Sea lice myths disspelled

Odd Grydeland
Published Modified

Odd Grydeland

While Environmental Non-Government Organizations (ENGO's) in North America have been quick to use the experience of sea lice researchers in Europe to point fingers at the B.C. salmon farming industry, research conducted by scientists from the Canadian Department of Fisheries and Oceans show that the Salmon louse Lepeoptheirus salmonis behave quite differently in the Pacific Ocean compared with lice in the Atlantic. There are also genetic differences between the two lice populations, according to two published studies.

At an aquaculture conference in Campbell River last week, Dr. Sonja Saksida from the BC Centre for Aquatic Health Sciences delivered a presentation entitled "Mythbusters- Sea Lice in British Columbia". ENGO's claims of extremely high mortalities in juvenile pink salmon exposed to 1-2 lice per fish has been soundly dismissed. The smallest of pink salmon fry (under 0.7 gram) suffered mortality at infection intensities of 4.7 lice per fish on the average, while fish larger than 0.7 gram showed little or no mortality associated with sea lice. Some of the published studies;

Jones et al (2006) Journal of Fish Diseases;
• Lab study- salmon >1.5g exposed to 155 to 271 copepodids 
0% mortality. Infection declined over time
Webster et al (2007) Canadian Journal of Fisheries and Aquatic Sciences
• Lab study- Pink salmon >0.6g exposed to bath with 4000 copepodid
0% mortality. Levels decreased over time
Jones et al (2007) Diseases of Aquatic Organisms
• Lab study- 19g fish exposed to 243 to 735 sea lice copepodid
0% mortality. Pacific salmon are relatively more resistant to L.salmonis than Atlantic salmon (in Europe). Infections densities of L.salmonis on pink and chum salmon are reduced more rapidly than on Atlantic salmon (in Europe). Pinks appear to be highly resistent to infection
Jones et al (2008) Journal of Fish Diseases
• Lab study- Pink salmon 0.3g, 0.7g and 2.4g exposed to 25 to 100 copepodids 
35% mortality in smallest fish (mean intensity of 4.7lice). 5% in the midsize fish and 0 in the largest fish

Dr. Saksida also stated that other ongoing studies are showing the same results.

Treatments of farmed Atlantic salmon is made mandatory in B.C. when fish are found to have 3 or more motile L. salmonis per fish- a trigger that is lower than other salmon farming jurisdictions. Despite this, salmon farmers in B.C. are applying on average 1.4 treatments of Atlantic salmon per generation, while farmers in Norway apply over 3 treatments, Scotland over 4, and both Ireland and Chile apply treatments for sea lice at least 6 times per generation.
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