Glad you found that study, Steel4life.
I don't know the specifics of that, but I do know there is active research happening to determine if the non-native Skamania strain (summer run steelhead) are spawning with and diluting out the small run of native winter run fish.
The Army Corps has promoted the summer run plants as partial remediation for the dams that cut off spawning grounds to the native fish. Not very logical since there wasn't any summer runs in the Willy valley before the dams, but lots of us do enjoy catching them. Anyway they seem to favor the status quo.
Other groups are wondering if the relatively large numbers of non native summer run fish are having a negative influence on the winter runs. So, ODFW is spending some considerable time and resources to find out how much interbreeding is happening. Hopefully the science will show very little and both runs can continue. If not, say goodbye to town run fishing in the summer.
We shall see.
Best,