A study to be published this week by the U.S. National Academy of Sciences suggests sea lice, cited as the key reason for the drop in wild salmon returns, were not the cause of one of the largest declines in pink salmon at the Broughton archipelago in 2002.
The massive decline at Broughton 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.
Gary Marty, a veterinary pathologist and research associate at the UC Davis School of Veterinary Medicine as well as the study’s lead author, said, “Sea lice from fish farms have no significant effect on wild salmon population productivity.”
His study analyzed 20 years of fish production data and a decade of sea lice counts from every salmon farm in the Broughton archipelago and compared them against 60 years of population counts of adult, wild pink salmon. Marty and his colleagues compared sea lice levels from each farm when the young pink salmon went to sea and how many of those salmon returned to spawn.
According to his analysis, sea lice could not have caused the decline in pink salmon in 2002, when only 3% returned to the area.
“The salmon that returned in such low numbers in 2002 were exposed as juveniles to fewer sea lice than were salmon that returned in record numbers in 2001. Sea lice from farm fish could not have caused the 2002 wild salmon population crash.”
While much of the same data was used in previous studies, the UC Davis study reached different conclusions because fish farmers provided their records, and the old and new data were analyzed using common veterinary methods not used in many of the previous studies.
“The major lesson of this study is that we cannot settle for simple explanations for wild-animal population declines. There are very complex interactions among disease, environment and animal population health.”
B.C. salmon farmers were happy with the study’s findings. Mary Ellen Walling, executive director of the BC Salmon Farmers Association, said, “It really shows, based on more information than ever, that properly managed sea lice are not the concern.”