European regional assessment: Critically Endangered (CR)
EU 27 regional assessment: Critically Endangered (CR)

Russian Sturgeon is an extremely rare species in the Black Sea basin, with natural populations having been reduced by 99% over the last three generations. This is attributed to overharvesting and loss of habitat, where spawning and nursery sites have been lost due to dam construction. The Caspian basin has lost 70% of spawning grounds since the 1950s, mainly due to hydroelectric power stations. The population is migrating to the Danube, where it has been heavily overfished and poached (Ludwig et al. 2015, Jahrl et al. 2021), and has only been recorded as single individuals in the last 10 years. The Caspian populations are also under massive pressure from overfishing and loss of spawning habitats. Most migrating spawners are poached, and the majority of the remaining fish only spawn once during their lifetime. This decline is predicted to continue as illegal fishing at sea and in rivers for caviar and meat continues. For the Black Sea this will soon result in the extinction of the remaining natural wild populations, while in the Volga River increasing proportions of wild fish have been documented over the last years, although recruitment takes place at a low level (M. Chebanov pers. comm.). In the immediate future, the survival of this species depends on stocking, which has to be performed avoiding the risk of outbreeding depression.

Globally, this species is assessed as Critically Endangered due to a population size reduction of more than 80% over the last three generations. This is based on approximately 90% decline in global catches of the species within just 15 years, despite large levels of stocking (average global catch from 1992 to 1999 was 1,531.75 tonnes, reduced to 175.37 tonnes from 2000 to 2007); a 92.5% decline in estimated spawning stock biomass in the Volga between 1961–1965 and 1998–2000; an 88% decline in the average number of spawners entering the lower Volga between the 1962–1975 average to the 1992–2002 average; and a 99% decline in the Juvenile Production Index from the Romanian Danube. It is assumed that the population is in decline at the same rate in its European and EU 27 range. Therefore, this species is assessed regionally as Critically Endangered. It will possibly become Regionally Extinct in the next 10 years in the EU 27.

In Europe, this species is known from the Black, Caspian and Azov seas, where it once spawned in all larger tributaries. Only single individuals of a spawning population are remaining in the Danube (last confirmed natural reproduction in 2006) with very few individuals entering the river annually. In recent years in the European part of the Caspian Sea catchment, reproduction of A. gueldenstaedtii is described only in the Volga and Ural rivers on a regular basis. Occasionally, the species spawns in other rivers in the range. Individuals originating from stocking programs are released in the northern tributaries of the Black Sea, the Caspian Sea (except Ural) and in the Sea of Azov. Considering the long lifespan of the species, it cannot be excluded that mature, wild-born individuals from these rivers still persist in the Azov, Black or Caspian seas but these seem to spawn irregularly or do not spawn successfully anymore.

Globally, the range of this species extends to other parts of the Black, Caspian and Azov seas outside of Europe.

The wild, native populations of A. gueldenstaedtii have undergone a major decline which is currently continuing. Despite many release programmes (introducing millions of fingerlings annually), several populations are now on the verge of extinction and major populations have been lost recently. Extinction of the species (in the wild) is expected within the next decade if there is no major breakthrough in conservation efficiency.

Russian Sturgeon is now very rare in the Danube and only occurs as single individuals in recent years, while no reproduction seems to have taken place in the last decade (Danube Sturgeon Task Force 2019). Romanian catch data (Danube) show that in 2002, 3,726 kg were caught; in 2003, 1,499 kg; in 2004, 440 kg; and in 2005, 37 kg, showing a 99% decline in just four years (Paraschiv et al. 2006). A juvenile production index (evidence of breeding) for the Danube (Romania) also shows a decline: CPUE was just over 0.7 in 2000.

In the Volga, 30 million fingerlings are released annually. In the northern Caspian Sea about 80% of juveniles originate from artificial reproduction, while about 20% are believed to come from natural spawning. Data from the Caspian Sea (Khodorevskaya et al. 2009) reports catches were between 6,000 and 9,000 tonnes per year in the 1960s, to a peak of around 14,500 tonnes in the late 1970s early 1980s, to less than 1,000 per year from 2000 to 2008. The estimated spawning stock biomass in the Volga has also drastically declined, from 13,200 tonnes (1961-65) and 22,200 tonnes (1966-70) to 1,000 tonnes (1996-97) and 1,000 tonnes (1998-2002). Average number of spawners (1,000 individuals) passing fishery zones to the spawning grounds in the lower Volga (per year) has declined by 88% from the 1962-75 average to the 1992-2002 average.

