Diving Behaviour and Foraging Ecology of Female Southern Elephant Seals from Patagonia

We asked if non-gestating adult female southern elephant seals, Mirounga leonina, from Peninsula Valdes, Argentina, forage on the wide continental shelf off the peninsula during the post-breeding trip to sea (PB females), or whether they forage in deep water, where gestating, post-moult (PM) animals have been shown to do. More than 16,600 dives were recorded with geographic-location time-depth recorders deployed in five PB females. Data was compared with about 19,500 dives from six gestating PM animals. Four satellite transmitters linked to the Argos system were deployed in PB (2) and PM (2) animals. During both trips females displayed continuous deep and long-duration diving. PB females crossed the shelf in 3-7 days, spending 89% of the recorded time at sea over waters deeper than 200 m. A diel pattern in frequency distribution of dives/hr, dive depth and dive duration was apparent in both PB and PM individuals beyond the continental shelf. Deeper and longer dives were observed during daylight hours, consistent with feeding on dielly-migrating prey. PB females concentrated their foraging effort in temperate waters of the SW Atlantic between 36 degrees and 46 degrees S and up to 1200 km from shore. PM females travelled further, reaching ~50 degrees S and 2281 km east from the rookery. The longest migration was a PM trip of 11,600 km. Females from Peninsula Valdes, the only colony for the species with an increasing birth rate, do not feed near or south of the Antarctic Polar Front, where most seals from more southerly stable or decreasing rookeries forage.