Hunting and social behaviour of leopard seals (Hydrurga leptonyx) at Seal Island, South Shetland Islands, Antarctica

The hunting behaviour of leopard seals Hydrurga leptonyx was monitored oppo rtunistically at Seal Island, South Shetland Islands, during the austral su mmers from 1986/87 to 1994/95. Leopard seals used several methods to catch Antarctic fur seal pups Arctocephalus gazella and chinstrap penguins Pygosc elis antarctica, and individuals showed different hunting styles and huntin g success. One to two leopard seals per year were responsible for an averag e of 60% of observed captures of fur seal pups. Leopard seals preyed on pen guins throughout the summer, but preyed on fur seal pups only between late December and mid-February. Hunting behaviour differed significantly between different locations on the island; fur seals were hunted only at one colon y, and penguins were hunted in several areas. The relative abundance of pre y types, size of prey in relation to predator, and specialization of indivi dual leopard seals to hunt fur seal prey probably influence individual prey preferences among leopard seals. On five occasions, two leopard seals were seen together on Seal Island. Possible interpretations of the relationship between the interacting leopard seals included a mother-offspring relation ship, a consorting male-female pair, and an adult leopard seal followed by an unrelated juvenile. In two incidents at Seal Island, two leopard seals w ere observed interacting while hunting: one seal captured fur seal pulps an d appeared to release them to the other seal. Observations of leopard seals interacting during hunting sessions were difficult to confirm as co-operat ive hunting, but they strongly implied that the two seals were not agonisti c toward one another. The hunting success of individual leopard seals pursu ing penguins or fur seals is probably high enough for co-operative hunting not to become a common hunting strategy; however, it may occur infrequently when it increases the hunting productivity of the seals.