The Persian sturgeon may
also be divided into the Volga, Ural, Kura and Sefidrud populations. The
Kura and Sefidrud populations are the most abundant. Like Russian sturgeon,
the Persian sturgeon has two seasonal races: spring and winter. N.L.
Gerbilsky (1950) described five biological groups in the Kura population of
Persian sturgeon: early and late spring, spring form of summer and autumn
run. Two biological groups were described in the Volga River population of
Persian sturgeon -early and late spring, and one group (late spring) in the
Ural River population (Artyukhin, 1983).
Thus, only Russian sturgeon has at least some twenty populations and
biological 
groups while
Persian sturgeon has not less than 18. In other words, the intraspecific
composition of these species is too complicated which should be taken into
account when performing investigations including those under CITES
(Perevaryukha, 2001).
Anadromous migration of the greater part of Russian sturgeon (as well as
beluga and stellate sturgeon) into the northern rivers - Volga and Ural
indicates their northern origin. The spawning populations of sturgeons in
the southern rivers of the Caspian Sea basin - Terek (Dagestan), Kura
(Azerbaijan), Sefidrud (Iran), are not abundant and could appear later.
Because of removal of spawning sites due to river damming, the natural
reproduction of sturgeons occurs mostly in the Volga (about 60%) and Ural
(more than 30%) Rivers while southern Caspian sturgeons turned out to be on
the verge of extinction. They may have been caught for culture purposes and
are maintained at hatcheries now which facilitates their conservation.
Being aware of the fact that the Caspian sturgeon population is the most
abundant in the sea (52.3 million specimens of beluga, Russian and
stellate sturgeon in 1999) and the most diverse in species (six species),
it was decided to prohibit the introduction of any other sturgeon species
into the sea and rivers of the basin and rearing of sturgeon hybrids
including those of indigenous fish species for their release into the basin
in order to preserve the unique gene pool. This provision is observed at
present by all the Caspian Sea States. Introduction of any living aquatic
organism into the sea and rivers of the basin should be based on biological
consideration, sound expertise, agreement with all the Caspian States. But
unintentional invasion of some animals can not be excluded and individual
species, mostly invertebrates, invade the Caspian Sea through the Volga-Don
Canal. Just in this way, the Caspian Sea was invaded by comb jelly fish Mnemiopsis
leidey that is responsible for a drastic decline in the biomass of
plankton and planktivorous fish (kilka).
At the same time, it may be asserted with certainty that despite the
fact that the Caspian Sea is not an absolutely isolated water body now,
intentional or unintentional introduction of Siberian sturgeon into it is
excluded. This species can not get into the Caspian Sea unintentionally
because of a long distance, isolation and low abundance of the species,
lack of possibility to transport it unnoticed and survival of fish during
transportation. Intentional introduction of Siberian sturgeon into the
rivers was not carried out. The captive breeding of Siberian sturgeon is
conducted in small quantities in ponds isolated from natural water bodies,
it is under strict control of Glavrybvod and the State Fisheries Committee
of Russia that prevents their release or adventitious invasion of the
rivers.
