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

Stellate Sturgeon was known from the Caspian, Black and Aegean seas. It is now extirpated from the Aegean Sea, and in the Black Sea basin the last natural populations migrate up the Danube. Only very few spawners remain in the rest of the Black Sea basin. The Caspian Sea population is under massive pressure from overfishing (including poaching) and loss of spawning sites, resulting in the stocks declining very fast. Almost all migrating spawners are poached in the sea before maturity. Few individuals live long enough to spawn a second time. In the immediate future, survival can only depend on stocking and effective fisheries management and combating illegal fishing. Based on catch data, and the number of individuals migrating into the Volga and Ural rivers it is estimated that the species has undergone a global population decline of at least 95% in the past three generations, which is expected to continue.  It is assumed that the population is in decline at the same rate or even faster in its European and EU 27 range. Therefore, this species is assessed regionally as Critically Endangered under Criterion A.

In Europe, the Stellate Sturgeon inhabits the Caspian, Black and Azov seas and was historically present in the northern Aegean Sea basin (Evros River). The Volga, Ural, Don, Danube, and Kuban Rivers werethe major spawning rivers. It migrated in the Danube up to Germany, but migration is prevented today by the Iron Gate in Romania/Serbia. In the Volga it historically migrated up to Rybinsk, in the Ural - to Uralsk, in the Don - to Pavlovsk, in the Kuban - to Armavir.

Today, the species still spawns in the Danube River (and the Rioni River, outside of Europe) in the Black Sea, as well as in the Ural and Volga rivers in the Caspian Sea basin. The last reproduction in the Sakarya River (Türkiye) was reported in 2011 (Memis pers. comm). There is no more confirmed reproduction of this species from other areas in Europe. Considering the long lifespan of the species, it cannot be excluded that mature, wild-born individuals still persist in the Azov Sea and other areas in the Black and Caspian Seas, but these seem to spawn irregularly or do not spawn successfully anymore.

Today, the largest natural population occurs in the Caspian Sea basin, where the Ural is the major spawning river, while other stocks mentioned above are much smaller. Population assessment of wild fish is hampered by massive releases of hatchery fish in the Caspian Sea basin.

Globally, the distribution of this species extends to parts of the Black, Azov and Caspian Sea basins outside of Europe.

Globally, the species has declined by more than 99% in the last 40 years. Three generations correspond to about 78 years in this species. Currently, most spawners are first-time spawners with only few individuals surviving to participate in a second spawning period. Stellate Sturgeon seems to have vanished from the Aegean Sea, where only single individuals are reported occasionally. Since the early 1990s, 100% of the Sea of Azov population and those from the northern Black Sea basin as well as large parts of the Caspian Sea population depend on stocking.

Catches have drastically declined in the 21st century and legal fishing has now been banned except for scientific and re-stocking reproduction. The decline in commercial catch is believed to reflect a decline in the population size (CITES 2000), while natural populations were largely replaced by ranched stocks already in the late 20th century, blurring the information gained from catch statistics and monitoring surveys.

Illegal fishing, including taking fish from by-catch, is a large issue and seems to inhibit stock recovery. Furthermore, fishing bans have resulted in a strong decline of population trend data in the last 10 years, making it difficult to update the details listed below for former time periods. These details are kept in the actual assessment not to lose the valuable information, which are presented in the collection below. There were four major stocks in Stellate Sturgeon. The one from the Aegean Sea seems to be completely lost with no individuals being maintained ex situ. In the Azov Sea, no wild mature females have been caught for a stocking programme since 2007 (Chebanov pers. comm.) and the entire Azov population seems to depend on stocking. However, there is a large captive stock of this population which would allow reintroduction, if threats were to cease.

Black Sea populations in Europe have continued to decline dramatically in the 21st century despite occasional releases and the species is now very rare even in the Danube, which was its remaining European stronghold in the later 20th century. The Caspian population is the largest one remaining but spawning in the southern Caspian basin is almost negligible. The Ural and, to a lesser degree, the Volga are now the global strongholds of this species.

