ORIGINAL PAPER High diving metabolism results in a short aerobic dive limit for Steller sea lions (Eumetopias jubatus) Carling D. Gerlinsky • David A. S. Rosen • Andrew W. Trites Received: 18 October 2012 / Revised: 19 December 2012 / Accepted: 22 December 2012 / Published online: 25 January 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The diving capacity of marine mammals is typically defined by the aerobic dive limit (ADL) which, in lieu of direct measurements, can be calculated (cADL) from total body oxygen stores (TBO) and diving metabolic rate (DMR). To estimate cADL, we measured blood oxy- gen stores, and combined this with diving oxygen con- sumption rates (VO 2 ) recorded from 4 trained Steller sea lions diving in the open ocean to depths of 10 or 40 m. We also examined the effect of diving exercise on O 2 stores by comparing blood O 2 stores of our diving animals to non- diving individuals at an aquarium. Mass-specific blood volume of the non-diving individuals was higher in the winter than in summer, but there was no overall difference in blood O 2 stores between the diving and non-diving groups. Estimated TBO (35.9 ml O 2 kg -1 ) was slightly lower than previously reported for Steller sea lions and other Otariids. Calculated ADL was 3.0 min (based on an average DMR of 2.24 L O 2 min -1 ) and was significantly shorter than the average 4.4 min dives our study animals performed when making single long dives—but was sim- ilar to the times recorded during diving bouts (a series of 4 dives followed by a recovery period on the surface), as well as the dive times of wild animals. Our study is the first to estimate cADL based on direct measures of VO 2 and blood oxygen stores for an Otariid and indicates they have a much shorter ADL than previously thought. Keywords Diving metabolism  Oxygen stores  Aerobic dive limit  Blood volume  Steller sea lion  Otariid Abbreviations ADL Aerobic dive limit cADL Calculated aerobic dive limit TBO Total body oxygen stores VO 2 Oxygen consumption rate DMR Diving metabolic rate MR S Pre-dive (surface) metabolic rate RMR Resting metabolic rate Introduction Marine mammals that exploit resources at depth rely on physiological adaptions to extend the time they can remain submerged to increase their foraging efficiency (Houston and Carbone 1992). Foraging ability for a marine mammal inher- ently depends on overall diving ability, with the most efficient foraging thought to be done aerobically. This aerobic diving capacity is typically defined by the aerobic dive limit (ADL or diving lactate threshold; Butler 2006). The ADL is measured as the maximum dive duration before there is an increase in post-dive blood lactate concentration beyond resting levels (Kooyman 1985). An increase in post-dive lactate indicates anaerobic metabolism is being used to conserve onboard oxygen stores for critical systems that can only function aer- obically (Kooyman et al. 1980). It is thought that marine mammals should preferentially dive within their ADL (Kooyman 1989); the extra time needed to recover from anaerobic dives would result in a lower overall foraging effi- ciency, as the surface interval needed to recover increases dis- proportionately with longer dive times (Kooyman et al. 1980). Communicated by I.D. Hume. C. D. Gerlinsky (&)  D. A. S. Rosen  A. W. Trites Department of Zoology and Marine Mammal Research Unit, Fisheries Center, University of British Columbia, 2204 Main Mall, Vancouver, BC V6T 1Z4, Canada e-mail: c.gerlinsky@fisheries.ubc.ca 123 J Comp Physiol B (2013) 183:699–708 DOI 10.1007/s00360-013-0742-7