The loss of arctic sea ice is bad for walrus populations, which means the walrus may soon be listed under the Endangered Species Act (ESA).

Though drops in walrus population haven't been documented, scientists and Natives are afraid the ripple effects of climate change could thin walrus numbers.

Walrus need to rest on sea ice no more than 400 feet above the ocean floor so they can dive down to eat shellfish and plants. But sea ice is retreating so far north that the waters are too deep for walrus to feed. This forces them to squeeze onto land, and last summer about 4,000 young walruses were trampled to death by males in the crowded conditions.

"On land, they are really vulnerable to predators and to being trampled by big males; when a human or polar bear shows up, they panic and stampede," said Shaye Wolf, a staff biologist for the Center for Biological Diversity, which is petitioning for an Endangered Species Act listing for the walrus.

The Center for Biological diversity is the same group that successfully petitioned the Fish & Wildlife Service to list the polar bear as a threatened species under the ESA.