CONTENT
Environmental Concerns and the State of Aquatic Environment
Ecological and fi sheries aspects of the formation of the modern hydrological regime of the water bodies of the Azov–Don Region. Part 2: Fisheries requirements to the geobotanical conditions of the Lower Don fl oodplain; salinity regime of Taganrog Bay; effi ciency of the Ust-Manych fi sh passage channels
Zhukova S.V., Podmareva T.I., Taradina E.A., Lutynskaya L.A., Burlachko D.S., Karmanov V.G., Bugaev L.A., Belousov V.N.
Abstract
Background. The second part of the article examines the features of the floodplain landscapes of the Lower Don, evaluates the salinity regime and the formation of desalinated zones in Taganrog Bay in 2006–2023, and considers issues related to the operating efficiency of the Ust-Manych fish passage channels during the spring spawnings of 2017–2024. Relevance. The current understanding of the geobotanical features of the Don River floodplain and the transformation of its landscapes is incomplete, which contributes to the relevance of assessment of the quality of spawning grounds and their compliance with the fisheries requirements. Compilation of historic and current data provided the basis for geobotanical characterization of the floodplain area of the Azov–Don Fishery Region and made it possible to present new data on the habitat conditions of aquatic biological resources in Taganrog Bay, as well as on the efficiency of the Ust-Manych fish passage channels. The aim of this article was to investigate the compliance of the geobotanical conditions in the floodplain areas of the Azov– Don Region with the fisheries requirements, to determine the extent of the formation of desalinated zones in Taganrog Bay, and to evaluate the efficiency of the Ust-Manych fish passage channels in the spring season. Methods. The data collected over the course of the annual expeditionary (Taganrog Bay) and field (Ust-Manych channels) studies, the materials from AzNIIRKH archives, and the information from literary sources on the research topic have been used. When collecting, processing and analyzing samples and relevant data, the methods recommended in [1] have been used, including mathematical and statistical analysis, analytical graph plotting and mapping. Results. The fisheries requirements to the geobotanical conditions in floodplain spawning grounds have been formulated; based on the summarized modern and historical data, the features of the Don River floodplain landscapes have been studied, and an assessment of the compliance of the geobotanical conditions with the fisheries requirements has been given. The analysis of changes in water salinity and the formation of desalinated areas in Taganrog Bay for the period 2006–2023 has been carried out. The operating efficiency of the Ust-Manych fish passage channels has been estimated for the spring seasons of 1917–2024. Conclusion. The transformation of the Lower Don floodplain landscapes led to the non-compliance of its geobotanical characteristics with the fisheries requirements. The increase in salinity of the Taganrog Bay water observed in the period 2006–2023 (from 5.26 ‰ in 2006 to 11.78 ‰ in 2020) and the reduction in the area of desalinated zones in salinity gradations from 4 to 9 ‰ provide evidence of the deterioration of the habitat conditions both for juveniles and for mature individuals of the semi-anadromous commercial fish species of the Azov–Don Region, as well as serve as an indicator of reduction in the volume of the water bodies receiving the released juveniles obtained through the artificial reproduction. In 2017–2024, the Ust-Manych fish passage channels generally ensured the passage of semi-anadromous fish species to their spawning grounds, although during certain periods the flow velocities exceeded 1 m/s, reaching carrying speed.
Keywords: floodplain area, fisheries requirements, geobotanical characteristics, salinity, desalinated zones, fish passage channels, flow velocities
Characteristics of the habitat conditions of aquatic bioresources in the Mius River in 2024
Kulik Ya.S., Kosenko Yu.V., Korablinа I.V., Trushkov A.V., Baskakovа T.E., Dolzhanov P.B., Alekseevа N.V.
