Iron Head -
remember that sea-run browns are much like steelhead, altantic salmon or our sea-run cutthroat in that they spend several years (usually 2?) in the rivers until they are large enough to migrate to the marine waters. This means they would be in direct competition with the native fishes of the river system for rearing space and food resources.

Don't know whether the sea-run adults on their spawning runs upstream feed much or not. However it seems that browns run up from lakes and/or lower rivers are still active feeders so it seems likely that there would be at least some active feeding. I'm sure that the post-spawn adults would be very active.

Tight lines
Smalma