Animal Diversity Web

Ge­o­graphic Range

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). (Bemis and Ky­nard, 1997; Bemis, et al., 1997; Berg, 1948; Doukakis, 2000; Krykhtin and Svirskii, 1997)

• Biogeographic Regions
• palearctic
  • native

Habi­tat

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

Phys­i­cal De­scrip­tion

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).

• Other Physical Features
• bilateral symmetry

• Average mass

  1.1396e+06 g

  40162.11 oz

  AnAge

• Range length

  6 (high) m

  19.69 (high) ft

De­vel­op­ment

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.

Re­pro­duc­tion

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).

• Key Reproductive Features
• iteroparous
• seasonal breeding
• sexual
• fertilization
  • external
• oviparous

• 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

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

Lifes­pan/Longevity

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

Be­hav­ior

Bel­uga con­gre­gate only dur­ing spawn­ing times and seem to be a less gre­gar­i­ous species then other Ponto - Caspian stur­geon (Levin 1997).

Acipenser­i­form species use en­vi­ron­men­tal pa­ra­me­ters such as water tem­per­a­ture, flow ve­loc­ity, and tur­bid­ity as spawn­ing cues (Beames­der­fer & Farr 1997; May­den & Kuha­jda 1996, Scarnec­chia et al. 1989, Sulak & Clugston 1998). Damming al­ters these cues, lim­it­ing nat­ural re­cruit­ment. A high rate of tumor de­vel­op­ment and sig­nif­i­cant per­cent­age of goan­dal re­sorp­tion near the Vol­gograd dams re­veal that stur­geon species, in­clud­ing Huso huso, are often in a state of chronic phys­i­cal stress caused by habi­tat de­gre­da­tion (Altuf'ev et al 1981).

• Key Behaviors
• natatorial
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

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)

• Primary Diet
• carnivore
  • piscivore

• Animal Foods
• fish
• mollusks
• aquatic crustaceans

Pre­da­tion

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.

Ecosys­tem Roles

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.

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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.

Con­ser­va­tion Sta­tus

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.

• IUCN Red List

  Endangered
  More information

• IUCN Red List

  Endangered
  More information

• US Federal List

  No special status

• CITES

  Appendix II

Other Com­ments

Acipenserids have been hunted for their roe since at least 1100 B.C. (Wei et al. 1997). An­cient Greek, Roman and Chi­nese lit­er­a­ture make ref­er­ence to acipenser­i­form species and caviar; and the Chi­nese re­ported trade as early as the 10th cen­tury A.D. (De­Meu­le­naur & Ray­mak­ers 1998, Bur­ton & Bur­ton 1975).

For more in­for­ma­tion on bel­uga stur­geon and to learn how you can help save this species visit, http://​www.​caviaremptor.​org

Con­trib­u­tors

William Fink (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Prosanta Chakrabarty (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

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