The “yabby”. It’s the little name we give her in Australia, where she’s from. Murray’s crayfish was detected for the first time in France, in a small coastal river in northern Finistère. Now, this “Invasive alien species” is endowed with a great capacity to extend its territory and colonize the rivers. And the consequences can be dramatic on local environments and ecosystems: proliferation of pathologies, competition with other species, predation, etc.
Introduced for breeding
But how did it get there? In Europe, it was mainly introduced for breeding. Sometimes it is used in aquariums. “People like to put crayfish in the ponds to have fun, fish and eat them, explains Thibault Vigneron, head of the knowledge service at the Brittany regional office of the French Office for Biodiversity. The crayfish then reach the natural environments which they colonize. “
Environments often already destabilized by human activities and therefore much less resistant.
Example in Loire-Atlantique, where crayfish from Louisiana escaped from a farm colonized and completely upset the environments of the Vilaine, Brière, and from Grand-Lieu lake.
For our “yabby”, we are not there yet. It was a river technician who discovered the first specimen in late 2018. The information was reported to the French Office for Biodiversity. A scientist from the University of Poitiers confirmed, by genetic analysis, that it was indeed Cherax destructor (the Latin name for Murray’s crayfish). Field analyzes then determined that it was present in 4 artificial water bodies and on 3-4 kilometers of stream.
Present in an area in northern Finistère
Or exactly ? Thibault Vigneron does not wish to give the precise location: “We want to avoid any risk of people going to look for them and putting them in other ponds and thereby gaining other parts of the territory. “ Because, for the moment, the population of “yabbies” has remained limited to this area of northern Finistère. She would probably have been there for over ten years! “The fairly low temperatures and the fact that the river overlooks the sea may explain this fact. “
Work to level artificial water bodies must be carried out to restore the environments there. “This should limit the expansion of their population. “ To eradicate them completely would require drastic means, such as the use of a biocide, with collateral damage to other species. There is no question at the moment.
As for trying to fish them all, it’s counterproductive: “When we fish, we boost populations: the large individuals eliminated, the reproduction rate increases to fill the void. “
Thibault Vigneron therefore calls on everyone’s responsibility not to introduce exotic species of crayfish into ponds or watercourses and thus commit an irreparable upheaval.