The beluga sturgeon, Huso huso, is endemic to the Ponto-Caspian Sea region that includes the Caspian Sea (the largest inland body of water in the world) as well as the Sea of Azov and the Black Sea (Bemis & Kynard 1997, Berg 1948).

Acipenseriformes, including fossil species, are restricted to the Northern Hemisphere; closely tied to former Laurasian landmasses (Eurasia, North America) (Bemis et al. 1997). The lone congener of the beluga sturgeon, the kaluga (Huso dauricus) is endemic to the Amur River, which runs along part of the Chinese/Russian border (Krykhtin & Svirskii 1997). Although these two species are the only members in the genus Huso, there are some doubts whether they are sister species (Doukakis 2000).

Biogeographic Regions: palearctic (Native )

Acipenseriformes are primitive actinopterygians that have a fossil record dating back to the Lower Jurassic (200 mya), with an origin perhaps even earlier in the Mesozoic (Bemis et al. 1997). Acipenseriformes possess a unique blend of teleost-like character (high fecundity small egg size) and elasmobranch-like characters (cartilaginous endoskeleton, hyostylic jaw suspension). They also possess a heterocercal caudal fin and remnants of ganoid scales; both are uncommon among extant actinopterygians. Sturgeon species are noted by a spindle-shaped body with five rows of bony scutes and a long snout with sensory barbels.

The genus Huso can be distinguished from other sturgeon by possession of branchiostegal membranes that are joined and form a flap (Berg 1948). The two species in the genus also possess a relatively large crescent shaped mouth (Berg 1948). Berg (1948) gives the following key for distinguishing between Huso congeners:

1. H. dauricus First dorsal scute the largest. Barbels without foliate appendages. Fewer than 60 rays in dorsal fin. Found in the Amur Basin.
2. H. huso First dorsal scute the smallest. Barbels with foliate appendages. Usually not less than 60 rays in dorsal fin. Found in the basins of the Caspian, Black, and Adriatic Seas.

Among freshwater fish species, H. huso may have be the largest that has ever lived (Freedman 1999). Based on Debus's (1997) reports on bones excavated from the 14th century, one fifth of all H. huso catches of that time were between 4-6 meters in length. Beluga this size today are extremely rare. Bemis et al. (1997a) report that this species may have reached nearly ten meters in length. The largest beluga ever recorded measured six meters in length and weighed 3,200 kg (Berg 1948, Birstein 1993, Freedman 1999). The decreased size of individuals today may reflect the shift to catching younger individuals because of overfishing of older and larger fish, polluted living conditions for beluga in the Caspian and other parts of its range, and the possible loss of large individuals from the gene pool. Large beluga sturgeon have been targeted by fisherman for centuries.

Sexual dimorphism is weakly expressed, and may only be notable in overall size and weight. This dimorphism is particularly notable in gravid females that bear the weight of heavy egg masses (Berg 1948, Raspopov 1993).

Range length: 6 (high) m.

Other Physical Features: bilateral symmetry

Average mass: 1.1396e+06 g.

• Freshwater
• Marine

• Freshwater

• Freshwater

• Freshwater
• Marine

• Freshwater

Beluga sturgeon are considered euryhaline, capable of moving freely between freshwater and estuaries. Species of the order Acipenseriform often enter rivers for migration to other areas or for spawning.

Beluga sturgeon spawn at a water temperature of 9-11 degrees C and they are sensitive to these water conditions during periods of spawning (Levin 1997). However, other than spawning times, adults are fairly resilient to many environmental factors, particularly considering that they live in some of the most polluted and altered waterways in the world.

Habitat Regions: temperate ; freshwater

Aquatic Biomes: pelagic ; lakes and ponds; rivers and streams

Other Habitat Features: estuarine

Adult beluga sturgeon are mainly piscivores, swimming at middle depths and preying mostly on pelagic fish species. This is unlike most other sturgeon species, which normally feed on bethic invertebrates while swimming along the bottom. In the Black Sea they feed on species such as flounder (Platichthys flesus) and other flatfish, gobies (Gobiidae), and Black Sea anchovy (Engraulis encrasicolus) (Berg 1948). In the Caspian they are reported to feed mainly on the Caspian roach (Rutilus rutilus), but also on herring and native gobies. Little is known about the diet of larval and juvenile H. huso.

