Efforts underway to reduce giant catfish numbers in Dordogne and Gironde

Efforts are underway to reduce the numbers of giant catfish in rivers in Dordogne and Gironde, in a bid to protect biodiversity.

Giant freshwater catfish - a major predator, and sometimes called ‘the monster of the rivers’ - were introduced into the region’s rivers in the 1980s, from other major European and Russian rivers including the Danube and the Volga. The fish can grow to be more than 2.5 metres in length and 100kg in weight.

Now, its numbers are threatening other species, including the migratory endangered lamprey and eel, as well as European and Atlantic shad, sturgeon, sea trout, and salmon.

Local authorities, including CAPENA (Centre pour l'Aquaculture, la Pêche et l'Environnement de Nouvelle-Aquitaine) are now organising professional fishing campaigns to help control the catfish population, without eradicating it completely. 

Since February 10 this year, all fishermen in the area are also now banned from releasing any caught catfish back into the rivers, via decree from the Fédération de Pêche de la Gironde (see below).

“We have already caught more than 200 in this area in the space of two or three weeks,” said François Druyer, who is part of the CAPENA anti-catfish mission, to France 3.

“We capture between 800 and 1,200 every year, from a short [river] stretch of just two kilometres. The closer we get to the estuary, the larger and deeper the river, and the bigger the catfish.”

Migratory meals

Mr Druyer also looks at what the recently-caught catfish have eaten over the past 12 hours (by literally emptying and reviewing what is in its stomach) in a bid to improve monitoring of their impact. This is a technique repeated across the region.

“I have found as many as seven lampreys in the stomach of a single catfish,” said Robert, a professional fisherman in the Garonne, to France 3. “As the catfish population grows, the populations of other species are declining.”

“In the four years I have been here, we have been finding more and more migratory species in their stomachs,” said Mr Druyer. “The lowest figure I have recorded was 85%, that rose to 99% last year.”

“There are already plenty of other factors affecting the decline [of migratory species] populations: pollution, climate change, the destruction of habitats, spawning grounds, and dams,” said David Dubreuil, from the Fédération de Pêche 33 (Gironde). “But the fear today is that the catfish will deliver the final blow."

Slow-but-sure results

The campaigns to reduce the numbers of catfish do not bring results immediately, explains Mr Druyer, but consistent action now can bring tangible results in future.

“Like many things in ecology, we are taking action that will only become apparent in the years to come. This is not something that happens overnight. We have to continue until we have removed enough catfish so that the lampreys and shad can swim upstream unhindered,” he said.

“By applying pressure like this every year for a month or two, we can reduce the population a little,” added Robert. “After all, most of these fish are 15 to 20 years old. If we keep at it, we should eventually manage to clear the river.”

Overall, campaigns like this in the Garonne and Dordogne rivers over the past six years have managed to catch hundreds of tonnes of catfish, without eliminating the species entirely.

“[The fishermen] are here to study the stomach contents, and also to reduce the pressure on migratory species,” said Mr Dubreuil. “We know we will never manage to eradicate the catfish, and that is not the goal.”