The center argues the Pacific walrus is threatened by climate change and should be added to the list of threatened or endangered species. The center wants stricter regulation of oil and gas development, shipping and greenhouse gas emissions that affect the Arctic. The center was among several environmental groups that successfully petitioned and sued to add polar bears to the threatened-species list last May. As with polar bears, melting Arctic sea ice is making it harder for walruses to survive, according to the group.