DOI: 10.5281/zenodo.7628450
title: Data from: Population recovery and occurrence of the endemic Rhine sculpin (Cottus rhenanus)

description: Two datasets belonging to the paper "Population recovery and occurrence of the endemic Rhine sculpin (<em>Cottus rhenanus</em>)" published in Knowledge and Management of Aquatic Ecosystems, are provided here. Since little was known about the occurrence, densities and habitat use of<em> C. rhenanus, </em>this study was conducted. The study area was located in the River Geul and tributaries, in the south of the Netherlands. The first dataset "WFD 2005-2010-2015 fish data.csv" contains data of fish in transects sampled as part of ecological status assessments of water systems according to the EU Water Framework Directive. Average 300-metre transects in upstream direction in one run using handheld backpack electrofishing equipment. The second dataset "Habitat characterization Cottus rhenanus 2014.csv" contains data of the Rhine sculpin (and other encountered fish species) in relation to its habitat. The data were collected in the same way as described above. In addition, we estimated the relative abundance of each sediment type (bed substratum) per transect, which yielded the ordinal categories: 0%, &lt;5%, 5-10%, 11-25%, 26-50%, 51-75%, and 76-100%. Distinguished sediment types were silt (mud/sludge), sand, fine granule (0.1-20 mm), pebble (21-65 mm), cobble (66-200 mm), and boulder (&gt;200 mm). Furthermore, we estimated the percentage area of large structures (e.g., woody debris) and riffles. Finally, we measured stream width (m) and depth (cm). This was done by recording width with a tape measure and depth with a measuring rod at five (beginning, middle, end and two representatives in between) locations in a transect. The mean values were recorded as stream width and depth. The included coordinates refer to the start and end of a transect. The coordinate system used here concerns Amersfoort RD (EPSG: 28992). Abstract The Rhine sculpin (<em>Cottus rhenanus</em>) is a benthic rheophilic fish species that is endemic to tributaries of the rivers Rhine and Meuse in North-western Europe. Little is known about its occurrence and individuals density in relation to habitat characteristics. A core population of <em>C. rhenanus</em> occurs in the River Geul in the Netherlands. Since the late 19<sup>th</sup> century, this river was heavily polluted by communal and industrial wastewater, causing a strong population decline. As the core population of <em>C. rhenanus</em> is recovering, the status, distribution, and habitat use should be studied to facilitate recovery in other locations. <em>Cottus rhenanus</em> density of individuals significantly increased over the period 2005-2015 and it became one of the most abundant fish species in assemblages. Negative relationships were observed between <em>C. rhenanus</em> densities and a high abundance of boulders (&gt; 200 mm), large structures such as woody debris, and water depth. The population increase and recolonization of <em>C. rhenanus</em> coincided with water quality improvement, which suggests that this fish species can be used to assess small streams ecosystem integrity. The recent range expansion of the Ponto-Caspian round goby (<em>Neogobius melanostomus</em>) poses a high risk of negative effects on <em>C. rhenanus</em> populations via food and shelter competition. Further water quality improvement, habitat conservation, and prevention of the spread of invasive gobies could favour <em>C. rhenanus</em> populations within their natural range.