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Dépôts récents
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On spring and summer spawning of Baltic sprat in the years with different hydrological regimesThe size-age structure of the spawning stock, the spawning efficiency, the regularities of egg and larval distribution and the conditions of reproduction affecting sprat (Sprattus sprattus balticus) year-class abundance are considered during three years (1974, 1975 and 1977). Two groups of sprat larvae and fry were determined: The spring (of larger size) and summer (small) larvae. The difference of larval sizes in modal groups was 30 mm. The spring generation, the area of which coincides with the area of cod in winter-spring period, is subjected to a greater influence of predators than the summer one.
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Formation regularities of Baltic sprat year class abundance at the early ontogenetic stagesEarly estimation of sprat (Sprattus sprattus balticus) year-class is given based on the quantitative calculations using the eggs and larval abundances. The main reproductive centres for eggs (Bornholm Deep, Baltic Sea) and larvae (Gotland Deep, Baltic Sea) are determined. Their importance depends on the hydrological regime and spawining stock abundance. Sprat eggs and larval dynamics are considered according to the areas and the periods of years (1968-1970, 1971-1974, 1975-1977, 1978-1980), during which the winter severity, hydrological conditions, spawning stocks and spawning efficiency were different. The factors, causing low abundance of sprat year-classes during warm-water period (1971-1977) are analyzed.
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Prognosing of periods and spawning migration intensity in spring-spawning Baltic herring of the Gulf of Riga according to the temperature factor of environmentThe relations of prognostic importance between the temperature regime in the Gulf of Riga (Baltic Sea) in February, April, May, the winter severity and the beginning of spawning migration, mass spawning as well as the intensity of Baltic herring (Clupea harengus membras) migrations to the spawning grounds at the Latvian coast of the gulf are considered. The corresponding correlation coefficients and regression equations important in planning of Baltic herring pound net fishery are given.
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Furcellaria storm casts to the coast of the Baltic Sea and their main characteristicsFurcellaria casts to the coast of the Baltic Sea are described and their main quantitative and temporal characteristics are determined. The estimation of the cast phenomenon and its industrial processing is given. The conclusion on the possibility of short-term prognosing of storm casts was made. The recommendations for the increase of storm casts processing efficiency are given.
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The characteristics of body mass changes in the main zooplankton species in the Gulf of Riga (Eurytemora hirundoides and Acartia bifilosa)Data on the seasonal variability of body mass in all age stages of of development of Acartia bifilosa and Eurytemora hirundoides in the Gulf of Riga (Baltic Sea) and its dependence on the environmental factors are given. The biomass of these species, calculated according to the body weight, obtained earlier for the Gulf of Riga, are considerably different. This shows that it is necessary to determine the body masses of separate species for every reservoir taking into account the seasonal variability.
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Seasonal changeability of mysid number and distribution in the Eastern BalticThe data on seasonal variations of mysid number and distribution are given. The maximum mysid abundance and biomass was found in autumn: The Mysis mixta stocks were found at the depth of 30-60 m and the Neomysis vulgaris - at the depth of 20-30 m. The productive zones during the year were differentiated: The Klaipeda area (Baltic Sea) - above the depth 50-70 m, the area near Irben Strait and the Ventspils area - above the depths 20-40 m and 50-60 m correspondingly.
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Baltic herring feeding during the period 1976-1980The dynamics of herring (Clupea harengus membras L.) feeding in the Baltic Sea during the period 1976-1980 is considered. The data on seasonal and annual changes of food spectra and fish feeding intensity are given. The influence of thermal regime, food supply and herring physiological condition on fish stomach fullness in different years of the investigated period is shown.
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The dynamics of nuclein acids content in Baltic cod tissues as the index of growth processes intensityFish growth is one of the main indices which characterize the reaction of the species on environmental conditions, this determines the importance of this index when studying the dynamics of fish abundance. The aim of the given investigation was studying the dynamics of nuclein acids content in different tissues of Baltic cod for the estimation of the changes of protein growth intensity during the annual cycle in different years according to inhabitance conditions. It is shown that quantitative determinations of nuclein acids in cod tissues sensibly reflect changes in the intensity of growth processes. This permits to recommend to use this index when studying fish growth in different according to inhabitance conditions periods.
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On the influence of currents on zooplankton distribution in the Baltic SeaOn the basis of the analysis of long-term abundance dynamics in Oithona similis, and the dynamics of water masses in various areas of the Baltic Sea the influence of the deep-water currents on the transfer of plankton from the southern sea areas to the eastern ones is shown.
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The peculiarities of eelpout stock distribution and composition in the Gulf of RigaThe size and age composition of eelpout (Zoarces viviparus) in the Gulf of Riga (Baltic Sea) for the 1974-1978 period is given. The peculiarities of its distribution by regions and depth zones under the influence of hydrological factors in different years are examined. The distribution of eelpout in spring depends on changes in salinity and temperature in the near-bottom layer of the Gulf of Riga.
