There's no doubt that the poster animal for changes in Arctic sea ice cover is the polar bear. But the species on which the polar bear primarily preys – the ringed seal – is also at risk as a consequence of declines in sea ice extent. Like its predator, the ringed seal is uniquely adapted to the sea ice environment, boasting a set of claws that allows it to maintain holes in ice floes, through which it breathes and over which it builds lairs in which to rest, give birth, and raise pups.
A new study in the journal Geophysical Research Letters highlights one way in which disappearing sea ice imperils ringed seals: by resulting in a decrease in snow cover that seals can use to build their caves.
Those dens require snow depth of at least 20 centimeters, or eight inches. And models predict that mid-winter snowfall will actually increase slightly by the end of the century. Unfortunately for the seals, that winter increase won't compensate for the fact that snow earlier in the season – which is also when snowfall is the heaviest – will have far less sea ice on which to land, and so will drop straight into the ocean. As a consequence, the amount of area that will have accumulated eight inches or more of snowfall by spring pupping season will decline by almost 70 percent during the 21st century, say the study's authors.
And even where snow does accumulate, building and maintaining caves will prove more difficult for ringed seals. Snow will melt earlier, so the lairs may not last until the young seals are old enough to venture out on their own.
As if all that weren't bad enough: more precipitation will fall as rain, which soaks into the snow and can cause the caves to collapse.
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Photograph: A ringed seal in its lair. Brendan Kelly/National Science Foundation