Some peculiarities of herring (Alosa) distribution and behavior in the Caspian sea

The data on herring horizontal and vertical distribution related to food as well as its preferred habitats are presented. The peculiarities of behavior of herrings, inhabiting the western shelf of the Caspian Sea as well as the time and the routs of their migration from the North to the South are studied. It is shown that together with evolutionary adaptations the distribution of herrings is strictly affected by food. The distribution of herrings is related to horizontal and vertical distribution ofplankton. There are formed favorable conditions for the supply of herring due to a high density of organisms and a good food supply in pelagic habitats of aquatic organisms, including plankton, mainly sprats. Comparative analysis of distribution of brazhnikov's herrings points out the direct dependence of this phenomenon on the distribution and concentrations of sprats. The main places of wintering of herrings in the western coast of the South Caspian Sea are areas of the Kur Stone i.Sara, Lenkoran and Astara that consistently have the highest biomass of plankton and sprats, as well as hydrological conditions. However, between the distribution of herrings and biomass of food objects there is not always observed a direct relationship. There are stations with high food (plankton, sprats) biomass, but small catch of herring, or vice versa. Besides, some abiotic factors, especially stream and temperature, influence the distribution of herrings. They do not occur in cool water in winter and in warm parts of the sea in summer. When surface waters become cool in winter, there is hemotery at the depth of 50 m. Temperature gradients within this depth are very insignificant and do not affect migration of herrings from one horizon to another. As the temperature jump is expressed at the depth below 50 m, the movement of herrings in winterfrom one zone to another is primarily influenced by the flow, caused by storms and light, which the majority offish meet in the course of their life. In winter herrings avoid cold water, and spend this period mainly in areas with a temperature not lower than 8 °C, in summer they avoid very hot spots, with water temperatures above 25 °C. Temperature jumps depending on the specific area of the Caspian Sea are registered at different depths (no more than 20-25°C), hence relatively large herring concentrations in summer in different layers of water. A strictly pronounced ecological detergency of Caspian herrings is recorded.

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