Scientific Evidence of Sea Lice from Fishfarms Seriously Harming Wild Stocks



“THERE IS NO DOUBT THAT SALMON FARMS PRODUCING SEA-LICE ARE THE MAJOR CONTRIBUTING FACTOR TO THE SEA-TROUT COLLAPSE.” Dr. Paddy Gargan, Senior Research Officer for Ireland’s Central Fisheries Board 2003. see study which supported this conclusion (2002)

“Despite the initiatives undertaken both in the freshwater and marine environment since 1990, there has not been a recovery of sea trout stocks along the western [Irish] seaboard. . . . Sea trout continue to be recorded annually with heavy sea lice infestations ONLY in rivers entering bays with salmon aquaculture.” Central and Regional Fisheries Boards (Ireland) – ‘Action Plan for Sustainable Management and Development of Salmon Aquaculture and Sea Trout Fisheries’, p. 6, February 2001.

“The board has considered everything in its efforts to establish a cause for the decline in wild-fish stocks; forestry, over-grazing, angling, but it all came down to one thing – sea-lice emanating from salmon farms.” Mr Michael Kennedy, of the Irish Western Regional Fisheries Board, 2003.

“Sea-trout fishing was sustainable and eco-friendly, but the salmon farms killed it off within a decade.” Peter Mantle, who owned a wild salmon and sea-trout sport fishery in Delphi on the west coast of Ireland, 2002. (this last example is not scientific but one of many anecdotal experiences)


In 1999 Professor David McKay, a regional director of the Scottish Environmental Protection Agency, told a Norwegian conference it should be accepted “beyond reasonable doubt” that sea lice from salmon farms were killing sea trout returning to Scotland.

Two Scottish studies use the fact that in Scotland all the fishfarms in some areas start their two year production cycle at the same time. The number of sea lice in the fishfarm pens is low in the first year and greatest in the second year when the farmed fish are larger.

James R. A. Butler et al. (2001) analyzed three years of data from five rivers and found that wild fish sea lice infestations were related to salmon farm production cycles.

  • Scotland’s Fisheries Research Services further analyzed this relationship and found the amount of wild sea trout infested with immature lice rose from zero to 75 percent during the second year of the production cycle at local salmon farms.2002


P.A., Bjørn, B. Finstad and R. Kristoffersen did a study (2001) in Norway and found that: “…salmon lice infection on wild sea trout and Arctic char differed significantly between the area close to and the area distant from salmon farming activity. Furthermore, the results from the exposed locality show that high lice infections may have profound negative effects upon [wild] populations of sea trout. In the area without salmon farms, no heavy salmon lice infections were recorded”. A further study published by Bjørn and Finstad in 2002 concluded that fish farming contributes to an elevated lice level in wild fish.

The results from a co-operative research project between the Institute of Marine Research, Bergen, Norway and the University of Bergen indicate that more than 86% of the wild postsmolts of Atlantic salmon migrating out of the Sognefjord, and between 48.5% and 81.5% of the postsmolts from the Nordfjord were killed as a direct consequence of sea lice infections. (ongoing research of fjords with fishfarms).


“This report looks at lice infestations on wild juvenile pink and chum salmon as they migrated past an isolated salmon farm down a long and narrow migration corridor in the Broughton Archipelago, British Columbia, Canada… The calculations suggest the infection pressure near the farm was approximately 70 times greater than natural ambient levels and exceeded ambient levels for 30 km of migration route. This amounts to a total direct contribution of sea lice from the farm that was approximately 30,000 times greater than the natural production of sea lice in the length of habitat occupied by the salmon farm. M. Krkosek, M.A.Lewis and J.P. Volpe-see study published by the Proceedings of the Royal Society B, March 30, 2005


“”We found 3 cases of sea lice in a sample of 1,018 juvenile salmon outside of the Broughton Archipelago. Within the Broughton Archipelago,” where there are 28 Atlantic salmon farms, “we found 4,338 of this species of sea louse on 1,138 salmon,” – a 1,000-fold difference, said Morton. Her study showed potentially lethal levels of infection in 90 percent of wild juvenile salmon.” National Research council Canada site re Alexandra Morton’s Canadian Journal of Fisheries and Aquatic Sciences paper

“1) Salmon farms contribute sea lice to wild fish.”

“3) Sea lice can kill juvenile fish…”

“5) There is suggestive evidence of population impacts (on wild salmon in BC)”

These are exerpts from the “Statement of Agreement” from the roundtable meeting of twenty-five Scientists from around the world November 2004-held at Simon Fraser University in Vancouver

There have been many false and misleading reports concerning a 2003 DFO sea lice study in the Broughton. A Positive Aquaculture Awarenesss news release (dated May 10th, 2004 widely reported and continued to be referred to) stated: “Latest DFO study finds no link between salmon farms and sea lice on wild salmon” “This … proves Ms Morton wrong”. The DFO study referred to did not even look for a relationship between sea lice infestation and fishfarms so no wonder it did not find any. The following is a quote from the Pacific Scientific Advice Review Committee (PSARC) 2004 meeting which reviewed the DFO study in question. “Although some reviewers commented on the lack of a specific study design for hypothesis testing that linked captive fish in farms, wild fish and sea lice, the authors (of the DFO study) noted that the study objectives were not designed to examine cause and effect relationships among sea lice infection rates and fish farm site location.”