Sea Lice microscopic view (Photo: www.abdn.ac.uk)
Timing of sea lice treatments crucial to reduce infestation of wild salmon: study
Friday, November 16, 2012, 23:20 (GMT + 9)
Researchers from the University of Alberta have discovered how to help wild pink salmon in British Columbia (BC) recover from sea lice infestations.
The team found that by altering the timing of sea lice treatments, the Broughton Archipelago salmon farming region was able to boost the health of its farmed Atlantic salmon, thereby also helping the struggling population of wild pink salmon recover from sea lice.
The researchers chose Broughton Archipelago to conduct the study because it is considered the historic ground zero for analysing the impact of aquaculture on wild Pacific salmon stocks.
These results were published in this week’s issue of Ecological Applications.
Over the past 10 years, salmon farmers in the region have gradually shifted the timing of the anti-parasite treatment Slice to the fall and winter months so that there would be fewer sea lice in coastal waters at the time when juvenile pink salmon swim out to sea in the spring.
By 2009, researchers estimate that juvenile pink salmon’s mortality rate from sea lice when moving out to sea through the archipelago diminished to less than 4 per cent, even when accounting for the salmon that survive natural causes of death such as predation.
In contrast, sea lice linked to the Broughton salmon farms had an overwhelming effect on migrating wild juvenile salmon during the early 2000s, killing an estimated 90 per cent of the fish that survived natural mortality causes.
“[Slice is] a very effective drug for now in British Columbia, as long as it’s used at the right time,” said Stan Proboszcz, one of the authors of the paper and a biologist with Watershed Watch Salmon Society, The Globe and Mail reports.
Lead University of Alberta researcher Stephanie Peacock noted that juvenile pink salmon are especially susceptible to the effects of sea lice because of their small size.
“During a period in their life cycle, lice are free-living and are easily swept out of fish farming enclosures into the path of migrating wild fish,” said Peacock.
The researchers determined that the new pattern of applying anti-parasite treatments in the fall and winter greatly reduced louse numbers on the penned Atlantic salmon by the time wild juvenile pink salmon swam past the farming sites every year.
Still, Peacock recognised there are still some concerns.
“The ecological effects of anti-parasite chemicals are poorly understood, and lice have developed resistance to parasite treatments in other salmon farming regions,” she stressed. “Government regulators should take note of this independent research and consider adjusting sea lice management regulations accordingly.”
Mary Ellen Walling, executive director of the BC Salmon Farmers Association (BCSFA), said farmers are also aware of the risk that sea lice could develop a resistance to the treatment, so they are applying the chemical in small amounts as a preventative measure.
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