So a little twist on the feeding idea. It is obvious they are willing to 'eat' while in fresh water, but that doesn't mean they are feeding. Just like with most other animals, etc., when it comes to breeding and continuing the life cycle, there is a distinct advantage when you wipe out the competition via any means available. With fish, the easiest way to do that is to suck down the competition's eggs, leaving more space, food, river for your own offspring. As far as birds and other little smolts or what have you, the steelie may be in protection mode knowing those are threats to it's redd.

This would seem to have a potential to hold water since there doesn't seem to be a lot of digestion going on, but plenty of eating.