ACIPENSERIDAE, Bonaparte, 1831

Family ACIPENSERIDAE View in CoL

Genus Acipenser Linnaeus 1758

2. Persian sturgeon Acipenser persicus Borodin, 1897

This is an anadromous, valuable commercial species, endemic to the Caspian Sea basin. The Persian sturgeon is distributed throughout most of the Caspian Sea ( IUCN, 2024), including the shallow waters of the Northern Caspian Sea ( Khodorevskaya et al., 2007). It spawns mainly in the Kura River and rivers along the Iranian coast. The species enters the Volga River in much smaller numbers and is the least abundant species among the sturgeons of the Volga-Caspian basin ( Guteneva and Ivanova, 2015). The main habitat in winter is the continental slope of the Northern Caspian Sea and the eastern shelf of the Middle Caspian Sea ( Khodorevskaya et al., 2007). The main reason for the decline of Persian sturgeon stocks is IUU fishing on migration routes, within feeding and spawning grounds ( Guteneva and Ivanova, 2015), as well as the regulation of the Volga River flow by the Volzhskaya HPP, located on migration routes. The main current conservation measures aimed at the recovery of the population are the prohibition of commercial fishing (with the exception of fishing for research purposes), as well as the listing of this species in various RDBs and CITES Appendix II. However, the existence of these measures has not contributed to an increase in the population and it continues to decline ( Rustamov and Shakirova, 2013; Guteneva and Ivanov, 2015), which requires the development of additional conservation measures.

3. Ship or fringebarbel sturgeon Acipenser nudiventris Lovetsky, 1828

This species is an anadromous fish and one of the least abundant sturgeons in the Caspian Sea with limited commercial value ( Chebanov et al., 2018; Orlov et al., 2022d). It is mainly found in the Middle and Southern Caspian Sea and is rare in the Northern Caspian Sea. This sturgeon spawns mainly in the Kura and the Ural rivers, rarely in the rivers of the Iranian coast and in the Volga River ( Bogutskaya et al., 2013). This species is listed in the RDBs of the Russian Federation ( Pavlov, 2021), the Astrakhan Region ( Pilipenko et al., 2014), the Republics of Kalmykia ( Ochirov, 2014) and Dagestan ( Magomedov, 2009), as well as Tajikistan ( Rustamov and Shakirova, 2013; Artaev et al, 2025) (category I as vulnerable species), Azerbaijan ( Habibbayli and Babayev, 2023) (category II as not abundant, declining species) and Kazakhstan ( Meldebekov, 2010) (Aral Sea population, category I as vulnerable). Along with other sturgeons, international trade is regulated by CITES ( CITES, 2023) and fishing is prohibited everywhere. Despite substantial artificial propagation, the population remains very low due to loss of natural spawning grounds, intensive IUU fishing, pollution of habitats with industrial wastes, and disruption of natural spawning migration routes ( Ponomarev and Ponomareva, 2009; Orlov et al., 2022d). Therefore, additional conservation measures need to be developed for this species.

4. Stellate sturgeon Acipenser stellatus Pallas, 1771

This species is distributed throughout the Caspian Sea and occurs in the Middle and Southern Caspian Sea to depths of 75-100 m ( Kazancheev, 1981). Recently, in the northern part of the sea, there has been a shift in feeding aggregations from the western coast to the eastern shallow areas with warmer and saltier waters ( Zykova and Konopleva, 2011, Ruban et al., 2022). It enters rivers from the Ural to the Sulak to spawn ( Bogutskaya et al., 2013). Since the 1990s, there has been a steady decline in the abundance of A. stellatus due to both anthropogenic impacts and climatic changes. Its abundance is extremely low in the modern period and this species is considered to be threatened with extinction ( Khodorevskaya and Kalmykov, 2014; Fazli et al., 2021). Therefore, additional conservation measures need to be developed for the stellate sturgeon.

5. Russian sturgeon Acipenser gueldenstaedtii Brandt et Ratzeburg, 1833

The population of the Russian sturgeon is more stable compared to the stocks of beluga and stellate sturgeon, but the tendency to reduce its commercial stocks remains as a result of insufficient recruitment ( Khodorevskaya and Kalmykov, 2014). In the sea, it occurs everywhere at depths down to 40- 50 m. The densest feeding aggregations are formed in the western and central parts of the Northern Caspian Sea ( Ruban et al., 2019). It spawns mainly in the Volga and Ural rivers, and to a lesser extent in the Terek River ( Bogutskaya et al., 2013). In the late 1950s, after the construction of the Volga hydroelectric cascade, a significant part of the spawning grounds in the upper and middle reaches of the Volga River were lost ( Zykov et al., 2013). In this context, measures have been taken to artificially propagate Caspian sturgeon stocks. For this purpose, sturgeon hatcheries have been built in the lower reaches of the Volga, Kura and Ural rivers, which ensure the breeding and annual release of juveniles into the sea ( Zykov et al., 2013). In addition to artificial propagation, CITES has imposed a moratorium on fishing for sturgeon, while the Russian sturgeon has been listed with other Caspian sturgeon in various RDBs. However, this species continues to decline due to IUU fishing and other anthropogenic impacts ( Ivanov et al., 2020), and therefore additional conservation measures required to save and restore this valuable species.

Genus Huso Brandt et Ratzeburg 1833

6. Beluga or giant sturgeon Huso huso (Linnaeus, 1758)

This is an anadromous fish. It is found everywhere in the Caspian Sea, where it inhabits a depths of 40-60 m from the surface most of the year and migrates down to 180 m for the wintering. This sturgeon does not usually form shoals. Beluga of Volga origin migrates south to the waters of Turkmenistan, Iran and Azerbaijan for feeding. It used to spawn in all rivers from the Ural to the Gorgan, but the Volga was the main spawning river ( Bogutskaya et al., 2013). After the regulation of the flow of the Volga River, a significant part of the species' spawning grounds was lost, and since the mid-1950s its reproduction has been mainly artificially supported ( Zykov, 2011). Despite intensive artificial reproduction, beluga stocks have been declining steadily in recent decades mostly due to IUU fishing ( Ivanov et al., 2020) that require development of additional conservation measures.