- Acipenser huso Linnaeus, 1758
Beluga, Giant Sturgeon, European Sturgeon, Great Sturgeon
IUCN: СR; Be (II); Bo (II); EUHD (V); CITES (II); RDBUkr: Зникаючі
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.
Global fisheries statistics show that there has been a 93% decline in catch from 1992 (520 tonnes) to 2007 (33 tonnes) (FAO 2009).
The number of Beluga annually entering the Volga dropped from 26,000 (1961-65) to 2,800 (1998-2002), a decline of 89% in 33 years (Khodorevskaya et al. 2009). Only 2,500 migrated up Ural in 2002 (Pikitch et al. 2005).
Currently it is thought that nearly 100% of Beluga in the Volga are hatchery reared, but there is evidence of spawning elsewhere in its distribution (Khodorevskaya et al. 2009). Despite intensive restocking in the Caspian Sea (91% of each generation is estimated to come from hatchery stock), the annual catch in the northern Caspian Sea has drastically fallen. Catches in the Caspian were: 1945-55 average of 1,380 tonnes; 1956-65 average of 1,283 tonnes; 1966-75 average of 1,623 tonnes; 1976-85 average of 849 tonnes; 1986-95 average of 506 tonnes; 1996-2003 (latest data) average of 60.8 tonnes (in Doukakis et al. accepted). This shows a decline of 95%. The official catch statistics support this trend, as they show that the species was abundant in 1938 and then stable to the late 1980s, with the major decline starting from 1990 to the present showing over a 90% decline in the past 60 years (see Khodorevskaya et al. 2009). The agreed Beluga catch quota for all of the Caspian Sea (2007/8 - 28th session of the Commission) was 99.8 tonnes; this quota was not achieved. The proportion of Beluga (to other sturgeon species) in trawl catches of the northern Caspian Sea in all seasons of observations was at an average of 11%. Over the recent years, this percentage has decreased to 8.3%, and the catch of beluga during trawl surveys did not exceed 31 specimens per year (Khodorevskaya et al. 2009).
Spawning numbers for the Volga from 1961-65 was 26,000, whilst in 1996/1997 it was 1,800 (Khodorevskaya et al. 2000), with 2,800 in 1998-2002 (Khodorevskaya et al. 2009).
In the Sea of Azov, between 1979-1981 it is estimated that 551,000 individuals existed (from stocked, and dominated by sub-adult and juveniles); in 1988-1993 there were 25,000 and after 1994 they were only caught sporadically, despite banning of commercial fishing of Beluga in 1986. After 1986 the major threat was from bycatch. Since 1994, 98% of individuals recorded in the Azov Sea have been juvenile. In 2001 the first individuals were produced from captive bred individuals and released (Chebanov and Koziritskaya 2007).
Catches in the Danube have also declined. In the mid-Danube the annual catch was 23 tonnes (average between 1972-76) which dropped to 7.5 tonnes (average between 1985-89), a decline of 67% in around 12 years (CITES 2000). In 2002, 21.3 tonnes were caught in Romania, whilst only 8.4 tonnes were caught in 2005, showing a 60% decline in three years. The percentage of catch quota achieved in Romania was 85% in 2002, 84% in 2003, 46% in 2004, and 34% in 2005. In 2006 the catching of Beluga was banned in the Danube (Paraschiv et al. 2006).
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.).
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