—: A new model describing the dynamics of sturgeon (Acipenseridae) population unable to recover or ranked as depleted is proposed as a depleted artificially-stocking population (DAP) model. The model composed of two submodels is implemented in the R language. One of the submodels provides the opportunity to adjust the appropriate parameters used in a global model (the rate of natural mortality of a mature fish stock in a population and the artificial reproduction efficiency) with the optimization-based methods, while the second submodel deals with various scenarios for fish stock recovery over the forecast period. Scenarios are characterized by two parameters: the quantity of juvenils released by sturgeon hatcheries and the commercial fish catch decline caused by the illegal fishing practices and the fish catch for science-based targets. The estimates for the pattern of the Russian sturgeon Acipenser gueldenstaedtii in the Sea of Azov indicate that its stock may be recovered to the target level of 10 thousand tons with the baseline and optimistic scenarios by 2037—2048 relative to the artificial reproduction efficiency and the extent of illegal, unreported, and unregulated fishing. With respect to pessimistic scenarios, the stocks are not expected to recover.

Stock assessment of Azov sea roach Rutilus rutilus (Linnaeus, 1758) has been performed by CMSY model in period 1999-2019 by data-limited modelling in R. The current population status – in biological safe zone for stock biomass and no overfishing signals (B2019/BMSY = 1,32, F2019/FMSY = 0,53). Perhaps, current paper results can be a slightly incomplete in background that there is no relevant data about IUU fishery ever exists, which can lead to fishing mortality underestimation. Azov sea roach population continue to be in “depleted” status after river flow regulation in 1950’s. Joined continuous biomass estimates time series over whole fishing his-tory 1932–2019 showed at least 2 population collapses: in 1940’s and 1980’s years. According to model re-sults TAC (total allowed catch) should be accepted at level 516.9 t. If the recommendation is followed stock biomass will stay at safety in level 1828.1 t. Data limited modelling shows a good performance for sea roach in background of data lucking and in this reason still the best choose against cohor or surplus production models.

This study performs approbation of trend CMSY model on the example of Black sea sprat fishing unit, localized in Russian waters. Data sources has been reduced to the level of data limited modeling for indicator and trend models approach. CMSY population model results were compared with previously performed estimations by more powerful cohort model - XSA. CMSY results shows no significant deviations from the XSA results. Forecast scenarios and conclusions based on CMSY model fitting leads to the same statements with previously published results by XSA. CMSY model shows next results: stock biomass in 2019 B2019 = 63,9 ths. t, fishing mortality – F2019 = 0,29. Stock biomass in 2019 was significant below the target reference point BMSY = 105 ths. t and higher then limit reference point Blim = 52,7 ths. t. Some uncertain overexploitation in 2019 was underlined, F2019/FMSY = 1,12. Investigation of forecast scenarios with different total allowed catch levels indicates that there are no features for increasing the catch capacity in short-term projection. CMSY model fitting have passed the necessary stability tests and confirm previously founded results. In summary of this study, we can recommend to use CMSY model for stock assessment procedure in terms of data-limited information background.

Stock assessment of vimba population Vimba vimba (Linnaeus, 1758) in period 2015–2020 was performed by qualitative indicator method LBI (Length-Based Indicators) that allows to assess qualitative characteristics of the population and fisheries and MSY biological reference points. The indicator, qualitative approach to stock assessment was applied due to absence vimba population of stable stock-recruitment relationship (due to artificial reproduction exist), which makes impossible to apply surplus production approach to solve production equation dB/dt. LBI model was performed based on available length-weight vimba frequencies dynamics information, which allows to evaluate qualitative population characteristics and fisheries impact. Model results shows no overexploitation signals: in period 2015–2020 fisheries are carried out in maximum sustainable yield level. Indicator results according to reference points indicate no significant signals of reduction optimal length class (Lopt), small-size or large-size class. In 2016 and 2018 uncertain overexploitation of small-scale classes leads to no significant changes was underlined. In terms of biological and fisheries data lacking, LBI methods allow to perform stock assessment procedure more stable and robust then surplus or cohort approach, and output scientific advice to fisheries management.

The population biomass, fishing mortality dynamics and reference points of the rational exploitation of the Black-Azov sea shad during the period 2004-2020 were evaluated using the JABBA surplus production model in “catch-only” version. IUU estimation and preliminary parametrization by CMSY model was performed to improve assessment accuracy. According to the model output, during the 2004-2020 period shad stock biomass was in interval 1315-1341 t, fishing mortality in range 0,03-0,38. During the implementation and review of model results there was 3 period of shad stock status identified: 2004-2009 – the period of moderate shad stock recovery (from 1315 tons to 3347 tons), 2010-2013 – the period of stable stock status (at the level of 3300-3400 tons), 2014-2020 – the period of moderate reduction of the fishing stock biomass (from 3353 tons to 1791 tons). The moderate reduction of the fishing stock biomass in period 2014-2020 is due to a moderate increase in the level of fishing mortality. Currently, since 2018, there was a moderate trend of increasing fishing mortality above the level of target exploitation, leads to moderate reduction in the stock biomass (in 2020 fells below the target exploitation first time). According to the authors, one of the main reason of human activity, that leads to shad stock biomass reduction is a IUU fisheries. Authors note that there are actions required to annihilate the illegal, unregistered and unreported fisheries of the Black-Azov sea shad.

Аналитическая оценка запаса азовского леща Abramis brama (Linnaeus, 1758) для периода 2002-2020 гг. выполнена при помощи трендовой модели для ограниченных данных CMSY в среде R. Текущее состояние запаса находится на уровне целевого ориентира по биомассе запаса и имеет признаки значительной переэксплуатации промыслом (B2020/BMSY=0,989; F2020/FMSY=1,82). Учет и включение объемов ННН-промысла при помощи косвенных оценок делает результаты данной работы более полными, избегающими недооценки запаса и уровня промысловой смертности. Объединенный ряд оценок биомассы запаса леща за исследуемый период свидетельствует о произошедшем коллапсе численности популяции в период с 2005 по 2013 г., который, вероятно, был связан с изменением климатических и гидрохимических условий Азовского моря и не был вызван переэксплуатацией популяции в данный период. В современный период популяция леща продолжает находиться в угнетенном состоянии с предпосылками к восстановлению запаса. В соответствии с результатами моделирования и рассмотренными прогнозными сценариями, величина легального рекомендованного вылова в 2022-2023 гг. может составить от 40 до 110 т. в зависимости от степени контроля, учета и пресечения ННН-добычи. В случае эксплуатации популяции в данном объеме, биомасса запаса будет находиться на безопасном уровне и может достичь 950 т. Результаты работы подчеркивают необходимость контроля и предотвращения ННН-промысла леща в Азово-Донском бассейне - данный фактор является одним из ключевых, оказывающих влияние на популяцию леща в последние...