Why are EU countries collaborating to reduce the population of Chinese mitten crabs?
The reason is that the Chinese mitten crab (scientific name: Eriocheir sinensis) is listed by the International Union for Conservation of Nature (IUCN) as one of the “100 Worst Invasive Alien Species in the World.”
It is no coincidence that the IUCN classifies the Chinese mitten crab among the 100 worst invasive alien species globally. This species is virtually indestructible: They eat almost anything; can live both on land and in fresh and saltwater; particularly, they reproduce very rapidly, with females laying between 250,000 to 1 million eggs at a time.
The IUCN further describes: “Eriocheir sinensis is a migratory crab that has invaded Europe and North America from its native Asia. During its mass migration, it contributes to the temporary local extinction of native invertebrate species. They alter habitats through erosion caused by their burrowing activities and inflict hundreds of thousands of dollars in damages to fisheries and aquaculture each year due to predation and gear destruction.”
Close-up of a Chinese mitten crab. (Photo: Aphotomarine).
Underside of the Chinese mitten crab. (Photo: Aphotomarine).
The Chinese mitten crab (also known as the Shanghai crab) is a medium-sized burrowing crab. They are named so because their hairy claws resemble furry gloves.
CNN comments that the Chinese mitten crab is a formidable species. Their dark brown bodies can grow up to 8 cm, and when their claws are extended, their total body length can reach up to 25 cm.
EU Loses Tens of Billions of Euros Due to Invasive Alien Species
It’s hard to believe! But EU member countries estimate that invasive alien species have caused economic damages to member states amounting to 12 billion Euros annually.
The EU’s Environment website states that invasive alien species (IAS) are animals and plants that have been introduced, either accidentally or intentionally, into a natural environment where they are typically not found, causing severe negative consequences for their new environment.
IAS pose a major threat to native plants and animals in Europe and are one of the five primary causes of biodiversity loss. They can also have significant negative impacts on the economy (their economic impact in the EU is estimated at around 12 billion Euros per year) and human health, such as causing severe allergies and burns.
Close-up of the “hairy” claw of the Chinese mitten crab. (Photo: Aphotomarine).
This is why the EU has announced a 2030 Biodiversity Strategy to commit to managing IAS and preventing their spread. The Chinese mitten crab is one of them.
The Chinese mitten crab was first identified in Europe over a century ago, in a river near Bremen, Germany.
According to scientists, they likely made their journey from their native Asia in the ballast water of ships. Since then, the population of Chinese mitten crabs has exploded across the European continent. This species’ population began to increase exponentially, with numbers estimated in the millions.
Today, 18 out of 27 EU member countries report large populations of this species and have included the Chinese mitten crab on the EU’s list of invasive alien species of concern.
Environmental and biodiversity organizations in the EU continuously warn of the negative impacts of the invasive species, stating that the Chinese mitten crab: disrupts aquatic food chains; spreads crayfish plague; and increases bank erosion due to their burrowing activities.
Recognizing the economic, human health, and biodiversity impacts on the continent, eight scientific organizations from four EU countries (France, Belgium, Germany, Sweden) have collaborated to develop a Europe-wide strategy to effectively and sustainably mitigate this invasive species. In 2023, European scientists agreed on a continent-wide project funded generously by the EU called “Clancy” (full name: European CLANCY project).
Clancy aims to address the massive invasion of the Chinese mitten crab by finding various ways to reduce their population and protect the native ecosystems that are being destroyed by invasive species.
So far, the most successful strategy has been a crab trap (crab catch trench) developed by the University of Antwerp and the Environment Agency Flanders in Belgium. Since 2018, Belgium has piloted this trap and has captured 3 million Chinese mitten crabs.
Metal trap installed in the riverbed, where migratory crabs fall in. (Photo: Paul Van Loon/CNN)
“Our trap is like a mini metal channel, installed in the river – where the crabs fall in while foraging. Since they cannot swim out like other aquatic species, they are forced to crawl along pipes leading to cages on both banks. At this point, we collect and process them,” explained Jonas Schoelynck, a professor of aquatic ecology at the University of Antwerp (Belgium).
Another trap of a similar design, independent of the EU project, was installed in the UK in 2023.
Clancy plans to deploy more types of traps across Belgium, Germany, France, and Sweden in the coming years, followed by broader replication in other EU countries.
Chinese Mitten Crabs Invading Cities
The traps will target areas where large numbers of Chinese mitten crabs migrate. In the autumn, adult crabs migrate from freshwater to the sea to spawn, and in the spring, juvenile crabs move upstream from the sea. They may be small but can persistently travel remarkable distances, up to 10 km a day, Professor Jonas Schoelynck stated, adding that some have been spotted over 1,000 km from the coastline.
During these extended periods lasting for months, they appear most often, gathering around drainage outlets or moving on land to avoid weirs and other obstacles.
Professor Schoelynck, recalling hundreds of crabs crawling through the streets of Lier, a small town in Belgium at the confluence of two rivers, said: “Sometimes they go the wrong way and end up in the city center.” Here, they can also crawl up walls and sneak into residents’ damp bathrooms.
European scientists say that this crab species thrives in the European environment for many reasons. Like most invasive species, the Chinese mitten crab has no natural predators, is an opportunistic feeder, and is highly resilient. Climate change may also play a role, as warmer waters may make the crabs feel more comfortable.
Additionally, there is a strong genetic diversity of this species. Scientists in Europe have reported on crabs that are hybrids between the Chinese mitten crab and the Japanese crab. This hybridization allows these crabs to survive better against challenges. This, along with improved water quality (in recent decades) and possibly climate change, is contributing to the population explosion of crabs that the entire continent is witnessing.
Belgium has captured 3 million Chinese mitten crabs from its trapping initiative. (Photo: Heleen Keirsebelik/CNN).
One of the major unanswered questions is what to do with the crabs once they have been collected.
A scientist at the Alfred Wegener Institute (based in Germany) and involved in the Clancy project noted that different EU countries have different animal welfare regulations. In Germany, scientists are only permitted to kill crabs by boiling or using electric shock. In Belgium, they freeze the invasive crabs.
While the Chinese mitten crab is considered a seasonal delicacy in China, Professor Jonas Schoelynck stated that they have little meat and are therefore not favored in the European market. He added that many of the crabs caught in traps are often juvenile crabs, while those consumed in China are larger, mature crabs.
Scientists acknowledge that this is a work in progress, but they hope that Europe’s coordinated efforts will help gather knowledge and data about this invasive species and its impacts, assisting in forming an international strategy to control the population of the Chinese mitten crab.