Unlike other Ponto-Caspian sturgeon species beluga do not congregate, but remain dispersed when not migrating (Levin 1997). Sturgeon species can endure long periods of starvation and often do not eat for long periods during spawning migrations (Beamesderfer & Farr 1997)

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Piscivore )

Beluga are the largest piscivores in the Pronto-Caspian region. It difficult to determine their role in the past given their endangered status, but in periods where they were quite abundant (before 1950) they would have been among the top predators in the Ponto-Caspian, playing a similar role as the fish eating seals of the region.

The large size of adults makes predation on them difficult, and a natural predator besides humans is unknown. Many juveniles fall prey to pollution and hydroelectric dams (Altuf'ev 1997). Most populations are supported solely by hatchery released individuals. In the 1980's the number of young beluga's released from the Volga river per year was 19.4 million. The survival rate of these individuals was estimated to be 0.1% (Khoderevskya 1997). The number killed by natural causes or causes other than fishing pressures has not been documented.

Since fisherman or poachers capture nearly all beluga sturgeon before they can die of natural causes, the development of this species is little known. Length and weight increases much more rapidly earlier in the life history of these fish than during later in ontogeny (Raspopov 1993). Length and weight can range greatly in a given age class depending on environmental conditions of the sturgeon habitat (Raspopov 1993).

After hatching, downstream migrations of beluga larvae occur between May and June (Levin 1997). From hatcheries data, it is observed that the weight of beluga after 28-45 days averages around 2.5-3 g (Levin 1997). By the time they enter the sea they are 6-11 cm in length. Recently hatched larvae are also purported to move at about 24 km per day during their migration to the sea. By the forth year, beluga may reach a meter in length. In the spring, mature fish enter the rivers to breed, while younger individuals (less than 10 years) disperse near the Northern Caspian, their distribution based mainly on ecological factors like water temperature and benthic silt (Levin 1997).

Beluga sturgeon mature later than most other acipenseriforms, usually after their 12th year (Lelek 1987). Raspopov (1993) estimated that beluga sturgeon in the Caspian become sexually active every 4-8 years for females, and every 4-7 years for males. Under favorable conditions, a beluga may spawn up to nine times in its lifetime.

From 1987-1997 in the Volga River (which was once the most important spawning habitat of beluga), female spawners have ranged from 199 to 236 cm, and weighed between 48 to 160 kg (Levin 1997). These are much smaller than recorded sizes for previous years.

The beluga sturgeon is one of the most long-lived of all vertebrate species. Reportedly it may have reached ages over 100 years (Ono et al. 1983, Birstein 1993, Khodorevskya 2000). Most acipenseriform species mature at a late age (normally greater than 10 years). Females mature later than males, normally after 15 years for females and 10 for males (Berg 1948). Individuals no longer die of natural-age related causes, with most being fished soon after reaching reproductive maturity. The world demand for caviar (sturgeon and paddlefish roe) is to blame for the shortened lifespan of these fish. The demand far exceeds the available supply, forcing legal fishers to catch increasingly younger and smaller fish, and providing fuel for a growing black market. Individuals today are not found beyond their 56th year (Raspopov & Novikova 1997).

Typical lifespan

Status: wild: 56 (high) years.

Beluga do not spawn every year and females will resorb eggs unless conditions are suitable (Artyukhin et al. 1979). Sturgeon can take between 6 and 25 years to reach sexual maturity, and females of this species may reproduce only every four to eight years (Raspopov 1993).

Mating System: polygynandrous (promiscuous)

Beluga sturgeon are anadromous, migrating to freshwater spawning grounds in rivers from larger seas (either the Caspian, Azov or Black). Migrations occur in these populations twice a year in spring and autumn (Berg 1948, Hensel & Holcik 1997). Some authors have divided beluga populations into Winter or Spring races by the period they choose to spawn (Berg 1948). Distances for spawning migrations for this species are legendary, exceeding 2500 km in the Danube and Volga basin (Hensel & Holcik 1997, Khoderevskaya et al. 1997).

