Submerged swimming and resting metabolic rates in Southern sea lions

Abstract

We measured the metabolic rate of nineteen wild and three captive, trained Southern sea lions (Otaria flavescens, Shaw 1800) during three behavioral states: resting in air (V˙O2restair), resting in water (V˙O2restwater) and submerged swimming (V˙O2subswim) using open flow respirometry. We then used these values to estimate total cost of transport (COT) and cost per stroke (CPS) during submerged swimming. Wild animals were placed in a metabolic chamber and captive animals were trained to breathe under a plexiglass dome mounted at the end of a pool. General linear modeling was used to determine whether the incidence of each type of response variable (V˙O2, CPS, COT, swim speed and stroke rate) could be associated with several explanatory variables (sex, age, animal identity, behavioral state, swimming distance and body mass). The overall mean V˙O2restair was 6.8±1.1mlO2min−1kg−1 (n=20 animals; 7 subadult males, 10 sub-adults females, 3 adults females), which was 2.1 times greater than the predicted basal metabolic rate (BMR) for terrestrial mammals of similar size, and neither body mass nor sex had a significant effect. The mean V˙O2restair when only adults were considered (6.3±0.3mlO2min−1kg−1; n=3 females) was similar to the overall value. The mean V˙O2restwater (9.0±0.8mlO2min−1kg−1) and the mean V˙O2subswim (21.2±7.4mlO2min−1kg−1) estimated from repeated measurements in two adult females were 2.9 and 6.8 times greater than the predicted BMR, respectively. Both V˙O2restwater and V˙O2subswim were significantly greater (1.4 and 3.4 times respectively) than the mean V˙O2restair estimated in this study, when only adults were compared. The mean COT was 0.14±0.1mlO2kg−1m−1 (2.6±1.0Jkg−1m−1), and the mean CPS was 0.38±0.3mlO2−1kg−1stroke−1; none of these values were significantly different among animals.