Some Behaviour Patterns and Distribution of Caspian Ordinary Sprat Species - Clupeonella Delicatula Caspia Svetovidov

Abstract

The global environmental changes that occurred in the Caspian Sea in the last decade, as well as the population outbreak of Mnemiopsis leidyi invasive from the Black Sea resulted in extinction of the most important food item of endemic sprat species, which caused biological wellbeing of ordinary sprat. The data of multi-year observations obtained in the course of studying the abundance and biology of the species have been generalized in order to improve methods and fishing gear and to organize ordinary sprat fishery. The article presents study results of ordinary sprat’s behavior. The analysis has revealed that ordinary sprat is less photophilous in strong light zones, compared to anchovy sprat, and forms exploitable concentrations under the light exposure from 45 min and longer. In the light field ordinary sprat species keep away from the light source and create a second ring at a distance 0.8-2.5 m from the light bulb. The fish aggregation in the light field of the DNaT 400 lamp occurs at smaller exposures than of the SC-102 lamp. The experiment with concurrent use of two different light sources demonstrates some preference of monochromatic light collecting in its light field up to 75% fishes of the total number. The contrast of light and shade created by a light source with a partially darkened bulb changes the fish behavior and increases the density of their aggregation in the light sector near the bulb of the lamp. According to the study results, the article presents considerations concerning new fishing gear in fishing industry that allow to regulate fish species composition in the catch in the Caspian Sea with an increase in the proportion of ordinary sprat.