Event Title

Wild salmon may prevent evolution of drug resistance in sea lice on salmon farms

Presentation Abstract

Globally, open-net-pen salmon farms rely on chemicals to manage infestations of sea lice (Lepeophtheirus salmonis and Caligus spp). In many regions, sea lice have rapidly evolved resistance to the chemicals used, presenting management challenges and endangering sympatric wild salmonids that are susceptible to infestation by farm-origin lice. In the eastern north Pacific, however, treatment of sea lice has proceeded without signs of resistance. We extended a simple host-parasite model to explore the spread of treatment resistance in sea lice, and how wild hosts could provide an oceanic treatment-free refuge and connect sea louse populations on coastal farms to that refuge. Parameterising our model based on published findings, we investigated the potential effects of population sizes, treatment levels, and resistance constraints. Our model analyses reveal that the balance among multiple factors could affect whether or not treatment resistance evolves in sea lice on salmon farms. First, our model reproduced results consistent with existing theory surrounding treatment resistance: both high levels of treatment on farms and a large oceanic wild-host population were required to prevent the evolution of treatment resistance in sea lice. Second, resistance was liable to invade when the resistant phenotype was more resistant to treatment and associated costs were low. Third, the rates of infestation by free-swimming louse larvae and the persistence of the wild-host population near farms (which served to transfer lice between the farm and oceanic environments) were both critical in maintaining treatment susceptibility in sea lice. In our model, treatment both selects for resistance and protects the nearby wild host population, thereby maintaining the service those wild hosts provide in opposing resistance evolution. Our work highlights the potential for wild salmon to provide a direct benefit to farms, giving salmon farmers a reason that protecting wild salmon may be in their own best interest.

Session Title

The Impacts of Open Net Pen Salmon Farming on Wild Salmon

Conference Track

SSE11: Species and Food Webs

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE11-647

Start Date

4-4-2018 1:45 PM

End Date

4-4-2018 2:00 PM

Type of Presentation

Oral

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 4th, 1:45 PM Apr 4th, 2:00 PM

Wild salmon may prevent evolution of drug resistance in sea lice on salmon farms

Globally, open-net-pen salmon farms rely on chemicals to manage infestations of sea lice (Lepeophtheirus salmonis and Caligus spp). In many regions, sea lice have rapidly evolved resistance to the chemicals used, presenting management challenges and endangering sympatric wild salmonids that are susceptible to infestation by farm-origin lice. In the eastern north Pacific, however, treatment of sea lice has proceeded without signs of resistance. We extended a simple host-parasite model to explore the spread of treatment resistance in sea lice, and how wild hosts could provide an oceanic treatment-free refuge and connect sea louse populations on coastal farms to that refuge. Parameterising our model based on published findings, we investigated the potential effects of population sizes, treatment levels, and resistance constraints. Our model analyses reveal that the balance among multiple factors could affect whether or not treatment resistance evolves in sea lice on salmon farms. First, our model reproduced results consistent with existing theory surrounding treatment resistance: both high levels of treatment on farms and a large oceanic wild-host population were required to prevent the evolution of treatment resistance in sea lice. Second, resistance was liable to invade when the resistant phenotype was more resistant to treatment and associated costs were low. Third, the rates of infestation by free-swimming louse larvae and the persistence of the wild-host population near farms (which served to transfer lice between the farm and oceanic environments) were both critical in maintaining treatment susceptibility in sea lice. In our model, treatment both selects for resistance and protects the nearby wild host population, thereby maintaining the service those wild hosts provide in opposing resistance evolution. Our work highlights the potential for wild salmon to provide a direct benefit to farms, giving salmon farmers a reason that protecting wild salmon may be in their own best interest.