Their fur is very dense, otter fur has more hairs per square inch than any other mammal, a million per square inch, like a hundred times what humans have. The oils excreted into their fur creates a hydrophobic layer that keeps the water on the outside. It's in nowhere near shark skin (which exhibits incredibe hydrodynamics, like we're studying it in labs to better improve aerodynamics of cars and planes, a single bite of food is enough to get a great white shark from California to Japan their skin is so efficient at moving through water), but it's very good at keeping the water out and their movement efficient, their hair does not cause Resistance like human hair does. Our hair hangs out and gets water in it and creates drag, otter hair seals itself around the meat and creates a cylinder, keeping happy warm dry otter inside.
I got the treat of touching/petting a wild otter while it was sedated, it's on of my top 10 experiences. It was not a happy camper when it woke up. It had to be in an ice bath while sedated otherwise it's hair/fur coat would've caused it to overheat while being knocked out because it is incapable of homeostatic regulation while sedated. When it woke up it was a wild otter in an ice bath, lil (haha, huge actually) dude was pissed.
Huh, thanks for the detailed reply! I suspected some of them must have something extra going on to help their time in the water, but wouldn't have thought this!
Were you able to feel how dry the otter was through the sealed fur, or was it sealed enough that you couldn't really tell?
I've never felt one under water, nor did I try to go skin deep when I had my opportunity, but I would guess they're pretty dry under there, I couldn't say for sure though.