Antarctic fur seal population dynamics update and assessment of census error at SSSI No. 32, Livingston Island, South Shetlands, Antarctica (2000/2001)

Cape Shirreff and San Telmo Islets (SSSI Nº32) shelter the largest breeding population of Antarctic fur seals, Arctocephalus gazella, in the South Shetland Archipelago. Since all censuses up to date have been single counts and do not allow the calculation of confidence limits, a protocol was developed for assessing uncertainties in the estimates of the counts (inter and intra-observer error) and put into practice during the 2000/2001 field season. Intra-observer error was between 0,15-1,74%CV, while inter-observer error was within 3% of the overall mean. The relationship between census error and pup numbers show a linear trend, however, some outliers (outside the 95%CI) could be identified and corresponded to beaches in which variation cannot be entirely attributed to inter-observer error. It can be suggested that topography, density, tides and meteorological conditions can affect pup censuses in a considerable way. These factors should all be assessed and taken into account when undertaking regional surveys of land-based predators in the future. Censuses developed at the SSSI have proved to be quite precise and this suggests that previously reported trends are not an artifact of counting error, thus supporting the hypothesis that the A. gazella population at SSSI Nº32 is reaching stability since more than 87% of K has already been attained.