the north-western Black Sea and all over the Romanian coast (Paraschiv et al.
2006).
Sizes The largest sturgeon in Romanian waters. Usual size 4–6 m and 100–250 kg.
Maximum 9 m (Maximov and Zaharia 2010).
Biology and Ecology Being a marine anadromous species, the beluga lives solitary
and only in winter it forms larger groups. Migration into the Danube starts in
January, when there is an early spring, and late March, when there is a late spring,
at a water temperature of 4–5
C. The highest intensity of spring migration is
reached in March or April; in June, migration ceases and resumes in autumn,
reaching the peak in October–November, after which it stops.
The existence of two migration periods made some authors assume the existence
of two sympatric breeds, the spring and autumn ones, while others believe that
specimens migrating in spring are older and their gonads started maturing in the
sea; females migrating in spring have stage IV gonads, while those migrating in
autumn usually have gonads in stage III (Zaharia 2013).
Gonad maturation in young specimens occurs in the river during winter.
Spawning takes place for all individuals in spring, from April until mid-June,
with a peak in May; the optimal temperature for spawning is around 15–17
C.
Belugas reach sexual maturity at 12–14 years (males) and 14–16 years
(females). The breeding grounds are located at 4–20 m water depth, on rocky or
rough bottoms, with crevices that shelter the eggs and hatchlings against predation
by gobies. After spawning in the river, belugas return to the sea, where they
disperse, living on rocky bottoms at 50–70 m depth (sometimes beyond 100 m).
Fingerlings slowly travel towards the sea, along the river bottom, halting in various
sites with proper conditions, where large sturgeon fingerlings agglomerations are
found. The retreat into the sea occurs in July–September.
Initially, juveniles remain in the brackish waters off the Danube mouths and only
later travel to deeper waters, spreading across the entire Romanian continental
shelf. During their time in the Danube, beluga fingerlings mainly feed on
gammarids, other crustaceans and insect larvae. In the sea, mysidaceans and
lalaemonids are dominant.
Specimens larger than 20 cm start feeding of fish. Adult belugas feed mainly on
fish (80%), in the Danube on Cyprinds and in the sea on gobies, red-mullet, turbot,
anchovies, crustaceans (Crangon), mollusks (Modiola) and algae. Feeding is very
weak in winter. Belugas are the most long-lived sturgeon species, usually living up
to 30–60 years, but they can reach 100 (Radu et al. 2012).
Fishery Belugas are fished using sturgeon hooked lines and other stationary fishing
gears and, incidentally, using the trawl. Currently, in Romania there is a ban on
commercial beluga fishery until 2020, confirmed by the annual Prohibition Orders
(currently Order no. 154/2016).
Commercial Importance The beluga is the most valuable sturgeon species, its meat
being extremely tasty (fresh, refrigerated, frozen, salted, smoked, canned). Its eggs
(caviar) are highly valuated, being marketed fresh or salted (Maximov et al. 2014).
26 Conservation Status of the Fish Fauna in the Danube Delta Marine Zone
449
2006).
Sizes The largest sturgeon in Romanian waters. Usual size 4–6 m and 100–250 kg.
Maximum 9 m (Maximov and Zaharia 2010).
Biology and Ecology Being a marine anadromous species, the beluga lives solitary
and only in winter it forms larger groups. Migration into the Danube starts in
January, when there is an early spring, and late March, when there is a late spring,
at a water temperature of 4–5
C. The highest intensity of spring migration is
reached in March or April; in June, migration ceases and resumes in autumn,
reaching the peak in October–November, after which it stops.
The existence of two migration periods made some authors assume the existence
of two sympatric breeds, the spring and autumn ones, while others believe that
specimens migrating in spring are older and their gonads started maturing in the
sea; females migrating in spring have stage IV gonads, while those migrating in
autumn usually have gonads in stage III (Zaharia 2013).
Gonad maturation in young specimens occurs in the river during winter.
Spawning takes place for all individuals in spring, from April until mid-June,
with a peak in May; the optimal temperature for spawning is around 15–17
C.
Belugas reach sexual maturity at 12–14 years (males) and 14–16 years
(females). The breeding grounds are located at 4–20 m water depth, on rocky or
rough bottoms, with crevices that shelter the eggs and hatchlings against predation
by gobies. After spawning in the river, belugas return to the sea, where they
disperse, living on rocky bottoms at 50–70 m depth (sometimes beyond 100 m).
Fingerlings slowly travel towards the sea, along the river bottom, halting in various
sites with proper conditions, where large sturgeon fingerlings agglomerations are
found. The retreat into the sea occurs in July–September.
Initially, juveniles remain in the brackish waters off the Danube mouths and only
later travel to deeper waters, spreading across the entire Romanian continental
shelf. During their time in the Danube, beluga fingerlings mainly feed on
gammarids, other crustaceans and insect larvae. In the sea, mysidaceans and
lalaemonids are dominant.
Specimens larger than 20 cm start feeding of fish. Adult belugas feed mainly on
fish (80%), in the Danube on Cyprinds and in the sea on gobies, red-mullet, turbot,
anchovies, crustaceans (Crangon), mollusks (Modiola) and algae. Feeding is very
weak in winter. Belugas are the most long-lived sturgeon species, usually living up
to 30–60 years, but they can reach 100 (Radu et al. 2012).
Fishery Belugas are fished using sturgeon hooked lines and other stationary fishing
gears and, incidentally, using the trawl. Currently, in Romania there is a ban on
commercial beluga fishery until 2020, confirmed by the annual Prohibition Orders
(currently Order no. 154/2016).
Commercial Importance The beluga is the most valuable sturgeon species, its meat
being extremely tasty (fresh, refrigerated, frozen, salted, smoked, canned). Its eggs
(caviar) are highly valuated, being marketed fresh or salted (Maximov et al. 2014).
26 Conservation Status of the Fish Fauna in the Danube Delta Marine Zone
449