Abstract
Background. The study of the hydrochemical and toxicological status of the Mius River is of great ecological and fisheries importance. Relevance. The high anthropogenic pressure on the Mius River, as well as insufficient knowledge of this water body in the modern period dictate the need for a comprehensive analysis of the habitat of aquatic biological resources. The aim of this work is to investigate the habitat conditions of the aquatic biological resources of the Mius River in 2024. Methods. Hydrochemical and toxicological studies of the water and bottom sediments of the Mius River were conducted in the river section spanning from the city of Miusinsk to the river confluence with the Mius Estuary (Liman) in August and November of 2024. Hydrochemical analysis involved the determination of dissolved oxygen, pH, ammonium nitrogen, nitrite nitrogen, nitrate nitrogen, phosphates based on phosphorus, total mineralization, calcium ions, sulfate ions, and chloride ions. Toxicological analysis of water and bottom sediments has also been conducted and involved the determination of heavy metals (mercury, lead, cadmium, arsenic, iron, manganese), polychlorinated biphenyls (PCBs), and petroleum products. Results. The oxygen regime and concentrations of biogenic elements in the Mius River and the Mius Estuary (Liman) were favorable for hydrobionts. Based on the salt content, the water was characterized as slightly brackish in the Mius River and brackish in the Mius Estuary (Liman), with prevalence of sulfate ions (highly likely due to the influence of mine waters), an increase in chlorides in the lower reaches of the river, and calcium content sufficient for the development of fish. It is highly probable that the increased concentrations of iron and manganese in the water had a natural origin. It is also possible that the mercury was introduced into the water from a natural source. Increased concentrations (up to 3.4 MPCfishery) of petroleum products with high resinous substance content were recorded in the water of the lower reaches of the Mius River. In the bottom sediments of the middle and lower reaches of the Mius River, high concentrations of petroleum products exceeding the threshold level by up to 12 times could exert an adverse effect on the development of bottom communities. Conclusion. In general, the aquatic environment of the Mius River and Mius Estuary (Liman) in 2024 could be considered as relatively favorable for hydrobionts. The quality of aquatic biological resources (namely, crucian carp) met the regulatory requirements for food products.
Keywords: Mius River, hydrochemical regime, toxicological regime, water, bottom sediments, aquatic biological resources
Biology and Ecology of Aquatic Organisms
Macrozoobenthos of Kruglaya Bay (Crimea, Black Sea) in the second decade of the 21st century
Alyomov S.V.
Abstract
Background. The shallow Kruglaya (Round) Bay on the Herakleian Peninsula of Crimea is characterized by high biological diversity and low pollution of bottom sediments. Relevance. Its operation as a recreation area exerts a strong pressure on the ecosystem of the bay and necessitates the monitoring of its condition. The aim of this work is to assess the composition, structure and quantitative development of macrozoobenthos in Kruglaya Bay in 2012, 2015 and 2018. Methods. The analysis has been conducted based on the samples of macrozoobenthos collected with the Petersen dredge (0.038 m2) at four stations in the central part of the bay in 2015–2018, in triplicate at each point. Results. In total, 81 species and supraspecific taxa of macrozoobenthos were recorded in the bay during the period 2012–2018 (47 for 2012, 33 for 2015, and 52 for 2018). The average abundance of macrobenthos was 2512–3526 ind./m2, and the average biomass was 53.5–140.2 g/m2. Conclusion. The species most typical for this aquatic area comprise 60–80 % of the total list of species and generally provide up to 90 % of the total benthic abundance and 95–99 % of the total benthic biomass.
Keywords: macrozoobenthos, abundance, biomass, communities, trophic structure, Kruglaya Bay, Black Sea
Abstract
Background. Species richness (SR) is recognized as the main parameter in calculating the structural biodiversity indices of any community. The relevance of SR evaluation is determined by the need to assess taxonomic knowledge of biota in the course of various ecological studies. The aim of this study is to perform a comparative prognostic assessment of the expected species richness (Sexp) of macrozoobenthos in 8 silty sand biotopes along the Crimean coast. Methods. This study involves the use of the data collected over the course of benthic surveys conducted in 1957‒2009 (about 290 samples in total). The nonparametric extrapolation algorithms (estimators) from the groups Chao, jackknife and bootstrap have been applied for calculation of the parameters of region-specific model cumulative curves. Results. With application of various estimation algorithms, the pattern of randomized increment in the number of new species with the increase in the number of samples has been identified, as well as the realism of estimating the Sexp level relative to the number of observed species (Sobs) at different sampling efforts. The Chao-2 and JN-1 algorithms have been found to be the most feasible estimators for the expected species richness, as they provide the most realistic (20–38 %) exceedance of Sexp over Sobs at similar sampling effort. It is shown that the use of these estimators is effective when more than 20‒25 samples are taken. A practical graphic calculation method for determining the conditionally complete species richness (or total observed species richness, Sobs-total) is proposed, which allows for optimization of the ratio between the number of samples and the completeness of the list of identified species. On the example of zoobenthos communities from the areas with different environmental conditions, it was calculated that, on average, at least 3–4 random samples should be taken to reveal 33 % of Sobs-total, and at least 6–7 samples should be analyzed to detect 50 % of it. Detection of 75 % and 90 % of the total number of species in a benthic community is possible with sampling more than 16–18 samples and 25 samples, respectively. Conclusion. The use of the proposed calculation method and the empirical relationships (number of species vs. number of samples) obtained on its basis is recommended for the enhancement of the completeness of benthos species richness assessment in insufficiently studied coastal aquatic areas of the Black Sea.
