Optimal foraging in an amphibious mammal. I. The aqualung effect

The marginal value theorem of Charnov is extended to a simple model covering the case of mammalian carnivores hunting underwater, in which situation their total search time and pursuit effort is constrained by the limited oxygen capacity of their lungs. In the mink Mustela vison hunting rudd in an experimental tank the duration of dives, of giving-up times, and of the pursuit phase of underwater hunts, as well as the frequency of dives, were consistent with the usual marginal value predictions. Giving-up times were also essentially constant within bouts, as expected. An interaction between foraging economics and oxygen reserves derived from the extended model was confirmed experimentally.