For those who believe in natural selection, consider that hatchery fish are harvested at high rates. Used to be over 90%, maybe still is. That means only 10% of the total return actually make it to the hatchery and of that ben less are spawned.

What do they spawn? What makes it back. The fish that didn't bite, the fish that blew through the net fisheries, the fish fish that swam through the nets (too small or too big), the fish that returned after fishing closed, and so on.

It should come as no surprise, especially in a high harvest situation, that what is left evolves to not get caught. That is why, in a lot of places, we have wild coho that spawn in January and February.