Keywords: zoobenthos, expected species richness, species accumulation curves, prognostic estimation, estimators, sampling effort, Black Sea
Variability of characteristics and oceanographic conditions of anchovy spring migration to the Azov Sea
Panov B.N., Shlyakhov V.A., Belousov V.N., Spiridonova E.O.
Abstract
Background. In autumn, after feeding in the Azov Sea, anchovy (Azov anchovy Engraulis encrasicolus maeoticus Pusanov & Zeeb, 1926) migrates to the Black Sea for wintering. In late March – early April, the majority of the Azov anchovy usually returns to the Azov Sea, while its lesser part remains in the coastal shallows of the Black Sea. To a large extent, the stock of anchovy in the Azov Sea depends on the oceanographic conditions of migration. Relevance. The study of the oceanographic conditions at the migration paths of the Azov anchovy is currently essential, because these conditions can influence its abundance and biomass in the Azov Sea. There has also been observed a low yield period in the reproduction of the Azov anchovy after 2016, which reasons remain unclear. The aim of this work is to evaluate the influence of currents and seawater temperature on the spring migration of anchovy in the Kerch Strait. Methods. This study is based on the data collected in 2005–2021 over the course of observations conducted by AzNIIRKH and YugNIRO at monitoring stations, as well as on the results of monitoring of fishery operations carried out by coastal fishing crews. As a source of oceanographic data, the website of the Copernicus Marine Service information system has been used. Results. The spring migration of anchovy through the Kerch Strait was observed within the time range from 23 March to 4 June with water temperatures ranging from 10 to 20 °C when currents in the north-eastern part of the Black Sea changed from north-western to south-eastern. Conclusion. The most favourable years for anchovy migration to the Azov Sea are those when the sea surface temperature by its beginning had already exceeded 11 °C and the prevailing winter north-western currents had not yet changed to south-eastern ones.
Keywords: Kerch Strait, Azov anchovy, spring migration, mass migration, water temperature, currents
Monitoring of commercial crustacean populations in the Northern Azov Region in 2024
Saenko E.M., Kotov S.V.
Abstract
Background. In the Azov Sea, an increase in the abundance and catches of shrimp of the genus Palaemon has been observed. The key area for their harvesting is the Northern Azov Region (Northern Cis-Azov littoral zone). Relevance. Due to the absence of information on the status of crustacean populations in the Northern Azov Region, it is relevant to conduct their investigation in the coastal part of this Azov Sea area. The aim of this work is to assess the status of commercial crustaceans in the coastal zone of the Northern Azov Region (Northern Cis-Azov littoral zone). Methods. Pontogammarus samples were collected in the coastal zone using a benthic frame and a sampling trap; shrimp samples were collected by a hand net. The samples were fixed with a 4 % aqueous formaldehyde solution. The laboratory processing included determination of the species, sex, size characteristics, the number of individuals in the sample, and the individual weight of the crustaceans. Results. Three shrimp species have been recorded in the catches: Palaemon adspersus Rathke, 1836, P. macrodactylus Rathbun, 1902 and Crangon crangon (Linnaeus, 1758). P. adspersus was the most abundant species, occurring in seagrass thicket biotopes, as well as on sandy, sandy silt and sandy gravel sites. Shrimp species C. crangon and P. macrodactylus were recorded in sandy silt and sandy gravel biotopes. Within the salinity range of 16.07–21.29 ‰, a positive relationship (r=0.80–0.98; p˂0.05) between the weight gain and the length gain has been established for P. adspersus; it can be described by a linear function (R2=0.65–0.97). The highest growth rate of shrimp was recorded in the northern part of Sivash Bay, the lowest one was observed in Obitochny Bay. At a salinity of 16.07–17.61 ‰, the individual weight gain relative to the length gain in males and females was essentially the same, and at a salinity of 21.29 ‰, it was higher in males than in females (p<0.05). P. macrodactylus was recorded in commercial catches by set (fixed) seines in Obitochny Bay in areas with a salinity of 14.64–16.07 ‰. C. crangon occurred in Obitochny Bay and the Utlyuk Liman in the catches obtained by set seines at a salinity of 16.07–17.61 ‰. A positive relationship (r=0.92–0.98; p˂0.05) between the weight gain and the length gain described by a linear function (R2=0.91–0.97) has been established. At a salinity of 16.07 ‰, the highest individual weight gain relative to the length gain in the population was observed in males.Pontogammarus maeoticus occurred within the salinity range of 6.76–14.67 ‰. The dependence of the Рontogammarus abundance and biomass on the salinity level in 2024 is described by an exponential function (R2=0.98–0.99). This dependence represents a strong negative significant relationship (r=–0.90). Conclusion. The formation of numerous shrimp aggregations of the genera Palaemon and Crangon is recorded in the coastal waters of the Northern Azov Region, providing considerable resources for coastal fisheries. The obtained data indicate that the salinity regime in the range of 16.07–21.29 ‰ both provides favorable environment for P. adspersus in the Azov Sea and does not present the upper boundary of the comfort zone in terms of the salt content. Within the salinity range of 16.07–21.29 ‰, the abundance and biomass of exploitable aggregations of the genera Palaemon and Crangon should be expected to persist with a tendency for their exploitable biomass to increase. The increase in the salinity of the Azov Sea water reduces the distribution area of P. maeoticus with high abundance and biomass and confirms the previously established similar relationship for the Eastern Azov Sea (R2=0.98–0.99).
