Run‐of‐river dams as a barrier to the movement of a stream‐dwelling amphibian

Griffin C Dare,Rylee G Murray,Danielle M M Courcelles,Wendy J Palen,Joshua M Malt

doi:10.1002/ecs2.3207

Griffin C Dare, Rylee G Murray + Show 3 more

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https://doi.org/10.1002/ecs2.3207

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Abstract

AbstractHuman activities frequently create structures that alter the connectivity among habitats or act as barriers to the natural movement of animals. Movement allows individuals to access different habitats, connect life history stages, and maintain genetic diversity. Here, we evaluated whether run‐of‐river (RoR) hydropower projects, an emerging renewable energy source in British Columbia, interrupt the longitudinal connectivity among larval stream amphibians, by altering larval rearing densities, with possible repercussions on growth and survival. In three watersheds, we tested for differences in the average upstream and downstream density of larval coastal tailed frog (Ascaphus truei), as well as changes to their longitudinal distribution upstream of the dams, as would be expected if RoR dams or their headponds act as barriers to the natural downstream drift of larvae. We found a 60% decrease in larval densities downstream compared to upstream of dams, consistent with RoR dams interrupting the natural pattern of downstream A. truei drift. Larval densities in the first 10 m above RoR headponds were 3 times higher compared to 100 m upstream, and when expressed in terms of relative abundance, we find a similar pattern, with between 2.5 and 3 times more larvae in the first 10 m above of the headpond than expected if larvae followed a uniform distribution. Our results are consistent with the hypothesis that RoR dams alter the spatial connectivity of A. truei larvae, leading to an accumulation of larvae directly above the dam, with unknown consequences for larval growth and survival. Our findings suggest caution is warranted when interpreting before–after monitoring studies that are often used to evaluate the impact of dams, whereby we find that reductions in downstream densities could be due to interruptions of downstream movement as opposed to direct mortality.

Highlights

Human activities, such as the construction of roads, powerlines, railroads, and energy infrastructure, often interrupt connectivity among habitats and the movement of individual species (Schreiber and Graves 1977, Goosem and Marsh 1997, Ito et al 2005, Masden et al 2009, v www.esajournals.orgAugust 2020 v Volume 11(8) v Article e03207 DARE ET AL.Clark et al 2010)
We found approximately three times higher larval A. truei density above each RoR dam compared to below (Fire = 2.67, Tipella = 2.74, Stokke = 2.77), where Fire Creek had the highest density of larvae with an average of 1.15 larvae/m2 upstream and 0.43 larvae/m2 downstream, and Tipella Creek, 0.85 larvae/m2 upstream and 0.31 larvae/m2 downstream, and Stokke Creek had the lowest densities, with 0.36 larvae/
Model average coefficients and relative variable importance (RVI) values revealed that four additional environmental variables have a large influence on A. truei larval density—higher densities are found in areas of higher flow (β = 0.67, CI = Æ0.42, RVI = 0.97), at shallower depth (β = −0.46, 95% CI = Æ0.28, RVI = 0.97), less embedded substrate (β = −0.34, 95% CI = Æ0.26, RVI = 0.90), and higher biofilm chlorophyll content (β = −0.39, 95% CI = Æ0.36, RVI = 0.86; Fig. 3)

Summary

Introduction

Human activities, such as the construction of roads, powerlines, railroads, and energy infrastructure, often interrupt connectivity among habitats and the movement of individual species (Schreiber and Graves 1977, Goosem and Marsh 1997, Ito et al 2005, Masden et al 2009, v www.esajournals.orgAugust 2020 v Volume 11(8) v Article e03207 DARE ET AL.Clark et al 2010). Human activities, such as the construction of roads, powerlines, railroads, and energy infrastructure, often interrupt connectivity among habitats and the movement of individual species For many species with complex life histories, ontogenetic movement is necessary to connect habitats required by different life history stages (Werner and Gilliam 1984, Taylor et al 1993, Lucas and Baras 2001). In river networks connectivity between downstream and upstream reaches, known as longitudinal connectivity, is often essential for population persistence (Fagan 2002) and such movements are often vulnerable to instream structures such as culverts, roads, weirs, and dams (Lucas et al 2009). Hydropower dams are one of the most common forms of instream barriers, with nearly 3000 projects globally (>1 megawatt) estimated to be operational by 2020 (Lehner 2011)

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