Clustering of colonies in an expanding population of New Zealand fur seals(Arctocephalus forsteri)

New Zealand fur seals in the New Zealand area are increasing in number foll owing earlier depletion by Polynesians and Europeans. Otago Peninsula, Sout h Island is a region where recent re-colonization has occurred. We identifi ed 27 breeding and 41 non-breeding colonies in 1998, At higher densities th e shortage of space in breeding colonies may initiate emigration by first-t ime breeders to suitable sites nearby. This hypothesis assumes philopatry ( repeated return to a natal site) and site fidelity (repeated return to a no n-natal site). We quantified the rate of increase in pup production at Otag o Peninsula since the early 1980s using annual counts of fur seals ashore f rom 1994 to 1998 and data on pup numbers before 1994 from the literature. T he exponential rate of increase (b) ranged from 0.22 to 0.30 (95% confidenc e interval) and the average (arithmetic) rate of annual increase (r) was 0. 30. To search for evidence of philopatry, site fidelity and immigration, re lationships between counts of pups established colonies in 1996-1998 were m easured and found to be highly correlated. We then tested whether new breed ing colonies were established nearer to existing breeding colonies than wou ld be expected by chance. There was significant spatial clustering of new b reeding colonies around the 6 focal (established) colonies. We found no evi dence for an association between the appearance of new colonies and r at ne arby established colonies. Increasing numbers of fur seals on Otago Peninsu la have resulted in the rapid proliferation of colonies, and their clusteri ng is indicative of a 'spill-over' effect where young individuals choose to breed near to established breeders.