Seasonal oscillation in shore attendance and transience of New Zealand furseals

The New Zealand fur seal (Arctocephalus forsteri) appears to show regular s hore attendance in the form of seasonal oscillations. This phenomenon shoul d be quantified to properly interpret counts of fur seals >1 year old (i.e. , non-pups). Here we test the predictability of peaks in the annual shore-a ttendance oscillation on Otago Peninsula using an autoregressive sine model and >2 years of intensive survey data. We predicted that the peak in fur s eal numbers ashore would lie between 14 January - 4 April (1996) and 8 Janu ary - 2 April (1997), although this low predictability is undesirable when attempts are made to monitor population trends. Estimating population size from counts of non-pups also requires knowledge of the rate of turnover of individuals. Therefore, we tested the hypothesis that ragged animals from o ther colonies are immigrants to Otago Peninsula. With sightings on Otago Pe ninsula of fur seals tagged elsewhere in New Zealand, we used a Monte Carlo approach to simulate the expected frequency of single and multiple sightin gs of individuals. We found that the observed frequency of multiple sightin gs was significantly less than predicted by the model (P < 0.0001), indicat ing that tagged animals were transients. We also discovered that the sex ra tio of tagged animals varied with breeding colony of origin (G(1) = 52.07, P < 0.0001), suggesting that the impetus for emigration differs among colon ies. We concur with the view that counting pups is the only way to estimate the relative abundance of New Zealand fur seals. In addition, we showed th at counts of non-pups cannot be used to estimate population size because an unknown proportion of individuals is transient. However, counting of pups does not address the issue of estimating relative abundance for locations w ith large numbers of nonbreeding individuals and few or no breeders. With f ew or no pups it is impossible to estimate relative abundance using counts of pups.