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While the beluga sturgeon is popular for its fillets, its eggs, known as "true caviar," are regarded as a delicacy. Native to the Caspian Sea, these ancient fish can grow to 15 feet in length, weigh more than a ton and live to be 100 years old. Due to the popularity of their eggs, they're heavily overfished -- typically with gill nets. This particularly problematic because this species that doesn't reach sexual maturity until 20 or 25 years of age. In addition to fishing pressures, beluga sturgeon suffer from habitat reduction, having lost 90 percent of their historic spawning grounds over the past several decades. Because of these pressures, the IUCN classified the beluga sturgeon as endangered, and the population is expected to continue its decline.
This species has been recorded in the basins of the Caspian, Black, Azov, and Adriatic Seas, however its current native wild distribution is restricted to the Black Sea (in the Danube only) and the Caspian Sea (in the Ural only). It is one of the largest anadromous fish in the Caspian Sea, where at least three Beluga populations have been identified by microsatellite technique (Pourkazemi 2008). It does occur in the Azov Sea, and Volga River but these are stocked fish.
At sea, this species is found in the pelagic zone, following food organisms. It migrates further upriver to spawn than any other sturgeon; however this migration has now been disrupted due to river regulation (in the Danube drainage up to Morava River). It spawns in strong-current habitats in the main course of large and deep rivers on stone or gravel bottom.
This species is anadromous (spending at least part of its life in salt water and returning to rivers to breed). Males reproduce for the first time at 10-15 years, females at 15-18 years, with an estimated generation length of 20-25 years. This species spawns every 3-4 years in April-June. A complicated pattern of spawning migrations includes one peak in late winter and spring and one in late summer and autumn. In spring, it migrates from the sea before spawning. Individuals migrating in autumn remain in the rivers until the following spring. Spawning occurs at temperature from 6 to 14 °C in the channel and spring flooded spawning grounds at a current speed of 0.8-1.2 m / sec. Spawners the late winter/spring run dominate the spawners in the Volga River (80%), whereas the late summer/autumn run dominates in the Ural River. Yolk-sac larvae are pelagic for 7-8 days and drift with current. Juveniles migrate to sea during their first summer and remain there until maturity.
In the past this species was the largest fish of the Caspian Sea, reaching lengths of more than 5 m and a weight of 1,000 kg. The lifetime of such large specimens, apparently, exceeded 100 years. Currently there are individuals up to 280 cm, weighing up to 650 kg. Average length of females is 240, males is 220 cm, weight respectively is 130 and 65 kg. The maximum age of 53 years was observed in 2003.
Various environmental factors influence the distribution of the species in the Caspian Sea. One factor is water temperature, as mature Beluga prefer water temperatures not exceeding 30°C. They spend the spring and summer mostly in the northern and middle parts of the Caspian Sea and then move southwards to spend the winter in the southern areas, which coincides with highest densities of food organisms. The diet includes roach Rutilus rutilus (L.), common carp (Cyprinus carpio L.), herrings (Clupeidae), kilka (Clupeonella), crayfish (Astacus), gobies (Gobiidae), pike-perch (Sander lucioperca (L.)), birds, sturgeons (Acipenseridae), and even seal (Khodorevskaya et al., 1995). Mature individuals of Beluga are less sensitive to low temperature than the immature, as they feed in the northern part of the Caspian Sea under the ice. With water temperatures decreasing, Belugas reduce the range of depths at which they feed. Immature individuals in spring and autumn prefer the more desalinated sea areas. In summer the highest concentrations occur at the salinity of 3 to 7%. The largest concentrations of Beluga in the northern Caspian occur during the migration of its main prey organisms (herrings, kilka, gobies, roach, etc.).
Since it is difficult to distinguish between a male and a female without dissection, males are as susceptible to fishing pressure as females full of roe. To keep up with fishing pressure, Khoderevskya (1999) reports that between 15-20 million fingerlings need to be released annually from hatcheries in order to maintain a beluga population in the Caspian Sea. This figure is not currently being met. Birstein and colleagues (1997) report that in 1995 due to the lack of broodstock, there was no artificial breeding or natural reproduction in the Volga River that year. This river historically held most of the world's beluga spawners and releases (Artyukhin 1997). International trade in beluga caviar should be halted in order to relieve the pressure on this species. Although currently placed under CITES Appendix II, an uplisting to Appendix I would provide a working ban on international trade. The IUCN has also listed this species as critically endangered. As the U.S. is the second largest importer of beluga caviar in the world, placement of this species under the U.S. Endangered Species Act would provide immediate relief from much of the pressure to fish this species. Declaration of any ban must also be enforced, as a well-established black market has been successfully operating since the fall of the Soviet Union (DeMeulanaer & Raymakers 1996, Khordorevskaya et al. 1997).
Habitat destruction also threatens this species. Dams block migratory routes. In its major spawning river the Volga, only a small percentage (less than 20%) of beluga are able to migrate upstream past the major dam on that river the Volgograd Dam (Rochard et al. 1990, Gertsev 1999). Fish lifts and elevators must transport these individuals across the dam. Often they find water conditions on the other side of the dam unsuitable for reproduction because of water temperature and flow rates. Problems of migrating larvae moving toward adult grounds upstream from the dam are little studied. Debus (1997) considers that the passage of juveniles downstream the Volga River as normally lethal, because juveniles do not survive passage through the hydroelectric power turbines of the dams.
Overfishing at sea and poaching in estuaries and rivers for meat and caviar is a major threat to the species. Overharvesting and a sharp increase in poaching has led to the largest and most mature specimens being removed from the population and reducing natural reproduction to almost zero (Krassikov and Fedin 1996). In the Ural river current fishing rates are 4 to 5 times sustainable levels (F Max) (Doukakis et al. accepted).
Bycatch is also a threat to the species. The species caviar is very high value (8,000 USD per kilo in 2009).
Impoundment of rivers has destroyed most of the species spawning grounds. The Volgograd dam, built in 1955, has decreased the area of available spawning grounds by 88-100% in the Volga river, similar areas have been reduced in the Terek and Sulak rivers from 132 ha and 202 ha, respectively. The Don river dam removed 68,000 ha of spawning ground and flow regulation in the Kuban river led to the loss of 140,000 ha (CITES 2000).
Due to the longevity of the species there is evidence of pesticide contamination, leading to many problems including reduced reproductive success (Gessner, J. pers comm.).
Sturgeon have survived since the time of the dinosaurs but some populations of the beluga are today threatened with commercial extinction, principally as a result of overfishing (9). The eggs are highly prized as caviar, for both their quality and quantity (4). The beluga is the most famous of the caviar sturgeons, and is featured in the Guinness Book of Records as the most expensive fish (3). Previously effective management of Caspian Sea fisheries have recently collapsed and illegal fishing is now rife; the U.S Fish and Wildlife Service estimated in 1998 that more than 50% of worldwide caviar trade was illegal (9). In addition, habitat destruction through the pollution of coastal habitats and the alteration of river systems through dams, pollution and silting have further affected beluga numbers (4). The Volgograd Dam for example, has blocked almost all beluga spawning grounds (9).
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