Changes in the abundance of New Zealand fur seals, Arctocephalus forsteri, in Western Australia

Abstract

New Zealand fur seals, Arctocephalus forsteri, have been increasing in abundance in South Australia for at least the past three decades. A survey of New Zealand fur seals during the 1989/90 breeding season determined that about 20% of the Australian population bred at 16 sites in Western Australia, amounting to 1429 pups and an absolute abundance estimate of 7100 fur seals. A further survey of all fur seal colonies in Western Australia to determine current pup production and abundance estimates, and trends in pup production since the previous survey was undertaken in January 1999.

Of the 17 breeding sites now known in Western Australia, 16 were surveyed and pup production had increased at all but one. The rate of change in pup production at the one unsurveyed site (West Island), was estimated as being equivalent to the mean rate of change at other sites. The estimated mean annual, exponential rate of increase (r) for all sites was 0.09, equivalent to a 9.8% annual increase in pup production and an overall increase in pup production in Western Australia of 113.3% between surveys. Total annual pup production has increased to 3090. The estimate of absolute abundance of New Zealand fur seals in Western Australia is now 15 100, in contrast to the 7100 estimated for the 1989/90 season. Mortality of pups at the time of the survey was estimated to be at least 1.3%.

It is predicted that New Zealand fur seal populations will continue to increase in Western Australia. This is likely to have important management implications regarding aquaculture and fisheries activities. The increase in fur seal populations appears to be in contrast to populations of Australian sea lions, Neophoca cinerea, for which preliminary data show no evidence for a population increase. It is unknown whether the dynamics affecting these two species are related.