Juvenile survival and population regulation in southern elephant seals at Marion Island

We examined annual juvenile survival in southern elephant seals (Mirounga leonina) at Marion Island for the period 1994–1999 during which time the population was stable. Using mark–recapture models, we tested for age- and sex-specific differences in survival rates over the first three years of life. We found that survival was age- but not sex-related and compared our estimates to similar estimates from a previous study on the same population while in a state of decline. This was done to determine whether changes in juvenile survival were instrumental in terminating the population decline at Marion Island. On average, the probability of survival was 59.5 %, 81.4 % and 78.1 % for the first, second and third year respectively. These estimates were remarkably similar to those previously calculated for the population while in a state of decline, and we dismiss juvenile survival as a major population regulating component in southern elephant seals at Marion Island.Keywords: southern elephant seals, juvenile survival, mark–recapture, population regulation

Pup growth and maternal attendance patterns in Subantarctic fur seals

Samples of pups from the expanding populations of Subantarctic fur seals  (Arctocephalus tropicalis) at Marion and Gough islands were weighed at specific ages between birth and weaning in the period 1993-2000. Growth was estimated and compared between years, sexes, sites of different density, and populations. Pups of comparable age were consistently heavier at Marion Island than at Gough Island, probably reflecting relative prey resource abundance. No changes in pup growth rates were apparent over the study period, nor was there any evidence that growth was affected by ENSO events. Measures of pup growth at Marion Island were complemented by measures of maternal attendance behaviour during three summer and winter  seasons. More years of data are required to determine patterns between attendance, growth, resource conditions and population abundance trends.Key words: Subantarctic fur seal, Marion Island, Gough Island, pup growth, maternal attendance behaviour

Evidence for density dependent population regulation in southern elephant seals in the southern Indian Ocean

The means by which populations are regulated form a central theme in conservation biology, and much debate has revolved around density dependence as a mechanism driving population change. Marion Island (46°54’S, 37°45’E) is host to a relatively small breeding population of southern elephant seals, which like its counterparts in the southern Indian and southern Pacific Oceans, have declined precipitously over the past few decades. An intensive mark– recapture study, which commenced in 1983, has yielded a long time-series of resight data on this population. We used the program MARK to estimate adult female survival in this population from resight data collected over the period 1986–1999. Including concurrent population counts as covariates significantly improved our mark–recapture models and suggests density dependent population regulation to be operational in the population. Although  predation may have been involved, it is far more likely that density dependent regulation has been based on a limited food supply. A significant increase in adult female survival was evident which is likely to have given rise to recent  changes in population growth.Key words: density dependence, southern elephant seals, Marion Island, population regulation

Long-term variation in the breeding diets of macaroni and eastern rockhopper penguins at Marion Island (1994–2018)

Populations of the macaroni penguin Eudyptes chrysolophus and the eastern rockhopper penguin E. filholi breeding at Marion Island (Prince Edward Islands) in the sub-Antarctic Indian Ocean decreased from 1994 to 2018. We examined their diets when rearing chicks during this period. There was substantial overlap in the diets of the two species, with crustaceans, dominated by the euphausiids Thysanoessa vicina and Euphausia vallentini, making up >80% of the diets by number and >60% by mass over the study period. The lanternfishes Krefftichthys anderssoni and Protomyctophum tenisoni were the most-commonly consumed fish in the diet of breeding macaroni penguins and dominated in their diet in three of the 25 years (1994, 1998 and 2014); they were also the most commonly consumed fish by eastern rockhopper penguins. Macaroni penguins consumed more of the amphipod crustacean Themisto gaudichaudii and the lanternfish Electrona carlsbergi as well as a greater diversity of and larger-sized fish than did eastern rockhopper penguins. The horsefish Zanclorhynchus spinifer was found in substantial amounts in the diet of eastern rockhopper penguins in 1996 and 1997. Despite annual variations in relative prey contributions to the diets, there were no significant long-term changes in the diet of either penguin species over the study period or when compared with an earlier assessment in 1982. We conclude that changes in the relative proportions of prey in the diets of these penguin species during breeding are unlikely to account for the recent declines in these penguin populations

Haulout site selection by southern elephant seals at Marion Island

Using data from an ongoing mark–resight programme at Marion Island, we tested  empirically whether southern elephant seals prefer certain terrestrial sites to others during the breeding, moulting and winter haulouts, and whether the pattern of site use is the same for different age and sex groups. Southern elephant seals preferred some sites, while discriminating against other sites, with different age and sex classes using different sites for certain haulout events. Wintering young animals did not show strong site selection. Some popular sites were used for all haulouts by all age and sex groups, and apparently have all the requirements of a good site for terrestrial haulout by southern elephant seals. Site selection becomes more apparent with age, suggesting the role of haulout experience in site selection.Key words: southern elephant seal, Mirounga leonina, Marion Island, age group, haulout, site selection

Errata: In the article ‘Haulout site selection by southern elephant seals at Marion Island’ that appeared in

ErrataIn the article ‘Haulout site selection by southern elephant seals at Marion Island’ that appeared in African Zoology 43(1):25–33 (April 2008), the institutional affiliations of the authors should have read:T.W. Mulaudzi1*, G.J.G. Hofmeyr1, M.N. Bester1, S.P. Kirkman1, P.A. Pistorius1,F.C. Jonker1, A.B. Makhado1, J.H. Owen2 & R.J. Grimbeek21. Mammal Research Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0002 South Africa2. Department of Statistics, University of Pretoria, Pretoria, 0002 South Africa*Author for correspondence. Present address: National Zoological Gardens of South Africa, P.O. Box 754, Pretoria, 0002 South Africa.E-mail: [email protected]