Main results of studies of pelagic resources in the Azov and Black Seas | Основные результаты исследований пелагических ресурсов Азово-Черноморского бассейна

The basic long-term information concerning pelagic fish abundance (biomass) as well as seasonal and interannual dynamics of abundance indices has been collected in fisheries surveys using standard fishing gear. YugNIRO has developed most appropriate fishing gear and determined the optimal time and seasons for surveys of each group of species. Principal results of research were implemented into the practice of fisheries and management starting from early years of YugNIRO activity (1920-1930s). In the pre-World War II period purse seine fisheries for Azov Sea population of European anchovy Engraulis encrasicolus was developed in the Kerch strait only; after the war owing to YugNIRO data on areas and environmental conditions of wintering of this population of anchovy in the Black Sea the fishing fleet expanded greatly the zone of operation. Research of the Black Sea population of anchovy revealed the biggest anchovy stocks in the area. It gave a jump for the development of purse seine fleet capable to carry fishing operations at the great distance from the home ports. The important contribution of scientists to the rational exploitation of fish resources in the area was the development of the scientific advice for trawl fishing of Black Sea sprat Sprattus sprattus. By early 1970s the first signs of degradation of pelagic biocenosis structure were recorded despite general trend of increasing of total catch of pelagic fish. First of all were recorded sharp decrease in the catches of large pelagic predators: bonito Sarda sarda, mackerel Scomber scombrus, large jack mackerel Trachurus mediterraneus, bluefish Pomatomus saltatrix. YugNIRO research of the population structure of the Black and Azov Sea anchovy populations made possible to outline this species migration pattern as well as elaborate morphological, genetic and parasitological criteria for the stock identification by aggregations at fishing grounds. Anchovy fisheries developed within the winter borders were regulated for optimal distribution of fishing efforts among two stocks. In the same time were introduced acoustic surveys for estimates of anchovy biomass in wintering aggregations in the Black Sea which increased greatly precision of stock assessments. The average level of the biomass of Black Sea anchovy stock in 1970-1980s was about 750000 tons, and its biomass in the waters adjacent to Georgia was 309000 tons in average. Observed twice in 1985 and in 1989-90 sharp declines in the catch of Black Sea anchovy are the consequences of the overfishing by common efforts of the USSR and Turkey that in previous years yielded about 500000 tons (up to 60% of the stock). The recent decrease of anchovy catches was related with outburst of the ctenophore Mnemiopsis leidyi. This introduced species are food competitor for pelagic species and even predator for eggs and larvae of pelagic fishes. Among the pelagic fishes of Azov Sea the tyulka Clupeonella cultriventris suffered most greatly, as obligatory zooplankton-feeder. In the Black Seas sprat S. sprattus are the only reliable reserve for the fisheries among pelagic species. In some years sprat biomass in the aggregations estimated in acoustic surveys reached 600,000 tons. The total stock biomass is considerably higher. For recent years the level of the sprat exploitation decreased due to fishing fleet shrinking. Published information about the serious negative impact of ctenophore Mnemiopsis on the sprat population is an erroneous interpretation of the data on decreasing catch. Sprat is winter-spawner and reproduces at temperature that is not suitable for the ctenophore. The maximum food consumption is observed for the sprat in spring when the ctenophore biomass is low, in summer sprat moves to the near-bottom strata of the sea where ctenophore does not penetrate mainly.

Имеющиеся в литературе сведения о серьезном негативном воздействии гребневика-мнемиопсиса на состояние популяции шпрота являются следствием ошибочной трактовки данных об уменьшении объемов добычи. Результаты тралово-акустических съемок и анализ многолетней динамики улова на промусилие свидетельствуют об отсутствии значительного воздействия мнемиопсиса на ресурсы шпрота в Черном море, поскольку этот объект отличается от большинства населяющих пелагиаль теплолюбивых рыб. Являясь зимненерестующим видом, шпрот размножается при тех температурных условиях, которые малоприемлемы для развития гребневика мнемипсиса. Максимальное потребление пищи у шпрота имеет место в весенний период, когда биомасса гребневика также еще не велика, а летом шпрот переходит к обитанию в придонные горизонты моря, куда гребневик в основном не проникает. Таким образом, целесообразность интенсификации промысла шпрота для украинского рыболовства не может вызывать сомнений. Приведенные сведения о ресурсах пелагиали Азово-Чериоморского бассейна говорят о кризисном состоянии основных компонентов сырьевой базы промыслов в регионе. Первоочередного вмешательства требует ситуация, возникшая после случайной интродукции гребневика мнемиопсиса. Скорейшее решение проблемы оценки ресурсов и регулирования рыболовства по всей акватории бассейна объединенными усилиями всех заинтересованных стран также является насущной необходимостью. Немалую роль при реализации этих задач может сыграть накопленный в ЮгНИРО арсенал методов мониторинговых исследований.

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