Roads, gardens and even parking lots, crayfish are invading the Saint-Nazaire region

“I had one this morning in my garden in the middle of a subdivision “, “There were loads of them at the Saint-Joachim college”… Since mid-June 2024, the so-called invasive species has never lived up to its name so well. Indeed, near Saint-Nazaire, the inhabitants of the communes of Briere almost no longer count Louisiana crayfishwho took possession of the gardens and roads in the area.

Colonize other territories

“This year, it’s clear, there is a very clear increase in the population made visible by hydrological conditions . The crayfish have left the waterways to colonize other territoriesand reach the gardens and bocages”, notes Jean-Patrice Damien, head of the biodiversity service and referent on invasive species for the Brière park.

But for the specialist, we must not confuse population dynamics and the factors that make them visible. “Once the water level goes down in the marsh, we won’t see them anymore.”

“Avoid the spread”

Introduced by man in France, in the 70s the exotic species disrupts the ecosystem and affects the biodiversity of the Brière park :

It is omnivorous and burrowing (which digs the ground with ease, Editor’s note). It therefore increases the turbidity of the water which will create a lack of oxygen in the aquatic environment.

Nearly 200 crayfish captured in 24 hours

Within the Park, the first proliferations were noted at the end of the 90s. Since this period, scientists have regularly observed population explosions as well as declines.

These are population dynamics for which we do not necessarily know the reasons.

The results of on-site monitoring demonstrate this: in 2022, 15 crayfish were captured in 24 hours.

« Nearly 200were recovered on June 25,” indicates the manager who felt a shift last year.

Birds and humans alike enjoy it

A source of food for many birds (spoonbills, egrets, storks, etc.), crayfish are also edible for humans (cold, on the barbecue, in the pan, etc.).

“It is absolutely necessary to prevent its spread and do not put them back in the water», Recommends Jean-Patrice Damien.

Within the park, amateur fishing is authorized (or even encouraged) by holding a permit.

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