Strategy and capability of wild belugas, Delphinapterus leucas, during deep, benthic diving

The diving capability and behavioural strategy of wild belugas or white whales (Delphinapterus leucas) was investigated during periods of sustained deep diving. Analysis was limited to dives with a "square" time-depth profile, the most common type of deep dive, which invariably reached the seabed. As water depth increased, whales partially compensated for the greater commuting distance by increasing dive duration and rates of descent and ascent. But time at the target depth (bottom time) still diminished as depth increased. The duration of a dive was independent of the surface intervals preceding and following it. The aerobic dive limit of wild adult belugas probably exceeds the submergence times (mean 13.1 min, maximum 22.9 min) routinely recorded in this study. Belugas extended the duration of dives after slow descents, so bottom time was not reduced, substantiating the impression that they were not working at their physiological limit during sequences of deep dives. Larger belugas dived for longer and had lower rates of vertical travel. For their body size, belugas have average diving capability compared with other odontocetes but perform poorly compared with pinnipeds. Belugas are much larger than sympatric pinniped competitors, however, so they dive for longer and have unique access to deeper benthic resources.