Unfortunately, the cormorant hasn't been introduced to the practice of "Selective Harvest". It's likely their prey will be the slowest as the fishes scatter for "cover".
And, unfortunately, that may be the older/bigger fish!
Maybe pounding in a post within the bedding flat and adding a SCARECROW with wind energized FLAPPERS would discourage them.
It's not likely to discourage the "mating rituals" of the gills!