I'm definitely not qualified to answer that question, but since you asked for my opinion, I'll give you my opinion.
There are a suite of survival filters for any salmonid. I'm sure you've probably taken a look at the document that was done for the Pacific Salmon Commission this past summer, the summary of the weight of evidence for the mostly downward trend in productivity in the Fraser stocks. I think they identified a number of very likely survival filters, including disease, either natural or from anthropogenic activities; competition in the open ocean; competition in the watershed; and, very much, the marine environment.
While we had a perfect storm in 2009, I think everything hit “all systems go” in 2010.