Global catches in 1992 reached 2,730 tonnes, falling to a low of 38 tonnes in 2004, and 50 tonnes in 2007 (a decline of over 98% in 15 years). The average catch between 1992-1999 was 1,063 tonnes, and between 2000 and 2007 it was 132 tonnes, a decline of 87% (FAO 2009). For the whole Caspian basin, catches peaked in 1977 with 13,700 tonnes; this has shown an almost continuous decline to 305 tonnes in 2003 (most recent data) (over 97% decline in 32 years) (Pikitch et al. 2005). In 2008 the agreed upon catch quota for Acipenser stellatus for all Caspian Sea countries was 240 tonnes, including commercial and scientific catch; the quota has not been met (Pourkazemi pers. comm.).

No actual catch data are available since 2011 due to the moratorium. Khodorevskaya et al. (2009) shows that the average numbers of spawners entering the lower Volga per year has fallen from a peak of 230,000 (between 1986-90) to just 50,000 (between 1998-2002), a decline of 78%. It is expected that the decline has continued at a similar rate to the present time (though data does not exist) and will continue. In the Ural the estimated number of migrating individuals per year has also shown a decline, in 1970: 1,100,000; 1979: 1,050,000; 1990: 300,000 migrating individuals (Veschev 1995); 1998: 103,600; 2001: 87,400 (Pikitch et al. 2005). This shows a 92% decline from 1979 to 2001 (also from 1970 to 2001, as migrating individuals per year remained relatively stable between 1970 and 1979).

Over recent decades, Stellate Sturgeon abundance in the Caspian Sea has reduced. Evidence of this is shown in the decrease of the average catch per unit effort during trawl surveys between 1978-1999. These showed a three-fold decrease in the northern Caspian Sea, a 2.7-fold decline in the middle part of the Caspian Sea and a six-fold decline off the Dagestan coast (Vlasenko et al. 2003). Decrease of CPUE has been more apparent in the southern part of the sea. The Stellate Sturgeon population has declined from 69.7 million specimens in 1978 to 15.6 million in 2002, and 7.6 million specimens in 2008. Commercial stock decreased by 12 times during this period (Khodorevskaya et al. 2009).

In Romania, from 2002-2005 the catches of wild individuals (stocking only started in 2006 and ceased by 2010 in the Danube) dropped from 12.427 tonnes to 3.43 tonnes (72.5% in 4 years). In the Danube, legal fisheries were stopped in 2006 (Suciu pers. comm.) and fish are only taken for research and artificial reproduction. As of 2019 there are no legal sturgeon fisheries in the Black Sea basin anymore, however by-catch and illegal fisheries are an issue leading to a continuous decline of the species.

This species is anadromous, spending at least part of its life in salt water and returning to rivers to breed. At sea, in coastal and estuarine areas, it mainly forages on clay-sand bottoms, as well as in middle and upper water layers. Juveniles inhabit shallow riverine habitats during their first summer (Khodorevskaya et al. 2009).

Caspian fish first mature at 6–8 years for males, and 8–12 years for females, with an average generation length of 28 years. Females reproduce every three to four years and males every two to three years in April-September. It spawns only under relatively constant hydrological conditions, as fluctuating hydrological conditions lead to high egg mortality. This species migrates upriver at higher temperatures and therefore later than other sturgeons, with two peaks, in spring and in autumn. It spawns in strong-current habitats in the main course of large and deep rivers, on stone or gravel bottoms. It is also known to spawn on flooded river banks, on sand or sandy clay. Males remain at spawning sites no longer than six weeks, and females only 10–12 days. Spent individuals migrate directly back to sea. Yolk-sac larvae are pelagic for two to three days and drift with the current. Stellate Sturgeon stop eating after the beginning of the spawning migration. After spawning, they return downstream into the sea, where they begin actively feeding. The juveniles of Stellate Sturgeon also do not delay in the river and migrate for feeding into the sea.

Juveniles migrate to sea during their first summer and remain there until maturity. At sea, this species feeds on a wide variety of crustaceans, molluscs and benthic as well as pelagic fish (Khodorevskaya et al. 2009). The main habitat in the Caspian Sea of the Stellate Sturgeon in the winter is the middle part of the sea (Legeza 1970). In the spring they migrate to the north, with its maximum density being observed off the mid-west coast in shallow water rich in food organisms (Legeza 1970). In late spring they move to the north-west coast.

