Turbot is one of the most valuable fish species in the Black Sea commercial fishery. The serious, dramatic depletion of the turbot stock and catches that began in the 1980s was caused by overfishing and poor ecological conditions. The state of the turbot stock began to improve in the northwestern part of the Black Sea in 2016. Landings were at their 30-year maximum in this part of the sea. Catches per unit effort (CPUEs) have been at a stable, high level there for the last few years. Average turbot weight and length have also been increasing. The Stock Synthesis (SS3) framework was used in the stock assessment. According to SS3 analysis, fishing mortality (F) reached the minimum level of 0.29 in 2018. The cumulative SPR (Spawner Potential Rate) index was 0.27, which approximately equaled SPRMSY = 0.25. Thus, currently the turbot stock is mostly moderately exploited at a level close to the management target in the northwestern part of the Black Sea. However, the entire Black Sea population has not fully recovered yet.

A fundamental problem in distributed computing systems is to make the same decision on an issue. The consensus protocol de-scribes a process to agree on some data value that is needed during computation. The work is devoted to development of the consen-sus algorithm based on the Nxt consensus protocol which can be implemented to blockchain systems with PoS (Proof-of-Stake). PoS consensuses based on node balances, and unlike PoW (Proof-of-Work) methods, are environmentally friendly and more energy effi-cient. Nowadays such types of consensuses are getting more popular. However, they remain less scrutinized than PoW. Moreover, there are some attacks and threats that cannot be completely resolved under PoS consensuses, and in particular under the Nxt.In this article we propose a modification of the Nxt protocol which solves some problems of PoS in accordance with modern requirements. The asymmetric method was used to select the best Nxt consensus parameters for decreasing of the blocktime variance. This im-proves theperformance and reliability of the entire blockchain system eliminating the risk of disruptions due to overflowing the transaction pool. For the Nxt consensus protocol researching, the mathematical simulating model was developed using Anylogic 8.4 software. Implementation of economic leverages (tokenomics), which we called Proof-of-Greed approach, allows to prevent some types of attacks, e.g. large stake attack, and to set a fair market-based transaction fee. The using of economic mechanisms to protect distributed systems allows to prevent a number of attacks that are resistant to cryptographic methods. But at the same time, theto-kenomics of the system should be strictly consistent with the protocols for the functioning of all system objects, combining them into an integrated unitary ecosystem. Also, a payback period of harvesters was investigated within Proof-of-Greed protocol. The parame-ters of such approach for sustained operation of a network were obtained as a result of mathematical simulating with Anylogic 8.4 software. The Proof-of-Greed approach can be implemented not only in the Nxt consensus but in some other blockchain systems based on PoS consensuses.

Background. Atmospheric pressure is one of the most important factors affecting fish activity, but the potential influence on migration patterns of fish lacking a gas bladder is unclear. In this study, we analysed the influence of atmospheric pressure on round goby, Neogobius melanostomus (Pallas, 1814), from the coastal waters of the Black Sea. Material and methods. Gobies were maintained at low pressure, decreased by 1333 Pa (= 10 mmHg), for several hours a day at temperature intervals of 10-12°С, 14-16°С, 18-20°С, 22-24°С, and 26-28°С for 5 days and subsequently the pressure was returned to 1333 Pa and the results were compared to controls without pressure/ temperature changes. Results. We found that increasing the atmospheric pressure at temperatures 10-24°C influenced the activity of round goby, which then stabilised within one hour. Fish activity then decreased till it matches the level observed before experimental pressure changes. Changes in atmospheric pressure did not influence fish activity at higher temperatures of 26-28°C. Conclusions. We intended to determine the influence of atmospheric pressure and water temperature on the swimming activity of round goby. The association between the atmospheric pressure, thermal tolerance, and the fish activity levels is suggested as a possible mechanism driving migrations of the round goby.

The aim of this study is to assess the level of the red mullet stock exploitation in Georgian coastal waters using the CMSY, LBB and LB-SPR modeling methods. The samplings were carried out using bottom trawls in 2019-2021. In total 4957 individuals were sampling (1 508 cases age was determined using scales and otoliths). Average annual catch of the red mullet make up 11.7±3.3 t (0.3% of the total annual Black Sea countries landings). The total length ranged from 6.1 to 20.7 cm. 70% of landings consisted of 3+, 4+ and 5+ age. The length-weight relationship was calculated as W=0.0072 × L3.20. Average von Bertalanffy growth parameters were L∞=18.00±0.27 cm, k=0.31±0.03, and t0= –0.93±0.26. LBB method demonstrate that the red mullet stock was overexploited (F/M=2.7 more than optimal level F/M=1.0). According to CMSY analysis, biomass has been decreasing to Blim for the researched period. The LB-SPR result showed that the estimated SPR was 23%. The exploitation of the stock was steadily intensive according to CMSY and LB-SPR methods. Increase in fishing mortality is not recommended.

A consensus protocol is a crucial mechanism of distributed networks by which nodes can coordinate their actions and the current state of data. This article describes a BlockDAG consensus algorithm based on the Proof of Stake approach. The protocol provides network participants with cross‐voting for the order of blocks, which, in the case of a fair vote, guarantees a quick consensus. Under conditions of dishonest behavior, cross‐voting ensures that violations will be quickly detected. In addition, the protocol assumes the existence of a Coordinating network containing information about the approved ordering, which qualitatively increases security and also serves to improve network synchronization.