For salmon a certain % of jacks are added to the spawning. Bit more than in the stream as I have watched spawning and the jacks sneak right in while the big guys duke it out or if they are the only male. What we never understood is the hatchery % as way more jacks in hatchery adults than wild in fact you seldom see jacks get to sneak in the wild. They try like all get out but in adult fish fights size does matter!