Pseudorasbora parva or asian stud. Introduced accidentally in Eastern Europe in the 1960s, the species spread to France from the 1980s, on the occasion of exchanges of fish between fish farms. Today, its possession, transport and marketing are prohibited because it can be a healthy carrier of a pathogenic germ that is deadly to other aquatic animals.
In Aurillac, in Cantal, the alert was given last fall, after this invasive alien species was spotted in a basin. Exceptional measures have been taken: installation of very fine mesh grids at the exit of the body of water, capture by electric fishing of all the fish fauna to be euthanized… And complete liming of the basin to increase the pH, in order to complete the eradication of the last individuals and facilitate the mineralization of the muds. If so many means are deployed, it is because invasive alien species also represent an economic scourge. They would have generated between 1980 and 2019 up to 1,200 billion dollars of losses in the world, according to a recent study published in Perspectives in Ecology and Conservation by French researchers. That’s more than the cost of storms and floods.
A time bomb”
“We had to act quickly,” says Romain Max, technical manager at the Federation for fishing and the protection of the aquatic environment of Cantal. The Asian gudgeon having already spread widely on this small body of water, the only solution was to eradicate all the species present via a drain. “We were lucky, says the specialist, this type of operation can only be carried out from April to October. But the month of October was coming to an end and the next heavy rain could have overflowed the basin, and contaminate the Jordanne River downstream through the storm sewer network, which then flows into a dam lake.
The last emptying dated from 2011: catfish were found there, also classified as invasive alien species. “Twelve years later, no trace remains in the rivers downstream,” rejoices Thierry Pantarotto, deputy head of the Cantal department of the French Office for Biodiversity (OFB). But in this department, which has no less than 11,000 kilometers of waterways, the risk of seeing certain invasive species proliferate cannot be minimized. “With the Asian gudgeon, the contamination of an entire hydrographic chain is at stake, summarizes Thierry Pantarotto. This vector of disease is a time bomb.”
The Fishing Federation and the OFB work hand in hand with local associations, collecting data and organizing prevention at basin level. “Biological invasion is only in its infancy, and aquatic environments are often weakened by a plurality of factors which makes it difficult to distinguish between things”, underlines Nicolas Poulet, research officer at the OFB . But there are worrying precedents: “In Corsica, on Lake Calacuccia, populations have dropped massively because of this species which has started to swarm.”
Another fear persists. Global warming, if it is not directly responsible for the introduction of the Asian gudgeon in Europe, will not help the situation. Scientists are adamant: rising temperatures are weakening ecosystems, whether terrestrial or aquatic, thereby extending the areas conducive to the development of harmful species. This also explains the heightened vigilance of the authorities and their responsiveness. Because in this department of fishermen, there is no question of seeing the local aquatic fauna becoming scarce. “A reduction in the fishing appeal would have significant economic consequences in a fragile rural context,” sighs Thierry Pantarotto. Decline in visits to hotels, campsites, restaurants and specialty stores… That’s a lot, for ten centimeters of silver scales.