I think many inexperienced people want to see easy and simple answers, WitW:
There's
* many large-scale and localized environmental variables; including inriver habitat, riparian impacts, turbidity, water quality & water withdrawals,
different watershed sizes and dynamics, including access to anadromous species - or not,
* different sizes, species & life history stages and migratory routes of fish - each with their own needs and ways to capture them that may or may not work,
* many different agencies involved in regulating some of these numerous impacts,
* different fisheries management regimes between watersheds with only a few with inseason management - or none at all,
* many different ways to capture fish including both active & passive methods, including fixed and mobile gear - ALL with their strengths & weaknesses and places they can or can't be used. All and each have their installation, operating & maintenance costs, as well.
Fish traps are but only 1 way to capture fish out of dozens. And they have their very specific requirements about where they can be used. Fish wheels, likewise. Nets - both passive & active, likewise. Hooks & set gear, likewise. Electrofishing, likewise.
And nobody has yet to suggest how numerous communities with fishing fleets and other fish capture methods would transition & divide up fish caught in any such trap that like would be many km downstream or down the coast from each community - and how they would compensate their individual fishermen for giving up their livelihoods into some yet undetermined and unproven communal hand-out (after operating costs are taken out). And who gets to own the trap & the operating/maintenance costs and liabilities?
And that's another big highly unlikely unspoken assumption - that the numerous communities & their many fishermen both need and want this switch.
And it is highly unlikely that all communities on any river would be able to access and use fish traps. Fish traps (with piles) only work in low-gradient, soft sediment stretches where the sediment is some feet thick, and there isn't too much current. Fish wheels, on the other hand - only work in narrow canyons with bubbles/turbidity.
And then there is the bycatch issue. Many smaller watersheds on the coast have very clean runs of fish with minimal bycatch and no risks to any weak stocks. Not every watershed is as large and complicated as the Skeena or worse - the Fraser wrt weak stock management. Only naïve & inexperienced people wouldn't catch those differences.
Like I posted earlier - It is extremely naïve to expect any 1 type of fishing methodology to solve all the myriad of problems in any watershed.
But as long as any fisheries consultant is getting his fees to promote any asserted silver bullet - they will keep making that claim. I call that taking advantage of people's inexperience & ignorance.