not found in thelowerreaches of theriverduring prise30.5% of thefood.Fishes arerepresented by
the 1980s. C. kuschakewitschiand species of thegenusRhino-
The large Amu-Dar shovelnosesturgeonlives in gobius.
turbid, muddy waters. It inhabitsshallow-water Under thecurrentconditions, the large shovel-
parts of theriverwithsandy or stony-pebble bot- nosesturgeon continues to reproduce in the Amu
toms(Nikolskii 1938,Tleuov &Sagitov 1973). In DaryaRiver. InApril–May1989 we did notfind
1989–1991, Ialsofound sturgeon in themainchan- ripe females ready for spawning or already
nel of the riverwithsandybottom at a depth of 1.0- spawned. Femalesweremostly atstage II or II–III
1.5 m, as well as at theedges ofpools withturbid of maturity[according to thescale ofNedoshivin
water, and near sandbars. (1928)].However,thereweremales atstage IV or
In the past, themaximum sizereported of the IV-V. According to the results obtained by Boris
large shovelnosesturgeon was 75 cm, and themaxi- Goncharov (personalcommunication), in the re-
mum weight, 2 kg(Berg1948). In1965–1966, the av- gionnear thetown ofChardzhou in21–30Septem-
eragebody length was 37 cm and the average ber 1991, individuals at stage IVpredominated
weight, 241 g (Tleuov &Sagitov1973). The size of amongmales,whilefemales weremostly atstage II.
fishstudied by us in1989 and 1991variedfrom 9.3 to The rate ofreproduction of the population isvery
38.0 cm,being23.6 cm onaverage, and the weight, low. In1991,only asinglelateembryo and two one-
from 3.2 to 270 g(100.2 g onaverage). The age of year old juveniles werecollected in the lowreaches
individuals caught wasfrom 1 to 6years. The whole of the river (Pavlovskaya & Zholdasova 1991).
length of thelargest fish,including thetailfilament Early development andlarvae of P kaufmanni
was 69.4 cm(33.5 cm without the filament). and the weredescribed recently(Schmalhausen et al.1991,
weight was 250 g. Dettlaff et al. 1993).
The age of individuals in the population has In1993, Icaughtthreelarge shovelnose sturgeon
changedcompared to that in the1960s. In the1960s, during myexpedition to theOrdybaiChannel of the
the age of fishvariedfrom 1+ to 14+with a predom- AmuDarya River delta.They were young individu-
inance of 3 to 6year oldfish(Tleuov &Sagitov als of about 20 cm inlength (without thetail fil-
1973). In thelate1980s, thepopulation consisted ament) and about 50 g in weight. Ashovelnose stur-
mostly ofyoung (from l to 6 yearsold)fish, with a geon ofa similarsize,caughtnear thetown of Nu-
predominance of 3-year(36.8%) and 4-year old in- kus in the Kattyagarirrigation channel was also re-
dividuals(41.6%)(Zholdasova et al.1990). Therate ported in summer 1993. Theappearance ofsturgeon
of linear growth hasalso sloweddown compared in theirformerhabitats in thelowerreaches of the
with the1960s.Apparently,thisdecrease ingrowth AmuDaryaRiver isevidentlyrelated to asignif-
rate wascaused by a change insturgeondiet: an icant volume andstable downstreamflow in 1993. It
analysis of thecontent of stomachsshowed a de- is noteworthy thatduring the lastthreeyears the
crease in a proportion offishesconsumed by stur- meandischarge in the AmuDaryaRiver hasbeen
geon compared to the1960s. 3.7times higherthanduring the previousdecade.
Adultshovelnosesturgeon are benthophagous Also, theriver flow is turbid and goesapparently
withpredatoryinclinations(Nikolskii 1938, Berg directly through theTuyamuyunReservoir. Unfor-
1948,Tleuov &Sagitov1973). In the1960s. in the tunately, I have noinformation on the level of
middlereaches of the AmuDaryaRiver,five fish chemicalpollution of thewater in1992–1993. But a
speciesconstituted up to64.5% of thediet oflarge generaldecrease inusage of pesticides and mineral
shovelnosesturgeon:juvenileBarbusbrachycepha- fertilizers hasrecentlybeenobserved,mostly due to
lus,Aspiusaspius,Acipensernudiventris,Capoeto- economic problems.
bramakuschakewitschi, andNoemacheilusoxianus. The large shovelnosesturgeonoccursexclusively
A t present, thediet is morediverse; inaddition to in thefastrunningturbidwaters of the AmuDarya
fishes(36.6% of the food biomass), the larvae of 15 River. Sincethesefishwere never found in the
species of midges of thefamily Chironomidae com- lakes,Nikolskii(1938)believedthat in stagnant wa-
martin jones
(Martin Jones)
#1