7B is Bellingham Bay is a a fishery directed at Nooksack/Samish Chinook. Interceptions of NS fish would be of concern. 7" minimum mesh would pass any encountered immatures.

The Chum fishery occurs after the adult Chinook have passed. Chinook taken are (were) estimated as 10% (7) and 5% (7A) of WA origin with each stock present in its whole-sound strength. Chum fisheries are conducted with 6 or 6.5" minimum which again passes Chinook.

There is pretty good daily catch data from the 60s on, by gear, by day for those fisheries and they include the number caught and average weight.

Not to say interceptions of black mouth don't happen, but generally at negligible levels. Since they are known and have a long track record they have surely been looked at.