With the completion of the construction of the Rhine–Main–Danube Canal in 1992, a free passage was created for fish between the drainage basins of the Danube and the Rhine. As a result, a variety of species of goby have now been observed in the Lake IJssel (IJsselmeer) region for the first time.
Photo: Round gobies have been seen in the Netherlands since 2004
In recent years, a number of goby species have been seen in the Netherlands for the first time: the western tubenose goby in 2002, the round goby in 2004, the Kessler's goby (or bighead goby) in 2007 and the monkey goby in 2009. All these species were observed in the Lake IJssel region in 2012. The round goby showed a spectacular increase in numbers in Lake Marken (Markermeer) in 2012.
Monitoring and sampling
IMARES Wageningen UR takes various samples and carries out various monitoring projects in Lake IJssel and Lake Marken. To this end, samples are taken from both open water and the shores. In addition, catch data are collected from a number of professional fishing companies in a project aiming to map out rare fish and diadromous fish. The data offer a good basis for monitoring the advance of the exotic gobies in Lake IJssel and Lake Marken.
Round goby doing well
The round goby in particular (see photo) has shown a spectacular increase in numbers. The round goby was observed for the first time in the southern part of Lake Marken, by Muidenberg-Muiden (see figure, bottom left) in 2011 in the shore sampling project, while the standard sampling in open water did not reveal its presence in 2011. The species was also detected in 2011 by professional fishing companies working on Lake Marken, as well as in Lake IJssel. In 2012, the species was found all over Lake Marken, both in open-water samples and in shore samples (see both figures on the right). At a number of locations in the shore sampling, the round goby was by far the most common fish species, and in open-water sampling, too, the species was one of the most common species in sample catches. Furthermore, in 2012 the fish species was once again found in Lake IJssel in fishing catches, despite not being found in the shore samples and open-water samples.Figure: Catches of round goby in the trawl net during the standard open-water sampling (top two figures) and alongside stone shores during the shore sampling (bottom two figures) in 2011 and 2012. In 2012, the round goby is found in both the open-water samples and the shore samples throughout Lake Marken, but not yet in Lake IJssel.