Fewer mitten crabs = healthier waters?
But why go to so much trouble? “The sheer mass of crabs that migrate along the rivers is a huge problem,” says Sengdavanh Thepphachanh, a researcher at the Institute of Hydraulic Engineering and Technical Hydromechanics, Dresden University of Technology (TUD). “Although no-one knows exactly how many there are, various sources indicate that we’re talking about several million. And we can safely assume that these massive numbers also negatively impact the aquatic ecosystem.” For example, studies have shown that the appearance of large numbers of mitten crabs corresponds to a decline in soil biota (worms, bivalves and insects) and water plants. In addition, they damage riverbank structures and clog up water intake points – like those of power plants located near major rivers. The crabs also pose a problem for fishers, as they not only eat their bait, but also damage their nets and traps and gnaw on the fish they’re trying to catch. “Therefore, if we can manage to substantially reduce the mitten crab population, we’ll also be making an important contribution to reaching the targets of the EU’s Water Framework Directive, since it will mean improving the ecological status of our rivers,” says Torsten Heyer, the project’s coordinator at the TUD.
Testing the trap at a variety of locations represents an important first step in that direction. At the same time, valuable data will be gathered on the size of the mitten crab population and interrelatedness within it. All results will then contribute to a Europe-wide strategy for effectively combating the mitten crab. “The project is the first step towards combating this invasive species across borders, and ideally, to restoring native waters and waterways to their original state. Needless to say, the mitten crabs caught in the process will have to be killed humanely. There’s also the question of finding a sensible use for the meat,” explains AWI researcher Björn Suckow, who coordinates public relations for the project. “Consequently, the project will be accompanied by public campaigns, along with information on the steps planned.”
Eight institutes, one goal
In this regard, the project’s collaborative international approach will be critical to achieving a lasting success. Along with Dresden University of Technology and the Alfred Wegener Institute, Flanders Environment Agency, the Province of East Flanders and the University of Antwerp (Belgium), GEMEL and the Cellule de Suivi du Littoral Normand (France), and the University of Skövde (Sweden) will contribute essential expertise in a range of areas.
In this context, the TUD’s research focus lies in particular on investigating the mitten crab’s rheotactic behaviour, i.e., on the question of which flow conditions it prefers and under which hydraulic conditions it can no longer migrate. Armed with this knowledge, it will then be possible to identify potential, optimal and water-body-specific locations for the crab traps. In addition, the TUD will install and maintain a trapping site on the Elbe near Dresden to determine whether, and if so, in what numbers mitten crabs from the North Sea are capable of migrating hundreds of kilometres upriver.
Besides the international coordination of public relations, the AWI will be responsible for maintaining, and assessing the catches for, four traps in the catchment area of the Weser River. It will also collaborate with partners from industry to find sensible use concepts for the crabs trapped. Here, the focus will be on using them for feeds in aquaculture and on harvesting chitin from their shells for use e.g. in the pharmaceutical industry.
This project receives funding under the Grant Agreement Number 41-2-51-22 from the Interreg North Sea Programme co-funded by the European Union. You can find more information about the project here: https://www.interregnorthsea.eu/clancy