Predatory Strategies of Great White Sharks at Seal Island
From direct observation and the data collected, hunting White Sharks apparently:
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stalk surface-swimming Cape Fur Seals from near the bottom, probably relying on crypsis afforded by the murky water and the dark, rocky bottom against which their dark dorsal surfaces render the predators all but or wholly invisible (direct observation indicated that Great White Sharks at Seal Island were very difficult or impossible to detect visually below a depth of about 2.5 metres; all recorded attacks took place in water at least 6 metres deep)
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target young seals, which are presumably less experienced at predator avoidance and smaller than are older seals, probably making them easier to catch, overpower, and consume
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target lone or small groups (2-6) of seals (all recorded attacks in which it was possible to estimate group size prior to attack were on fewer than 7 seals), which may be more vulnerable due to limited vigilance capabilities of such a small group
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target groups of seals as they return to the island, possibly because they are tired, well-fed, and less attentive than groups of seals heading seaward to forage
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initiate attacks on seals offshore, which probably enhances a White Shark’s likelihood of success because the prey animals are far from the safety of the shore, seal subsurface vigilance is limited to the sensory capabilities of the small group targeted, and water depth is sufficient to allow an efficient and forceful vertical strike from beneath
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make the initial strike seals just as or immediately before they surface while travelling, probably because the path of the seals is relatively easy to predict and/or, as they surface, the mammals themselves are momentarily unable to see beneath the waves
- attack seals at or near the surface via a sudden, vertical rush, which probably maximises a White Shark’s likelihood of successful prey capture because the seals’ location is clearly silhouetted against the brightness of Snell’s window, the prey has limited options for escape, and the seals’ likelihood of detecting an attacking shark is minimised by the directness – and thus briefness – of the shark’s attack, the minimisation of the shark’s profile during attack (limited to its cross-section rather than it’s full length), and the difficulty in judging distance to the attacking shark; the resulting factors conspire to make it difficult for seals to properly assess the immediacy of threat posed by an attacking shark and to decide upon an appropriate course of action quickly enough to avert capture
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bite seals engaged in evasive zig-zag manoeuvers on the surface via a sudden lateral snap of the jaws (a movement at which the fast-twitch muscles of the head, such as the dorsal and lateral constrictors and the anterior epaxials, are particularly adept), catching the seal with the lateroposteror teeth near the fulcrum of the jaw, where the bite is most powerful and thus devastating
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consume the disabled prey promptly (i.e., without the ‘classic’ bite-spit-and-wait behaviour described for White Sharks in California waters; the collected data indicate the average duration of a predatory event, from initial strike to consumption is less than 2 minutes), possibly due to the high level of competition among Great White Sharks at Seal Island for access to a kill; observations indicate that a seal kill at Seal Island may be attended by at least four individual great white sharks
In short: the Great White Sharks’ main predatory strategies rely on stealth and surprise.
