A new study from the University of California Davis School of Veterinary Medicine found that sea lice is not responsible for the 2002 crash of the Broughton Archipelago wild pink salmon population in western Canada.
Published in the online journal Proceedings of the National Academy of Sciences this week, the study rules out sea lice but does not identify what caused the crash.
“For anybody concerned about the effect of farm salmon on wild salmon, this is good news,” said Gary Marty, a University of California Davis veterinary pathologist and the study’s lead author. “Sea lice from fish farms have no significant effect on wild salmon population productivity.”
The study claims to be the first to analyze 20 years of fish production data and 10 years of sea-lice counts from every Broughton Archipelago salmon farm and compare them against 60 years of population counts of adult pink salmon.
Record high numbers of pink salmon returned to spawn in Broughton Archipelago rivers in 2000 and 2001, but only 3 percent of that number returned in 2002 and only 12 percent in 2003. The environmental camp pointed to the spread of sea lice from farmed to wild salmon as the cause of the crash.
But Marty and his colleagues discovered that the pink salmon that returned in such low numbers in 2002 were exposed as juveniles to fewer sea lice than the fish that returned in record high numbers in 2001.
“Sea lice from farm fish could not have caused the 2002 wild salmon population crash,” said Marty, after examining, year by year, how many lice were on the farms when the pink salmon went to sea and how many of those salmon returned to spawn.
“The major lesson of this study is that we cannot settle for simple explanations for wild-animal population declines,” said Marty. “There are very complex interactions among disease, environment and animal population health. Sustainability studies must engage all the science specialties to pursue a better understanding of these relationships.”
None of the authors received compensation for the study, emphasized Marty. Sonja Saksida, director of the British Columbia Centre for Aquatic Health Sciences, and Terrance Quinn, professor of fish population dynamics at the Juneau Center of the School of Fisheries and Ocean Sciences at the University of Alaska Fairbanks, co-authored the study.
Marty is also the fish pathologist for the British Columbia Ministry of Agriculture and an affiliate faculty member of the University of Alaska School of Fisheries and Ocean Sciences. He said he has never worked for any fish farm company in Canada; in the United States, he consulted for the industry in 2000 and 2001. Since 2004, he has analyzed fish-farm samples for the British Columbia provincial government.
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