Was told by a biologist in Alpena Michigan several years ago the the brown trout planted had a survival rate of only 1/10th of 1 percent in Thunder Bay thanks to the cormorants and walleye. He said the cormorants actually could be seen chasing down the brown trout right after they were planted. They used to have a brown trout festival in Alpena as the brown trout fishing in the bay was phenomenal. Not sure if they do anymore.
I deal with another species of predatory bird on my fish farm: Great Blue Herons. I pay a hundred dollars a year for a federal permit to take the ones out that don't respond to nonlethal measures.
Here's a brook trout that was too big to swallow so the bird just kept pecking at it. This was a week ago. The light areas are due to leaves that the fish rolled in as the bird impaled it. Needless to say the bird is no longer with us as he made the mistake of coming back for another try. I was ready with a goose load to reach out and touch someone.