Which marine mammal is known for having the densest fur of any animal? The answer is the sea otter.
The sea otter has the densest fur of any animal, with an exceptionally thick undercoat that can contain up to about 150,000 hairs per square centimetre. Unlike most marine mammals, it has no insulating layer of blubber, so its fur is essential for surviving cold North Pacific waters.
Long guard hairs help keep water away from the soft underfur, where trapped air provides insulation. Because this system depends on cleanliness, sea otters spend substantial time grooming. Their loose skin and flexible bodies help them reach nearly every part of the coat, including areas that are difficult for many mammals to clean.
Sea otters are also important to coastal ecosystems. They eat sea urchins, crabs, molluscs, and other marine invertebrates, helping prevent sea urchins from overgrazing kelp forests. They are famous for using stones as tools to break open hard-shelled prey. Intensive fur hunting from 1741 to 1911 reduced their population drastically, and conservation programs later helped many populations recover.