Why must sea otters groom their fur so carefully?

Sea otters must groom their fur meticulously because it is their primary method of insulation against the cold, as they lack the thick layer of blubber found in other marine mammals.1

Their fur is the densest in the animal kingdom, featuring specialized guard hairs that interlock like scales to create a waterproof barrier, while soft underhairs trap air near the skin for warmth. Grooming is essential to maintain the integrity of this coat; any matting or damage allows water to penetrate the fur and reach the skin, which can lead to fatal hypothermia. Because diving compresses the air within their fur, otters also groom to work air back into the coat, ensuring its protective layers remain effective. Consequently, sea otters spend nearly one-third of their day maintaining their fur to survive in near-freezing waters.1