The
Climate Conundrum
Baffin Bay Narwhals, Out in the Cold
The narwhals (Monodon monoceros) of Baffin Bay have a very different problem than polar bears do. In the past several decades, there has been an increase in surface ice on Baffin Bay during the winter. This puts narwhals at risk because, like all whales, they must periodically surface to breathe.
Global warming does not produce even heating all over the Earth, and Baffin Bay, which is between Greenland and Canada, is actually cooling slightly. Satellite data collected over the last two and a half decades shows a trend toward increasing ice coverage of the bay. Climate change models predict that this trend could continue for the next 50 years.
At least 85 percent of the world’s narwhals spend their winters in Baffin Bay. In the fall, about 50,000 narwhals migrate south from the high Arctic to two separate parts of Baffin Bay—the northern wintering grounds and the southern wintering grounds. There they spend six months gorging on fish, primarily the Greenland halibut (Reinhardtius hippoglossoides). Scientists believe that this winter feeding supplies the whales with the majority of their annual caloric intake.
When the whales arrive at their wintering grounds in late October or early November, about 40 percent or less of the surface is covered with ice. As the winter progresses, however, more and more of the surface freezes. Kristin L. Laidre, a post-doctoral research scientist, and Mads Peter Heide-Jørgensen, a senior scientist, both with the Greenland Institute of Natural Resources in Nuuk, Greenland, have studied satellite data from 1978 to 2001. They found that, on average, by mid-January, no more than 5 percent open water remains in both wintering grounds. By the end of March, on average, there is only 2 percent open water in the southern wintering grounds and only 0.5 percent open water in the northern wintering grounds.
With such a small fraction of the surface available for breathing, narwhals are very vulnerable to even small increases in ice. It might seem to the casual observer that male narwhals could use their long tusks to break breathing holes in the ice, but in reality they are unable to do so, and narwhals must breathe wherever they can find a natural opening. In severe cold snaps, hundreds of narwhals have become trapped at a single opening, and many of them eventually died as a result. If the amount of ice cover continues to increase, these "ice-entrapment events" could become more common.
Narwhals could avoid the problem by migrating farther south in Baffin Bay, where there is less ice. However, narwhals show remarkable fidelity to their wintering grounds, returning to the same location year after year, despite the lack of landmarks in the open water. In the past, narwhals did not alter their migration routes even when faced with intense hunting by indigenous populations, so it appears that they do not change their travel paths or destinations based on outside stimuli. Furthermore, there is always plenty of open water in the fall, when the whales select their wintering grounds.
Laidre notes that in the last two years, there has actually been less ice on Baffin Bay than usual. Only time will tell whether the climate models for that part of the Arctic are correct in predicting an increase in ice coverage. In the meantime, Laidre is continuing to study narwhals and keep an eye on ice trends in Baffin Bay.
—Mary-Russell Roberson
ZooGoer
34(4) 2005. Copyright 2005 Friends of the National Zoo.
All rights reserved.
