Australian fur seals (Arctocephalus pusillus doriferus) breeding in Tasmania: population size and status

Abstract

This study confirms the persistence of five major breeding colonies of Australian fur seals (Arctocephalus pusillus doriferus) in Tasmanian Bass Strait waters. Incidental births also occasionally occur in very low numbers at other sites. Data collected between 1989 and 1999 shows that estimates of the minimum number of pups born at the major colonies varies considerably between sites and years. No colony has shown a consistent trend in pup production over the last 11 seasons. The most recent count for all Tasmanian colonies for the 1999 breeding season provided a minimum estimate of 3254 pups produced, similar to the estimate of 3373 in 1989. The highest estimate was recorded in 1995 when at least 6024 pups were born. Combining the most recent counts with the numbers estimated for the four Victorian colonies (13 872) gives a minimum pup production of 17 126 for the species, with only one-fifth of all pups being born on Tasmanian islands. Application of population estimators to translate pup numbers to population size for the species results in a conservative estimate of 68 500 individuals with upper and lower bounds of 60 000 and 77 000 Australian fur seals. Numbers of Australian fur seals remain low relative to other fur seal populations, with Australian fur seals being less numerous by an order of magnitude compared with their South African counterpart (A. p. pusillus). The current estimate of the total population of Australian fur seals is approximately half that of pre-sealing levels. The current number of breeding colonies in Tasmania indicates that the population of Australian fur seals breeding in Tasmanian waters has stabilised at well below their historic pre-sealing levels, with at least four sites remaining vacant. The species remains vulnerable due to its small population size, with Tasmanian breeding colonies being particularly vulnerable because of low numbers and due to the profound influence of weather events on pup survival.