Foraging insights from whisker isotopic signatures of southern elephant seals around the Antarctic Peninsula

The Antarctic Peninsula is one of the most rapidly warming regions on Earth and is home to a diverse and rich community of life, especially along its continental shelf. The biophysical characteristics that define these regions of highly localised productivity are associated with processes that are driven by climate. Climate changes will therefore potentially alter the oceanographic features and processes on which top predators rely to find their food. Studying the foraging behaviour of apex predators, such as southern elephant seals (SES), Mirounga leonina, is important during this time of rapid change to detect changes in prey availability. Carbon and nitrogen stable isotope (SI) analyses were performed to assess the dietary history (e.g. delta N-15) and infer the foraging habitat (e.g. delta C-13) on consecutive sections of whole whiskers from 119 southern elephant seals from Elephant Island (61 degrees 13'S 55 degrees 23'W) from all age and sex classes. Whisker SI values were spread over a large range, with delta C-13 and delta N-15 values varying from-23.21 to-16.344to (a 6.87 parts per thousand difference) and from 8.90%parts per thousand to 15.47%o (6.57 parts per thousand), respectively. SI analyses also confirmed marked differences in the feeding ecology of southern elephant seals according to sex (e.g. delta N-15 significantly different between sexes in adults, GLMM, p = 0.001) and age group (e.g. delta C-13 related to age classes in females, GLMM, p < 0.001). Results suggest that yearlings foraged more frequently in the sub Antarctic zone whilst adult seals stayed south of the polar front and, adult and sub-adult males fed on higher trophic level prey than other sex and age classes. We discuss how these differences are likely a result of a combination of antra-specific competition, ontogenetic factors and resource distribution. Studying the degree and the ontogeny of individual specialisation within a population is a first step towards understanding its implications in various dimensions of ecological and evolutionary processes and hence for adapting to climate changes.