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Unintended consequences and trade-offs of fish passage

Authors

  • Robert L McLaughlin,

    Corresponding author
    1. Department of Integrative Biology, University of Guelph, Guelph, ON, Canada
    • Correspondence:

      Robert L McLaughlin, Department of Integrative Biology, University of Guelph, ON Canada N1G 2W1

      Tel.: +519 824-4120 extn: 53620

      Fax: +519 767-1656

      E-mail: rlmclaug@uoguelph.ca

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    • Equal co-authors.
  • Eric R B Smyth,

    1. Department of Integrative Biology, University of Guelph, Guelph, ON, Canada
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    • Equal co-authors.
  • Theodore Castro-Santos,

    1. S.O. Conte Anadromous Fish Research Laboratory, USGS-BRD-Leetown Science Center, Turners Falls, MA, USA
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    • Order of secondary authors determined alphabetically.
  • Michael L Jones,

    1. Quantitative Fisheries Center, Department of Fisheries and Wildlife, Michigan State University, East Lansing, MI, USA
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  • Marten A Koops,

    1. Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, Burlington, ON, Canada
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  • Thomas C Pratt,

    1. Great Lakes Laboratory for Fisheries and Aquatic Sciences, Fisheries and Oceans Canada, Sault Ste. Marie, ON, Canada
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  • Luis-Antonio Vélez-Espino

    1. Pacific Biological Station, Fisheries and Oceans Canada, Nanaimo, BC, Canada
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Abstract

We synthesized evidence for unintended consequences and trade-offs associated with the passage of fishes. Provisioning of fish passageways at dams and dam removals are being carried out increasingly as resource managers seek ways to reduce fragmentation of migratory fish populations and restore biodiversity and nature-like ecosystem services in tributaries altered by dams. The benefits of provisioning upstream passage are highlighted widely. Possible unwanted consequences and trade-offs of upstream passage are coming to light, but remain poorly examined and underappreciated. Unintended consequences arise when passage of native and desirable introduced fishes is delayed, undone (fallback), results in patterns of movement and habitat use that reduce Darwinian fitness (e.g. ecological traps), or is highly selective taxonomically and numerically. Trade-offs arise when passage decisions intended to benefit native species interfere with management decisions intended to control the unwanted spread of non-native fishes and aquatic invertebrates, or genes, diseases and contaminants carried by hatchery and wild fishes. These consequences and trade-offs will vary in importance from system to system and can result in large economic and environmental costs. For some river systems, decisions about how to manage fish passage involve substantial risks and could benefit from use of a formal, structured process that allows transparent, objective and, where possible, quantitative evaluation of these risks. Such a process can also facilitate the design of an adaptive framework that provides valuable insights into future decisions.

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