Knowledge of the spatio-temporal distribution of salinity provides valuable information for understanding different processes between biota and environment, especially in hypersaline lakes. Remote sensing techniques have been used for monitoring different components of the environment. Currently, one of the biggest challenges is the spatio-temporal monitoring of the salinity level in water bodies. Due to some limitations, such as the inability to be located there permanently, it is difficult to obtain these data directly. In this study, machine learning techniques were used to evaluate the salinity level in hypersaline East Sivash Bay. In total, 93 in situ data samples and 6 Sentinel-2 datasets were used, according to field measurements. Using linear regression, random forest and AdaBoost models, eight water salinity evaluation models were built (six with simple, one with random forest and one with AdaBoost). The accuracy of the best-fitted simple linear regression model was 0.8797; for random forest, it was equal, at 0.808, and for AdaBoost, it was −0.72. Furthermore, it was found that with an increase in salinity, the absorbing light shifts from the ultraviolet part of the spectrum to the infrared and short-wave infrared parts, which makes it possible to produce continuous monitoring of hypersaline water bodies using remote sensing data.

A comprehensive analysis of the physiological state of the so-iuy mullet, inhabiting the Sea of Azov, has been carried out during its pre-spawning period in 2020–2021. The hematological characteristics of the investigated individuals have been evaluated. It has been revealed that the content of protein and lipids in fish tissues was at the level of average longterm values. The content of protein and lipids in the gonads of females was significantly higher than that of males, which is explained by the forthcoming stage of spawning. It has been determined that the contribution of albumin to the total blood serum protein was minimal, which could be a consequence of the low feeding rate of the fish. At the same time, no stress effect was identified-glucose was within its normal range.

The reproductive system of the female so-iuy mullet Liza haematocheilus (Temminck & Schlegel, 1845) from the Azov-Black Sea basin has been analyzed regarding the season of observation, fish sex and stages of gonad maturity. The median and percentile values which can be used like control values for formation of qualitative characteristic of variational range of certain individual diameters of oocyte based on the empirical median calculated for this individual were calculated basing on the assessment of variational ranges of the large samples of oocyte of trophoblastic growth. It was demonstrated that in Azov-Black Sea basin’s conditions the so-iuy mullet spawning occurs as a single-portioned type except the years with protracted and cold winter. In such conditions is possible a two-portioned spawning.

The trends in climatic changes in hydrometeorological, biological, fisheries and anthropogenic characteristics of the Sea of Azov and the Black Sea ecosystems during 1980-2010 are considered. Despite the high annual variability in means of the characteristics, the significant amount of analyzed variables can be described with both linear and periodic trends. The main changes in variables considered fall on the periods of 1989-1990 and 2005-2006. The changes are explained by both natural and technogenic reasons. It is concluded, that there is a high probability of fish productivity recovery in 30th-40th of XXI century to the level of 1970th-1980th in the Sea of Azov and the Black Sea if anthropogenic impact will decrease of stabilize.