Metabolic effects of low-energy diet on Steller sea lions, Eumetopias jubatus

Diets of six Steller sea lions (Eumetopias jubatus) were switched between a high (herring) and a low (squid) energy density food for 14 d to determine the effects on ingested prey mass, body mass, resting metabolic rate, and the heat increment of feeding. Body mass was measured daily, and resting me tabolism was measured weekly by gas respirometry. Ingested food mass did no t differ significantly between the squid diet and the control or the recove ry herring diet periods. As a result of differences in energy density, gros s energy intake was significantly lower during the squid diet phase than du ring either the control or recovery periods. As a result, sea lions lost an average of 1.1 kg/d, totaling 12.2% of their initial body mass by the end of the experimental period. The heat increment of feeding for a 4-kg squid meal was significantly lower than for a similarly sized meal of herring. De creases in both absolute (24.0 to 18.0 MJ/d, -24%) and mass-corrected (903 to 697 kJ/d/ kg(0.67), -20%) metabolism were observed by the end of the squ id feedings. This study suggests that sea lions can depress their resting m etabolism in response to decreases in energy intake or body mass, regardles s of satiation level.