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Spatial distribution of flounder eggs and larvae in the Baltic SeaThe regularities governing the spatial distribution of flounder Platichthys flesus eggs and larvae in its main spawning area (from Bornholm to Saaremaa-Hiiumaa area, Baltic Sea) based on the results of observations in 1969-1978 are considered. The distribution of flounder eggs and larvae depends on the hydrological regime. The distribution of eggs and larvae at different depths is analyzed. The size composition of flounder larvae from March to June is compared.
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Fishing and biological characteristics of the Baltic herring in Ventspils zone of the Baltic SeaData on the size-age composition of the Baltic herring (Clupea harengus membras) stock in the Ventspils area (Baltic Sea), the annual cycle of the maturity stages of their gonads, the stomach fullness, and the fat accumulation in the gut are given. It is shown that the most active fishing is carried out in May-June. The changes in the composition of the Baltic herring population in the annual cycle depend on the spawning migration of the sea herring to the Gulf of Riga and the feeding migrations of herring. Baltic herring feeds all the year round, the maximum feeding intensity occurs in June-August. The fat accumulation in herring guts begins in May, reaches its maximum in July and the amount of fat gradually decreases beginning from September.
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Some observations on development cycle of Temora longicornis and Centropages hamatus in the Baltic SeaThe data on development and generations’ number of plankton crustaceans Temora longicornis and Centropages hamatus in the Baltic Sea depending on thermal regime of the upper sea level are given. The determination of the duration of development cycle and generations’ number was made according to age composition of the population and female sizes in some seasons.
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Investigation of ecological characteristics of main zooplankton species in the central BalticSpatial distribution of 15 main zooplankton species in the Baltic was investigated. The material was collected in 1973-1976 in different sea areas. It is shown that mass zooplankton species are sharply different according to temperature and salinity. Vertical and regional distribution of some zooplankton species testifies to that. Spatial disconnection of mass species promotes the reduction of the role of food competition in plankton community.
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Quantitative distribution and migrations of mysids in the Gulf of RigaThe data on qualitative and quantitative distribution of mysids in the Gulf of Riga in spring and summer periods are given. Some environmental factors (temperature and water salinity) influencing qualitative and quantitative distribution of Neomysis vulgaris, Mysis mixta, Mysis relicta, Praunus flexuosus and Praunus inermis are revealed.
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On the reproduction of two species of relict arctic mysids in the Gulf of RigaOn the base of the analysis of dynamics of sexual structure and size composition of populations as well as the analysis of maturity stages of female sexual products the peculiarities of reproduction of two mass species of relict arctic mysids Mysis mixta and Mysis relicta are revealed.
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On the relation of the dynamics in zooplankton abundance in the Baltic with phosphorus and Kattegat waters advectionThe relationship between the dynamics of the abundance of the crustacean plankton and the phosphorus concentration in the active (0-60 m) layer, and the advection of the Kattegat waters in the Baltic in the 1960-1977 are considered. It is shown that in spring (May) the abundance of the crustacean plankton is relatively poorly connected with the dynamics in phosphorus amount. It has distinctly been observed only in the years following warm winters (r=0.94, alpha =0,01) when phytoplankton vegetation begins early and the decrease in microalgae spring bloom is considerable. In summer and autumn clear and direct connections are observed between the abundance of crustacean plankton and phosphate concentration (r sub(1)=0,79, alpha sub(1)=0,01; r sub(2)=0,90, alpha sub(2)=0,01). The advection of Kattegat waters influences greatly the dynamics of biogenies promoting the outflow of nutritional salts from the deep-water layer. The effect of advection on the formation of productive zones (by zooplankton) is revealed the most distinctly in the Southern and North-Eastern Baltic in summer.
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On maturation and spawning of Baltic spratOn the basis of long-term data the age of maturation of sprat (Sprattus sprattus balticus) males and females, the reproduction cycle in relation to spring and summer thermal conditions, as well as the spawning terms depending on the environmental factors, the physiological state of fish and the composition of parent stock are considered.
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Population fecundity of Baltic salmon at artificial and natural reproductionThe size-weight, age and sexual structure of salmon (Salmo salar L.) at artificial and natural reproduction and their individual and population fecundity was studied in the Daugava River (Latvia). It was revealed that the stocked and wild salmon have almost the same indices of individual fecundity and growth in the sea. However the stocked females are characterized by earlier maturation in the sea, their share in the spawning stock is relatively less than that of the wild salmon. It was calculated that the population fecundity of the stocked salmon is by 14 % lower than that of the wild salmon. Further investigations for the optimization of salmon population structure at artificial reproduction are necessary.
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Long-term changes of sprat eggs and larvae abundance in the Baltic SeaOn the base of long-term (1968-1977) material on ichthyoplankton the dynamics of sprat eggs and larvae abundance on its main spawning grounds depending on the changes of hydrological conditions is considered. Spawning periods according to areas and main spawning areas are revealed. Sprat eggs and larvae abundance in sea depths in spring and summer periods is shown.
