Preliminary findings indicate that the ship sturgeon Acipenser nudiventris, long thought to have been extirpated from the Black Sea basin, in fact survives, and is still spawning in Georgia. The ship sturgeon was historically found in the Black, Azov, Caspian and Aral Sea basins. Overfishing, destruction of spawning grounds, and habitat degradation combined to cause a catastrophic decline of all sturgeon populations worldwide (Ludwig, 2006, European Journal of Wildlife Research, 52, 3–8). The ship sturgeon was no exception; its population has decreased so dramatically that it has been considered extinct in the Black Sea basin, and Azov and Aral Seas, and dramatically reduced in the Caspian Sea (Mugue et al., 2016, Mitochondrial DNA Part B, 1, 195–197). It is categorized as Critically Endangered on the IUCN Red List.
After decades without confirmed evidence of ship sturgeon in the Rioni River, Fauna & Flora International collected photographic evidence and genetic samples from eight ship sturgeons in the Rioni River in 2020. Taking into account the biology of the fish, and the apparent maturity of these eight individuals (20–75 cm in length) the species appears to survive in the Rioni River. Initially, we suspected these individuals were releases from an ongoing captive breeding programme in the Kuban River in Krasnodar. In this breeding programme, ship sturgeons bred from Caspian Sea stocks are hatched and released into the Kuban River (N. Mugue, pers. comm., 2020). We therefore presumed the individuals from the Rioni River were most likely captive-bred individuals that had dispersed to the Rioni River after their release into the Kuban River c. 950 km distant. However, mitochondrial DNA sequence data indicates that the Rioni specimens are genetically different from the Kuban River breeding stocks. This, in turn, suggests that the Rioni River individuals are in fact from a surviving breeding population that spawns in the Rioni River, and that the species, once thought to be extinct in the Black Sea basin, has persisted. It is therefore likely that the Rioni River still hosts native stock of the ship sturgeon.
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