DOI: 10.5061/dryad.cjsxksnkn
title: Data from: Like a fish takes to water: Minimum discharge requirements to sustain rheophilic fish community dominance in bypassed river reaches

description: Hydropower production leads to losses of species and ecosystem types in
 rivers. A major knowledge gap is represented by bypassed reaches where all
 or most discharge is diverted to hydropower stations. Bypassed reaches may
 have some flow, derived from tributaries and dam leakage, along with
 minimum flow. In Sweden, mandates for minimum discharge are lacking for
 most bypassed reaches, and when present, generally amount to only a few
 percent of mean annual discharge. We asked how fish communities in
 bypassed reaches differ from comparable non-regulated reference reaches,
 and whether minimum discharge can help sustain fish faunas typical of
 non-regulated rivers. We assembled a unique dataset of 2693 samples
 collected via electrofishing by wading from 166 bypassed reaches and 247
 free-flowing reaches spread across Sweden. To quantify flow-related
 community changes, we compared the relative dominance of rheophilic
 (preference for high flow conditions) versus limnophilic (preference for
 slow-flowing to stagnant conditions) fish species, fish density, and fish
 species richness between bypassed and free-flowing reaches, and
 investigated the effects of minimum discharge on community structure.
 Bypassed reaches had lower rheophilic dominance and fish density, but
 slightly higher fish species richness than comparable free-flowing
 reaches. Minimum discharge had positive effects on rheophilic dominance
 and fish density but not fish species richness. For relatively low values
 of minimum discharge, small changes in flow corresponded to large changes
 in the predicted values of fish density (up to about 0.5 m3/s) and
 rheophilic dominance (up to 2 m3/s), after which curves flattened. When
 minimum discharge was expressed as a percentage of mean annual discharge,
 rheophilic dominance and fish density increased almost linearly with
 increasing discharge, but effects on fish density were dependent on river
 size. We conclude that small increases in minimum discharge can
 be particularly beneficial to the restoration of rheophilic community
 structure, especially at low levels of minimum flow, even though the area
 of lotic habitat has been reduced to a fraction of natural conditions.
 Implemention of minimum discharge in bypassed reaches can thus be an
 effective rehabilitation measure, providing ecological benefits helping to
 meet environmental objectives.
description: # Data from: Like a fish takes to water: Minimum discharge requirements to
 sustain rheophilic fish community dominance in bypassed river reaches
 Dataset DOI:
 [10.5061/dryad.cjsxksnkn](https://doi.org/10.5061/dryad.cjsxksnkn) ##
 Description of the data and file structure This dataset contains data on
 river reaches in Sweden that have been sampled using electrofishing,
 encompassing bypassed reaches affected by hydropower and unregulated
 reference reaches.  ### Files and variables #### File:
 variable_explanation.csv **Description:** This file explains the nature of
 the data in the columns in the data_file #### #### File: data_file.csv
 **Description:** This file contains the data described in the
 variable_explanation file. Note that comma is used as decimal delimiter.