Sea otters are fortunate in that they have few natural predators. Killer whales will prey on sea otters but appear to prefer blubber-laden seals, porpoises and dolphins. Bald eagles also take sea otters, often providing their offspring with sea otter pups. Starvation is the greatest source of mortality in sea otter populations which have grown beyond the capacity of their habitat to support them. Female sea otters have one pup per year, but the low mortality rate, coupled with an abundance of resources, allows most sea otter pups born in Canadian waters to survive.
Sea otters are the smallest of marine mammals.
An adult male may weigh up to 40 kg. Sea otters lack the thick layer of blubber found in most marine mammals and depend upon a dense fur coat and high metabolic rate to maintain body heat in the chilly north Pacific. Their high metabolic rate requires that sea otters eat up to one-third of their weight in food each day. In British Columbia, sea otters act as a keystone predator, a species that exerts a strong influence on the nearshore community, affecting its structure and biological diversity. In particular, sea otters feed on herbivorous invertebrates such as sea urchins, which graze intensely on seaweed and soft-bodied invertebrates.