Assessment of the impact of the great cormorant (Phalaсrocorax carbo sinensis Shaw et Nodder, 1801) on fish resources of the Obytichna Spit the Sea of Azov

Purpose. Assessment of the impact of the great cormorant (Phalacrocorax carbo) on fish resources of the Sea of Azov and determination of dietary needs and feeding habits of this species during its nesting period on the Obytichna Spit (Zaporizhzhia region). Methodology. The study is based on field materials collected between 2015 and 2017 on the Obytichna Spit (Berdyansk district, Zaporizhzhia region). Data collection and processing were carried out according to generally accepted methods. The analysis of food samples was conducted by collecting regurgitations within the nesting colony and by analyzing the stomach contents of cormorants (n = 50) obtained from individuals eliminated by employees of the State Enterprise “Prymors’k Forestry” during planned population control measures. Based on these analyses, the daily fish consumption of the cormorant colony was estimated over the annual period, and the ratio of fish removed by cormorants to the official fish catch by fishermen was also analyzed. Statistical data processing was carried out using MS Excel. Findings. The study showed that the diet of the great cormorant in the Obytichna Spit area consisted of eight fish species, with the round goby (Neogobius melanostomus Pallas, 1814) and the monkey goby (Neogobius fluviatilis Pallas, 1814) being dominant. The total fish consumption by the cormorant colony on the Obytichna Spit amounts to 9563.75 tons per season. The impact of cormorants on fish resources in the northwestern Azov region is significant, accounting for 26.39% of the annual fish catch in 2016, and almost half (43.37%) of the annual fishermen’s catch for gobies, which form the basis of the cormorants’ diet in this colony. Originality. For the first time, detailed quantitative estimates of the daily fish consumption by a large colony of cormorants in the context of the species’ nesting at the Obytichna Spit were provided, particularly considering changes in the size structure of the prey in different years. Practical value. The obtained data can be used for managing fish resources and developing measures to minimize conflicts between fisheries and the great cormorant population in the Azov-Black Sea region of Ukraine. Additionally, the results of the study are successfully applied in the work of higher education institutions in Ukraine during the teaching of natural sciences for specialties 014.05 Secondary Education (Biology and Human Health), 091 Biology and Biochemistry and 101 Ecology.