|Scientific Name:||Acipenser ruthenus|
|Species Authority:||Linnaeus, 1758|
|Red List Category & Criteria:||Vulnerable A2cde ver 3.1|
|Assessor/s:||Gesner, J., Freyhof, J. & Kottelat, M.|
|Reviewer/s:||Pourkazemi, M. & Smith, K.|
The species has undergone a large population decline, but local populations are still surviving in most parts of its range (rivers draining to Black, Azov and Caspian Seas; Siberia from Ob eastward to Yenisei drainages). Recorded catches in the Russian Federation decreased by nearly 40% between 1990 (116 tonnes) and 1996 (80.6 tonnes). It is stocked in large numbers in Danube and Russia (but it is unknown if the stocked individuals reproduce in the wild). It is impossible to identify the exact rate of decline of wild individuals and while some populations, e.g. Don (estimated >80% decline), Kuban (estimated >80% decline), Ob (<50% decline, Ruban pers. comm.), Irtysh (<50% decline, Ruban pers. comm.) and Dniestr (>80% decline) have declined heavily, other stocks, e.g. Yennisey (estimated 40% decline), upper Volga (possibly stable but large stocking, Mugue pers. comm.), Ural (unknown decline) have seen smaller declines. The major parts of the population exist in the Ural, Volga and Danube (where populations have stabilised in recent generations after a previous large decline); therefore the overall estimated wild native population (excluding stocked individuals) decline over the past three generations (21-30 years) is more than 30% but not more than 50%. However many populations of this species are undergoing a serious and dramatic decline in recent years and need immediate conservation action.
|Range Description:||This species is known from rivers draining to Black, Azov and Caspian Seas; Siberia from Ob eastward to Yenisei drainages. Its current strong holds are the Volga, Ural and Danube systems. It was introduced in Pechora drainage in 1928-1950 and in Lake Ladoga basin (most likely not self-sustaining). Aquaculture has resulted in intentional and accidental introductions throughout Europe, without formation of self-sustaining populations. This species has formed self sustaining populations in reservoirs in Russia.|
Native:Austria; Azerbaijan; Belarus; Bosnia and Herzegovina; Bulgaria; China; Croatia; Germany; Hungary; Kazakhstan; Moldova; Romania; Russian Federation; Serbia (Serbia); Slovenia; Ukraine
|Range Map:||Click here to open the map viewer and explore range.|
Comprehensive catch data are not currently available but recorded catches in the Russian Federation decreased by nearly 40% between 1990 (116 tonnes) and 1996 (80.6 tonnes) (CITES 2000).
In the Danube drainage, the only available catch data is from 1958 to 1981, where catches ranged from 117 tonnes in 1963 to 36 tonnes in 1979, with an average catch of 63.5 tonnes per year (CITES 2000). In the mid and lower Danube catches are not often reported as it is a small species so catch data is suspect. Surveys (Juvenile Production Index) show that there is good current spawning in the Danube in Romania, Hungary and Serbia upstream of dams (Paraschiv et al. 2006; Knight et al. 2010). In the mid Danube the species supported large scale fisheries at the end of the 19th century, though currently this is much smaller. Over the past 21 years (estimated three generations in the Danube), a decline has happened but it is unknown to exactly what extent. The population has shown some recovery since the 1980s as the pollution from agriculture has been reduced. Hungary has had a re-stocking programme but its success is in question due to lack of brood fish used in the stocking (Guti pers. comm. 2007, to Suciu).
|Habitat and Ecology:||
The Sterlet is found in large rivers, usually in the current and in deep water. As water level rises, it moves to flooded areas to feed. It spawns on gravel in strong-current habitats.
It is a freshwater species; anadromous populations have been extirpated. Males reproduce for the first time at 3-5 years, females at 5-8 (Siberian populations mature later: males at 7-9 years, females at 9-12 years). The average reproductive age is about 10 years, but in the Danube this is lower (seven years) due to intensive fisheries. Females reproduce every 1-2 years and males every year in April-June when the temperature rises above 10°C. This species is largely sedentary; undertaking only short spawning migrations (322 km reported from Danube). There was a migratory population with large-growing individuals in Volga until end of 19th century, feeding in the northern Caspian Sea and moving upriver in autumn. The Sterlet feeds on a wide variety of benthic insect larvae and molluscs.
Overfishing, mostly for their meat, is the major threat to the species. However, in the year 2000 the Russian Federation established an export quota for 300 kg caviar, possibly from aquaculture. In the Caspian Sea and Sea of Azov the illegal sturgeon catch for all species was evaluated to be 6 to 10 times the legal catch (CITES 2000). International trade is mostly made up of live individuals (juveniles) for the aquaculture and aquarium trade, almost exclusively sourced from aquaculture.
Dam construction, which began in the 1930s, led to the loss of spawning grounds across the species' range. Now spawning success is reliant upon the correct level of water being released by hydroelectric power stations; lowered water levels in rivers can cause mass death of fingerlings (CITES 2000).
Pollution, including oil products, phenols, PCB's and mercury has threatened the species in the Volga system and Siberian rivers.
Hybrids (artificially produced with Huso huso) released in the beginning of the 1980s in Don, are now possibly breeding with native populations (Chebanov pers. comm.)
Most range states have legislation regulating or banning the catch of the species, and there are stocking programmes for the Danube and Drava rivers. Restocking of the species is reported in Bulgaria, Hungary, the former Yugoslavia and Russian Federation. In 2009 Romania stocked A. ruthenus for the first time in the Danube (Suciu pers. comm.). The majority of international trade is taken from aquaculture in the form of live juveniles (CITES 2000). This species was listed on CITES Appendix II in 1998.
Better fisheries monitoring is needed along with enforcement to ban illegal catches.
Many populations of this species are undergoing a serious and dramatic decline in recent years and need immediate conservation action. Individual stock Red List assessments are needed for this species.
|Citation:||Gesner, J., Freyhof, J. & Kottelat, M. 2010. Acipenser ruthenus. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2. <www.iucnredlist.org>. Downloaded on 17 April 2014.|
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