Standard metabolic rate at the surface and during trained submersions in adult California sea lions (Zalophus californianus)

The metabolic rate (MR) of four adult California sea lions (Zalophus califo rnianus), two males and two females, was quantified during trained submersi on and stationing behavior in laboratory tanks. MR was measured, at rest an d for single submersions of increasing duration (1-7 min), by measuring oxy gen consumption using open-circuit, indirect calorimetry. Standard MR was m easured under conditions defined for basal MR and was found to be 1.9 to 3 times that predicted for terrestrial animals of similar size. Submersion MR s were calculated from the post-submersion oxygen debt and declined to as l ittle as 47% of standard MR on the longest submersions. This hypometabolic response was proportional to the duration of submersion and was greatest fo r the maximum duration submersions. Short submersions produced MRs equivale nt to measured standard MR. These data suggest that although California sea lions maintain an elevated metabolism under standard conditions, they are capable of reducing their metabolism in response to the needs of diving. Su ch metabolic flexibility enables sea lions to moderate their oxygen use dur ing diving and to extend their aerobic diving capability.