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Encouraging results in efforts to conserve the Rhone apron

Over the past 20 years, projects to conserve the Rhone apron have produced modest, but very real results. During the symposium on Aquatic biodiversity, organised by Onema, Pascal Roche from the Rhone-Alpes regional office presented the results obtained by current projects and discussed the potential for restoring the species.

According to the IUCN, the Rhone apron (Zingel asper) is critically endangered. This fish, endemic to the Rhone river basin, could be found throughout 2 000 km of river at the start of the 1900s. Today, it is observed in only a few sections of the Swiss part of the Doubs river and in the Loue, Ardèche, Drôme, Durance, Buëch and Verdon rivers, representing a total of approximately 300 km. The apron is a poor swimmer with low fertility rates and it requires habitats with a natural river morphology, clean water and fairly low temperatures (less than 30°C). The causes of its decline are well known, namely pollution and sediment extraction, obstacles that fragment its habitat, increasingly low flow rates, etc. A number of action plans have been implemented for the species since 1994, first by the Rhône-Alpes regional environmental agency, subsequently by Onema in the framework of the Life Nature projects 1 and 2.

Restoration has begun
In conjunction with research to improve our knowledge of the species, a number of concrete measures have been launched, ranging from modifications in installations to restocking of populations. Following the removal of the Saillans dam on the Drôme river in 1994 and the Serre dam on the Buëch, the Sainte-Tulle dam on the Durance river was eliminated during the second Live programme for the apron. Eight fish passes have been installed on river sections inhabited by the apron in the Ardèche, Drôme and Loue rivers. These efforts are now producing effective results. Over the past few years, the apron has recolonised several kilometres of the Ardèche river, upstream of Lanas and downstream of Vallon Pont d'Arc. In the fish pass at Quingey on the Loue river, the apron is now the second species most frequently observed and increases in the population have also been noted in the Buëch river.

A new national action plan for 2012 to 2017
These encouraging results confirm the effectiveness of projects to restore ecological continuity and water quality, and serve as an incentive to pursue the efforts because more progress can still be made. Serious concerns still exist, however, e.g. some isolated populations are threatened over time due to their insufficient genetic diversity and others due to increases in summer water temperatures. That explains why, in addition to efforts to remove obstacles and restore the hydromorphology of rivers, efforts that must be continued where possible, projects to restock and transfer populations should be pursued to counteract the above pressures. The Drôme river, for example, from which the apron had virtually disappeared in spite of newly favourable conditions, received first an influx of fish from the Durance river in 2006, than since 2008 a number of juveniles obtained through ex-situ reproduction. Work in favour of the apron continues in the framework of the national action plan drafted by the Rhône-Alpes conservatory for natural areas, with support from Onema, for the period from 2012 to 2017. The Rhône apron, a fragile symbol of our rivers, still exists and is even staging a comeback!

Contact:
pascal.roche@onema.fr

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