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Influence of environment, feeding, and dive activity on the use of heart rate to predict oxygen consumption in resting and diving Steller sea lions (Eumetopias jubatus) Young, Beth Lyn


Despite its essential role in bioenergetic modeling, reliable measures of energy expenditure (i.e., oxygen consumption) associated with the different activities of wild animals have remained elusive. Oxygen consumption rate (VO₂) associated with activity can be estimated as a function of heart rate (fh), and the empirical relationship between the two has been determined for several aquatic vertebrates while fasting and resting. However, the simplified fh:VO₂ relationships established from such studies may differ under more complex physiological circumstances, such as when animals are foraging at depth or feeding on prey. I assessed the efficacy of using fh to predict VO₂ in 7 captive Steller sea lions, Eumetopias jubatus, while fasting and feeding at rest (on land or in water) and while diving (up to 40 m in the open ocean). Linear mixed-effects models revealed that environment, amount of food fed, and type of diving activity all altered the fh:VO₂ relationship. They also showed that different linear equations are needed to predict VO₂ from fh for sea lions fasted while on land or in water, but that a single equation can predict VO₂ on land regardless of whether fasted or feeding. When in water, feeding animals a 4, 6, or 12 kg meal changed the fh:VO₂ relationship compared to fasted animals. While fh can reliably be used to predict VO₂ in diving sea lions, the relationship differed between single dive cycles (one dive +surface interval) and dive bout cycles (multiple dives+surface intervals). However, the equation that predicted VO₂ for single dive cycles did not differ from that for sea lions resting on the surface. Neither dive duration, dive depth, nor food consumed significantly affected the fh:VO₂ relationships. Heart rate could be used to predict VO₂ in diving sea lions, but only over complete dive cycles or dive bouts where animals recovered fully from the O₂ debt incurred underwater. Based on these results, separate equations that distinguish among environmental, digestive, and diving states can be employed to accurately predict VO₂ from heart rate in wild Steller sea lions.

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