Dive durations in pinnipeds and seabirds

Many endothermic divers regularly exceed the theoretical limit to the duration of aerobic dives, suggesting that assumptions about either the oxygen storage capacity of tissues or the metabolic rate of divers are wrong. This study examined the frequency distributions of dive durations in five species of endothermic divers from the island of South Georgia, South Atlantic. The theoretical aerobic dive time (TADT), calculated from average field metabolic rates, was exceeded regularly by all species except the Antarctic fur seal (<6% of dives). In contrast, the gentoo penguin exceeded its TADT in 69% of dives and the elephant seal in 91%. The frequency distributions of dive durations were bimodal, most especially in the penguins, with one mode below the TADT and another above the TADT, suggesting two different physiological strategics for diving. Interspecific allometric comparisons of dive durations in endothermic divers showed that, in general, relative dive durations in seabirds were greater than in pinnipeds. Dive durations in pinnipeds scaled approximately to field metabolic rate, whereas in seabirds they scaled most closely to flipper surface area, suggesting that they may be partly limited by the rate and degree of conduction of heat to the water.