Availability of and access to critical habitats in regulated rivers: effects of low‐head barriers on threatened lampreys

Abstract

1. Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant smallscale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis, a threatened migratory fish. 2. Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007. 3. Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there. 4. In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.

Restoring River Connectivity: Prioritizing Passage Improvements for Diadromous Fishes and Lampreys

“…Impacts are invariably observed most rapidly and dramatically when watercourses are dammed, but the cumulative effects of large numbers of smaller obstructions can also be significant (Lucas et al 2009;Nunn et al 2008). Tools are available to mitigate the impacts of barriers, thereby facilitating the migration of fishes up-and downstream or into adjacent watercourses (Cowx 1998;FAO 2002;Larinier 1998Larinier , 2008.…”

Sea LampreyPetromyzon marinusBiology and Management Across Their Native and Invasive Ranges: Promoting Conservation by Knowledge Transfer

“…Nevertheless, 270 Lasne et al (2015) revealed that barrier removal can be the most effective mechanism to enable P. marinus passage, with higher numbers of nests that were more consistently distributed occurring several years after barrier removal in a French coastal stream. This con-275 trasts to Lucas et al (2009) who reported that in the River Derwent, England, only 2% of adult P. fluviatilis spawners were recorded in 98% of the river's total spawning habitat as this was located above a series of impassable low-head barriers.…”

“…The blockage of migratory routes can thus significantly affect the lifetime fitness of P. marinus, impacting their population growth 230 and distribution, spawning success and recruitment, and affecting their vulnerability to fishing and predators (Andrade et al, 2007;Klamath River Expert Panel, 2010;Mateus et al, 2012). The passage of river lamprey Lampetra fluviatilis over 235 anthropogenic barriers has received some attention in Europe in recent years (Masters et al, 2006;Lucas et al, 2009;Kemp et al, 2011;Russon et al, 2011;Foulds and Lucas, 2013) and this literature might be informative for P. marinus, although some caution is suggested given the 240 larger body sizes of the latter. Elevated water flow increases their migratory activity (Masters et al, 2006) and this assists their passage through barriers that otherwise can be impassable at reduced flows (Lucas et al, 2009;Foulds and Lucas, 2013).…”

“…The passage of river lamprey Lampetra fluviatilis over 235 anthropogenic barriers has received some attention in Europe in recent years (Masters et al, 2006;Lucas et al, 2009;Kemp et al, 2011;Russon et al, 2011;Foulds and Lucas, 2013) and this literature might be informative for P. marinus, although some caution is suggested given the 240 larger body sizes of the latter. Elevated water flow increases their migratory activity (Masters et al, 2006) and this assists their passage through barriers that otherwise can be impassable at reduced flows (Lucas et al, 2009;Foulds and Lucas, 2013). Where flows are exces-245 sive, however, movements of both species might be hindered by their elongated body morphology and lack of paired fins that reduces their ability of negotiating highvelocity flows when compared to most other migratory fishes (Keefer et al, 2013;Foulds and Lucas, 2013).…”

“…These obstructions severely fragment their habitats and thus can strongly restrict the riverine habitats available 225 to spawning adults (Lucas et al, 2009), as well as impede the downstream movement of larvae/juveniles (Nunn and Cowx, 2012;Hogg et al, 2013). The blockage of migratory routes can thus significantly affect the lifetime fitness of P. marinus, impacting their population growth 230 and distribution, spawning success and recruitment, and affecting their vulnerability to fishing and predators (Andrade et al, 2007;Klamath River Expert Panel, 2010;Mateus et al, 2012).…”