You left out the most important fact that the Cultus Lake Sockeye Salmon, which left the Fraser River and headed out through the Salish Sea to the Pacific Ocean, came back in record numbers. Why??
Conclusion is that because these fish did not have to swin pass the gauntlet of over 140 odd desease breeding Salmon fish farms that line the northern migratory route. Thus their survival rate was extremely high.

Cheers, Rod