So far I have only encountered them on Rag. They tend to follow you out of the water from what I have experienced. They do drain stamina and induce torpor. So either run or kill it. I have explored most of Rags ocean (I only play Rag) and I haven't seen them anywhere else except for in Viking Bay by around the sunken ship. scariest creature to me so far do to it following me out of the water.