MOBBING OF A GREAT WHITE SHARK (CARCHARODON CARCHARIAS) BY ADULT MALE AUSTRALIAN FUR SEALS (ARCTOCEPHALUS PUSILLUS DORIFERUS)

Abstract

When a group of prey detects a predator’s approach, one tactic to reduce the chance of predation is to mob the predator (Lorenz 1931). Mobbing is the close approach to, and aggressive display toward, a perceived predator (or competitor) by a group of potential prey (Altmann 1956, Wilson 1975). This behavior is adopted by many species of fish (e.g., Dominey 1983), colonial mammals (e.g., Owings and Coss 1977, Kobayashi 1994) and birds (e.g., Shields 1984, Flasskamp 1994, Arnold 2000), and often is associated with loud calling. Mobbing informs the predator that it has lost the element of surprise and alerts other potential prey to the threat of the predator. The behavior may protect offspring and other group members, especially if these are unaware of the predator’s approach (Curio et al. 1978, Kobayashi 1994). Participation in predator mobbing has a price, however. Energy is expended and there is a risk of injury or predation during the event (e.g., Denson 1979). For the behavior to survive through natural selection, it must impart some advantages to the individual. A greater understanding of the advantages comes from assessing the occurrence and form of predator mobbing in different species. Here we describe for the first time, the mobbing of a great white shark (Carcharodon carcharias) by adult male Australian fur seals (Arctocephalus pusillus doriferus). The mobbing event was observed by one of us (JD) at Seal Rocks (388309S, 1458109E), Victoria, on 7 March 2003, from a 20-m tour vessel stationed 50 m from the Rocks. Passengers on the vessel were first alerted to the presence of a shark by a change in the behaviour of seals ashore. The seals were all sitting upright, looking toward the water and several entered the water, which is the seals usual response to disturbance. About 12 min after the alert behaviour of the seals was noticed, a 4-m great white shark was observed at the bow of the vessel. The shark circled the vessel twice then moved toward the rocks where a group of juvenile seals and pups was swimming. About five large male seals then mobbed the shark. They focused on the