The fish is going to die anyway, so he would be just as well to have kept her and taken all of the eggs... he basically killed the fish for 1/4 of her eggs, so overall he will probably kill 4 times the number of fish that anyone else would for the same number of eggs.
...I'm not even going to start on the fact that he is wasting the salmon eggs if he is going to use them for steelhead....you can get 'em with salmon roe, but there are lots of better things he can be using.