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Weddell seal pups keep swimming while changing their fur

Open water swimming is far from easy, particularly when air and water temperatures are extremely cold. A research team led by the California Polytechnic State University has recently investigated how furry Weddell seal pups born on the Antarctic sea-ice can start swimming almost from birth in these extreme conditions, and continue to do so even while shedding and replacing their fur (a process called molting).

Although their blanket of fluffy insulation is very good for protecting them from cold temperatures when dry, as soon as they plunge into freezing waters, all these benefits are lost. The fact that the young seal pups enter the water and learn to swim and dive as early as two days old made scientists wonder how do they cope when they shed their fur, relying instead on their developing blubber stores – the thick layer of fat they have directly under their skins – for isolation. 

The research team traveled south to the McMurdo Station in Antarctica – close to a colony of Weddell seals – to monitor newborn pups through their first weeks of life, in order to understand how these fascinating animals manage to stay warm on ice and in water, and whether older pups with more developed blubber stores use less energy to stay warm. The scientists weighted and measured the pups, while noting the condition of their fur as they molted over a seven-week period. Moreover, by tagging their hind flippers, they also tracked how often and for how long each pup went for a dip.

The researchers discovered that, as the pups grew, their metabolic rates increased. Surprisingly though, when immersed in the water, the three- and seven-week-old pups had similar metabolic rates. By comparing how much time the youngsters spent in the water before, during, and after molting, the scientists were amazed to find that the molting pups spent three times more effort swimming before than after the molt, even if they expended more energy to remain warm in the water.

“These results support the idea of an energetic trade-off during early development; pups expend more energy for thermoregulation in water, yet gain experience needed for independence,” the study authors explained.

“Weddell seals are the southernmost breeding population of mammals in the world,” said Karla Heidelberg, a program director in National Science Foundation’s Office of Polar Programs. “These researchers are providing new information that’s changing how we view the life histories and physiological differences among these seals and other seal populations that live farther north in warmer regions of Antarctica.”

The study is published in the Journal of Experimental Biology.

By Andrei Ionescu, Staff Writer

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