Abstract
Conservation management of wild fish may include fish health management in sympatric populations of domesticated fish in aquaculture. We developed a mathematical model for the population dynamics of parasitic sea lice (Lepeophtheirus salmonis) on domesticated populations of Atlantic salmon (Salmo salar) in the Broughton Archipelago region of British Columbia. The model was fit to a seven-year dataset of monthly sea louse counts on farms in the area to estimate population growth rates in relation to abiotic factors (temperature and salinity), local host density (measured as cohort surface area), and the use of a parasiticide, emamectin benzoate, on farms. We then used the model to evaluate management scenarios in relation to policy guidelines that seek to keep motile louse abundance below an average three per farmed salmon during the March–June juvenile wild Pacific salmon (Oncorhynchus spp.) migration. Abiotic factors mediated the duration of effectiveness of parasiticide treatments, and results suggest treatment of farmed salmon conducted in January or early February minimized average louse abundance per farmed salmon during the juvenile wild salmon migration. Adapting the management of parasites on farmed salmon according to migrations of wild salmon may therefore provide a precautionary approach to conserving wild salmon populations in salmon farming regions.
Highlights
Global finfish aquaculture production grew by 65% between 2000 and 2010 [1,2], and likely will continue to grow [3,4]
On salmon farms in the Broughton Archipelago between 2002 and 2008, the average abundance per farmed salmon of motile sea lice (Lepeophtheirus salmonis) typically increased over time until farmed salmon were treated with SLICEH (Figures 2 and 3)
Precautionary management of parasites on Atlantic salmon farms in British Columbia that suppresses parasite abundance to coincide with the timing of juvenile wild salmon migrations may reduce the risk of infection for wild Pacific salmon
Summary
Global finfish aquaculture production grew by 65% between 2000 and 2010 [1,2], and likely will continue to grow [3,4]. Management of parasites is a challenge for finfish farms and as the density of aquaculture production grows, the risk of infectious disease may increase [5]. Sea lice (Lepeophtheirus salmonis) routinely infect farmed Atlantic salmon (Salmo salar) [8], but in British Columbia, Canada, sea lice are seldom a production or health concern for Atlantic salmon on farms [6]. Wild Pacific salmon (Oncorhynchus gorbuscha, O. keta, O. kisutch) that migrate near to Atlantic salmon farms may face an elevated risk of sea louse infection [9,10,11,12]. Sea louse management in British Columbia has sought to limit the exposure of wild Pacific salmon to high densities of sea lice by limiting the average number of motile lice per fish on Atlantic salmon farms [27]
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