I haven't fished the Chehalis system as long as some, but started fishing it in the late 70's. Those late coho are really something and seem to have a pretty unique life history which their late return and extended time in the salt.
I've gotten out of the river fishing, but it seemed over time there were less and less of them at least in my experience. I'd have to believe a good number of them got taken out when there were more intense net fisheries for steelhead.
What is the current status of the late Chehalis system coho stocks?
SF