The agency said the review for the ribbon seals, known for the distinctive black-and-white swirls on their fur, is warranted because the animals need seasonal sea ice to give birth to their young and to rest while moulting.

"Ribbon seals depend on sea ice in the Bering Sea for important life events in the springtime," said John Bengtson, director of NFMS' National Marine Mammal Laboratory.

The agency will also proactively evaluate the status of the three other types of Arctic seals that dwell in the icy waters off Alaska -- the bearded, spotted and ringed seals -- to see whether new protections are warranted for them as well.

"It seemed prudent. They all interact with the ice in different ways," said Bengtson.

Ribbon seals dwell in the waters between Alaska and eastern Siberia. Unlike other Alaskan seals, which rely on semi-permanent ice in the Arctic Ocean, ribbon seals depend entirely on ice that forms each winter in the Bering and Okhotsk Seas but melts in the summer, Bengtson said.

There are no reliable population estimates for any of the four ice-dependent seal species, but past estimates have put the US population at 100,000 to 300,000 for each type of seal, according to the agency.

"Any Arctic scientist paying attention knows it's not just the polar bear, it's not just the ribbon seal, it's the entire ecosystem and all of the species are in trouble," said Brendan Cummings, oceans program director for the Centre for Biological Diversity.

The Centre for Biological Diversity last week notified NMFS that it intended to sue the agency over its missed deadline for an initial response to the ribbon seal petition. Now there will be no need for such a lawsuit, the environmental group said.

The organization, along with other environmental groups, has also petitioned for an Endangered Species Act listing for the Pacific walrus and yellow-billed loon.