Anti-Predatory Strategies of Cape Fur Seals at Seal Island
From direct observation and the data collected, Cape Fur Seals apparently reduce their vulnerability to Great White Sharks by:
- taking advantage of the expanded vigilance of entire groups; sub-surface vigilance while rafting is accomplished via assuming a head-down posture, with only the tail and the tip of the rear flippers showing above the surface.
- leaving Seal Island as co-ordinated groups of 8 to 12 animals; multiple groups – ranging from 2 to as many as 5 - leave the island at intervals of approximately 45 seconds
- single or small groups (2-5) of individuals executing a finely controlled zig-zaging evasive manoeuver when a Great White Shark is spotted stalking below them; this tactic is referred to as “working the shark”
- when an individual is actively pursued by a Great White Shark, riding its slipstream – usually mid-body, at the level of its dorsal fin – to remain out of reach of the shark’s jaws; this tactic is referred to as “on the shark”
- when a group is “hit” (attacked) by a White Shark, the individual seals ‘explode’ from the water in all directions, presumably serving to confuse the predator – perhaps sufficiently to allow some or all of them to escape; this tactic is relatively infrequent but highly spectacular
- when an individual or group returns to the island, swimming the last 50 metes or so underwater, presumably because this tactic reduces vulnerability to attack by White Sharks
- when any or all of the aforementioned tactics fail and a predatory attack is successful, the surviving seals become extremely vigilant - often to the point of seeming momentarily stunned - but are, in fact, hyper-alert
In short, the Cape Fur Seals’ main anti-predatory strategies rely on vigilance and agility
