European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Not Recorded

Unio gontierii has been assessed as Vulnerable (VU A2bc) due to a population size reduction based on a suspected decline in habitat quality and number of subpopulations of at least 30% over the last three generations (30 years). The species is still widespread in rivers flowing into the Black Sea in southern Ukraine and southern Russia, but populations are isolated and declining. The species has not been recorded from the EU27 Member States.

In the European region, the species occurs in rivers and streams draining into the Black Sea from southern Ukraine to Southern European Russia. However, its presence in the proposed western range of the species in Crimea is based only on data from Haas (1969) and should be confirmed in the future. 

The global range extends eastwards to Georgia and in the Kura River basin (excluding the Arax River) draining into the Caspian Sea. In the absence of molecular data, the occurrence of U. gontierii in the rivers of the eastern and the south-eastern Greater Caucasus draining into the Caspian Sea and in the lower Kura River also needs to be confirmed. These areas are likely to be occupied either by Unio gontierii, by Unio mardinensis which occurs in the Arax River basin (a major southern tributary of the Kura River), or by both.

The species occurs in several rivers flowing into the Black Sea across Georgia, southern Russia and Crimea in Ukraine (Lopes-Lima et al. 2024).

There is no monitoring and therefore no quantification of population trends, but the quality of the species' habitat has declined dramatically due to changes in river hydromorphology and increased eutrophication from agricultural runoff, and the species is thought to be declining rapidly (Lopes-Lima et al. 2024). The species has been extirpated from most of its Crimean range (L. Shevchuk pers. data) over the last two decades and an overall decline in population size of at least 30% is also suspected for the entire European population, due to a decline in the number of subpopulations and habitat quality in southern Ukraine and Russia (L. Shevchuk pers. comm. 2022).

The species has been found in the Georgian, Russian and Ukrainian river basins where it occurs that still hold good water quality, in gravel and sand substrates (L. Shevchuk pers. obs. 2022).

Unio gontierii has the typical unique reproductive features of most Unionidae species including larval parental care (i.e. brooding) and larval parasitism on freshwater fishes (and occasionally other vertebrates) (Modesto et al. 2018). Besides this information, at present there are no scientific studies on the detailed ecology and habitat requirements of this species.

This species, like most freshwater species in the region, is threatened by hydro-morphological degradation, such as flood control measures involving the clearing of riparian forests and vegetation, as well as river channelling, water abstraction and dam construction, which affect the physical structure of the substrate and the hydrology of river systems (Japoshvili et al. 2021; L. Shevchuk pers. comm. 2022). In addition, there are significant levels of organic pollution from agro-industrial activities and agrochemicals (pesticides, fertilisers and other nutrient loads), which also affect freshwater species in the region (Japoshvili et al. 2021; L. Shevchuk pers. comm. 2022).

No trade or use is known for this species.

Unio gontierii is included (as a synonym for Unio crassus) in Annex B-II (species of community interest whose conservation requires the designation of Special Areas of Conservation) and Annex B-IV (species of community interest requiring strict protection) of the Habitats Directive. There are no known conservation measures in place for Unio gontierii.

The species should benefit from the development of an action plan to guide future conservation efforts. Habitat restoration is needed by restoring connectivity to rivers where the species occurs, including the removal of obsolete dams and barriers, and river management practices that involve excavation and disturbance of the substrate, banks and key hydromorphological elements of the channel should be adapted to avoid harming sessile benthic organisms such as freshwater mussels. Control of invasive species such as fouling mussels and macrophytes should also be undertaken in many areas, with the hulls of boats and other aquatic vessels being inspected for invasive fouling organisms when they are transported across different waterbodies. Outreach and education to relevant stakeholders such as environmental and water management agencies, farmers and farmers' associations, and the general public on the importance of the species and the ecosystem services it provides are also needed.

Research is required to determine this species' tolerance to contaminants, its detailed distribution, to assess threats, and to understand the basic ecology of the species. It is essential to understand the distribution and abundance of the main populations of the species using molecular methods and environmental DNA monitoring, this would allow priority populations to be identified for conservation in order to establish protected areas. It would then be beneficial to invest in long-term monitoring of these populations using standardised surveys to provide information on population trends. Tolerance to traditional and emerging pollutants should also be studied in detail and point and non-point sources of pollution identified and eliminated.