Keywords: Azov Sea, Northern Azov Region, commercial invertebrates, salinity, distribution, abundance, biomass
Ichthyofauna of Marine and Inland Water Bodies
Status of the sterlet Acipenser ruthenus Linnaeus, 1758 population and reproduction in the Lower Don River Basin
Luzhniak V.A.
Abstract
Background. Before the construction of dams and hydrotechnical structures, sterlet was a commercially valuable species, widespread in the Don River Basin. Due to the river regulation and changes in the hydrological conditions influencing the natural spawning process, the sterlet population abundance in the Don River had decreased so much that this species was included in the Red Book of the Russian Federation, as well as regional Red Books. Relevance. The status of the sterlet population in the Don River remains insufficiently studied, despite the measures taken for its artificial reproduction and the constant increase in the number of released juveniles. The aim of this study is to analyze the status of the sterlet population in the Don River and to assess the effectiveness of the measures for its artificial reproduction in the modern period. Methods. The analysis of the current state of the sterlet population was based on the statistical data on the number of its juveniles released by hatcheries into the Don River, information on the number of the mature sterlet individuals transferred through the fish-lifting lock (FLL) of the Kochetovsky Hydrotechnical System, as well as the data collected during field research. Results. The effectiveness of the measures aimed at facilitation of the sterlet artificial reproduction in the Lower Don Basin has been assessed, and the necessity of expanding the research into the current state of the sterlet population to alter its conservation status has been indicated. Conclusion. The observed trend for the increase in the sterlet abundance in the Lower Don following the sizable releases of its juveniles by hatcheries in the last decade provides the basis for removal of this species from the Red Book of the Russian Federation and the Red Book of the Rostov Region.
Keywords: sterlet, population, Don River, spawning, artificial reproduction, juveniles, Kochetovsky Hydrotechnical System
Informational Messages
The fi rst fi nding of the Black Sea golden grey mullet Chelon auratus (Mugilidae) in the lower reaches of the Don River
Luganskaya А.V., Luzhniak V.А., Klimenko Ya.V.
Abstract
Background. Due to the ongoing salinization of the Azov Sea and Taganrog Bay waters, an expansion of the habitat of many marine fish species has been observed. Relevance. Some sea-originated fish species, in the process of expanding their range, spread deep into continental water bodies where they have never been recorded, which enhances our understanding of the ecological characteristics of these species and the limiting factors of their habitat. The aim of this article is to describe the first case of finding the Black Sea golden grey mullet Chelon auratus in the Lower Don. Methods. Information about the first finding of golden grey mullet in the Lower Don was obtained over the course of monitoring of the spawning migrations of anadromous and semi-anadromous fish species at the fish-lifting lock (FLL) of the Kochetovsky Hydrotechnical System in autumn. Results. This species of the Black Sea mullets has not been previously recorded in the Don River. This is the first finding of golden grey mullet in the Don River at a distance of more than 178 km upstream from Taganrog Bay (Azov Sea). Conclusion. The observed trend of expansion of the range of some marine fish species in the Azov Sea Basin and their new findings in the water bodies where they have not been previously recorded result from the ongoing salinization of the Azov Sea waters.
Keywords: golden grey mullet Chelon auratus, range, Don River