Sea otters and River Otters are quite different species and they live in very different habitats. My understanding is that Sea Otters don't really travel very far. They have serious predator and there are large gaps in kelp Forrests so they ~stick a kelp bed that they like and live there. River otters in contrast are ~the apex predator of a river and have a pretty extensive range. A river otter traveling 100 miles is not uncommon.

Sadly the sea otter populations were decimated by Russian and later American hunters in the 19th century and never really recovered. My understanding (limited to California) is that the southern sea otter was thought to be extinct until they found a population in Big Sur. They have since been slowly trying to expand its range north, but 80 years on and they have not gone much farther than the Northern end of the Monterrey bay. I suspect that with enough time and patience the Sea Otter will slowly be reintroduced along the entire coast, but it will take a while.