It all gets caught up in impacts. The Nisqually and Puyallup have wild stocks of Falls that limit fisheries, even in the river. Unless you fish very selectively, a method with zero mortality, there will be that surplus at the hatchery.

Back in the 70s WDF was getting surpluses at the Chinook hatcheries, particularly in streams with good hatcheries but wild management (such as the Green). They reduced the problem of surpluses by reducing the escapement goal. There is a balance point, easily calculated, that would match the wild run with how large the hatchery program should be to not have surpluses. Unfortunately, on many of our streams, the wild run is so small that not much artificial production should occur.