Pitching and new angle on elephant seal dive patterns

SALA, J. E.; QUINTANA, F; WILSON, R. P.; DIGNANI, J.; LEWIS, M. N.; CAMPAGNA, C.

Puerto Madryn

Congreso; 15ª Reunión de Trabajo de Expertos en Mamíferos Acuáticos de América del Sur y 9º Congreso SOLAMAC; 2012

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 which additionally recorded body pitch and roll on 4 juvenile southern elephant seals (Mirounga leonina) foraging over the Patagonian Shelf to describe their diving behaviour and compared it to that 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 (defined by the shape in the dive profile and body orientation) 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. This study indicates that juvenile southern elephant seals from Península Valdés engage in diving behaviour that is similar to that of adults. Certain features that have emerged by using the accelerometers to define body pitch and roll appear to be new to this species. Most notable of these is the ?up-ending? behaviour that appears during the bottom phase of Eb dives. This indicates that juvenile elephant seals forage on truly benthic as well as pelagic prey. Or the ?belly-up? posture of animals during the second stage of the descent phase (i.e. drifting down) of type C dives, where seals appear to be resting and/or digesting food. Thus, accelerometer data suggest that several unique behaviours can ?hide? behind the same dive shape, highlighting the importance of having this information to study the diving behaviour, in general, and to conduct a functionality-based classification of dives in particular.