CONICET | Buscador de Institutos y Recursos Humanos

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 (VO2 rest air), resting in water (VO2 rest water) and submerged swimming (VO2 subswim) 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 (VO2, 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 VO2 rest air was 6.8 ± 1.1 ml O2 min-1 kg-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 VO2 rest air when only adults were considered (6.3 ± 0.3 ml O2 min-1 kg-1; n= 3 females) was similar to the overall value. The mean VO2 rest water (9.0 ± 0.8 ml O2 min-1 kg-1) and the mean VO2 subswim (21.2 ± 7.4 ml O2 min-1 kg-1) estimated from repeated measurements in two adult females were 2.9 and 6.8 times greater than the predicted BMR, respectively. Both VO2 rest water and VO2 subswim were significantly greater (1.4 and 3.4 times respectively) than the mean VO2 rest air estimated in this study, when only adults were compared. The mean COT was 0.14 ± 0.1 ml O2 kg-1 m-1 (2.6 ± 1.0 J kg-1 m-1), and the mean CPS was 0.38 ± 0.3 ml O2-1 kg-1 stroke-1; none of these values were significantly different among animals.