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Oceans: Some good news for wild salmon?

Wild sockeye salmon. Photo courtesy NOAA.

Study suggests there may be ways to reduce sea lice impacts on Pacific Northwest salmon populations

By Summit Voice

SUMMIT COUNTY — Canadian researchers claim a simple change in the timing of treatment for sea lice has promoted better health in both farmed and wild salmon populations along the British Columbia coast.

The University of Alberta study focused on salmon farming operations  inthe Broughton Archipelago, between the mainland and the northern tip of Vancouver Island. The researchers describe the area as the historic ground zero for studying the impacts of aquaculture on wild Pacific salmon.

During the past decade, salmon farmers in the area have gradually shifted the timing of anti-parasite treatments to the fall and winter months. As a result, there have been fewer sea lice in coastal waters as juvenile pink salmon migrate to sea in the spring. That may be helping populations of wild salmon recover.

The researchers estimated that by 2009 the mortality from sea lice for juvenile pink salmon moving out to sea through the Broughton Archipelago fell to less than 4 percent. This mortality estimate applies to the salmon that survive natural mortality such as predation.

During the early 2000’s sea lice associated with the Broughton salmon farms had a devastating effect, killing an estimated 90 per cent of the migrating wild juvenile salmon that were left after natural mortality had taken its toll.

Lead researcher Stephanie Peacock said that, because of their small size, juvenile pink salmon are highly susceptible to the effects of sea lice. 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.

Peacock says the fall and winter anti-parasite treatments greatly reduced louse numbers on the penned Atlantic salmon by the time wild juvenile pink salmon passed closed to the farming sites on the annual out migration from BC rivers to the ocean.

While changes to the parasiticide treatment schedule in the Broughton Archipelago show positive results, Peacock emphasizes 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,” Peacock said.

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