DOI: 10.5061/dryad.q659t
title: Data from: Hydropower impacts on reservoir fish populations are modified by environmental variation

description: Global transition towards renewable energy production has increased the
 demand for new and more flexible hydropower operations. Before management
 and stakeholders can make informed choices on potential mitigations, it is
 essential to understand how the hydropower reservoir ecosystems respond to
 water level regulation (WLR) impacts that are likely modified by the
 reservoirs' abiotic and biotic characteristics. Yet, most reservoir
 studies have been case-specific, which hampers large-scale planning,
 evaluation and mitigation actions across various reservoir ecosystems.
 Here, we investigated how the effect of the magnitude, frequency and
 duration of WLR on fish populations varies along environmental gradients.
 We used biomass, density, size, condition and maturation of brown trout
 (Salmo trutta L.) in Norwegian hydropower reservoirs as a measure of
 ecosystem response, and tested for interacting effects of WLR and lake
 morphometry, climatic conditions and fish community structure. Our results
 showed that environmental drivers modified the responses of brown trout
 populations to different WLR patterns. Specifically, brown trout biomass
 and density increased with WLR magnitude particularly in large and
 complex-shaped reservoirs, but the positive relationships were only
 evident in reservoirs with no other fish species. Moreover, increasing WLR
 frequency was associated with increased brown trout density but decreased
 condition of individuals within the populations. WLR duration had no
 significant impacts on brown trout, and the mean weight and maturation
 length of brown trout showed no significant response to any WLR metrics.
 Our study demonstrates that local environmental characteristics and the
 biotic community strongly modify the hydropower-induced WLR impacts on
 reservoir fishes and ecosystems, and that there are no one-size-fits-all
 solutions to mitigate environmental impacts. This knowledge is vital for
 sustainable planning, management and mitigation of hydropower operations
 that need to meet the increasing worldwide demand for both renewable
 energy and ecosystem services delivered by freshwaters.
description: Data of environmental
 characteristics and brown trout populations in 102 Norwegian hydropower
 reservoirsThe data contains
 field-collected data of brown trout populations in 102 Norwegian
 reservoirs with variable environmental characteristics. The brown trout
 data (i.e. response variables) include estimates of: "Biomass"
 (grams of fish per 100m2 net per night); "Density" (number of
 fish per 100m2 net per night); "Mean weight" (mean wet mass in
 grams); "Mean condition" (mean Fulton's condition factor);
 and "Mean maturity length" (mean total length of mature females
 in millimeters). All abbreviations for different variables (columns) are
 explained in the paper. Many reservoirs ("Lake") have various
 names, some including Norwegian letters (æ, ø & å). Hence, we
 recommend to use coordinate data (EPSG:4326; "decimalLongitude"
 and "decimalLatitude") and Norwegian national lake ID numbers
 ("Lake_nr"; managed by the Norwegian Water Resources and Energy
 Directorate; www.nve.no) to locate the reservoirs. The variables
 "Year", "Month" and "Day" refer to times
 when survey fishing was conducted. Lake morphometry data
 ("A"=surface area, "SD"=shoreline development) is
 obtained from NVE database. The lake climatic and catchment data
 ("T"=mean July air temperature, "NDVI"= Normalized
 Difference Vegetation Index, and "SL"=terrain slope) is obtained
 and measured as described by Finstad et al. (2014; DOI:
 10.1111/ele.12201). Other abbreviations include: "FC"=presence
 of other fish species (1=absent, 2=present); "GS"=gillnet series
 (1=Nordic, 2=Jensen); and "ST"=brown trout stocking (0=no
 stocking, 1=stocking). The water level regulation (WLR) metrics include:
 ): "WLR_magnitude"= maximum regulation amplitude;
 "WLR_frequency"=relative proportion of weeks with a sudden rise
 or drop in water level; and "WLR_duration"=the relative
 proportion of weeks with exceptionally low water
 levels.Data-in_doi.org-10.1016-j.scitotenv.2017.10.268.xlsx