Caspian Sea: State of the Environment 2019

Table 5.5: Zooplankton numbers (specimens/m 3 ) and biomass (mg/m 3 ) in the Azerbaijan sector of the Middle Caspian Sea

Indicator

2011

2012

2013

2014

2015

2016

12,116.4

11,903.3

Overall mean number

10,323.2

10,620.8

12,747.5

11,620.5

352.4

347.8

Overall mean biomass

275.4

301.8

312.9

308.6

Source: Azerbaijan Scientific-Research Fisheries Institute.

Table 5.6: Zooplankton numbers (specimens/m 3 ) and biomass (mg/m 3 ) in the Azerbaijan sector of the Southern Caspian Sea

2016

Indicator

2011

2012

2013

2014

2015

Overall mean number

3,326.7

4,005.7

4,109.0

4,225.7

3,835.2

3,753.6

Overall mean biomass

88.1

104.3

102.8

110.5

96.9

106.3

Source: Azerbaijan Scientific-Research Fisheries Institute.

Russian sturgeon. The highest catches of Russian sturgeon (14,100–14,600 tons) were recorded in 1980–1981. From 2005 to 2016, depending on the need for breeding, catch- es of Russian sturgeon ranged from 195 tons (2005) to 4.62 tons (2016). Commercial stocks amounted to 5,350 tons in 2015, 2.5 times low- er than in 2010. They continued to maintain a downward trend in 2016, totalling no more than 3,880 tons. Persian sturgeon. The absolute population size in 2015 was 0.696 million specimens, represent- ing a decline by a factor of 4.7 compared with 2010. Commercial biom ass fell from 920 to 280 tons. The 2016 catch amounted to 0.03 tons. To- tal stocks of Persian sturgeon in 2016 amounted to 0.582–0.43 million specimens with a biomass of 1,610–1,040 tons. Stellate sturgeon. The largest catches of stellate sturgeon in the Caspian Sea basin (over 5,000 tons) were recorded in the first years after the ban on sea fishing was introduced, with a subsequent decrease in the late 1980s to 2,990 tons, and to 200 tons in the 1990s. In 2010–2014, catches for breeding and research purposes varied within a range of 0.14-1.65 tons. The absolute number was estimated at 0.94 million specimens in 2015, with

timing and volume of the spring high water in the Volga River: the greater the river run-off, the higher the juvenile survival rate and spawn- ing productivity. In 2015, the spring high water reached a critical minimum, and stock replen- ishment of semi-migratory species was therefore estimated as low. Unregulated fishing by amateur fishers also is also reducing commercial stocks of semi-migra- tory species. Amateur fishers catch 19 species of fish, mostly Caspian roach, bream, catfish, pike, pike perch, carp, rudd, crucian carp, white bream, perch, blue bream, sabre carp, roach, Vol- ga pikeperch, asp, ruffe, tench, white-eyed bream and herring. A steady decline in commercial stocks of valuable fish species in the northern part of the Caspian Sea was observed during the period 2010–2016. Commercial stocks of semi-migratory Caspian roach and tench fell, while stocks of other fresh- water fish species tended to increase. Sturgeon are transboundary species which feed in the waters of all Caspian littoral states. No Caspian-wide acoustic trawl surveys have been conducted over the last decade to estimate total sturgeon numbers and biomass.

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