I have to agree with our Norwegian friend that the "law of unintended consequences" is a b$#%^. Introducing any no native species to a BOW where escape/release to another BOW is not only possible, but very likely is a bit reckless. Who knows what effect the fish could have on a local ecosystem? You just don't know what can happen and because of that I can not recommend you releasing them to the river.

I think the pinks would probably undergo severe predation in your pond as they will be at a competitive disadvantage to your actual established fish populations. As you said you think the birds already put a hurting on them.

If I was in your shoes I would have put the fish in my pond, just bc it would be cool as hell to have a pink salmon population in a pond! Then I would pull a quick "What have I done" and hope they don't survive. As I stated above it is probably for the best that they do not survive as a non-native anadromous fish species could create a real problem.