Habitat: At sea, it is found in shallow coastal and estuarine zones, and in deep parts of large rivers with moderate to swift current in freshwaters. It spawns in strong currents (1-1.5 m/s) in large and deep rivers on stone or gravel bottom.

Biology: There are anadromous and freshwater populations (freshwater populations existed in the Danube and Volga ). Its complicated pattern of spawning migrations includes spring and autumn runs. Individuals migrating in spring enter freshwater just before spawning; they tend to spawn in lower reaches of rivers. Individuals migrating in autumn overwinter in rivers and spawn the following spring further upstream.

Males reproduce for the first time at 8-13 years, females at 10-16 years of age. Females reproduce every 4-6 years and males every 2-3 years in April-June, when the temperature rises above 10°C. Generation length is estimated to be 35 years under natural conditions. Today, in the Caspian Sea almost all of the mature fish in the population are first-time spawners being caught illegally during their first spawning event.

Larvae drift with the currents; juveniles then move towards shallower habitats before migrating to the sea during their first summer. They remain at sea until maturity. The Russian Sturgeon feeds on a wide variety of benthic molluscs, crustaceans and small fish.

Within its large range, the species faces many threats, overexploitation, pollution, poaching, and dams being the major ones. These threats have been ongoing for decades. Most spawning sites have been lost due to dam construction. The Caspian basin lost 70% of spawning grounds since the 1950s, mainly due to the construction of hydroelectric power stations. For example, in the middle section of the Danube, the annual catch dropped from 14,636 kg in 1983 to 1,636 kg in 1985 (a decline of just under 90%), this is believed to be due to the construction of the Iron Gate II dam which was constructed in 1984, blocking access to the upstream spawning grounds for the species (CITES 2000).

In the Caspian Sea and Sea of Azov the illegal sturgeon catch for all species was evaluated to be 6-10 times the legal catch (CITES 2000). Bycatch is a threat to the species in both marine and freshwater too.

Artificial reproduction and stocking have been insufficient to stop the decline. While wild populations are lost, ex situ stocks have gained importance and there are several captive stocks of the species. As these are not only kept for conservation purposes but also for ranching and aquaculture, genetic pollution is an increasing threat. Fish from different populations are moved to different locations (e.g. Caspian stocks moved to Sea of Azov) and different species are hybridised on purpose (Jenneckens et al. 2000) or accidentally in the fish farms. This genetic pollution brings a high risk that the species gets completely lost in the wild and captive stocks as well as wild fish originating from stocking are impacted by hybridisation and the pure species goes extinct unnoticed.

This was earlier a major commercial species fished for caviar and meat, but its importance has reduced due to the drastic decline of the species and the resulting catch prohibitions.

The species is produced in aquaculture either as a pure species or as hybrids in large numbers, resulting in introductions for other sources even in its native range. The products deriving from the species are traded globally, providing the opportunity to black market illegally caught fish.

The species is fully protected in all range countries where it occurs or occurred but the fisheries ban is insufficiently enforced (Jahrl et al. 2021).

As the major threats to the species, as illegal fishing and dams, have not been overcome, artificial reproduction and stocking are the only ways means to prevent the species from full extinction in the wild. Priority should be given to combat illegal harvest and implement habitat restoration measures to improve natural reproduction, while releases based on genetic plans are recommended to be continued to maintain the species.

Fish lifts and artificial spawning grounds have been introduced constructed into parts of the Caspian and Black Sea region only (CITES 2000). Effectiveness largely varies between sites.

This species is listed by the Bern Convention, the EU Fauna-Flora-Habitat Directive, the Bonn Convention, Annex B of the EU regulation of trade of fauna and flora, and the CITES Appendix II and it is included in the Pan European Action Plan. A transnational action plan is still missing for the Caspian range states. Gene bank development for of live individuals and as well as cryopreservation are ongoing in several range countries.