Sea otters are the smallest marine mammals and are a part of the weasel or mustelid family. In California, females reach 35-60 pounds, males 90 pounds, and pups when born are around 3-5 pounds. Unlike most marine mammals, sea otters do not have a blubber layer to help keep them warm in the chilled waters of the Pacific. Instead of blubber, sea otters have the densest fur of any mammal. Their fur is so dense, there are about a million hairs in every square inch of their body. Besides just being extremely dense there are also two layers to their fur making their fur 1.5 inches thick when dry. Sea otter fur has an undercoat and a longer top guard coat. This double layer works extremely well in trapping air thus preventing water from ever making contact with the sea otters skin. In order to keep air trapped sea otters need to keep their fur pristine, this means constantly cleaning their fur.
To add air to their undercoat sea otters will lay on their backs in the water and tilt their head down toward their stomach where they then blow air into their fur. In addition to staying warm, this helps increase buoyancy that can help the sea otter swim heavier objects up from the bottom of the ocean. Sea otter pups are born with a special coat that acts like a lifejacket and prevents them from being able to dive. At two months old the pup sheds this special coat.
The special qualities of sea otter fur made it a desired resource in the 18th and 19th centuries and they were hunted nearly to extinction. In response, sea otters were made one of the first marine mammals protected in the state of California in 1913. Sea otters are still a threatened species in the state of California and today 100,000 to 150,000 are protected by law.
Allen G.S., Mortenson J., and Webb S. 2011. Guide to Marine Mammals of the Pacific Coast. Los Angeles, CA: University of California Press.