The state of crayfish (Astacidae) populations in a certain area of the Caspian Sea Eastern coast in 2022

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Abstract

The aim is to study crayfish (Astacidae) distribution, fertility and stocks in coastal waters on the Caspian Sea Eastern shelf in the area between cape Rakushechny and cape Tokmak. The research was carried out in summer 2022. The material was collected by shallow-water divers using the method of crayfish route census and selection at the transects with an area of 100-200 m2. Collected samples were speciated, measured, weighed and evaluated from fertility viewpoint. Population was estimated on the basis of crayfish clusters density en routes (ind./m2) with further reestimation within biotopes that were identified using the data of the Caspian Sea satellite monitoring and were specified with the help of a drone. The stocks were estimated on the basis of the collected animals’ length and weight characteristics. Two Astacidae species inhabit the area: Pontastacus eichwald Воtt – long-clawed crayfish, and Caspiastacus pachypus Rathke – thick-clawed crayfish. Comparative analysis of the current results and the data from the 1970s to 1990s has identified that the situation had changed. C. Рachypus habitat has expanded. Both Astacidae species working fertility has decreased. Crayfish stocks in the researched sector have commercial value. Using data from satellite survey and drone observation increase the research objectivity significantly.