No doubt the biggest issue is ocean survival. Most likely a combination of things like predation due to seals, hake and near shore food availability changes from changes to the ocean (acidity, temps etc).
At the SFAB South Coast meeting there were some very interesting science presentations on moving away from smolt release programs towards fry programs with fewer fish released. Seems that there is some recent work on coho fry release as opposed to smolt release that is showing higher (slightly) survival rates. There's nothing wrong with hatcheries per se, the thing that is wrong is flooding the ocean with smolts rather than trying to mimic mother nature as closely as possible to teach these fish some survival skills. I also saw some cool stuff showing the fry plant survival rate on the Puntlege River - they are now placing fry up in un-used habitat and seeing some good initial results.
Also interesting, they are playing with different smolt release timing (on those rivers with smolt programs) and finding that delayed release timing is working. Probably because the fish are coming out into the ocean after the predators have given up and moved on, or possibly there is more groceries to eat because they aren't in competition with all the other wild smolts migrating out in April and early May.
That is precisely the type of thinking that is going to result in finding some of the right keys to success, as opposed to what the Province of BC has done with their Ostrich (stick my head in sand) approach and doing nothing. Both extremes (full on hatchery smolt program or Ministry of Do Nothing) are simply wrong headed in my opinion. What we need is a balanced approach.