Determinants of the Aerobic Dive Limit of Weddell Seals: Analysis of Diving Metabolic Rates, Postdive End Tidal Po₂'s, and Blood and Muscle Oxygen Stores

The mean aerobic dive limit (ADL) for Weddell seals was calculated from data collected on diving metabolic rates (V̇o2) and blood and muscle O₂ stores. Mean diving V̇o2 of adult seals during predominantly exploratory dive patterns was 4.5 mL O2 kg−1 min−1; mean V̇o2 of a subadult seal engaged in foraging dive bouts was 8.5 mL O2 kg−1 min−1. The adult value was 30% greater than that used in past ADL calculations. Mean plasma volume was 7% body mass (BM); blood volume calculated with the highest hematocrit (Hct) observed (66) was 21% BM. Hemoglobin concentration at such an Hct was 26% by weight. End tidal Po2 (pre-and postdive) justified the use of 95% and 20% arterial O2 saturations in the blood O2 store calculation. Total blood O2 stores were 50% greater than those used in past ADL calculations. Mean myoglobin concentration (5.4% by weight) and more recent anatomical estimates of muscle mass yielded a 35% increase in muscle O2 stores. The mean estimated ADL for a 450-kg seal calculated with these new data was 19.1 min, 2.3 min greater than in past calculations and only 1 min less than the 20-min inflection point of the curve of dive duration versus postdive lactic acid appearance. For the subadult engaged in foraging dives, the mean estimated ADL was about 9 min, again quite similar to past ADL calculations.