Meeting Abstract
The aerobic dive limit (ADL) an important determinant of diving ability scales with body size. As metabolism scales with mass^0.75 and oxygen stores scale with mass^1.0, larger animals should have a greater diving ability than smaller mammals. We compared the ADL of pinnipeds with respect to their foraging behavior to determine when body size is important and when other physiological adjustments come into play. We compared the physiological determinants of ADL in all 6 extant species of sea lions. ADL was estimated from measurements of total body oxygen stores (muscle, blood and lung) and estimates and or measures of metabolic rate. If diving ability were the primary factor driving body size, we would predict that larger sea lions should dive longer and deeper than smaller sea lions, who should dive shorter and shallower. However, we found the opposite pattern the smallest sea lion, the Galapagos sea lion, had the longest average dive duration and was the second deepest diver, while the two largest sea lions, the Steller and southern sea lion, exhibited the shallowest and shortest dives. The oxygen stores of the longest divers had the greatest oxygen stores and in some cases lower metabolism. This suggests that differences in body size are more related to ecological factors (prey availability and abundance) than diving ability. We also observed that the physiological capacity (oxygen stores) tracked the seasonal changes in dive behavior. California sea lions that made shallower shorter dives in the winter had lower O2 stores than sea lions who made deeper longer dives during the summer, implying that sea lions are able to increase their diving capacity through “conditioning”.
