Sea lice studies in 2011

Looking through the new science papers published recently we came across this one from the summer titled “Sea lice on wild juvenile Pacific salmon and farmed Atlantic salmon in the northernmost salmon farming region of British Columbia” published in the journal “Aquaculture.”

The abstract is interesting. It  points out that at the low point of sea lice levels during the period studied, the levels of Lepeoptheirus salmonis (the salmon-specific lice parasite) were higher around salmon farms. However, it pointed out that “Over 91% of all the juvenile salmon examined had no sea lice.”

Hm. That’s not a number we’ve heard often. Out of 5,000 juvenile salmon they examined, only nine per cent had sea lice on them?

Full abstract below since Science Direct often changes the link making it annoying for bloggers like us…

Sea lice on wild juvenile Pacific salmon and farmed Atlantic salmon in the northernmost salmon farming region of British Columbia

Sonja M. SaksidaaCorresponding Author Contact InformationE-mail The Corresponding Author, Larry Grebab, Diane Morrisonc, Crawford W. Revied

a British Columbia Centre for Aquatic Health Sciences, PO Box 277 Campbell River, BC, Canada V9W 5B1
b Kitasoo Fisheries Program, 1201-675 West Hastings Street, Vancouver, BC, Canada V6B 1N2
c Marine Harvest Canada, 124-1324 Island Hwy, Campbell River, BC, Canada V9W 8C9
d Centre for Aquatic Health Sciences, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, PEI, Canada C1A 4P3

Received 21 May 2010; revised 8 July 2011; Accepted 20 July 2011. Available online 22 July 2011.


The Kitasoo/Xai’xais First Nation established a program to monitor sea lice levels on seaward migrating wild juvenile salmon in their traditional territory which contains the most northerly salmon farming region of British Columbia. A total of 12 locations were routinely sampled during the period between 2005 and 2008 to gain a better understanding of the levels and patterns of sea lice infestation on wild salmonids in the region. Over 5000 juvenile salmon were collected and examined for sea lice. Around 78% were identified as pink salmon, 18% were chum salmon and the remainder classified as ‘other’ salmon (coho and sockeye salmon). Two species of sea lice were observed: Lepeophtheirus salmonis and Caligus clemensi. Over 91% of all the juvenile salmon examined had no sea lice and there was no significant difference in L. salmonis prevalence levels among salmon species. However, chum salmon had significantly lower C. clemensi prevalence levels than either pink or ‘other’ salmon. There were significant annual and regional differences in L. salmonis prevalence on juvenile pink salmon; the lowest prevalence in all sampling zones occurring in 2008, while channels containing salmon farms consistently had higher levels than those without salmon farms. Mean prevalence of L. salmonis in the channels with salmon farms ranged from 2% to 9% which is lower than levels published for the same region in different years or for other areas without salmon farms. C. clemensi prevalence on wild pink salmon was associated with sampling zone and the size of pink salmon; larger juvenile fish were more likely to be infected than smaller fish. During the period of wild juvenile salmon migration, the mean abundance of motile stages of L. salmonis on farmed salmon ranged from 0.13 to 0.79 lice per fish but there were no significant differences among years. In comparison, C. clemensi abundance levels on farms were significantly higher in 2005. Factors contributing to variations in these observations are discussed.

For balance, we would like to contrast this with another sea lice study published this year, “Effects of parasites from salmon farms on productivity of wild salmon.” This study’s abstract reaches a different conclusion but provides no numbers. For that you have to read the whole study.

Effects of parasites from salmon farms on productivity of wild salmon

  1. Martin Krkošeka,b,1,
  2. Brendan M. Connorsb,c,
  3. Alexandra Mortonb,d,
  4. Mark A. Lewise,
  5. Lawrence M. Dillc, and
  6. Ray Hilbornf

+Author Affiliations

  1. aDepartment of Zoology, University of Otago, Dunedin, New Zealand, 9016;
  2. bSalmon Coast Field Station, Simoom Sound, BC, Canada V0P 1S0;
  3. cEarth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada V5A 1S6;
  4. dRaincoast Research Society, Simoom Sound, BC, Canada V0P 1S0;
  5. eCentre for Mathematical Biology, Department of Mathematical and Statistical Sciences, Department of Biological Sciences, University of Alberta, Edmonton, AB, Canada T6G 2G1; and
  6. fSchool of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98105
  1. Edited by William C. Clark, Harvard University, Cambridge, MA, and approved July 27, 2011 (received for review February 2, 2011)


The ecological risks of salmon aquaculture have motivated changes to management and policy designed to protect wild salmon populations and habitats in several countries. In Canada, much attention has focused on outbreaks of parasitic copepods, sea lice (Lepeophtheirus salmonis), on farmed and wild salmon in the Broughton Archipelago, British Columbia. Several recent studies have reached contradictory conclusions on whether the spread of lice from salmon farms affects the productivity of sympatric wild salmon populations. We analyzed recently available sea lice data on farms and spawner–recruit data for pink (Oncorhynchus gorbuscha) and coho (Oncorhynchus kisutch) salmon populations in the Broughton Archipelago and nearby regions where farms are not present. Our results show that sea lice abundance on farms is negatively associated with productivity of both pink and coho salmon in the Broughton Archipelago. These results reconcile the contradictory findings of previous studies and suggest that management and policy measures designed to protect wild salmon from sea lice should yield conservation and fishery benefits.

The first study relies on observational data and makes no claims about what the data means.

The second relies on a lot of mathematical modelling to explain why it is different from other studies which disagree, and concludes that  the previous work of the authors is right.

We leave it up to our readers to consider the differences here, but while we appreciate the work that went into the second study, setting out to prove you were right before isn’t really the basis of a great scientific study, in our opinion.

But the bottom line here in our opinion is that scientists disagree. And that is healthy. Hopefully we will see lots more research and the differing opinions can temper each other, until we get a definitive answer as to whether or not sea lice from farms kill wild salmon.


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