Global and European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

The French Nase does not approach the range size thresholds for Vulnerable under Criterion B1 (extent of occurrence (EOO) < 20,000 km²) or D2, and Criterion B2 is precluded by its uncertain area of occupancy (AOO). The population size is believed to exceed 10,000 mature individuals, hence it does not meet the thresholds for Criteria C or D. There exists no quantitative analysis which would permit application of Criterion E.

Although no explicit population trend data are available, a suspected ongoing reduction based on declining habitat quality and the effects of introduced taxa could meet the threshold for Vulnerable under Criterion A2 (≥ 30% over the past 18 years = three generations). As a result of this data uncertainty, Least Concern and Vulnerable are equally plausible Red List categories for the present assessment, and this species is assessed as Near Threatened both globally and for the EU 27 member states.

This species is endemic to France and Switzerland. It is present in the Garonne-Dordogne and Adour river systems in the Northeast Atlantic (Bay of Biscay) basin, although its native status in the latter catchment requires confirmation, and from the Berre River eastward to the Rhône River in the Mediterranean basin.

Outside of its native range, it has been introduced to the Loire River system, but is today restricted to the Haute-Loire region as a result of purported competition with the non-native Common Nase (Chondrostoma nasus).

This species' population size is unknown, but is believed to exceed the minimum threshold for Red List criteria (< 10,000 mature individuals). The current population trend has not been quantified, and the number of subpopulations is unclear.

Its area of occupancy (AOO) is understood to have decreased by at least 30% between 1996-2006, and this has largely been attributed to declining habitat quality and the effects of introduced taxa (see 'Threats'). This pattern is suspected to be ongoing to an as yet undetermined extent, especially in the Rhône River system.

This gregarious species inhabits flowing reaches of rivers and streams with rocky or stony substrata, where it feeds on small invertebrates and diatoms.

It is also known to enter artificial accumulation lakes, and in the Durance River (Rhône River system) is resident in canals constructed for irrigation and hydroelectricity generation.

Its maximum lifespan is c. 10 years, and individuals become sexually mature at age 3-4+.

The annual reproductive period is short and extends from the end of May to the beginning of June, during which time nuptial adults migrate to upstream spawning sites with coarse, well-washed substrata. It is a polygamous, fractional spawner, and individual females can deposit 1,500-15,000 eggs during a single season.

It hybridises extensively with the non-native Common Nase (Chondrostoma nasus) and to a lesser extent the native Riffle Dace (Telestes souffia) throughout much of the Rhône River system (see 'Threats').

This species is threatened by river regulation and other forms of anthropogenic habitat degradation. In particular, the construction of dams, sills, weirs and other barriers throughout its range has severely altered natural flow and sedimentation regimes, fragmented subpopulations, and reduced the extent of suitable habitat for all life stages. Hydroelectric schemes have created unnatural fluctuations in discharge and water temperature (hydropeaking and thermopeaking) which bring about artificial dewatering of downstream river stretches and loss of stable nursery habitat for juveniles. Furthermore, the combined effect of hydropeaking, dam flushing operations, changes in land use, and the removal of riparian vegetation has increased accumulation of fine sediments at some sites, plausibly impairing the hatching and survival rates of eggs and larvae.

The quality of habitat has been further diminished by bank stabilisation, channelisation and other efforts to enhance flood protection or exploit water resources for irrigated agriculture. Unregulated water abstraction may constitute a particular threat to this species' upstream spawning and nursery sites, some of which may also have been damaged by the industrial extraction of riverine gravel or other sediments for urban development.

This species is also threatened by diffuse and point source agricultural, domestic and industrial pollution, which has at some locations reduced the extent and quality of habitat due to eutrophication or discharge of toxic substances.

In the Rhône River, its decline has been significantly exacerbated by competition and introgressive hybridisation with the non-native Common Nase, which entered the system during the late 19^th century via artificial shipping canals connecting it to the adjacent Rhine River system. The artificial impoundment of many river stretches has been linked to the structuring of hybrid zones between the two species by weakening habitat segregation between them. Hybrid individuals are fertile and comprise c. 3-20% of overall abundance depending on location. There are currently very few sites occupied by French Nase in the Rhône system where no hybrid individuals are present.

The French Nase may also be negatively impacted by reduced fitness due to the transmission of novel parasites from the Common Nase.

This species is not used or traded.

This species is included (originally as Chondrostoma toxostoma) in Appendix III of the Bern Convention and Annex II of the European Union Habitats Directive.

At the national scale it has most recently been assessed as Near Threatened in France (2019) and Critically Endangered in Switzerland (2022).

It occurs within the boundaries of numerous protected areas, some of which are included in the European Union's Natura 2000 network.

Subpopulations inhabiting the Rhône River may have benefitted from efforts to improve the conservation status of the Rhône Streber (Zingel asper), which have included installation of fishways on barriers in the Ardèche, Drôme, Durance and Loue tributary systems.

However, management efforts to improve longitudinal fluvial connectivity through barrier removal has in some cases allowed the Common Nase to extend its range further upstream.

It is recommended that future research should focus on understanding this species' current distribution, population trend and life history, in addition to identifying priority conservation areas. In the Rhône River system, sites inhabited only by non-introgressed individuals in the absence of Common Nase are likely to require direct and urgent management.