Mitten crab plague: Researchers use traps in the Weser!

Mitten crab plague: Researchers use traps in the Weser!

The invasive mitten crab, which once reached Europe from distant China via ship ballast water, represents a serious problem for the native flora and fauna in the North Sea region. A team of researchers from the Alfred Wegener Institute (AWI) in Bremerhaven has now started an innovative project to counteract this threat. It is planned to close off the Weser in Bremen with special traps in order to better control the population of these crabs. [ZDF] reported on the first installations in April.

The mitten crab is not only a nuisance for fishermen and conservationists, but also one of the most feared invasive species in Germany. It can travel up to ten kilometers a day and migrates through the waters every spring to advance further and further into the rivers. In comparison, the local fauna hardly dares to undertake such a migration. While the crabs in their environment multiply at lightning speed - females lay up to a million eggs - this also has fatal effects on the populations of other animal species. According to reports from fishermen, there is a decline in worms, insects and mussels in the affected areas. [District newspaper] exposes the damage that crabs cause to fishing nets and puts pressure on ecosystems.

Unique traps for the Weser

The traps installed in the Bremen barrier are specifically designed to block the crabs' path back to the North Sea. In a clever procedure, the traps can be installed at low water levels without causing major disruption to the ecosystem. The researchers are confident: They expect that 80 to 90 percent of migrating crabs will fall into the traps. They also want to catch adult crabs on their return migration. [ZDF]

This measure is not only intended as a control, but also as part of a larger project. The “Clancy” project is investigating whether the trap concept can also be implemented in other river systems. In addition, the AWI team is competing with the aim of developing sustainable use of the crabs caught. At the moment, many of the captured specimens end up in biogas plants, mainly due to pollution. Nevertheless, work is being done on recycling them - flour is already being made from freeze-dried crabs, which is used as a substitute for fish meal in animal feed.

Global challenges and local solutions

The problem of invasive species such as the mitten crab is not just a regional but a global issue. The World Biodiversity Council IPBES recently published an assessment summarizing the negative impacts of invasive alien species on biodiversity and ecosystems. It is emphasized that the threat posed by such species may increase in the future, particularly due to human activities. [IPBES] calls for urgent action to counteract biological invasions.

Overall, it shows that the work on the trap concept offers important approaches to combating the mitten crab. A holistic approach that includes both control and exploitation of crabs could make it possible to better manage the problems caused by this invasive species and protect native ecosystems.

For further information on the topic and current developments, it is worth taking a look at the media reporting: [ZDF], [Kreizeitung] and the comprehensive analyzes of [IPBES].