Population status and seasonal haulout patterns of the southern elephant seal (Mirounga leonina) at Heard Island

Abstract

We surveyed the southern elephant seal population at Heard Island regularly from February 1992 to March 1993, and determined the haulout patterns of the major components of the population. While haulout patterns of moulting and immature seals may give broad indices of population trends, the breeding haulout of adult females was the only reliable haulout that could be used to determine annual pup production. During the breeding season 14 277 adult females were counted. Raw counts were corrected using two models, one purely mathematical and the other based on the haulout behaviour of adult female seals. The two models have slightly different assumptions, but both provided good fits to the observed haulout patterns and estimated total population with a coefficient of variation of less than 5%. Total pup production was estimated at between 17 000 and 18 000 for 1992. Previous counts of elephant seals from 1949–51, 1985 and 1987 were corrected using the same models. The two models gave estimates of the population that were within ± 2.5% for all but one year. The population declined by about 50% between 1949 and 1985 but there appears to have been little change from 1985–92. The previous decline may be related to changes in sea-ice.