It's not about that at all. Think about it. I'll even give you a clear example.

A river gets 600 returning fish. This river needs 500 to meet escapement leaving 100 for harvest. By law, the tribes get 50 of these fish and sportsmen get the rest. Now, due to the method the tribes use, they will easily kill their 50 and probably more whereas the sportsmen would only kill (assuming everyone killed every fish they caught) a small percentage of their allotted 50. Face it, hook and line is no where near as effective as netting. In this scenario, let's say the sportsmen kill 20 of their allowed 50. That leaves 30 more fish to go spawn above and beyond what's needed for escapement. I think we all can agree that is a good thing. However, if the tribes are able to target all 100 fish (which they will) not only will they catch all 100, preventing any extras at all, but because of mismanagement, and the ability of nets in general, they will kill far more than their allowed 100. So in reality, the run is hurt worse.