ISOTOPIC SIGNATURE AND FORAGING HABITATS OF SOUTHERN ELEPHANT SEALS, MIROUNGA LEONINA, FROM THE NORTHERN ANTARCTIC PENINSULA

MUELBERT M.; GALLON S.L.; LEWIS, M; HINDELL, M

Puerto Madryn

Congreso; 15 REUNION DE TRABAJO DE EXPERTOS EN MAMIFEROS ACUATICOS DE AMERICA DEL SUR; 2012

Sociedad Latinoamericana de Mamiferos Acuáticos

Elephant Island (EI) is uniquely placed to provide southern elephant seals (SES) breeding there with potential access to various foraging grounds such as the Weddell Sea, the frontal zones of the South Atlantic Ocean, the Patagonian Shelf (PS) and the Western Antarctic Peninsula (WAP). Twenty-nine SES (5 sub-adult males-SAM and 24 adult females-AF) were equipped with SMRU CTD-SLDRs during their post-breeding (PB 2008-09) and post-moulting (PM 2007-10) trips to sea. Whiskers were taken at the time of tag deployment and represented stable isotope (SI) signatures during the 3 to 4 months prior to the tracking period. Six females were re-sampled as they returned from their migration providing simultaneous SI signatures and tracking information. Striking intra-annual and inter-sex differences in foraging areas emerged, with most of the PB females remaining within 150km of EI while 16 of the 20 PM females foraged near the winter ice-edge south of the WAP. Most SAM remained close to EI although one male spent the early part of the winter foraging on the PS exhibiting higher 15N values (13.4 to 14.7?) and 13C values (-19.5 to -18.8 ?) than other SAM (11.1 to 13.5? and -22.6 to -20.6? for 15N and 13C, respectively). SAM and PB females that foraged around EI had different 15N values suggesting they were feeding at different trophic levels. PM females mainly fed on the shelf and their 15N values were positively related to body weight and time spent on the shelf. Heavier animals had higher 15N ratios independently of the sex of the animal. Our results suggest that sex and age differences are not the only forces driving the foraging strategies adopted by different seals: individuals of similar sex and age may forage in the same habitat but feed at different trophic levels influenced by body weight. Interestingly, AF from EI made more benthic dives than SAM in contrary to other sites where females are known to forage in open waters near frontal systems. While seals from EI had shorter migrations and were using shelf habitats more than other SES populations some individuals still employed open water foraging strategy. This study demonstrates the importance of shelf and slope habitats to SES and the influence of sea-ice, bathymetry and local ocean condition in the choice of foraging habitat. Quantifying where and at what trophic level seals from EI forage should provide new insights into the types of habitats available and which are of particular importance to SES.