I will take a shot at this although Salmo will correct me when I go off course or remind me that everybody knows that.

Stilly Chinook have been a long time coded wire tag indicator group for PSC ER assessment. They have been ad clipped and CWT'd since mid 1980's as I recall. Because they are used for fishery assessment, the ad clip coupled with the CWT has been the standard across many stocks and is part of the coastwise CWT sampling programs by a wide range of entities. Originally, samplers just looked for the ad clip and this would indicate that the snout would contain a CWT. With the advent of mass marking and the ease of fin clipping to designate hatchery fish (but not necessarily containing a CWT), sampling became more sophisticated to find those fish containing a CWT. This is where the electronic magnetic wands came into use to identify those fish with a CWT in the snout. The use of the wands have been phased in over time by the coastwide agencies. Washington was the first to use them in all fisheries for sampling both ad clipped and unmarked fish. Alaska used them for marked fish only. BC used them in the troll fisheries. In the Haida GWaii and Vancouver Island lodge sport fisheries ad clipped snouts were place in sampling buckets at the lodges and later picked up by CDFO to separate out the CWT'd snouts from the blanks. So coastwise sampling has kinda been a mixed bag (sorry) but an important part is that ad clipping was still important to distinguish fish that may contain a CWT.

The other key piece about mass marking was the fishery regulation benefits of having mark selective fisheries that allowed for harvesting hatchery fish while letting go the unmarked ("wild"). MSF regulations got the best bang for the buck because of the requirement to release unmarked fish while retaining hatchery fish. Therefore simply by switching from a standard "keep anything" fishery to MSF, the fishery could go longer and have higher harvest for the same number of dead unmarked. This is the standard MSF sales pitch.

Now come to Stilly, because the intent of the program is to get fishery information from as many fisheries as possible, ad clipping is necessary. Unmarked fish and any CWTs aren't kept in MSFs so you don't get any information from these even though you know that they are encountered. So for Stilly, ad clipping the fish allows you to get CWT information in keep-anything and MSF fisheries..which is what is intended. Of course the down side is that the ad clipped fish are harvested at a "hatchery fish" rate and the MSF regulation is no help and in fact aggravates the exploitation situation.

When the comanagers came up with the Stilly ER limits for unmarked and marked in So US. fisheries along with the total ER limit established by NMFS, they seemed to have selected a marked fish ER limit that is more restrictive than even the ESA NMFS limit. The other big downside is that with a more constraining marked fish ER limit, MSFs now become the bad guy and not a regulation that provides more access to harvestable hatchery fish. Hence, winter BM gone.

So going forward, not ad clipping the Stilly fish will diminish the fishery exploitation information from CWTS. But in so doing, Stilly fish would would be released in MSF because they were unmarked.

Let me just add, that there is a lot reluctance in management arenas to depart from long standing operations and data analysis systems. This especially holds true in PSC land. Compromising the CWT fishery information from the Stilly indicator group by not ad clipping would not go down easy.

Hope this helps. Salmo can fill in the missing pieces.


Final comment: This isn't really a PSC problem. Its the comanagers that have imposed a conservation constraint at a low run size that happens to be more restrictive than the ESA limit. And it happens to be on marked fish so MSF regulations make it worse. I can't think of any other instance where a comanagers conservation/recovery objective is more constraining than the ESA limit.