Sea otters have the densest fur of any mammal and, unlike most other marine mammals, replace their fur throughout the year instead of undergoing a seasonal molt (Tarasoff 1974; Williams and Allen et al., 1995). Sea otters have guard hairs and many fine under-hairs that are microscopically interlocked in order to trap air and thus provide waterproofing, thermal insulation, and buoyancy.

Have you ever spotted a sea otter hauled out on a rock and wondered if that meant the animal was sick?  Just like all wild animals sea otters have a set of normal behaviors including hauling out of the water. 

How do you know when a sea otter’s pelage has been fully restored? We know that sea otter’s rely on a unique form of thermal insulation among marine mammals. After being oiled and then washed, the natural oils that prevent the hairs from tangling and getting fouled with salts are washed away along with the oil.

It can sometimes be challenging to determine whether a sea otter has been oiled! Various other materials may be foul sea otter fur and this page describes how to distinguish between oil and other substances as well as how to collect oil samples.