Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 Dec 28;107(52):22599-604.
doi: 10.1073/pnas.1009573108. Epub 2010 Dec 13.

Relationship of farm salmon, sea lice, and wild salmon populations

Gary D Marty  1 , Sonja M Saksida, Terrance J Quinn 2nd
Affiliations

Relationship of farm salmon, sea lice, and wild salmon populations

Gary D Marty et al. Proc Natl Acad Sci U S A. .

Abstract

Increased farm salmon production has heightened concerns about the association between disease on farm and wild fish. The controversy is particularly evident in the Broughton Archipelago of Western Canada, where a high prevalence of sea lice (ectoparasitic copepods) was first reported on juvenile wild pink salmon (Oncorhynchus gorbuscha) in 2001. Exposure to sea lice from farmed Atlantic salmon (Salmo salar) was thought to be the cause of the 97% population decline before these fish returned to spawn in 2002, although no diagnostic investigation was done to rule out other causes of mortality. To address the concern that sea lice from fish farms would cause population extinction of wild salmon, we analyzed 10-20 y of fish farm data and 60 y of pink salmon data. We show that the number of pink salmon returning to spawn in the fall predicts the number of female sea lice on farm fish the next spring, which, in turn, accounts for 98% of the annual variability in the prevalence of sea lice on outmigrating wild juvenile salmon. However, productivity of wild salmon is not negatively associated with either farm lice numbers or farm fish production, and all published field and laboratory data support the conclusion that something other than sea lice caused the population decline in 2002. We conclude that separating farm salmon from wild salmon--proposed through coordinated fallowing or closed containment--will not increase wild salmon productivity and that medical analysis can improve our understanding of complex issues related to aquaculture sustainability.

PubMed Disclaimer

Conflict of interest statement

Conflict of interest statement: None of the authors received compensation from any source for this analysis. S.M.S., as part of her private veterinary practice over the past 15 y, has done contract work for all three fish farm companies that operate in the study area (these companies are cited in the acknowledgments, and this relationship was vital for obtaining all proprietary farm medical records for this study); S.M.S.’s spouse started working for closed-containment aquaculture operation in September 2010.

Figures

Fig. 1.
Fig. 1.
Monthly total number of farm fish, farm-source adult female sea lice, and sea lice treatments (n = 0–5 per mo; axis from top of figure not shown) in the Broughton Archipelago. L. salmonis numbers during the time of greatest concern (March and April) are highlighted in yellow. Error bars for L. salmonis estimates before 2003 denote the range of uncertainty during this period, when lice were not counted on every farm.
Fig. 2.
Fig. 2.
Mean number of motile L. salmonis sea lice per fish on farms that were treated after odd-year pink salmon runs (triangles) and even-year pink salmon runs (inverted triangles) and the total number of sea lice treatments (Tx; open circles) per year (September 1 to August 31). The treatment threshold (number of motile L. salmonis per fish; dashed line) for March through June was established by the British Columbia provincial government in 2004.
Fig. 3.
Fig. 3.
(A) Adult pink salmon returns in the fall (1999–2008) and total numbers of adult female L. salmonis sea lice on farm fish the next April (2000–2009). (B) Total number of adult female L. salmonis on farm fish in April and prevalence of L. salmonis on wild juvenile pink salmon in May (2002–2009; ± 95% prediction interval).
Fig. 4.
Fig. 4.
Observed values (closed triangles), predicted values (open circles), and P values for the two multiple linear regressions of pink salmon production [generational survival; ln (Rt − 2/St)]. (i) For 2001–2009 data, the relationship of generational survival to farm-source adult female L. salmonis sea lice was not significant (A), but the relationship of generational survival to parental escapement (St − 2) was significant (C). (ii) For 1991–2009 data, the relationship of generational survival to farm fish production was not significant (B), but the relationship of generational survival to parental escapement was significant (D). Dotted lines denote where returns equal parental escapement. For emphasis, solid trend lines are shown for significant relationships (C and D).
See this image and copyright information in PMC

References

    1. Costello MJ. How sea lice from salmon farms may cause wild salmonid declines in Europe and North America and be a threat to fishes elsewhere. Proc R Soc B Biol Sci. 2009;276:3385–3394. - PMC - PubMed
    1. Krkosek M. Sea lice and salmon in Pacific Canada: Ecology and policy. Front Ecol Environ. 2010;8:201–209.
    1. Krkosek M, et al. Declining wild salmon populations in relation to parasites from farm salmon. Science. 2007;318:1772–1775. - PubMed
    1. Morton AB, Williams R. First report of a sea louse, Lepeophtheirus salmonis, infestation on juvenile pink salmon, Oncorhynchus gorbuscha, in nearshore habitat. Can Field-Nat. 2003;117:634–641.
    1. Heard WR. Life history of pink salmon (Oncorhynchus gorbuscha) In: Groot C, Margolis L, editors. Pacific Salmon Life Histories. Vancouver: University of British Columbia Press; 1991. pp. 119–230.

MeSH terms

LinkOut - more resources