IUCN: СR; Bo (II); EUHD (V); CITES (II); RDBBS: VU; RDBUkr: Вразливі
Value of species
The species is now very rare in the Black Sea basin where almost all of the species' spawning sites have been lost due to dam construction, except in the lower Danube river where some spawning still exists (see Juvenile Spawning Index) but individuals are rare. The Caspian basin has lost 70% of spawning grounds since the 1950s mainly due to hydroelectric power stations; flow regulation of the Kuban has led to the loss of 140,000 ha and damming of the river Don removed 68,000 ha spawning ground (CITES 2000).
The last natural population still migrates up the Danube and the Rioni (last recorded in Rioni in 1999), where the sturgeons are heavily overfished and poached. The Caspian populations are also under massive pressure from overfishing and loss of spawning habitats. Almost all migrating spawners are poached below the Volgograd dam. The Ural river still has spawning individuals.
It is estimated that the species' wild native population has undergone a massive population decline of over 90% in the past three generations (estimated at 45 years). This is based on the 88.5% decline in global catches of the species in just 15 years despite large levels of stocking (average global catch from 1992-1999 was 1,531.75 tonnes; from 2000-2007 it was 175.37 tonnes), the 92.5% decline in estimated spawning stock biomass in the Volga from 1961-65 to 1998-2000, the 88% decline in the average number of spawners entering the lower Volga from the 1962-75 average to the 1992-2002 average, and the decline in the Juvenile Production Index from Romanian Danube.
This decline is predicted to continue as illegal fishing at sea, and in rivers, for caviar will soon result in the extinction of the remaining natural wild population. In the immediate future, survival can only depend on stocking.
This species is known from the Caspian, Black and Azov Sea basins. Aquaculture has resulted in intentional and accidental introductions throughout Europe.
It is currently only known from the Caspian Sea, where it spawns in the rivers Ural and Volga, and the Black Sea where spawning occurs in the lower Danube and Rioni rivers (last recorded in the Rioni in 1999 (Kolman & Zarkua 2002)). There is no native spawning population remaining in the Sea of Azov, only introduced (stocked) individuals. The species reproduction within the Kura is debated (Vecsei 2001).
Habitat: At sea, shallow coastal and estuarine zones. In freshwaters, in deep parts of large rivers with moderate to swift current. Spawns in strong current (1-1.5 m/s) in large and deep rivers on stone or gravel bottom.
Biology: Anadromous and freshwater populations (freshwater populations existed in the Danube and Volga - both are now extinct). A 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 (320-650 km in the unregulated Ural). Individuals migrating in autumn overwinter in rivers and spawn the following spring further upstream (900-1200 km in the Ural).
Males reproduce for the first time at 8-13 years, females at 10-16. Generation length (average age of parents of current cohort) is estimated to be 15 years under natural circumstances, but due to the impacts this species is facing the generation length ranges from between 12 years in the Caspian Sea to over 20 in the Danube. Females reproduce every 4-6 years and males every 2-3 years in April-June, when the temperature rises above 10°C. Larvae drift on 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.
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