Mitten crabs are found along the entire North Sea and Baltic Sea coast, with larger numbers in Belgium, the Netherlands, France and Germany. The larvae are spread by coastal ocean currents. Therefore, successful control in Europe can only succeed if all countries make a joint effort to reduce the population. How such international cooperation should look like will be developed in the Clancy project.
A total of 10 stationary traps will be installed in 6 different river systems. In addition, 56 to 58 mobile traps will be deployed, including shellfish traps in France and Sweden. These will be used to identify suitable sites for the possible construction of further stationary traps.
Information on the activities at country level can be found here.
Situation of the Chinese mitten crab in Belgium
The Chinese mitten crab was first observed in Belgium in 1933. In the following years the crabs became very abundant until they largely disappeared around the 1950s. Since the 1990s the population has increased again, which is evidenced by the large catch numbers in the recent years. Currently, three crab traps are already operational in Belgium. Two traps are managed by VMM and are located in the Kleine Nete River in Grobbendonk and the Driessesloot in Kalken. The third trap is managed by the Province of East-Flanders and is located in the Melsenbeek.
What CLANCY is doing in Belgium
In Belgium, the Flanders Environment Agency, Province of East-Flanders and University of Antwerp work together to control the Chinese mitten crab. Within CLANCY, the patrimony of crab traps will be expanded. There will be additional traps on the Zwalm, Wimp and Bollaak. The VMM is lead partner and will build an updated version of the current trap in Grobbendonk, collect the caught crabs and deliver samples to the University of Antwerp as part of population and genetic research.
The University of Antwerp will act as data- and knowledge hub. This means that they will combine the data from the different traps (e.g. catch numbers), of the different populations (e.g. DNA) and of the different effects after placing the traps (e.g. regrowth of macrophytes) across Europe, and make them available to the broad public.
The Province of East-Flanders will install two more traps and will monitor, together with the University of Antwerp and the VMM, the impact and functionality of these traps.
Catches in Belgium
After a large peak in 2019, the catch numbers decreased in the trap of Grobbendonk. In 2023, lower numbers were observed in Grobbendonk, but high numbers occur in the Melsenbeek. The flow or water temperature possibly lures the crabs to one or the other direction.
Situation of the Chinese Mitten Crab in Northern France
The first Chinese mitten crab in France was found in Boulogne harbour (Northern France) in 1930. Since then, it has been regularly observed in rivers in the Hauts-de-France and Normandy regions, but there is no data on the number of specimens per river as no monitoring has been carried out. Numerous catches, particularly of ovigerous females, are made by fishermen during the spring and summer periods in coastal areas. These catches are observed in the monitoring of ichthyofauna for the WFD in the Somme, Authie and Canche estuaries, and abundances show seasonal, spatial and interannual fluctuations.
What Clancy is doing in Northern France
GEMEL and CSLN will be responsible for acquiring scientific data (abundance, sex-ratio, population dynamics, reproductive cycle, sea-river migration, state of aquatic ecosystems colonised by crabs, etc) on 23 rivers in France between the Belgian border (Aa river) and the Normandy region (Orne river) during the 4 seasons of the year (i.e. winter, spring, summer, autumn) in order to follow the spatial and temporal distribution and monitor the state of colonisation of the Chinese crab at the Northern France scale, as no data currently exist.
Scientific data will be acquired throughout 3 years (2023 to 2026) in order to have a good representation of the colonisation of the rivers of northern France by the Chinese mitten crab. We will set our own traps (shellfish traps) since the VMM trap is not adaptable to all our rivers. We will provide samples from its 23 study sites to the Antwerp University for genetic studies to know if the populations are connected to each other at the North Sea level.
We will communicate the results to the general public (GEMEL and CSLN websites, local scientific events, schools, etc.), to water managers (Artois-Picardy and Normandy Water Agencies, French Office of Biodiversity, Fishing Federations, Fisheries and Marine Farming Committee, etc.) and to State services (Affaires Maritime, Hauts-de-Franceand Normandy Region, etc.)
Situation of the Chinese mitten crab in Germany
The first Chinese mitten crab in Europe was found in 1912 in the river Aller close to the village Rethem. Since then, it has spread steadily and is now found in all northern German river systems, often in large numbers. However, the number of crabs decreases somewhat as they migrate upstream. In the Rhine, Elbe and Oder, animals have been found up to 500 km upstream.
