Changes in the abundance and distribution of the New Zealand fur seal (Arctocephalus forsteri) in Western Australia: Are they approaching carrying capacity?
Faculty of Health, Engineering and Science
School of Natural Sciences/Centre for Marine Ecosystems Research
New Zealand fur seals have been increasing in abundance across Australia over the past 20 years, with annual population growth rates of 10-15%. Recent changes in distribution in Western Australia suggested that the population was increasing and expanding in range beyond the known historical distribution. We aimed to determine the growth rate of individual colonies and the overall population across Western Australia and identify new breeding and haulout sites. We used the direct count technique to estimate New Zealand fur seal pup production at 17 breeding sites. We estimated pup production to be 3518 in the 2010/11 austral summer, producing a resultant population estimate of ∼17 200 New Zealand fur seals in Western Australia. This represented an exponential growth rate over the past 12 years of ∼1% per annum, a significant reduction from the estimated rate of 10% per annum between 1989 and 1999. There were clusters of colonies that showed large annual declines of 6-7% in pup production over the past 12 years and at other colonies maximal rates of increase of pup production were 6-9% per annum. Three new breeding colonies were discovered. It appears that the New Zealand fur seal population is nearing its carrying capacity in Western Australia.