Are invasive gobies a risk for the River bullhead in the River Geul? Invasive Ponto-Caspian gobies, in particular the Round goby (Neogobius melastonomus), have led to a strong decline of the native River bullhead (Cottus perifretum) in the River Meuse. The same risk exists for the Rhine sculpin (C. rhenanus), of which the largest population in the Netherlands occurs upstream in the River Geul. In this study we examined goby dispersion in the lower River Geul by PIT-tagging 55 individuals of Round goby and 11 Bighead goby (Ponticola kessleri). The fish were tracked from September until December 2016. The results suggest that for both species the home range was limited during the research period; the largest dispersal that was established was 30 meter in a downstream direction. Furthermore, we determined the occurrence of invasive gobies and other species in 10 transects. High numbers of river bullhead were found in the absence of round goby in more upstream transects. In 2015, the first round goby was found in the direct debouchment of the Geul River into the River Meuse. In 2017, 300 meters upstream of this location a round goby was found. This implies an upstream colonisation rate of 150 meter per year for this species, which is very low compared to the River Meuse (30 km year-1). It is unclear what causes the low colonisation rate in the River Geul. A reason could be that there is too little intraspecific competition in the River Meuse that causes round gobies to colonize the Geul River and stronger colonisation rate might be expected when densities in the River Meuse increase. Therefore, we advise to closely monitor the goby colonisation which can lead to new insights.

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RAVON

CC BY 3.0 NL ("Naamsvermelding")

RAVON

P. Lemmers, B. Crombaghs, R. Gubbels, & H. Bakker. (2018). Bedreigen invasieve grondels de donderpadden van de Geul?. RAVON, 20(3), 42–45.