Study suggests sea lice on salmon is under-reported at B.C. salmon farms

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By Milthon Lujan

Canada – A new study, published this week in Ecological Applications, shows striking evidence that counts of parasitic sea lice are under-reported by British Columbia’s salmon farms.

Salmon farms in B.C. regularly count the number of parasitic sea lice on their fish, and if these counts are high enough, the farms are required by their license conditions to perform costly delousing treatments. These policies are in place to prevent the spread of sea lice to vulnerable wild salmon.

Sean Godwin, a PhD student at SFU at the time of the research (currently a Liber Ero Fellow at Dalhousie University) and the study’s lead author, says that the Department of Fisheries and Oceans Canada (DFO) tries to ensure the accuracy of these sea louse counts by performing occasional, pre-arranged audits of the counting process, but that these audits aren’t enough.

“Our team found that when DFO is auditing the farms, industry counts increased, on average, by almost 20 per cent for one species of sea louse, and nearly doubled for the other species,” says Godwin. “So when DFO is not auditing, which is most of the time, the reported industry counts seem to be underestimates.”

Sea lice have previously been linked to declines in wild salmon populations in B.C. “This study’s findings therefore have major implications for wild salmon,” says SFU professor emeritus Larry Dill, a fellow of the Royal Society of Canada.

“Assuming sea lice aren’t attracted to the fish farms by the presence of DFO employees, these results strongly suggest that counts by industry staff are much less accurate when someone’s not looking over their shoulders. The risk to wild salmon is therefore greater than the aquaculture industry would have the public believe, emphasizing the need for greater oversight and regulation,” says Dill.

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The study authors provide several potential solutions to increase the reliability of sea louse counts on B.C. salmon farms, including a shift to independent third-party monitoring.

Dill says the results come in a key month for B.C. salmon farming, with a September 30 deadline looming for the removal of salmon farms from a critical wild salmon migration route unless the farms pose “at most a minimal risk of serious harm” to these fish. The Cohen Commission—the $37-million federal inquiry that set this deadline—also recommended the collection of pathogen data from salmon farms, but it did not consider the accuracy of this information.

Godwin, S.C., Krkošek, M., Reynolds, J.D. and Bateman, A.W. (2020), Bias in self‐reported parasite data from the salmon farming industry. Ecol Appl. Accepted Author Manuscript. doi:10.1002/eap.2226 

Source: Simon Fraser University

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