Flipper stroke rate and venous oxygen levels in free-ranging California sea lions.
The depletion rate of the blood oxygen store, development of hypoxemia and dive capacity are dependent on the distribution and rate of blood oxygen delivery to tissues while diving. Although blood oxygen extraction by working muscle would increase the blood oxygen depletion rate in a swimming animal, there is little information on the relationship between muscle workload and blood oxygen depletion during dives. Therefore, we examined flipper stroke rate, a proxy of muscle workload, and posterior vena cava oxygen profiles in four adult female California sea lions (Zalophus californianus) during foraging trips at sea. Flipper stroke rate analysis revealed that sea lions minimized muscle metabolism with a stroke-glide strategy when diving, and exhibited prolonged glides during the descent of deeper dives (>100 m). During the descent phase of these deep dives, 55±21% of descent was spent gliding, with the longest glides lasting over 160 s and covering a vertical distance of 340 m. Animals also consistently glided to the surface from 15 to 25 m depth during these deeper dives. Venous hemoglobin saturation (SO2) profiles were highly variable throughout dives, with values occasionally increasing during shallow dives. The relationship betweenSO2and flipper stroke rate was weak during deeper dives, while this relationship was stronger during shallow dives. We conclude that (1) the depletion of oxygen in the posterior vena cava in deep-diving sea lions is not dependent on stroke effort, and (2) stroke-glide patterns during dives contribute to a reduction of muscle metabolic rate.
Scripps Institution of Oceanography, University of California San Diego, Center for Marine Biodiversity and Biomedicine, 8655 Kennel Way, La Jolla, CA 92037, USA tift.mike@gmail.com.
Michael S
0000-0002-0563-0509
MS
Tift
Department of Ecology and Evolutionary Biology, University of California Santa Cruz, Long Marine Lab, 100 Shaffer Road, Santa Cruz, CA 95060, USA.
Luis A
LA
Hückstädt
Moss Landing Marine Laboratories, 8272 Moss Landing Road, Moss Landing, CA 95039, USA.
Birgitte I
BI
McDonald
Institute of Marine Sciences, University of California Santa Cruz, Long Marine Laboratory, 100 Shaffer Road, CA 95060, USA.
Philip H
PH
Thorson
Scripps Institution of Oceanography, University of California San Diego, Center for Marine Biodiversity and Biomedicine, 8655 Kennel Way, La Jolla, CA 92037, USA.
Paul J
PJ
Ponganis
D000818:Animals; D001784:Blood Gas Analysis; D004242:Diving; D005260:Female; D006454:Hemoglobins / Q000032:analysis; D009132:Muscles / Q000502:physiology; D010100:Oxygen / Q000097:blood*; D046070:Sea Lions / Q000097:blood* / Q000502:physiology*; D013550:Swimming
D006454:Hemoglobins; D010100:Oxygen
Diving physiology; Flipper stroke rate; Marine mammal; Venous oxygen