Restoring River Connectivity: Prioritizing Passage Improvements for Diadromous Fishes and Lampreys
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Physical obstructions are becoming increasingly recognized as major factors influencing the migrations, population structures, spawning success and recruitment of freshwater organisms. This paper presents a simple but effective method, intended for use by environmental managers, government agencies and conservation bodies, of rapidly assessing and prioritizing barriers to the migrations of diadromous fishes and lampreys for passage improvements. A prioritization matrix was developed using information on fish stock status, the passage efficiency of fishes at individual structures, the distance from the tidal limit and the passability of downstream barriers, and the quantity and quality of habitat upstream of each structure. Importantly, the ‘Likelihood of access’ was incorporated into the matrix to account for passage efficiency at downstream barriers. Barriers ranked as the highest priority for passage improvements were those characterized by poor fish stocks upstream, low passage efficiency, easy passage from downstream, and a large quantity and high quality of habitat upstream. Prioritization of migration barriers should ensure that access improvements are targeted to achieve optimum benefits.
KeywordsBarrier Habitat connectivity Habitat fragmentation Migration Obstruction Rehabilitation
The authors would like to thank the Environment Agency for partly funding both case studies, and Steve Axford, Barry Byatt, Paul Frear, Tim Jacklin, Mike Lee, Alex Lumsdon, Joel Rawlinson, Darren Rollins, Dan Smallwood and Neil Trudgill for conducting independent prioritizations. The prioritization matrix was developed, with permission, from an early draft of the (unpublished) Environment Agency’s National Fish Pass Prioritization Project. The views expressed in the paper are those of the authors and not necessarily those of the Environment Agency. The paper benefited greatly from the constructive criticism of two anonymous referees.
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