Efficiency of Sonar Fish Protection Device at the Kokaral Dam of the Small Aral Sea

The study aimed to assess the efficiency of the pilot hydro-acoustic (sonar) fish protection device (SFPD) installed at the Kokaral Dam of the Small Aral Sea. For this purpose, between August 27 and September 5, 2020 experimental and control fish catching was carried out using fixed fishing nets (30×60 mm mesh). The SFPD’s effectiveness was assessed based on the amount and species diversity of the caught fish with and without the SFPD operating. Fish behavior and distribution were monitored using an echo sounder. In terms of quantity, 173 fish were caught with the SFPD off, and 94 with the SFPD on. In terms of biomass, the values were 37.5 kg and 27.6 kg, respectively. With the SFPD off, the ichthyofauna composition was represented by 12 fish species: carp, crucian carp, roach, ide, bream, common rudd, saber carp, snakehead, pike perch, perch, pike, and asp. With the SFPD on, roach and ide were absent in the catch, and the quantity of common rudd significantly decreased. In both catches, the quantity of carp and crucian carp was similar; bream and saber carp specimen were sporadic. The number of predatory fish (pike, perch, snakeheads, and pike perch) in the catches increased. Asp was absent in the net catches also; however, this fish species represents the main object of amateur hook and line fishing. Based on the catch-per-effort unit, it can be concluded that whereas the SFPD observed efficiency for small non-predatory fish like ide, roach, and common rudd was 95%, it was 0% for large non-predatory fish (carp and crucian carp); and negative for predatory fish.