Natural predation by Great White Sharks on Cape Fur Seals

Natural predation by Great White Sharks on Cape Fur Seals

 

Anti-predatory strategies of Cape Fur Seals are often observed at Seal Island in False Bay, South Africa. Seal Island provides unique opportunities to observe natural predation by Great White Sharks on Cape Fur Seals, and to observe social interactions among both species.

Cape Fur Seals are constantly aware of the imminent threat of Great White Sharks in the area, which is heightened during the winter months (June – August), when the predation of Great White Sharks on Cape Fur Seals is most intense. Cape Fur Seals have their own unique techniques to detect, avoid, outmaneuver and sometimes injure the Great White Shark in order to survive. These anti-predatory strategies of Cape Fur Seals primarily rely on vigilance and agility to outsmart their attacker. Great Whites often sport numerous scratches on their heads, most likely caused by seals defending themselves during predatory events.

Here are some of the anti-predatory strategies of Cape Fur Seals used to avoid falling prey to the Great White Shark.

  1. Cape Fur Seals will often take advantage of their broadened sub-surface vigilance by grouping together and forming “rafts” in shallower waters. Sub-surface vigilance is also sometimes accomplished by a head-down posture, with only the tail and the tip of the rear flippers showing above the surface, which allows the seal to obtain a better visual aspect of any threat close by.
  2. Many Cape Fur Seals will normally gather at a specific area of Seal Island, namely the “Launchpad”, and leave the Island in co-ordinated groups of between 6 and 12 animals. Multiple groups will form and leave the Island at seemingly regular intervals of around 45 seconds.
  3. If a Great White Shark is spotted while travelling in small groups form Seal Island, the individuals will execute an evasive zig-zagging manoeuvre to avoid being attacked by the shark. This tactic is referred to as “working the shark”.
  4. When an individual is actively pursued by a Great White Shark, the seal will try to remain out of reach of the shark’s jaws by attempting to get behind the shark’s dorsal fin. This tactic is referred to as “on the shark”.
  5. If a group of seals is “hit” (attacked” ) by a Great White Shark, the individual seals will “explode” from the water in all directions, presumably try to confuse the predator. This type of behavior is relatively infrequent as Great White Sharks generally prefer to attack lone seals, but it is highly spectacular to witness.
  6. When an individual or group of seals return to Seal Island, they tend to swim the last 50 metres or so underwater because this tactic presumably reduces their vulnerability to shark stack. The seals will dive to the bottom of the ocean around 12 metres deep, and will race towards the island, only surfacing as they reach the shallower edges. This tactic has been learnt and adopted by older and more experienced seals, and is mainly used during the winter months when predation is at its highest. Younger and less experience seals are often too tired to dive the last 50 metre stretch underwater, and will instead choose to swim the last stretch on the surface of the water. This makes them an easy target and they will often fall victim to attacks by the Great White Sharks.
  7. If a seal has been pursued by a Great White Shark and survives the initial attack, it becomes extremely vigilant, often to the point of seeming momentarily stunned. The seal is, in fact, hyper-alert as it tries to re-acquire the shark and the potential threat it holds. The shark can then use it’s highly maneuverable body to leap away from the shark’s jaws to evade a second strike.

Join Rob Lawrence and the African Shark Eco-Charters team on one of our popular “Airjaws” trips to experience the anti-predatory strategies of the Cape Fur Seal against the Great White Shark first-hand.

Data collected and observations by R. Aiden Martin of the ReefQuest Centre for Shark Reasearch, as well as Rob Lawrence.

 

Lucky Cape Fur Seal escapes Great White Shark attack with effective anti-predatory strategies

Lucky Cape Fur Seal escapes Great White Shark attack with effective anti-predatory strategies