The mitten crab is on the IUCN's list of the world's 100 most dangerous invasive species. In Germany, the crab is found in large numbers in practically all coastal watercourses. Every spring, millions of young mitten crabs migrate up the rivers. On their journey, they overcome the walls of weirs and other obstacles. Over the next four to five years they grow into crabs with a leg span of up to 30 cm. They eat everything that comes in front of their claws. Every year in autumn, hundreds of thousands of adult crabs make their way back to the sea to spawn, where they die exhausted after reproduction.
This mass occurrence of crabs has consequences for aquatic ecosystems, especially in the waters close to the coast. Damage to bottom-dwelling organisms (worms, mussels and insects) as well as a decline in aquatic plants have been linked to the crabs. The crabs also cause damage to shoreline structures and regularly block water intake points, e.g. from power plants, along the major rivers.
It is important that the fight against invasive species envisaged by the EU, and thus also against the mitten crab, is finally tackled in the member states. How this can be implemented in the case of the mitten crab will be demonstrated by the EU InterReg project "Clancy".
Institutions from Belgium, France, Sweden and Germany, including the AWI, are testing an innovative trap concept at suitable locations in various watercourses. The permanently installed traps can catch a large proportion of the migrating crabs. The aim is to significantly reduce the mitten crab population in the selected waters within the next 4 years.
The AWI is responsible for the supervision and evaluation of four of these traps in the Weser catchment area. In addition, the AWI is working with industry partners to develop sensible utilisation concepts for the caught crabs. The focus is to use the crabs as feed in aquaculture and the extraction of chitin from the crab shells, a polysaccharide that is currently in great demand by pharmaceutical and cosmetics industries. Together with industrial partners, a functioning medium-term financing model for the costly operation of the traps has to be found. The AWI is also responsible for the international coordination of the joint public relations and media work for this project.
The AWI will build and install four crab traps. The traps will be deployed in spring 2024 at three locations in Bremen, Bremerhaven and Lower Saxony.
We will evaluate the number and weight of the mitten crabs. In addition, a species identification is also carried out. For some years now, not only the Chinese mitten crab has been spreading in Europe, but also the Japanese mitten crab. In the meantime (at least in Belgium) hybrids of the two species have been found. Therefore, genetic methods will be used in random sampling. This campaign begins with the deployment of the traps and ends with the autumn migration in October 2027.
Besides catching the crabs, this project is also about informing and sensitising a broad public. Especially angling clubs, conservationists and authorities will be provided with information generated in this project in in the appropriate form. Together we can successfully combat the mitten crab and later perhaps also other invasive species.
For an optimal use of the resulting crab biomass, knowledge of the contents but also the pollutants of the crabs is crucial. For this purpose, juvenile crabs from the spring migration and adults from the autumn migration will be analysed at all trap sites for fatty acid profiles, protein profiles but also for pollutants as heavy metals, PCBs, pesticides and PFAS. These results are then used to determine the possible uses.
Are all European mitten crabs related to each other or does each river basin have its own mitten crab population? This is an important question that still needs to be clarified in order to develop the right control strategy. Therefore, mitten crabs from all sites are being examined for their genetic relationship and origin.
Together with partners from industry, research and authorities, we will look for a concept for the use of the caught mitten crabs. One goal is to develop a long-term financing concept for the expansion and permanent operation of the traps. Another topic will be the development of the necessary infrastructure as well as animal welfare aspects such as the professional killing of large amounts of crabs.
We will formulate new feeds for aquaculture to replace the fishmeal by crabmeal. These will be tested on shrimp and sea bass in our recirculation system. These species naturally feed on other crustaceans as well. In addition to the growth rate of the animals, we also focus on the digestibility of the feed.
Lead: Oliver Hauck
Media: Björn Suckow
Contact: Mail to Oliver or Björn
(0)471 4831 2813
Duration: 5 years
Partners: Flemisch environmental agency, Universität Antwerpen, Province of East-Flanders, Study Group of Coastal and Estuarine Ecosystems, CSLN, University of Skövde, Technische Universität Dresden
Funding: EU-Interreg North Sea Region
Would you like to participate in researching the right control strategy against the mitten crab? We offer you the opportunity to write practically relevant bachelor's and master's theses on this exciting topic. Just send an email with your study background, the time period and the topics that interest you to Oliver.
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.
