Stone crayfish released into the wild in the Sihlwald forest

Crayfish used to be widespread in Switzerland. However, the four native species are now under severe pressure. In 2011, the federal government launched the "Swiss Crayfish Action Plan". This proposes various measures to protect the native crayfish species. These include, among other things, colonization and reintroduction in suitable bodies of water.

And with good reason: crayfish play an important role in the aquatic ecosystem. As omnivores, they break down dead plants or the remains of dead fish, for example. They also serve as food for numerous animals, including larger fish such as pike, as well as foxes, otters, martens and herons.

Stone crayfish for the Chrebsächerli

Environmental engineer Marc Furrer from the ZHAW analyzed the habitat potential for crayfish in the northwest of the Sihlwald in 2022. The Chrebsächerli area is also located there. This field name indicates that crayfish used to be found here. Furrer no longer found any crayfish populations in the area investigated. However, he believes that the Tomenrainbach stream, which rises above the Chrebsächerli, is a suitable habitat for the reintroduction of stone crayfish and jackdaw crayfish.

Promoting rare native species

This afternoon, the time had finally come: 40 adult stone crayfish were released into the wild in Chräbsächerli. They come from donor streams in the Zimmerberg region.

"The stone crayfish is the smallest European crayfish species. It inhabits watercourses with a stony substrate that are free of organic wastewater and therefore finds good conditions in the Sihlwald", explains Karin Hindenlang Clerc, Managing Director of the Foundation Wildnispark Zurich. "In the strictly protected core zone of the park, humans should no longer have any influence on nature," explains the biologist, "but the nature experience zone still has great potential in various places to promote rare animal and plant species. We are seizing this opportunity."

Rolf Schatz, President of the Sihl Valley Nature Conservation Association and specialist in crayfish, was responsible for the transfer of the crayfish. He has already supported several crayfish reintroduction projects: "We also have to get involved with species that may not look very attractive at first glance." Crayfish are an important indicator of the good quality of a body of water. He then adds: "Crayfish are stubborn, that's what I like about them."

The reintroduction in Sihlwald will last a total of four years. From 2024 to 2026, crayfish will be introduced each fall. A final check will take place in 2028.

Harald Huber, President of the Förderverein Wildnispark Zürich, which now has over 600 members, also has reason to be pleased. The association is committed to the stone crayfish: it collects donations and actively helps with the reintroduction. Over 40 members were present at the reintroduction event. Further donations for the project are welcome.

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The four native crayfish

Habitat loss and invasive species are making it difficult for the four native crayfish species to survive. The noble crayfish, which mainly lives in still waters, is endangered, while the stone crayfish and jackdaw crayfish, which prefer streams and rivers, are highly endangered. The Italian jackdaw crayfish, which is native to the canton of Graubünden and Ticino, is even threatened with extinction.

Further information:

• Karin Hindenlang Clerc, Managing Director of the Zurich Wilderness Park Foundation, karin.hindenlang@wildnispark.ch, 044 722 55 18
• Mirella Wepf, Project Manager Communications, Zurich Wilderness Park Foundation, mirella.wepf@wildnispark.ch, 044 722 55 24
• Rolf Schatz, President of the Sihltal Nature Conservation Association, rolfschatz@hispeed.ch, 079 413 29 46

Images in high resolution:

ZIP with a selection of images below.

Captions:

• Young stone crayfish: crayfish have to shed their skin in order to grow. Image: Photo archive of Wildnispark Zurich 
• The release site: Thanks to its near-natural banks and lots of dead wood, the Tomenrainbach is a suitable habitat for crayfish. Image: Wildnispark Zurich /Mirella Wepf
• Lively interest in an endangered native species: over 40 members of the friends of Wildnispark Zurich took part in the reintroduction. Image:Wildnispark Zurich /Mirella Wepf
• Rolf Schatz: The crayfish specialist transferred 40 adult crayfish from waters in the Zimmerberg region to the Sihwald. Two thirds females, one third males. Image:Wildnispark Zurich /Mirella Wepf
• Karin Hindenlang Clerc, Managing Director of the Foundation Wildnispark Zurich: "We should use every opportunity to promote rare and endangered species." Image:Wildnispark Zurich /Mirella Wepf