The dynamics of commercial catches, stocks and forecast values of walleye catch on the Dagestan coast of the Caspian Sea with the analysis of factors affecting the state of stocks for a long-term period is presented. Data on seasonal distribution, migration, reproduction, as well as age and size-weight composition of walleye populations in the study area are presented. The forecast of prospects for the use of walleye by fishing is given on the basis of the analysis of commercial stocks for a number of years of observations, taking into account the coefficient of total mortality, the influence of fishing load, the values of the commercial population replenishment with first-matured fish.
Despite the role of planktonic organisms in the fishery value of the Caspian Sea and in addition to the increase in the plankton population in the Caspian Sea, there are few detailed studies regarding the determination of the planktonic organisms in the Caspian Sea. In the present investigation, we aimed to study the cell abundance and diversity of the phyto- and zooplankton in the eastern part of the Middle Caspian Sea in the spring of 2016. The composition of phytoplankton consisted of 50 species belonging to 4 systematic groups which were registered in the eastern part of the Middle Caspian: Cyanophyta (7), Bacillariophyta (24), Dinoflagellata (13), and Chlorophyta (6). Zooplankton were represented by 9 taxa: Cladocera—6, Copepod—1, and other groups—2. The most important phytoplankton species were Rhizosolenia calcar-avis, Anabaena bergii, Exuviaella cordata, and Binuclearia lauterbornii. The 0–50 m layer in the eastern Middle Caspian was the most productive, where the biomass varied from 98 mg/m3 to 109 mg/m3, consisting largely of diatoms. The cladoceran Evadne anonyx typica, the copepod Acartia tonsa, and the larvae of barnacle crustaceans (Cirripedia) were widely distributed in this layer. Zooplankton abundance decreased markedly with the depth. The maximum zooplankton concentrations were confined to depths down to 200 m.
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