Respiration and heart rate at the surface between dives in northern elephant seals

All underwater activities of diving mammals are constrained by the need for surface gas exchange. Our aim was to measure respiratory rate (fB) and hea rt rate (fH) at the surface between dives in free-ranging northern elephant seals Mirounga angustirostris, We recorded fB and fH acoustically in six t ranslocated juveniles, 1.8-2.4 years old, and three migrating adult males f rom the rookery at Ano Nuevo, California, USA. To each seal, we attached a diving instrument to record the diving pattern, a satellite tag to track mo vements and location, a digital audio tape recorder or acoustic datalogger with an external hydrophone to record the sounds of respiration and fH at t he surface, and a VHF transmitter to facilitate recovery. During surface in tervals averaging 2.2+/-0.4 min, adult males breathed a mean of 32.7+/-5.4 times at a rate of 15.3+/-1.8 breaths min(-1) (means +/- S.D., N=57), Mean fH at the surface was 84+/-3 beats min(-1). The fB of juveniles was 26 % fa ster than that of adult males, averaging 19.2+/-2.2 breaths min(-1) for a m ean total of 41.2+/-5.0 breaths during surface intervals lasting 2.6+/-0.31 min. Mean fH at the surface was 106+/-3 beats min(-1). fB and fH did not c hange significantly over the course of surface intervals. Surface fB and fH were not clearly associated with levels of exertion, such as rapid horizon tal transit or apparent foraging, or with measures of immediately previous or subsequent diving performance, such as diving duration, diving depth or swimming speed. Together, surface respiration rate and the duration of the preceding dive were significant predictors of surface interval duration. Th is implies that elephant seals minimize surface time spent loading oxygen d epending on rates of oxygen uptake and previous depletion of stores.