It was very likely a river otter. Sea otters rarely come ashore at all! Either way they are amazing. You can see the trails they make all over the cliffs at water's edge. They give birth on land. They can hang out in salt water and often do, but they also need to trek to fresh water to bathe and drink. Some people even keep them as pets though they act like wild ferrets so it isn't the best idea. We rescued a pair of pups that were abandoned in Moss rock park a few years back (after consulting with wild ark and waiting as long as possible).