No other porpoises or whales spend much time in the heavily ice-covered regions in the winter, meaning the narwhals face little competition for the Greenland halibut and squid that make up most of their diet.
But as the Arctic warms, different predator species could move in while prey species may move out.
Scientists are concerned that narwhals will be unable to adapt to rapid changes in their ecosystem.
"A contrast is the beluga whale, which is similar to the narwhal but able to exploit many different kinds of habitat in the Arctic and feed on many different kinds of prey species," Laidre said.
Whether or when the changing habitat might drive the narwhal to extinction, she added, is unknown.
Even if most of the population dies out, a few pockets of suitable habitat could remain indefinitely.
The World Conservation Union lists the narwhal as "data deficient" because too little is currently known about its population status. The animal is also not listed as a threatened or endangered species under the U.S. Endangered Species Act.
Laidre noted that the species' conservation status is outside the scope of her team's assessment.
Should a petition be filed, however, the process may prove less contentious than the current proposal to designate the polar bear as an endangered species, said Kassie Siegel, climate program director with the Center for Biological Diversity in Joshua Tree, California.
Yesterday Siegel's organization won a lawsuit against the U.S. government that requires the Bush Administration to decide by May 15 whether to list the bears.
In its suit, the center alleged that oil and gas development in polar bear habitat has been taking precedence over actions to protect the species.
But the narwhal is found primarily outside U.S. territory, so listing it in the U.S. would offer the animals fewer protections from actions such as offshore drilling.
"We don't have that kind of control over the habitat of the narwhal," Siegel said. "So it wouldn't be as big a deal."
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