The main sufferers so far have been the river fishermen, whose nets and fish traps have often been damaged by the crabs or whose catch has been eaten. But the crabs are also unpopular with anglers because they like to eat fishing bait. In addition, it happens that cooling water intake points of power plant rakes are clogged by huge numbers of crabs. The damage caused by the animals to the water ecosystem is difficult to estimate. This is partly due to the lack of long-term studies, but also to the fact that the lower reaches of the major rivers had already lost their natural species communities due to human activities before the arrival of the mitten crabs.
Find more information on our german project site
What Clancy is doing in Germany
In Germany, the TU Dresden and the Alfred Wegener Institute (AWI) are participating in the project.
The TU Dresden is planning to investigate the hydraulic conditions in the vicinity of the traps in order to identify preferred migration paths or possible hydraulic barriers. Thus, trap locations can be optimised. In addition, TU Dresden is setting up and maintaining a trap in the Elbe River, about 600 km upstream of the river mouth in the German Bight.
The Alfred Wegener Institute is responsible for the construction and supervision of four traps, among others at the Weser weir in Bremen. In addition, together with partners from industry and authorities, we are looking for ways to use the resulting crab biomass sensibly and to develop the necessary infrastructure concept. Tests with fish feed for shrimps and sea bass from the crabs are being investigated at the Centre for Aquaculture Research.
The fish ladder at the Weser weir. The mitten crabs have to pass through this canal to reach the Mittelweser region. An ideal spot to catch them.
Situation of the Chinese Mitten Crab in Sweden
The first observation of the Chinese mitten crab (Eriocheis sinensis) was noticed 1936 in Bråviken/Östergötland, Baltic Sea in Sweden. However, the situation differs from other countries that are joining the CLANCY project: Sweden has still no established population of the invasive Chinese mitten crab. Swedish winters are long and too cold, that is why the crab cannot reproduce. Adult individuals are reported along the Swedish west coast and the Baltic coastlines, but also in the Lake Vänern, Göta Älv and Lake Mälaren. No larval stages or juvenile crabs were observed yet.
In Lake Vänern, which is the third-largest lake in Europe, the first Chinese mitten crab was observed in 1954. At the beginning of 2000 different occurrence records were noticed in Kinneviken/Linköping of fishermen. Those observations were frequently until the year 2010, thereafter the observations decreased. Genetic analysis could show that those individuals collected 2003-2008 come from the Elbe River Population in Germany with ballast water exchanges from ships.
A recent pilot study, performed by the University of Skövde and the County Administrative Board Västra Götaland Region, mapped the situation in Lake Vänern in spring 2021. Some traps were placed in the Göta Älv and Lake Vänern, but without any catches. Fishermen was interviewed and asked for observations. They reported an increased occurrence between 2018-2020 in contrast to the years 2012-2017. In general, more observations were found on the western side of the lake (between Vänersborg and Kristinehamn) in contrast to the eastern side of the lake (between Karlstad and Mellerud). The pilot study did not observe any juvenile stages either.
An additional study was practiced by the County Administrative Board in Lake Mälaren (autumn 2022). By-catches were reported by fishermen between August and October. In total, 27 catches of adult specimens were observed. The caught Chinese mitten crabs were with PCR analysis tested for the crayfish pest and the white spot syndrome virus, but all tests showed negative results.
What Clancy is doing in Sweden
The School of Bioscience, University of Skövde and the Lake Vänern Society of Water Conservation will co-operate with local fishermen and recreational fishing clubs to monitor and catch the Chinese mitten crab in Lake Vänern and the Göta Älv. Additionally, we will install 8-12 mobile traps at 2-4 different localities. Different types of traps (e.g., crab creels) should be tested. One special focus will be laid on special developed ‘pipe traps’ to catch juvenile crabs.
Scientific data will be collected between 2023-2026, on sex-ration through gender determination, carapax measurements and abundance. Moreover, crab material will be collected for molecular studies to determine the origin of the crabs found in Sweden.
The project will also be communicated actively in different Swedish media channels.
Find more information on our Swedish project activities on those websites:
https://www.his.se/forskning/systembiologi/ekologisk-modellering/clancy/ (in Swedish)
https://www.his.se/en/research/systems-biology/ecological-modelling/clancy/ (in English)
Each yellow dot represents one occurrence record, while a blue dot symbolizes multiple records.
Our study area is Lake Värnern, the largest lake in Sweden. Each red dot is the catch of a mitten crab by one of our fishermen between 2005. to 2021.