Blood oxygen depletion in California sea lions

Abstract

The rate and magnitude of O2 store depletion is critical to the dive performance and foraging ecology of breath hold divers. We investigated blood O2 depletion with a backpack recorder for the partial pressure of O2 (PO2) in nine California sea lions during maternal foraging trips. During routine shallow dives, arterial and venous minimum PO2 were routinely greater than 30 mmHg (~50% hemoglobin saturation). However in deep dives greater than 4 minutes in duration, minimum venous PO2 reached values below 10 mmHg (~ 5% saturation), and in dives over 7 min, were as low at 5 mmHg. During deep dive bouts, both arterial and venous PO2 increased during ascent and minimum arterial PO2 was never below 30 mmHg (~ 40–50% saturation), even in dive durations greater than 5 min. In contrast to shallow dives, venous PO2 values less than 10 mmHg for over two minutes during long dives are consistent with near complete blood O2 depletion. During deep dives, the increase in arterial and venous PO2 during ascent suggests that re‐expansion of collapsed lungs and resumption of gas exchange during the “ascent tachycardia” allows for lung‐to‐blood O2 transfer. We suggest that the O2 reservoir remaining in the collapsed lungs at depth serves to supplement blood O2 levels during ascent, and prevent shallow water black out at the end of deep dives.