The ecology of the southern elephant seals Mirounga leonina (Linnaeus 1758), at Marion Island

Abstract

Southern elephant seals at Marion Island inhabit the leeward coasts, where the beaches have a flat profile and smooth surface. Bulls hauled out in August, pregnant cows hauled out in September reaching peak numbers in mid-October, and pups reached peak numbers in mid-November. The arrival and departure of the cows was well synchronized. The moulting season extended from November to April, different age and sex groups moulting at different times. Moulting adults and subadults moved inland, where they first caused and then maintained changes in the vegetation and topography of the moulting areas. Tagging was carried out over four years, effort being concentrated on the pups. No long-distance movement to other island groups was recorded, and no females tagged as pups matured during the three years of observations. Some tagged beachmasters maintained their status at the same sites for three consecutive seasons. Harems of 60 - 130 cows included an assistant beachmaster, and larger harems contained two assistant beachmasters. The breeding population (including pups) declined from 19 51 to 197 5 (r = -0,048), and present population size is approximately 4 500 seals. Mortality in the first and second years of life was high with female recruitment to the third year being the apparent population limiting factor and appeared to be the result of killer whale predation. Net reproductive rate was less than one (R0 == 0,69), and the mean generation interval (T) was 6,65 years. Pup development was similar to that which occurs elsewhere, but age specific body mass and size from birth to 40 days of age were the smallest so far recorded for this species.