Increased Metabolic Rate of Hauled-Out Harbor Seals (Phoca vitulina) during the Molt

Harbor seals (Phoca vitulina) live in cold temperate or polar seas and molt annually, renewing their fur over a period of approximately 4 wk. Epidermal processes at this time require a warm skin; therefore, to avoid an excessive energy cost at sea during the molt, harbor seals and many other pinnipeds increase the proportion of time they are hauled out on land. We predicted that metabolic rate during haul-out would be greater during the molt to sustain an elevated skin temperature in order to optimize skin and hair growth. To examine this, we measured post-haul-out oxygen consumption (VO2) in captive harbor seals during molt and postmolt periods. We recorded greater VO2 of seals while they were molting than when the molt was complete. Post-haul-out VO2 increased faster and reached a greater maximum during the first 40 min. Thereafter, VO2 decreased but still remained greater, suggesting that while metabolic rate was relatively high throughout haul-outs, it was most pronounced in the first 40 min. Air temperature, estimated heat increment of feeding, and mass also explained 15.5% of VO2 variation over 180 min after haul-out, suggesting that the environment, feeding state, and body size influenced the metabolic rate of individual animals. These results show that molting seals have greater metabolic rates when hauled out, especially during the early stages of the haul-out period. As a consequence, human disturbance that changes the haul-out behavior of molting seals will increase their energy costs and potentially extend the duration of the molt.

Automated summary

The study found that harbor seals have higher metabolic rates when hauled out during molting, especially in the early stages of haul-out. Oxygen consumption peaks in the first 40 minutes post-haul-out and then decreases but remains relatively high. Factors such as air temperature, feed heat increment, and body size all influence the metabolic rate of harbor seals.