Heart rate and behaviour of fur seals: implications for measurement of field energetics

Archival data loggers were used to collect information about depth, swimming speed, and heart rate in 23 free-ranging antarctic fur seals. Deployments averaged 9.6 ± 5.6 days (SD) and totaled 191 days of recording. Heart rate averaged 108.7 ± 17.7 beats/min (SD) but varied from 83 to 145 beats/min among animals. Morphometrics explained most variations in heart rate among animals. These interacted with diving activity and swimming speed to produce a complex relationship between heart rate and activity patterns. Heart rate was also correlated with behavior over time lags of several hours. There was significant (P < 0.05) variation among animals in the degree of diving bradycardia. On average, heart rate declined from 100-130 beats/min before the dive to 70-100 beats/min during submersion. On the basis of the relationship between heart rate and rate of oxygen consumption, the overall metabolic rate was 5.46 ± 1.61 W/kg (SD). Energy expenditure appears to be allocated to different activities within the metabolic scope of individual animals. This highlights the possibility that some activities can be mutually exclusive of one another.