Iced In
Climate shifts could be creating death traps for Arctic narwhals
When hunters spotted nearly 100 narwhals trapped in a tiny patch of ice-enclosed ocean off Greenland in the fall of 2009, the news attracted little notice. To narwhal specialists, however, it seemed a little strange. Although ice entrapments were known to routinely kill narwhals on their wintering grounds in the early spring, the Greenland entrapment was one of a string to occur on their summering grounds in the late fall. Now, a new study finds that the odd entrapments may be linked to a changing Arctic climate.
In all, an international team looked at four entrapment events between 2008 and 2010. “In each case, large groups (40–600 individuals) succumbed in the sea ice at three separate summering localities, two of these where entrapments had never before been reported,” they write in Polar Biology.
One idea was that that the whales might be becoming more vulnerable to entrapment because they were lingering longer in ice-free summering waters. To see if that concept had legs, the researchers used satellite and weather data to track changes in the “freeze-up” dates in the six largest narwhal summering areas. Overall, they found that over a 31-year period, autumn freeze-up has been coming later and later – slipping, on average, by one-half to one day per year, or 2-4 weeks over the 31-year span. “This indicates that sea ice conditions on narwhal summering areas are changing rapidly,” they note.
“The question still remains,” however, “whether the four recent ice entrapments are due to random variation in narwhal residence time in summer areas, or whether there is an actual trend in prolonged summer residence time as narwhals adapt to a longer open water season.” Rapid changes in weather and ice conditions “do not always trigger narwhals to move into open water areas,” they note, but more study will be needed to understand whether the whales are simply unprepared for the new world climate change is bringing their way. – David Malakoff | December 4, 2011
Source: Laidre, K., Heide-Jørgensen, M., Stern, H., & Richard, P. (2011). Unusual narwhal sea ice entrapments and delayed autumn freeze-up trends. Polar Biology, 35 (1), 149-154 DOI: 10.1007/s00300-011-1036-8
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