Maintaining control: metabolism of molting Arctic seals in water and when hauled out

Abstract

Seals haul out of water for extended periods during the annual molt, when they shed and regrow their pelage. This behavior is believed to limit heat loss to the environment given increased peripheral blood flow to support tissue regeneration. The degree to which time in water, particularly during the molt, may affect thermoregulatory costs is poorly understood. We measured the resting metabolism of three spotted (Phoca largha), one ringed (Pusa hispida), and one bearded (Erignathus barbatus) seal during and outside the molting period, while resting in water and hauled out. Metabolic rates were elevated in spotted and ringed seals during molt, but comparable in water and air for individuals of all species regardless of molt status. Our data indicate that elevated metabolism during molt primarily reflects the cost of tissue regeneration, while increased haul out behavior is driven by the need to maintain elevated skin temperatures to support tissue regeneration.

Breaking the fast: first report of dives and ingestion events in molting southern elephant seals

“…Avoiding cold water would limit energy expenditure and blubber depletion, while a faster molt would limit fasting duration and extend the next foraging period 72 , resulting in higher at-sea body condition, survival, and reproductive success 37 , 38 . Previous studies on ringed and spotted seals did not report supplementary energy expenditure at sea 16 , and our data did not show any difference in body mass loss between at-sea and on-land females. This highlights that the physiological cost of molting, i.e., for tissue regeneration, may be greater than the cost of heat loss in cold water.…”

“…Surprisingly, females that went to sea did not lose more body mass than females remaining on land but had higher stomach temperatures, which could reflect a higher metabolic rate, hence higher energy loss at sea. However, previous studies on molting Arctic seals (ringed Pusa hispida , spotted Phoca largha , and bearded seals Erignathus barbatus ) reported that metabolic rates were similar when resting in air and water 16 . An increase in stomach temperature might be detected at the onset of diving as a result of heat generated by muscles during swimming 73 , which questions the reliability of STP to estimate metabolic variation.…”

“…Molting is involved with a change in coat or plumage color, that may be related to reproductive success and camouflage in the environment 5 , 11 , growth 10 , thermoregulation 12 , and defense against parasites or pathogens 7 , hence playing an important role in the fitness of an individual. However, molt is an energy demanding process 13 requiring high peripheral vascular circulation to promote skin cell proliferation and tissue growth 14 , and a high metabolic rate to balance heat loss 15 , 16 .…”

“…In phocids, regrowth of skin and fur requires a skin temperature above 17 °C 19 . Maintenance of this warm temperature in polar regions leads to elevated metabolic rate 15 , 16 , 20 . To reduce energy expenditure during the molt, seals are insulated with thick subcutaneous blubber 21 , 22 , regulate peripheral blood flow, and avoid even higher heat loss by hauling out to minimize time in cold water, where heat loss is 25 times faster than in air 23 , 24 .…”