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The Journal of Experimental Biology 204, 3877-3885 (2001)
© 2001 The Company of Biologists Limited

Effects of training on forced submersion responses in harbor seals

P. D. Jobsis^*, P. J. Ponganis and G. L. Kooyman

Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0204, USA

*Present address: Loras College, 1450 Alta Vista, Dubuque, IA 52004-0178, USA (e-mail: pjobsis{at}uvi.edu)

Accepted August 16, 2001

In several pinniped species, the heart rates observed during unrestrained dives are frequently higher than the severe bradycardias recorded during forced submersions. To examine other physiological components of the classic ‘dive response’ during such moderate bradycardias, a training protocol was developed to habituate harbor seals (Phoca vitulina) to short forced submersions. Significant changes were observed between physiological measurements made during naive and trained submersions (3–3.5 min). Differences were found in measurements of heart rate during submersion (naive 18±4.3 beats min^–1 versus trained 35±3.4 beats min^–1), muscle blood flow measured using laser-Doppler flowmetry (naive 1.8±0.8 ml min^–1 100 g^–1 versus trained 5.8±3.9 ml min^–1 100 g^–1), change in venous P_O2 (naive –0.44±1.25 kPa versus trained –1.48±0.76 kPa) and muscle deoxygenation rate (naive –0.67±0.27 mvd s^–1 versus trained –0.51±0.18 mvd s^–1, a relative measure of muscle oxygenation provided by the Vander Niroscope, where mvd are milli-vander units). In contrast to the naive situation, the post-submersion increase in plasma lactate levels was only rarely significant in trained seals. Resting eupneic (while breathing) heart rate and total oxygen consumption rates (measured in two seals) were not significantly different between the naive and trained states. This training protocol revealed that the higher heart rate and greater muscle blood flow in the trained seals were associated with a lower muscle deoxygenation rate, presumably secondary to greater extraction of blood O₂ during trained submersions. Supplementation of muscle oxygenation by blood O₂ delivery during diving would increase the rate of blood O₂ depletion but could prolong the duration of aerobic muscle metabolism during diving. This alteration of the dive response may increase the metabolic efficiency of diving.

Key words: dive response, heart rate, laser-Doppler, muscle blood flow, myoglobin, near-infrared spectroscopy, oxygen store, harbour seal, Phoca vitulina.

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