Combining bio-logging and fatty acid signature analysis indicates spatio-temporal variation in the diet of the southern elephant seal, Mirounga leonina

Quantifying the foraging ecology of apex predators is crucial for understanding the predator–prey interactions in marine ecosystems. This is particularly important in the Southern Ocean ecosystem, where year-round studies are logistically and financially impractical. Detailed investigations into the diet of wide-ranging southern hemisphere marine predators, therefore, need to be quantified spatio-temporally. We coupled tracking data with fatty acid signature analysis (FASA) to investigate the foraging ecology of a wide-ranging Southern Ocean marine predator, the southern elephant seal (Mirounga leonina). Seal foraging areas varied spatially and over time, but seals concentrated their activities in three broad geographic regions (i) off the East Antarctic Continental Shelf (S-ACC), (ii) at the edge of the pack ice north of the Ross Sea (SE-RS) and (iii) north of the Sub-Antarctic Front (SE-SAF). There were significant differences in the fatty acid (FA) composition of the blubber from the seals that used these different regions. Seals foraging in the SE-SAF had blubber high in short chained mono-unsaturated fatty acids (SC-MUFAs), compared to those from the S-ACC and SE-RS habitats, which contained more poly-unsaturated fatty acids (PUFAs). Comparisons with FAs of known prey species in the region indicated that blubber collected from seals using the shelf and pelagic habitats (i.e. S-ACC and SE-SAF) were likely to have higher proportions of fish in the diet and, conversely, those from the pack-ice habitat (i.e. SE-RS) were more likely to have a cosmopolitan diet, i.e. an evenly mixed diet of fish and squid. Seal diet also varied annually, within the shelf and pelagic habitats changing from a diet relatively high in fish, to a diet relatively high in squid. Coupling tracking data with FASA is a powerful technique to investigate the spatio-temporal variations in the diet of wide-ranging marine predators.