Transmission dynamics of parasitic sea lice from farm to wild salmon

Krkošek, Martin; Lewis, Mark A.; Volpe, John P.

doi:10.1098/rspb.2004.3027

Cited by 244 publications

(271 citation statements)

References 30 publications

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“…1 and 3B). Collectively, these findings support the hypothesis that farm fish are the main source of L. salmonis infesting juvenile pink salmon, and they are consistent with indirect evidence from several other studies that did not have access to farm data (14,16,26,27). Because farm-source sea lice accounted for 98% of the variability in wild salmon sea lice prevalence from 2002 to 2009 and sea lice were sometimes common on farmed Atlantic salmon during the 1990s, farm-source sea lice probably infested juvenile pink salmon many years before they were first examined for sea lice in 2001 (1).…”

Section: Resultssupporting

confidence: 79%

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

Marty

Saksida

Quinn

2010

Proc. Natl. Acad. Sci. U.S.A.

134

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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.B ecause salmon aquaculture production has rapidly increased over the past three decades, the potential for environmental impacts of salmon farms has generated heightened scientific and public interest (1, 2). One concern about salmon farms is that they are the source of ectoparasitic sea lice infestations that might reduce the marine survival of wild salmon (3, 4). In the Broughton Archipelago region of Western Canada (Fig. S1), farming of Atlantic salmon (Salmo salar) began in the late 1980s, and annual farm salmon production increased steadily to 17 Gg by 1999 (Fig. S2). Pink salmon (Oncorhynchus gorbuscha) is the most abundant wild salmon species in the Broughton Archipelago; they enter the marine environment at a very small size (0.2 g), and they return to natal streams to spawn 2 y after their parents (5). Because age at maturity never varies, they have distinct evenand odd-year populations ( Fig. S2 and SI Text). Record high numbers of pink salmon returned to spawn in rivers of the Broughton Archipelago in 2000 and 2001 (Dataset S1), but these returns were followed by population decline of 97% in 2002 and 88% in 2003 (Figs. S2 and S3 and SI Text). When juvenile pink salmon in the Broughton Archipelago were first examined for sea lice in June 2001, more than 90% were infested-leading to the hypothesis that sea lice from fish farms were the cause of population collapse in 2002 (4).Adult pink salmon are a natural host for the sea louse species Lepeophtheirus salmoni...

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Section: Resultssupporting

confidence: 79%

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

Marty

Saksida

Quinn

2010

Proc. Natl. Acad. Sci. U.S.A.

134

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“…Models from fjordic habitats in Europe and Canada indicate sea lice can be dispersed on the order of 10 to 100 km from their source location before becoming infectious (Murray & Gillibrand 2006, Amundrud & Murray 2009, Foreman et al 2009). Those predictions are supported by empirical studies of the planktonic stages as well as the young parasitic stages on wild hosts in the surrounding environment (Krko$ek et al 2005, Costello 2006). The high dispersion of sea lice larvae indicates that parasite populations on domesticated fish can have high connectivity among farms.…”

Section: Empirical Evidence For Thresholdssupporting

confidence: 55%

“…There, aquaculture facilities typically occur in net pens, cages, rafts, or on ropes, all of which are open to the surrounding marine ecosystem. Wild and domestic marine populations are therefore connected by their shared parasites, which can be freely transmitted between the aquaculture environment and the surrounding ecosystem (Kent 2000, Krko$ek et al 2005. Such transmission between wildlife and domestic animal populations is termed spillover and spillback of parasites, and is a primary mechanism in the emergence of infectious diseases (Daszak et al 2000).…”

Section: Host Populations At Seamentioning

confidence: 99%

Host density thresholds and disease control for fisheries and aquaculture

Krkošek¹

2010

Aquacult. Environ. Interact.

106

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The outbreak, persistence, and eradication of infectious diseases often depend on the density of hosts. In coastal seas, many fisheries are fully or over-exploited; meanwhile, farmed populations are increasing rapidly with aquaculture growth. Marine aquaculture facilities are typically open to the surrounding ecosystem and, therefore, wild and farmed populations are connected by their shared parasites. At the core of epidemiological theory are host density thresholds, above which diseases can persist or invade and below which diseases can be eradicated. Host density thresholds in aquaculture-fishery interactions likely function at regional scales that encompass multiple farms, which are connected by pathogen dispersal and the movement of wild hosts. Sudden outbreaks of parasitic copepods in wild-farmed salmon systems may be linked to aquaculture growth exceeding host density thresholds. Abiotic (e.g. temperature and salinity), management (e.g. husbandry and farm siting), and biotic factors (e.g. migrations of wild hosts) likely affect threshold values. A connected wild-farmed host population can exceed a host density threshold due to an influx of wild hosts via migration, increases in aquaculture production, or environmental change such as climate warming. Coastal management and policy should heed the disease implications of climate warming, aquaculture growth, and fisheries restoration that suggest increasing host densities and decreasing threshold values.

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“…Ireland, Scotland, Norway, and Canada) suggest that the occurrence of diseases such as rickettsial septicemia and sea lice (Caligus spp.) in both salmonids and native fishes are directly related to higher concentrations of farmed fishes (Krkosek et al 2005, Naylor et al 2005. Also, a virus that regularly affects salmon farms in different countries including Chile is the infectious pancreatic necrosis virus, which has been detected in all salmon species at all developmental stages (freshwater and ocean phase of aquaculture) as well as in native fishes, mollusks, and crustaceans (Rodríguez Saint Jean et al 2003, Asche et al 2010.…”

Section: Spreading Of Pathogens and Diseasesmentioning

confidence: 99%