Research Paper

Population recovery and occurrence of the endemic Rhine sculpin (Cottus rhenanus)

¹ Natuurbalans – Limes Divergens, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands
² Radboud University, Radboud Institute for Biological and Environmental Sciences, Department of Animal Ecology and Physiology, P.O. Box 9100, 6500 GL Nijmegen, The Netherlands
³ Netherlands Centre of Expertise for Exotic Species (NEC-E), Nature plaza, P.O. Box 9010, 6500 GL Nijmegen, The Netherlands
⁴ Wildlife Ecology and Conservation Group, Department of Environmental Sciences, Wageningen University, Droevendaalsesteeg 3a, 6708 PB Wageningen, The Netherlands
⁵ Water Board Limburg, P.O. Box 2207, 6040 CC Roermond, The Netherlands
⁶ Naturalis Biodiversity Center, P.O. Box 9517, 2300 RA Leiden, The Netherlands

^* Corresponding author: lemmers@natuurbalans.nl

Received: 10 October 2022
Accepted: 10 February 2023

Abstract

The Rhine sculpin (Cottus rhenanus) 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 C. rhenanus occurs in the River Geul in the Netherlands. Since the late 19th century, this river was heavily polluted by communal and industrial wastewater, causing a strong population decline. As the core population of C. rhenanus is recovering, the status, distribution, and habitat use could be studied to facilitate recovery in other locations. Cottus rhenanus 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 C. rhenanus densities and a high abundance of boulders (>200 mm), large structures such as woody debris, and water depth. The population increase and recolonization of C. rhenanus 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 (Neogobius melanostomus) poses a high risk of negative effects on C. rhenanus populations via food and shelter competition. Further water quality improvement, habitat conservation, and prevention of the spread of invasive gobies could favour C. rhenanus populations within their natural range.