Breeding season: winter and autumn race (varying depending on Caspian, Asov or Black sea population)

Range age at sexual or reproductive maturity (female): 17-29 (high) years.

Average age at sexual or reproductive maturity (female): 6-30 years.

Range age at sexual or reproductive maturity (male): 11-23 (high) years.

Average age at sexual or reproductive maturity (male): 6-30 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; fertilization (External ); oviparous

These sturgeon typically spawn large numbers of eggs in shallow, gravely sites, and do not provide parental care (Bemis et al. 1997, Lelek 1987).

Parental Investment: no parental involvement

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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.

US Federal List: no special status

CITES: appendix ii

IUCN Red List of Threatened Species: endangered

There is some evidence that PCPs and other dangerous chemicals may be retained with the eggs of beluga sturgeon (Altuf'ev 1997). Small traces of environmental toxins appear in caviar (Boyle 1994). The levels of some of these chemicals were considered high from samples chosen from some major retailers in the U.S. (between 3.17-3.27 ppm of DDT, 410-640 ppb of Arclor 1254, and 2.1 - 2.8 ppm of selenium) but these numbers are lower than United States Food and Drug Administration action levels. It is doubtful that these traces can be harmful to anyone since few individuals consume such large amounts of caviar that the chemicals could accumulate to dangerous levels.

Due to the incredible value of the roe of this species known commercially as beluga caviar - the most expensive food item in the world(Birstein et al. 1998) - this species is among the most sought after naturally available commercial products in the world. Female beluga can produce 12 % of their body weight in caviar and beluga caviar can demand $200/kg. This species has become so depleted that its survival is supported entirely or nearly entirely by hatcheries throughout its limited range (Secor et al. 2000, Khodorevskya 1999). Without natural recruitment, population structure, age composition and genetic diversity of the beluga sturgeon have suffered (Secor et al. 2000, Raspopov 1993).

Most beluga sturgeon were historically found in the Caspian Sea. This sea is fed by over 100 rivers, the most important of these was the Volga in Russia which histrorically supplied 75% of the Caspian Seas's sturgeon catch (Artyukhin 1997, Khodershaya et al. 1997). Of the other rivers, the Ural River is the only remaining free-flowing major river feeding the Caspian. It is also the only such river where beluga sturgeon can reproduce naturally, without the benefits of hatcheries (Khoderoveskya et al. 1997, DeMeulanaer & Raymakers 1996). However, poaching and pollution problems are higher in the Ural than other parts of the sea, and about 50% of spawning grounds are lost there due to sedimentation and heavy agricultural and industrial pollution (Verina and Peseridi 1979).

The illegal catch of sturgeon in the Caspian Sea and Volga River may be ten times greater than the legal catch (TRAFFIC 2000). Poachers are reportedly removing half of the mature beluga individuals every year. From December 1995 to December 2000 U.S. Fish and Wildlife Services confiscated 3044.19 kg of illegally imported eggs of Huso huso (calculated from USFWS LEMIS system). With an average spawning size of Huso huso individuals being 70 kg (Khodorevskya 1999) and a gonadosomatic index (GSI) ranging from .07-.15 the number of individuals killed to obtain this caviar is between 290 to 621.

Because of the unsupportable demand for caviar, beluga sturgeon are being caught at ages closer and closer to sexual maturity. More than 80% of spawning females are between 17 and 29 years of age, and nearly 90% of males are between 11 and 23 years of age (Raspopov 1993, Rospopov and Novikova 1997). With proper management it is said that it may take between 40 to 45 years for stocks in the Caspian Sea just to return to stable levels (Artyukhin 1997). The slow maturation of sturgeon tied with low numbers have placed estimates of population recovery for some species at more than a century (Secor and Waldman 1999).

Positive Impacts: food ; research and education