Distribution and abundance of New Zealand fur seals, Arctocephalus forsteri, in South Australia and Western Australia

Abstract

A survey to determine the distribution and abundance of New Zealand fur seals, Arctocephalus forsteri, in South Australia and Western Australia was conducted in January-March 1990. Minor surveys were conducted in the summers of 1987-88, 1988-89 and 1990-91. Although the surveys were primarily of black pups in breeding colonies, opportunity was taken to count fur seals of all age-classes, including those in non-breeding colonies. Pups were counted and, in more accessible and larger colonies, numbers of pups were estimated by a mark-recapture technique. The latter technique gave higher estimates than counting, and was considered more accurate. In South Australia, the seals extend from The Pages in Backstairs Passage to Nuyts Reef in the Great Australian Bight. In Western Australia, the range comprised islands on the south coast from the Recherche Archipelago to islands near Cape Leeuwin. There are 29 breeding localities; 13 are in South Australia and 16 in Western Australia. Eighteen of these have not been reported previously. The term ''breeding locality'' is used for aggregations of breeding colonies as well as for isolated breeding colonies. Estimates of the number of pups for the 1989-90 breeding season were 5636 in South Australia and 1429 in Western Australia. This leads to a population estimate of approximately 34600 seals in these two states (using a multiplier of 4.9). But such estimates of overall abundance must be treated cautiously as the multiplier incorporates estimates of population parameters not available for A. forsteri. Most of the population (77%) is in central South Australian waters (from Kangaroo Island to the southern end of Eyre Peninsula). With the estimate of 100 for a breeding colony in southern Tasmania, the population of New Zealand fur seals in Australia can be estimated at 34700. Historical aspects of some colonies are outlined and evidence for increases described. The largest breeding localities are at South Neptune Islands (1964 pups) and North Neptune Islands (1472). The combined Neptunes group accounts for 49% of the pup estimate for Australia. One-fifth of the pups are from colonies on Kangaroo Island and the nearby Casuarinas.