Abstract

In the Caspian Sea the Astacidae are represented by Pontastacus leptodactylus eichwaldi (Bott, 1950) and Caspiastacus pachypus (Rathke, 1837). Crayfish habitats extend through different climatic zones. The objective of this work was to study the state of wild crayfish populations during the present period of sea level rise with particular emphasis on crayfish distribution (vertical and horizontal), analysis of habitats with high crayfish concentrations, stock dynamics and influencing factors, behaviour, and assessment of crayfish commercial stocks. Behavioural studies were made to elaborate new methods of catching based on the reaction of crayfish to light. Our research work was conducted on the eastern shelf of the Caspian Sea. Research methods included use of submerged light and underwater video survey. The results showed that the quantity and distribution of the crayfish in the Caspian Sea depend mainly on environmental conditions and to a great extent also on anthropogenic factors. During the period of the Caspian Sea transgression, a rise of the sea water level by 2.4 m and more have caused a considerable increase in crayfish habitats in the littoral shelf. The most numerous crayfish populations were identified on the eastern shelf of the Caspian Sea at depths from 5 m down to 20 m. High crayfish stock dynamics and changes in the species composition as well as in the trophic relations of the biocenoses were observed as a consequence of the sea level rise. The quantity of crayfish in some areas increased by 16 times. The study of crayfish behaviour revealed a positive reaction to sources of submerged light. Experimental field research showed that traps supplied with light concentrated crayfish in an area of 20-25 m² and made it possible to catch more than 53 kg (up to 1,500 specimens) per sampling night.

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