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Quantifying direct genetic impacts of escaped farmed Atlantic salmon on wild salmon in Atlantic Canada

PARR-2016-NL-02

Description

Aquaculture escapes can be a threat to the persistence and stability of wild salmon populations, with impacts occurring through both genetic and ecological interactions. The goal of this study was to quantify the presence and magnitude of direct genetic impacts that escaped farmed salmon have on wild salmon populations to inform management decisions and advise on mitigation strategies. Specifically, this study addressed three objectives to:

  1. quantify the magnitude of low level chronic escapes through an annual targeted survey
  2. quantify annual variation in hybridization among wild and farm escaped Atlantic salmon
  3. evaluate at sea survival of hybrids in Newfoundland

Identifying risks and potential mitigation strategies associated with Atlantic salmon aquaculture escapees is critical both to the continued growth of the aquaculture industry and to the successful conservation of wild salmon populations. For the first time, this quantified the extent of genetic impacts from farm escaped Atlantic salmon on wild populations over time and in different areas in Atlantic Canada.

Findings

Comparison across years suggested that the proportion of first-generation hybrids has declined since 2014; consistent with the 2013 mass escape event being the dominant source of hybrids. Nonetheless, additional first-generation hybrids were detected in each year surveyed. As such, introgression between wild populations and domestic lines is likely occurring with the potential for significant alteration of wild salmon life history traits (e.g., age at maturity) in the region.

Spatial surveys revealed fewer hybrids in larger rivers or in rivers with greater elevation or partial obstructions. Analysis of juveniles born in 2014 and recaptured in subsequent years indicated that juveniles with one or two aquaculture escapee parent displayed lower survival compared to wild salmon. Models reflecting our estimates of relative survivorship indicated that continued escape events likely influence declines in population size dependent on the size and frequency of escapes. However, the ultimate impact of introgression between wild and domestic Atlantic Salmon remains difficult to resolve or predict.

Publications

Wringe B, Stanley RE, Jeffery NW, Anderson EC, Bradbury IR. 2017. Parallelnewhybrid: an R package for the parallelization of hybrid detection using NEWHYBRIDS. Molecular Ecology Resources 17: 91-95. (data open access)

Keyser F, Wringe BF, Jeffery N, Dempson JB, Bradbury IR. 2018. Predicting the impacts of escaped farmed Atlantic salmon on wild populations in Atlantic Canada. Canadian Journal of Fisheries and Aquatic Sciences 75(4): 506-512.

Wringe BF, Anderson EC, Jeffery NW, Stanley RRE, Hamilton LC, and Bradbury IR. 2018. Development and evaluation of SNP panels for the detection of hybridization between wild and escaped Atlantic salmon (Salmo salar) in the West Atlantic. Canadian Journal of Fisheries and Aquatic Sciences Online early. (data open access) doi.org/10.1139/cjfas-2017-0394

Wringe BF, Jeffery NW, Stanley RRE, Hamilton LC, Anderson EC, Fleming IA, Grant C, Dempson JB, Veinott G, Duffy SJ, Bradbury IR. 2018. Extensive hybridization following a large escape of domesticated Atlantic salmon in the Northwest Atlantic. Biological Communications 1: 108(2018).

Sylvester EVA, Wringe BF, Duffy SJ, Hamilton LC, Fleming IA, Bradbury IR. 2018. Migration effort and wild population size influence the prevalence of hybridization between escaped-farmed and wild Atlantic salmon. Aquaculture Environmental Interactions 10: 401-411. (data open access)

Sylvester EVA, Wringe BF, Duffy SJ, Hamilton LC, Fleming IA, Bradbury IR. 2018.Estimating the relative fitness of escaped farmed salmon offspring in the wild and modeling the consequences for wild populations. Evolutionary Applications. Accepted November 15, 2018. (data open access) doi.org/10.1111/eva.12746

DFO. 2018. Review of the environmental impact statement for the Placentia Bay Atlantic Salmon aquaculture project. Canadian Science Advisory Secretariat Science Response 2018/045.

Program Name

Program for Aquaculture Regulatory Research (PARR)

Year(s)

2016 - 2019

Principal Investigator

Ian Bradbury
Research Scientist, Fisheries and Oceans Canada, Northwest Atlantic Fisheries Centre, Newfoundland and Labrador Region
Email: Ian.Bradbury@dfo-mpo.gc.ca

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