Forecast of probability of fish pre-suffocation and suffocation events in the Sea of Azov

In the previous study, based on the data on environmental conditions, which had been collected during YugNIRO’s oceanographic surveys in the western half of the Sea of Azov in the summer seasons of 1992–2006, the long-term inter-annual prognostic relationship between solar activity and certain values of near-bottom temperature and oxygen content, characterizing the possibility of an incoming pre-suffocation and suffocation event, was found out. As a follow-up to that research, the areas with various ranges of vertical thermohaline stability, near-bottom temperature and oxygen content have been calculated for the entire sea (excluding the Taganrog Bay), based on the results of the summer oceanographic surveys, carried out by AzNIIRKH in 1989–2016. For each summer season, conditional probabilities of pre-suffocation and suffocation events have been determined; they were calculated as a sum of products of areas of each parameter’s ranges by the conditional coefficients, which corresponded, according to the authors’ expert evaluation, to the degree of proximity of environmental conditions that could induce a fish pre-suffocation and suffocation event. Significant (with the confidence level of more than 99%) correlation of average annual values of solar activity (the Wolf number) and conditional probability of fish pre-suffocation and suffocation event by temperature and thermohaline parameters made it possible to predict this probability with one-year forecast interval. According to a provisional forecast, conditional probability of pre-suffocation and suffocation events for the summer seasons of 2019–2020 exceeds average multi-annual level by around 1.5 times.