Submerged swimming and resting metabolic rates in Southern sea lions

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 ± 1.1 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 V˙O2restair 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 V˙O2restwater (9.0 ± 0.8 ml O2 min− 1 kg− 1) and the mean V˙O2subswim (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 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 ± 0.1 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.

► Southern sea lions metabolic rate was measured using open flow respirometry.
► Resting metabolic rates were ca. 2–3 times Kleiber’s BMR prediction.
► Submerged swim metabolic rate was 6.8 times Kleiber’s BMR prediction.
► Cost of transport and cost per stroke were similar to other sea lions species.