A new UC Davis study contradicts earlier reports that salmon farms were responsible for the 2002 population crash of wild pink salmon in the Broughton Archipelago of western Canada.
The Broughton crash has become a rallying event for people concerned about the potential environmental effects of open-net salmon farming, which has become a $10 billion industry worldwide, producing nearly 1.5 million tons of fish annually.
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.
The study concludes that farm fish are indeed the main source of sea lice on the area's juvenile wild pink salmon, but it found no statistical correlation between lice levels on the farms and the lifetime survival of wild pink salmon populations.
Pink salmon (Oncorhynchus gorbuscha) are the most abundant wild salmon species in the Broughton Archipelago. When they are a few months old, juvenile pink salmon leave the streams where they were born. They mature at sea, then return to their native streams to spawn and die two years after their parents.
Because of their two-year lifespans
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University of California - Davis