First-year survival of southern elephant seals, Mirounga leonina, at sub-Antarctic Macquarie Island

Abstract

Juvenile seals branded on the isthmus of Macquarie Island as pups displayed a high degree of philopatry. They returned more often and in greater densities to the northern third of the island within 10 km of their birth sites. Juvenile seals were observed to haul out more frequently and in greater numbers on the east coast as opposed to the west. Juvenile seals typically hauled out on two occasions, once during the winter, and once to moult. The probability of recapturing (resighting) branded and tagged seals was greater during the mid-year haulout. First-year survival estimates were obtained from searches of all Macquarie Island beaches for marked (branded and tagged) seals. From a branded population of 2000 seals, 897 were known to be alive at age 1 year, and minimum first-year survival was calculated at 44.85%. To this minimum estimate was added the number of seals overlooked during systematic and standardised searches of the island, and a revised estimate of 65.60% was calculated. Survival rates calculated using a custom model and a conventional mark-recapture model (MARK) were compared and no differences detected. Actual survival data and probability of sighting estimates were included in the revised estimate of first-year survival of southern elephant seals at Macquarie Island. There were no differences in the number of surviving males and females.