If the effects you talk about are a river specific problem, then it is a problem with that river. If the problem is region wide, then it has to be something that every river has in common, like climate, oceans, or fishing presure (harvest).

When you take a river with little to no interfierence from man, and you still have a depleted stock, or an up and down pattern, then you must eliminate the things that can make it wrong.

You can't have harvest be a problem when you don't harvest any fish. Look at the Chum runs in the Tillamook district. I constantly refer back to the Nehalem as an indicator stock for wild steelhead. There are multilple reasons, but the best one is the lack of disruption from man. it is as pure as it can get. This River has good years and it has bad ones.

How can one explain the bumper crop of Coho the last two years? It sure as hell isn't going to be a habitat improvment that made these fish come back in good numbers to all areas. The habitat may have been an improving factor in some of the areas, but not every stream has had habitat improvments.

25,000 wild coho over the Willy falls. That river is a pit. it exceeds 80 degrees in the summer and is filled with raw sewage. You couldn't have a better example of poor habitat than the Willamette, yet these fish are popping up out of the clear blue. Why? The Ocean. It is the only factor that all coho share.