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Cumulative impacts of habitat fragmentation and the environmental factors affecting upstream migration in the threatened sea lamprey, Petromyzon marinus

Davies, Peter; Britton, J. Robert; Nunn, Andrew D.; Dodd, Jamie R.; Bainger, Chris; Velterop, Randolph; Bolland, Jonathan D.


Peter Davies

J. Robert Britton

Chris Bainger

Randolph Velterop



River ecosystems are often fragmented by artificial structures, such as weirs. For anadromous species, these structures can impede access to upstream spawning sites and ultimately lead to severe population declines. This study focused on the freshwater spawning migration of the sea lamprey, Petromyzon marinus, an anadromous species threatened by habitat fragmentation across its native range. To quantify the cumulative impacts of multiple weirs on upstream-migrating adults, and to explore the environmental factors affecting migratory movements, passive acoustic telemetry was applied to 56 individuals during their spawning migration in the heavily fragmented River Severn basin, UK. While 89% of tagged sea lamprey passed the first weir upstream of the release site on the main river, only 4% passed the fifth weir. For 85% of migrants, the upstream extent of migration was immediately downstream of a weir. Individuals that passed weirs upstream of the release site (n=50) took 21.6±2.8days to reach their most upstream location, experiencing cumulative passage times at weirs of 15.7±2.8days; these delays constituted a median of 84% of total upstream movement times. Multistate models showed that the weir passage rates of sea lamprey in tidal and non-tidal areas increased significantly when downstream river level and discharge were elevated. Upstream-to-downstream changes in direction were frequent downstream of weirs, but rare in unobstructed river sections. The results provided evidence for a cumulative effect of multiple weirs on sea lamprey movements, substantially delaying upstream migrants and limiting their spawning to atypical habitat. The results also demonstrated the crucial roles of high tides and elevated discharge events in enabling weir passage. Although the Severn Estuary features conservation designations for sea lamprey, this study reveals that barriers are inhibiting their upstream migration, a problem that should be addressed to assist sea lamprey conservation.


Davies, P., Britton, J. R., Nunn, A. D., Dodd, J. R., Bainger, C., Velterop, R., & Bolland, J. D. (2021). Cumulative impacts of habitat fragmentation and the environmental factors affecting upstream migration in the threatened sea lamprey, Petromyzon marinus. Aquatic conservation : marine and freshwater ecosystems, 31(9), 2560-2574.

Journal Article Type Article
Acceptance Date Apr 15, 2021
Online Publication Date Jun 28, 2021
Publication Date Sep 1, 2021
Deposit Date Jun 28, 2021
Publicly Available Date Jul 5, 2021
Journal Aquatic Conservation: Marine and Freshwater Ecosystems
Print ISSN 1052-7613
Electronic ISSN 1099-0755
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 31
Issue 9
Pages 2560-2574
Keywords Catchment; Engineering; Fish; Impoundment; Migration; Protected species; River; Tracking
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Copyright Statement
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.<br /> &copy; 2021 The Authors. Aquatic Conservation: Marine and Freshwater Ecosystems published by John Wiley &amp; Sons Ltd.

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