Concern around freshwater fish in Wallonia: 10 out of 40 species are threatened in waterways. In particular the drought, and the introduction of more aggressive exotic fish. The Walloon region and the University of Liège undertake a census.
In Moha (Wanze), scientists work with their feet in the water. The exercise requires patience and unfailing vision. The census of fish is carried out by electric fishing, a scientific process, in the Mehaigne river, a tributary of the Meuse.
“When the fish are close to the current, they are slightly stunned. We can capture them with the landing net and then place them in basins to control them scientifically”explains Michael Ovidio, director of the Aquatic Resources Management Unit at ULiège.
Eel population plummeted 97% in 20 years
Its teams identify populations, an essential means of monitoring the evolution of species and their development, especially since some are in critical danger.
Michael spots an eel: “It is a species that is threatened, its populations have dropped by 97% in 20 years in the Walloon region and therefore effectively it is a species that is in critical danger of extinction”.
Several threats to fish
The Red List, which also includes Atlantic salmon, is being developed. In the Walloon region, around ten species of freshwater fish are threatened. In addition to these two critically endangered fish, there are black bream, pike, grayling, bleak and brown trout.
Among the causes put forward, we note the destruction of the banks and the drought, accentuated in recent years, but not only. “There’s also the fact that there’s maybe less food in the streams or that sort of thing and they’re exhausted and they can’t get back to sea to reproduce. “emphasizes Justine Gelder, PhD student in the Aquatic Resources Management Unit at ULiège.
“Invasive Alien Species”
The fish caught are then listed and classified. Surprise for the scientists, they come across an exotic crayfish and it’s not necessarily good news. “According to international nature conservation organizations, the second cause of the collapse of biodiversity is invasive alien species, so it is not at all negligible in terms of problems and aquatic environments are no exception”specifies Samuel Vanderlinden, the coordinator of the river contract – Meuse Aval.
Of the ten species caught, the observed biomass seems lower this year. “There was definitely something that happened in the river that lowered the number of fish. It could be episodes of heat waves, it could be the floods in the summer of 2021. So there, it’s difficult to say for the momentsays Michael Ovidio.
These data will be used to complete the profiles of the species observed over the years. Each year, these scientists carry out around fifty surveys throughout Wallonia.