The new study, to be published online this week in Proceedings of the National Academy of Sciences, does not determine what caused the crash, but it acquits the prime suspect: small skin parasites called sea lice.

The study's lead author is Gary Marty, a veterinary pathologist and research associate at the UC Davis School of Veterinary Medicine. An expert in fish diseases, Marty has been studying the health of pink salmon since the 1989 Exxon Valdez oil spill in Alaska.

"For anybody concerned about the effect of farm salmon on wild salmon, this is good news," Marty said. "Sea lice from fish farms have no significant effect on wild salmon population productivity."

The new study is the first to analyze 20 years of fish production data and 10 years of sea-lice counts from every salmon farm in the Broughton Archipelago and compare them against 60 years of population counts of adult pink salmon.