When does physiology limit the foraging behaviour of freely diving mammals?

Diving animals offer a unique opportunity to study the importance of physiological constraint and the limitation it can impose on animal's behaviour in nature. This paper examines the interaction between physiology and behaviour and its impact on the diving capability of five eared seal species (Family Otariidae; three sea lions and two fur seals). An important physiological component of diving marine mammals is the aerobic dive limit (ADL). The ADL of these five seal species was estimated from measurements of their total body oxygen stores, coupled with estimates of their metabolic rate while diving. The tendency of each species to exceed its calculated ADL was compared relative to its diving behaviour. Overall, our analyses reveal that seals which forage benthically (i.e. on the sea floor) have a greater tendency to approach or exceed their ADL compared to seals that forage epipelagically (i.e. near the sea surface). Furthermore, the marked differences in foraging behaviour and physiology appear to be coupled with a species demography. For example, benthic foraging species have smaller populations and lower growth rates compared to seal species that forage epipelagically. These patterns are relevant to the conservation and management of diving vertebrates.