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Sea Lice Information

"Salmon farming has potential negative implications for its surroundings, including wild salmon. Addressing the sea lice challenge is one of the most important tasks for the salmon farming industry worldwide."

- Marine Harvest Sustainability Report 2008


What are sea lice?

The sea louse is an external parasite, living on the skin of many marine fishes in all oceans. Although there are several species of sea lice, the most common found in BC is the Lepeophtheirus salmonis and Caligus clemensi species.

Where do sea lice come from?

Sea lice are naturally occurring on many wild fish species - fishermen know that a healthy adult wild salmon can host several sea lice. When introduced into saltwater, our farm-raised salmon are free of sea lice (farmed salmon spend their first year in freshwater hatcheries and sea lice do not survive in freshwater), but as they grow, infection does occur as sea lice may be transferred to our farmed salmon from wild sources in the marine environment such as Pacific herring and mature wild salmon.

Why do we manage sea lice on our farmed salmon?

For farm-raised salmon in British Columbia, sea lice rarely reach levels where the health of the fish is compromised. A greater concern in British Columbia at present is the potential for farmed salmon, once infected by wild fish sources, to then be a source of infection to small juvenile salmon as they annually migrate to the open ocean in the spring.

Wherever salmon are farmed, sea lice and salmon must be managed to ensure the health and well being of both our fish as well as wild fish. At Marine Harvest Canada, we acknowledge that under certain circumstances, sea lice of farm origin can present a threat to juvenile wild fish. We focus our actions to minimize this risk and have implemented several direct and indirect measures to support conservation concerns for wild salmon.

What is the risk of sea lice to wild salmon?

It has been documented that high sea lice loads may kill individual wild fish, but the definition of high will depend on sea louse stage, fish size, fish species and developmental stage. Although early reports suggested mortality at one louse per gram, in controlled lab experiments Dr. Simon Jones (Jones et al 2008) has measured the actual risk to Pink salmon (Oncorhynchus gorbuscha) at a weight less than 0.7 grams and a load of 3-4 sea lice. When larger than 0.7 grams in size, the Pink salmon has developed an effective immune system and is able to shed lice and therefore is at little risk. Marine Harvest Canada continues to be a part of scientific research on this matter.

The level of risk to juveniles of other species of salmon (Sockeye, Chinook, Coho and Chum) has not been intensively researched. Even so, Marine Harvest Canada continues to adapt its operations to reduce transfer of sea lice to juvenile wild salmon, thus minimizing the risk from its salmon farms.

How do we monitor for sea lice?

Routine monitoring of our fish provides early information as to the presence of sea lice. Each month, we randomly select 60 salmon from each operating fish farm and check for the presence of sea lice. This data is collected through the entire saltwater lifecycle and reported to Fisheries and Oceans Canada. View the video on our sea lice management program.

Non-medicinal approaches for lice control.

Marine Harvest Canada has many years of experience in preventing and controlling sea lice but is continuously working to develop more effective tools for lice control.

Non-medicinal management tools are firmly integrated into husbandry, production management and planning, including synchronized fallowing, attention to clean nets and maximum stocking densities.

Do we use medicinal treatments to control sea lice?

We believe it is important to maximize the application of non-medicinal tools to control sea lice. While such tools have made a major contribution to the control of sea lice populations in recent years, medicinal treatments are required to maintain control and even the best managed farms may require the use of medicines from time to time in a coordinated and efficient way.

Strategically timed and coordinated use of SLICE® (emamectin benzoate) within appropriate biological areas, where companies develop their treatment strategies in consultation with others, has proved to be a necessary and successful approach to managing sea lice. By instigating a coordinated, synchronous and strategic treatment during the winter, sea lice levels are minimized.

Treatments are rare and only occurring once or twice during a farm-raised salmon’s lifecycle. In 2008, just 0.254 grams of emamectin benzoate was used per metric tonne of salmon produced at Marine Harvest Canada.

What are the results of our sea lice management program?

In British Columbia, we have been actively managing our farms to minimize risk to wild salmon. These actions are complimentary to natural environmental controls, such as temperature and salinity, with the result that sea lice prevalence during the March to June smolt migration period has been greatly reduced in areas where we operate. The Pacific Salmon Forum acknowledges this reduction of sea lice prevalence in their 2009 final report.

Recent research by Fisheries and Oceans Canada (FOC) has shown that the proportion of wild Pink salmon juveniles at risk from sea lice declined from 4.5% to 0% between 2005 and 2009 in the Broughton Archipelago region. In the spring of 2008, there were no recorded lethal infections of Lepeophtheirus salmonis on Pink salmon less than 0.7 grams in this region (lethal size thresholds based on published laboratory trials). In 2009, similar observations show that no Pink salmon less than 0.7 grams were at risk to Lepeophtheirus salmonis.


Fisheries and Oceans Canada publicly reports BC farmed salmon sea lice data quarterly here: view reports

Sea lice research

Stemming from a related collaborative initiated by Marine Harvest Canada (MHC) and the Coastal Alliance for Aquaculture Reform, the Broughton Area Monitoring Plan has brought together co-sponsors and scientists from Fisheries and Oceans Canada, the three largest salmon farming operators in BC (MHC, Mainstream Canada and Grieg Seafood), academic researcher Dr. Martin Krkosek and the professor of Epidemiology with the University of Prince Edward Island, Dr. Crawford Revie.

The Broughton Archipelago Monitoring Plan began in 2010 as a multi-year sea lice monitoring and research program involving federal government, salmon farm producers, conservationists and academic researchers. For more information about this unique research project, please visit www.bamp.ca.