The first sighting was in Fairbanks which is a long way from the sea but close enough to plenty of rivers and open lakes in summer. Yet this creature will be quite up to grabbing any deer it wishes. Otherwise i expect this creature to be adept at nocturnal underwater fishing to make its ordinary living.
Recall that with insulation you can dive into freezing water and work with a stable temperature regime not available up in the air. so this is not so far fetched as it looks at first glance. It also establishes a natural global range.