Thermoregulation and Resting Metabolic Rate of California Sea Lion (Zalophus californianus) Pups

Resting metabolic rate and body temperature of California sea lion pups (Zalophus californianus: Otariidae) were measured for 39 animals (12,000 g, mean body mass) captured from breeding areas on San Nicolas Island, California. These 3-5-wk-old pups had a mean specific resting metabolic rate of 0.780 ± .010 ml O₂ g⁻¹ h⁻¹, which is 2.380 times the value predicted by Kleiber for adult mammals with similar body mass; mean body temperature was 37.8 ± .08 C. This level of metabolism is similar to those reported for young seals (Phocidae). The heat-transfer coefficient (h) was 24.6 times that predicted from body mass, and it appeared that some individuals were on the verge of hypothermia at ambient air temperatures below 19 C. Although high metabolic rates are typically associated with high growth rates in terrestrial mammals, high heat loss associated with relatively poor insulation in sea lion pups may require allocation of relatively large amounts of energy to thermoregulation (=maintenance), thus limiting the amount of energy available for growth.