Diving behaviour of Southern elephant seals: new models of behavioural and ecophysiological adjustments of oxygen store management.

Among pinnipeds, Southern Elephant Seals (SES, Mirounga leonina) are extreme divers that dive deeply and continuously along foraging trips to restore their body stores after fasting on land during breeding or moulting. Their replenishment of body stores influences their energy expenditure during dives and their oxygen (O2) reserves (via muscular mass), yet how they manage their O2 stores during their dives is not fully understood. In this study, 63 female SES from Kerguelen Island were equipped with accelerometers and Time Depth Recorders to investigate changes in diving parameters through their foraging trips. Two categories of dive behaviour were identified and related to the body size of individuals, with smaller SES performing shallower and shorter dives requiring greater mean stroke amplitude compared to bigger body size individuals. In relation with the body size, the bigger individuals have lower estimated oxygen consumption levels for a given buoyancy (i.e., body density) compared to smaller SES. However, both groups were estimated to have the same oxygen consumption of 0.079  0.001 ml O2.stroke-1.kg-1 for a given dive duration and at neutral buoyancy when the Cost of Transport was minimal. Based on the relationships we build two models that estimated changes in oxygen consumption according to dive duration and body densities. The study highlights that replenishing body stores improves SES foraging efficiency, as indicated by increased time spent at the bottom. Thus, prey-capture attempts increase as SES buoyancy approaches the neutral buoyancy point.