ter sturgeon die rapidly. I assume that in the low-
waterperiodfrom themiddle1970suntil thelate
1980s, thedecrease in theflow velocity,clearing of
water and the decrease in thesize of riverbeds pre-
vented migration of shovelnosesturgeon from the
middle to thelowerreaches of the AmuDarya Riv-
er.
In 1989 and1991,sturgeonwere concentrated in
the regions of the riverwhere thedrainagewaste
enters into it.Possibly,this was caused by theexist-
ence of organisms inhabiting these waste waters be-
cause of their enrichedsalt andorganicmaterials
content.This influence ofdrainagewaterspossibly
resulted in a muchgreaterbiodiversity of the ben-
thicfauna: thenumber ofspeciesincreasedfrom 55
(10 higher taxa) in1974 to 83species (17taxa) in
1989.Speciesdiversity ofchironomids,ephemerop-
terans, andmolluscsincreased: new immigrant my-
sids and shrimpsappeared.Fifteenspecies and
forms ofchironomids werefound in diet ofstur-
geons in May andOctober1989.Studies on the dis-
tribution of benthic fauna in theriver bed andareas
of its concentration may facilitate a search for stur-
geons.
Unfortunately, the attempts to breed P. kaufman-
niin captivity in1983–1985wereunsuccessful: in all
experiments theembryosdied at10–12daysafter
hatching(Goncharov et al.1991).
theymoved1800 km ormoreupstream (Mitrofanov
et al. 1986). In the AmuDaryaRiver, the spawning
areas ofthisspecieswere located in alargeregion
from the KyzylzharCape(103 kmupstreamfrom
the rivermouth) up toFaizabadkalCape (more
than1500 kmfrom therivermouth).
Therewere twoforms of the ship sturgeon, the
winter andsummer ones. The Aral Sea population
of sturgeon was comprisedpredominantly of the
winter form. Its migrationinto the Amu Darya Riv-
er usuallystarted at thebeginning ofspring flood, in
the secondhalf ofApril.Massmigrationcontinued
from thebeginning of May untilSeptember.some-
times until the end ofOctober.Sturgeon stayed the
wholewinter in theriver andspawned nextyear in
spring. The age offishmigrating forspawninginto
the rivers wasfrom 7 to 30yearswith a predom-
inance (82.1%) of20–21year oldindividuals(Tleu-
ov 1981).
The main spawninggrounds of theshipsturgeon
were located in the middle reaches of the Amu Da-
rya River.between thetowns ofChardzhou and
Turtkulem:here about50–60% of theprogeny ap-
peared(Tleuov & Sagitov 1973). Spawningalso
took placenear thetown ofNukus Thespawning
period of ship sturgeon began inMarch at awater
temperatureabove 10°C and continueduntil the
end of May at a temperature of21–23°C. Theabso-
lute fecundity of theAralshipsturgeonvaried from
52 259 to 554 700 eggs, being 389 731 onaverageAfterspawning, shipsturgeon returned to the sea
wherethey feduntil thenextmaturation.They fed
mostly onmolluscs:among them,Hipanisminima,
Dreissenapolimorpha,andD. caspianapredomin-
ated(88%)(Tleuov1981).Fishyoung were rarely
found insturgeonstomachs.After introduction of
certainfishes in theAral Sea,whengobies and sand
smeltsappeared ingreatamounts in the sea, atran-
sition of theship sturgeon topiscivory wasnoticed.
Piseivorystarted at the age of twoyears and at the
age of threeyears sturgeon consumedmainly fishes
(up to 61 % of theirfood).This transition tomore
piscivorousfeeding occurred in thesecondhalf of
the 1960s(Tleuov1931).
From thelate1920s to the 1970s.therewere nu-
merousattempts to introduceothersturgeon spe-Ship sturgeon (Tleuov1981).The shipsturgeon,Acipensernudiventris,is a large
anadromousfishoccurring in theBlack,Caspian,
and Aral Seabasins(Berg1948,Sokolov &Vasilev
1989). In theAral Sea theship sturgeon was the only
representative of thegenusAcipenser(Nikolskii
1940). Ship sturgeon reached a length of 160 cm and
a weight of 45 kg(Tleuov &Sagitov1973). In 1933 -
1934,ship sturgeon wereintroduced from the Aral
Sea intoLake Balkhash(Kazakhstan),where they
grewfasterthan in theAral Sea(Dombrovskii et al.
1972).
Before theflow in the AmuDarya and Syr Darya
rivers wasregulated, theshipsturgeonthrived ev-
erywhere in the AralSea. For spawningthey mi-
gratedmainlyinto the Syr DaryaRiver inwhich