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

Archival data loggers were used to collect information about depth, swimmin g 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 ra te averaged 108.7 +/- 17.7 beats/min (SD) but varied from 83 to 145 beats/m in among animals. Morphometrics explained most variations in heart rate amo ng animals. These interacted with diving activity and swimming speed to pro duce a complex relationship between heart rate and activity patterns. Heart ; rate was also correlated with behavior over time lags of several hours. T here was significant (P < 0.05) variation among animals in the degree of di ving bradycardia. On average, heart rate declined from 100-130 beats/min be fore the dive to 70-100 beats/min during submersion. On the basis of the re lationship between heart rate and rate of oxygen consumption, the overall m etabolic 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 mutua lly exclusive of one another.