European regional assessment: Least Concern (LC)
EU 27 regional assessment: Least Concern (LC)

Onychogomphus uncatus is widely distributed and mostly common, with no serious present trends indicating a decline, and is therefore assessed as Least Concern.

Onychogomphus uncatus is a southwestern Atlanto-Mediterranean endemic with its core distribution on the Iberian Peninsula (Ocharan Larrondo et al. 2011) and France (Krieg-Jacquier 2022). The range extends to the Maghreb and western Italy. Among Mediterranean islands, the species is only present in Sicily (Boudot and Dommanget 2015). The species seems to be limited in its range by very cold temperature of waters in mountains and by a continental climate. The current extent of occurrence (EOO) is 2,312,564 km², based on records from 2000 onwards. Mild Atlantic climate has allowed the establishment of populations in northwestern France, such as in Brittany and Normandy, and the species might expand northwards in the future. The species in the last decades not been seen in Belgium, Switzerland (both unmapped) or Germany.

O. uncatus is fairly common in most of the region, with highest densities detected in southern France and Spain (Ocharan Larrondo et al. 2011). A slight decline in distribution seems to lately have occurred in France. The species is considered extinct on the High Rhine, where a long-lasting population formerly occurred (Suhling and Martens 2015). It has been listed as “Extinct” in the Swiss Red List since 2002 and in the Baden-Württemberg Red List since 2006.

The species is mainly found in rather fast-flowing watercourses with rocky outcrops, often in hilly areas with smaller watercourses at a slightly higher altitude, but also in wider and somewhat slower flowing rivers in the lowlands (Boudot and Dommanget 2015). The larvae of O. uncatus, as well as other gomphids, clearly preferred gravelly sand substratum rather than gravel or stone (Suhling 1996).

Some of the historical threats have ceased or lessened, especially water pollution, but locally a general degradation of water quality and the elimination of riparian vegetation resulting in destruction of bank structure might still be an issue. Introduction of invasive crayfish may also be a threat as they have on some other riverine species (Boudot and Dommanget 2015). As shown during the last couple of years, even larger rivers can be subject to drought during increasingly hot summers. Recurring and increasingly severe and longer droughts are a major reason why riverine species are decreasing. The drought is partly due to climate change but is often worsened by an ever-increasing withdrawal of water for human use and agricultural activities. Lower water levels mean higher water temperatures, which changes pH values, nutrient loads, and species composition.

There is no trade or use of this species.

No measures on European scale are needed. However, catchment management plans should be drawn up with particular attention to ecological flows in accordance with the European Water Framework Directive (WFD CIS, 2015). This should mitigate or even prevent water abstraction for agricultural or domestic use from streams and rivers.