies are stabilized and maintained largely through discrete behaviors, ranging from subtly synchronized swimming to overt displays. Many of these displays are defined and illustrated in R. Aidan Martin's book, Field Guide to the Great White Shark which is available at Elasmo-Research.org.
Publications Hammerschlag, Neil. 2004. Factors affecting predatory success of white sharks (Carcharodon carcharias) at Seal Island in False Bay, South Africa. Nova Southeastern University Publication, Masters Thesis, 85 pp.
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NOTE: The Seal Island work described below reports on over 2,500 natural predatory attacks by white sharks on Cape fur seals. It is a shared result of an 8-year collaboration among R. Aidan Martin, the principal investigator of this project, Chris Fallows & 
