Saturday May 4, an illustrated conference on two emblematic species of the lively and natural rivers of Haut Allier, the pearl mussel and the white-clawed crayfish, was held at the House of Birds and Nature in Lavoûte-Chilhac.
This conference was organized at the instigation of the SMAT du Haut Allier as part of the Natura 2000 program, a program resulting from the establishment of the European directorate known as “Habitats” (CEE 92/43), aims at the conservation of rare species. and threatened on a European scale, particularly on sites designated for this purpose, with notable populations. This is why these two species, the pearl mussel and the white-clawed crayfish, in sharp decline worldwide, but also locally, for several decades, are the subject of particular attention, to ensure their maintenance and the preservation of their aquatic habitat on which they depend.
Markers of good water quality
“Markers of good water quality and ecosystems, these species require constant vigilance regarding the risk of damage which can have a lasting impact on aquatic environments and the fauna that develop there. Our territory is home to populations of these two species, important on the scale of France, but they remain very sensitive and are threatened with disappearance in the medium term.
This conference led by the PANPA Haut Allier association with the support of Laurent Bernard, SMAT coordinator of the Natura action program, presented their biology and the reasons which led to their protection.
Decimated for its rare pearls
Thus the pearl mussel (Margaritifera margaritifera), which was harvested on an industrial scale from the Middle Ages to the 19th century throughout Europe where it lived, for the rare pearls they could contain (1 in 2000 to 3000 mussels) and to feed livestock (pigs and ducks), was decimated wherever it was present until its partial or total extinction in the waterways where it was so abundant before.
Water of very good quality and the presence of brown trout and salmon are essential for the development of young mussels which will attach to their gills to colonize new waterways.
The pearl mussel modestly present
Recent studies on the Haut Allier show that the species is still present on the rivers of Virlanges, Seuges, Ance, and Pontajoux and Allier upstream of Alleyras, in relict populations or locally in small “tiles” of a few hundred to a few thousand individuals, totaling nearly 40,000 estimated over 21 km.
The demanding white-clawed crayfish
The white-clawed crayfish has strong ecological requirements and seeks flowing rivers with natural and shaded features. This species, which originally extends throughout Europe, experiences strong competition from crayfish from North America, such as the so-called “American” crayfish (from the NE coast), the signal crayfish, Louisiana crayfish…, and Asia (slender-legged crayfish), the first of which were introduced into farms at the end of the 19th century. More prolific and more aggressive than the local crayfish, these species introduced a deadly pathogen for white-clawed crayfish, “aphanomycosis” otherwise called “crayfish plague”.
Its enemies: pollution, thresholds, predations
On the Haut Allier, the white-clawed crayfish is still present in a number of small tributaries on the right bank of the Allier upstream of Monistrol d’Allier, and on the left bank on the tributaries from Saint Arcon to Monistrol, and on the ‘Ance, la Seuge, la Besque. Like the pearl mussel, this crayfish is subject to chemical pollution of the water, impassable thresholds, and predation from exotic species such as raccoons and coypu.
