I have tamed 6 of them so far, all found along the Redwoods beach and in the river. They are very small and look like small bearers underwater but are easy to spot on the beach. I've only ever encountered one at a time, and never in the same place. They are fairly easy to tame, just pike fish (I recommend using a high level pike- work smarter, not harder) and walk up to the otter with the fish. It will prompt you to feed the fish to the otter, he will make an animation, and the taming bar should show up at the bottom. Don't worry about losing taming effectiveness as you go around gathering more fish, I don't think I've noticed a problem yet. On an Official PVE server
Their a rare/ uncommon spawn. They are mainly found down south in max of a pair of two. But their usually found alone. They are a passive non-agressive tame that wont flee. (They wear hats too). Have fun!