Shifting Seas: Harp Seals Threatened By Weak Sea Ice


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The Harp Seal: A Theatened Icon? Image credit: wallpaperbase


That is the sound of options getting more limited for harp seals.

Like the polar bear, these fluffy seals are icons of the North. Countless images of their limpid black eyes in a fluffy white face stare out at us from posters and cards, and thousands of little stuffed seals sit in stores, ready to go home to owners who will delight in their cuteness.

Unfortunately, the story of the seals is not nearly as delightful. Over the last few decades, thinning sea ice due to climate change has become a feature of the seals’ East Coast breeding grounds.

Harp Seals Live a Tenuous Life on the Ice

Harp seals live on the edge. They give birth on thick sea ice. The pups are designed for a speedy exit from infancy, weaning after a mere 12 days of nursing. After that, the pups fast, and the fat from nursing turns into muscle. The seal becomes a lean diving machine.

The harp seal’s birth and nursing habits are closely connected to the development and dispersal of the sea ice. Changes in the sea ice directly impact their populations.

In a study out of Duke University, researcher David W. Johnston and his colleagues discovered that thinning sea ice leads to dramatically high death rates in seal populations, particularly amongst vulnerable pups. If the ice cracks before the seals are ready to survive in the water, baby seals fall into the water, where they get hypothermia or moving ice crushes them.

Why Is the Ice Pack Changing?

The study discovered that two overall trends influence the conditions of the sea ice in the Gulf of St Lawrence.  One is the North Atlantic Oscillation, a climatic event that influences the development of sea ice, the other is an overall trend towards thinner ice pack. In the case of the North Atlantic Oscillation, when the Oscillation is strong, the ice cover is stronger. As the North Atlantic Oscillation weakens, this brings lighter ice cover to the region.

From 1950 to 1972, the number of harp seals in the area greatly diminished. This was also a period of time with a weak North Atlantic Oscillation, and sea ice was not thick and strong. From 1973 to 2000, the sea ice became stronger, and populations of harp seals jumped once again, likely due to stronger sea ice and a stronger North Atlantic Oscillation. This past data shows the connection between strong sea ice and strong seal populations.

Unfortunately, the data also shows that, in addition to changes in the sea ice reduction due to the North Atlantic Oscillation, the overall current trend is toward a reduced and thinner ice pack. Sea ice levels have been decreasing, and the question is whether the seals can adapt.

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