Pitching a new angle on elephant seal dive patterns

Abstract

Elephant seals are one of the most proficient diving mammals in the world and are also one of the most studied. However, their long periods at sea and pelagic habits make research into their foraging ecology particularly challenging. Most current understanding comes from the use of time-depth recorders (TDRs). We used TDRs that additionally recorded body pitch and roll on four juvenile southern elephant seals (Mirounga leonina) foraging over the Patagonian Shelf to describe their diving behaviour and compared them with those of adults, using standard descriptions of elephant seal dive profile types provided by the literature. Over 280 days of diving data showed that dive types were similar to those of adults (types: A, B, C, D, Eb and Ef) but that dive types A and C differed slightly, probably because our animals were constrained by bottom topography. Steep dive and return-to-surface angles in all dive types except type B indicate that animals generally attempt to maximize vertical displacement. Horizontal displacement was much greater in type B dives, which indicates a travelling function. Pitching and rolling behaviour lends support to the functions ascribed to the dive types already described for adult elephant seals, although type Eb dives are unusual in that the animals appear to be taking prey by up-ending in the benthos.