In autumn, Stellate Sturgeons begin migrating to the south of the Caspian Sea (earlier than other species), concentrating at the mid-western coast and the south-eastern coast (Legeza 1970). The spawning migration starts in April. Spawning occurs at temperatures from 9 to 16 °C in the channel and spring flooded spawning grounds at the current speed of 0.8–1.2 m / sec. The greatest number of Stellate Sturgeon migrate to the Ural River (Peseridi et al. 1986, Dovgopol et al. 1992).

The decline in Stellate Sturgeon abundance is primarily caused by fishing and a sharp increase of poaching, seizing the largest and most mature fish. Before 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). Today, only illegal catches take place at unidentified intensity.

Dams, mostly constructed in the 1960s and 70s, have led to the loss of many spawning grounds and to a strong decline in natural reproduction. For example, the Volgograd dam (built in 1955) led to loss of 40% of spawning sites formally available in the Volga (Khodorevskaya et al. 2009). The species is also considered extirpated from the upper and middle Danube since the building of the Iron Gate Dams. The Don River dam removed 68,000 ha of spawning ground and flow regulation in the Kuban led to the loss of 140,000 ha of spawning grounds.

These losses were partly compensated by massive release programs that utilised wild fish as broodstock. Legal, and recently only illegal, massive overfishing continued to decrease populations.

Overfishing increasingly prevents hatcheries from catching sufficient numbers of mature individuals to maintain the necessary broodstock (Khodorevskaya et al. 2009). Controlled reproduction due to a lack of efficient management is no longer able to compensate for the illegal removal. The annual release (between 1998 until 2008 of sturgeon juveniles from sturgeon hatcheries in Russia amounts to from 3 to 20 million specimens; in Kazakhstan - from 2.5 to 4.1 million specimens; in Azerbaijan - from 2.5 to 6.8 million specimens; in Islamic Republic of Iran - from 0.2 to 1.3 million specimens. This quantity of stocks recruitment of Stellate Sturgeon from industrial sturgeon culture is not enough to supply the population at an optimum level (Khodorevskaya et al. 2009).

Pollution is a threat to the species since gonad maturation, early life phases and juveniles are massively affected by it, showing reduced reproductive efficiency and malformations. Introduction of fertilised eggs (from before 1986 and again 2003/4, and it may continue) from the Caspian Sea into the Azov Sea may impact the genetic integrity of Azov Sea population (Chebanov pers. comm.). Introduced Mnemiopsis (from USA), which impacts the species food source, has impacted the Black Sea population (impacts now reduced in Black Sea) and is also now impacting the Caspian Sea populations. As demonstrated in recent investigations, poaching for meat and caviar is still a major threat for the Black Sea population (Ludwig et al. 2015, Jahrl et al. 2021).

The species is mostly used for meat and caviar.

As the major threats to the species - illegal fishing and dams, have not been overcome, artificial reproduction and stocking are the only ways to prevent the full extinction of the species. Priority should be given to combat harvest and habitat restoration measures to improve natural reproduction, while releases based on genetic plans are recommended to be continued to maintain the species. The species is now fully protected by national laws all over its range and no commercial fishing is allowed. There are regional coordination units as the Caspian Sea Bioresource Commission and the Azov Sea Commission to coordinate the management programs for the conservation of sturgeon resources. However, the results of these activities if not sufficient to stop the decline. There is a pan-European Action plan (Friedrich et al. 2019) under the EU Flora-Fauna-Habitat directive adopted in 2019 and the species is protected by several legislations; Bern Convention, CITES Appendix II in 1998, the Bonn Convention, the EU regulation of trade of fauna and flora, and many national laws. Ex situ conservation and cryopreservation measures are in place in several countries holding considerable captive stocks of the three remaining management units (Azov, Black and Caspian Seas). In situ conservation measures are proposed to establish protected areas in the seas at the major feeding grounds as well as the river mouth areas to better protect the species.