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Modern management of fish stocks is based on integrating the precautionary approach with the maximum sustainable yield framework. It relies on accurate estimation of precautionary limits, defined as levels of spawning biomass where a stock has reduced reproductive capacity, and harvesting targets aimed to maximise future yields. Therefore, it is heavily depending on productivity assumptions. Most fish stocks are managed assuming that productivity will increase as the stock size decreases (i.e., density dependent compensatory stock and recruitment relationship). However, several biological and ecological processes will result in a decreased productivity below a certain population size, referred to as the Allee effect or depensation. Through a meta‐analysis of 81 Northeast Atlantic fish stocks, we investigated the impact of assuming compensatory recruitment in the presence of depensation in fisheries management. Across life histories, depensation results in a 22% reduction of the fishing mortality rate leading to extinction. On average, the maximum reproductive rate per spawning biomass was found at 35% of BMSY, which was also the biomass where stocks have a 5% risk of extinction without fishing. Finally, the presence of depensation resulted in increased rebuilding times when stock spawning biomass falls below the limit reference point. When depensatory effects are present, assuming increasing productivity at low biomass will generally result in over‐optimistic perceptions of rebuilding and stock status at biomass below 25% and 45% of BMSY in general, and for pelagic stocks respectively. When not accounted for, depensation will potentially lead to unsustainable harvesting practices of marine living resources. [ABSTRACT FROM AUTHOR]

Simple Summary: This study presents a refined approach for assessing Japanese sardine (Sardinops melanostictus) stock in the Northwest Pacific Ocean (NPO), addressing seasonal and spatial variations in abundance. We developed a seasonal spatio-temporal model that accounts for migration patterns to generate seasonal abundance indices, which were applied in the AMSY stock assessment method. The results indicate a steady increase in sardine abundance, with a significant northeast shift in the population center of gravity, confirming a sustainable stock status with a 94.8–99% recovery probability. The study underscores the benefits of spatio-temporal indices over conventional models for precise stock assessments and highlights the need for cautious management to ensure long-term stock health, given the historical fluctuations in Japanese sardine abundance. This framework offers an innovative method for managing distant-water fisheries and supporting offshore fishery research. Accurate estimation of fish stock abundance and exploitability is critical for effective fishery management; however, fishery-dependent data are often affected by temporal and spatial heterogeneities due to the seasonal migration of fish, posing challenges for refined stock management. Previous studies have largely ignored these spatio-temporal dynamics, assuming static populations. This study develops a seasonal spatio-temporal model for Japanese sardine (Sardinops melanostictus) in the Northwest Pacific Ocean (NPO), using fishery-dependent data from 2014 to 2022. Seasonal standardized abundance indices (spring, summer, autumn, and an overall average) were generated and integrated with the abundance maximum sustainable yield (AMSY) method for stock assessment. The performance of the AMSY method using a spatio-temporal index was compared with the conventional model-based index, showing the superiority of the spatio-temporal approach. Results indicate a gradual increase in sardine abundance, with a significant shift in the center of gravity toward the northeast. The stock is in a sustainable state with a 94.8–99% probability of recovery. Although the stock is recovering, careful management is advised to prevent future declines. This framework offers a novel approach for assessing distant water and coastal fishery resources. [ABSTRACT FROM AUTHOR]

Dynamic shifts in fleet structure and gear usage lead to complex implications for representing fishery selectivity in stock assessment models. There is generally a lack of consensus on how assessment models should be configured to confront changes in fishery fleet structure or associated selectivity forms, while balancing complexity-parsimony tradeoffs. We conducted a simulation analysis to evaluate the performance of alternative assessment models when confronted with fleet transitions among gear types, which included differences in (1) rates of transition (i.e., a fast or slow transition among gears), and (2) selectivity forms for each modeled fleet (i.e., asymptotic or dome-shaped). In general, explicitly modeling fleet structure (i.e., multi-fleet models) performed well, but demonstrated bias in biomass estimates and management reference points when selectivity forms were mis-specified. Single-fleet models were only unbiased when time-varying selectivity (e.g., using time blocks or continuous formulations) was estimated to account for changes among gear types. Our results suggest that single-fleet models with time-varying fishery selectivity are adequate for operational management advice, but research oriented multi-fleet models should be used as validation tools to explore model consistency within single-fleet models. [ABSTRACT FROM AUTHOR]

A novel approach to gobies stock assessment based on training an artificial intelligence model using long-term historical ecosystem data was proposed. This research uses data from the historical archive for annual parameters of the Azov Sea ecosystem, including the Don River flow volume, water salinity, zoobenthos relative biomass, sander catches, sturgeons catches and fishery biomass, gobies catches (predictor factors), gobies stock biomass (predictable variable) dynamics during the period 1970–2022. In the preliminary data analysis, no evidence of non-stationarity factors or predictable factors collinearity was found. Based on this datasets, three types of models were trained to predict the gobies stock biomass based on environmental factors: a random forest model, Bayesian regularized neural network model and generalized linear model. Lags between biomass of gobies and predictable factors was introduced from 1 to 4 years to make forecasting possible. The best results and diagnostics were observed with the RF model (R2 = 0.85 with no lags). The acceptable predictive models were found with a lag of up to 2 years based on the random forest model ( , ). Considering the forecast for the 2 years ahead, no prospects have been found for restoring the gobies population in the short term. [ABSTRACT FROM AUTHOR]

Lane snapper Lutjanus synagis (Linnaeus 1758) is abundant in Northeastern Brazil and economically relevant to the artisanal fishery. Population and reproductive aspects of lane snapper wereinvestigated to assist assessment. Lane snappers were acquired in Pernambuco (n = 406) from 2013 to 2015. Sex ratio is close to 1 : 1 (213 males and 179 females). For males, the total length, TL (mode) ranges from 16.3–27.8 cm (20.4 cm). For females, TL ranges from 17.0–29.9 cm (21.0 cm). The species have negative allometric growth (b < 3). The length that 50% of the population reach maturity (L50) using TL is 17.7 cm for both sexes. Macroscopical and microscopical gonadal stages are described per sex, and the gonadosomatic index indicates that reproduction happens during the dry season, between September and March, and two maturational peaks are observed, the first between September and November and the second between January and March. [ABSTRACT FROM AUTHOR]

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Stock depletion level is an important concept in the assessment and management of exploited fish stocks because it is often used in conjunction with reference points to infer stock status. Both the depletion level and reference points can be highly dependent on the stock–recruitment relationship. Here, we show how depletion level is estimated in stock assessment models, what data inform the depletion level, and how the stock–recruitment relationship influences the depletion level. There are a variety of data that provide information on abundance. In addition, to estimate the depletion level, unexploited absolute abundance needs to be determined. This often means extrapolating the abundance back in time to the start of the fishery, accounting for the removals and the productivity. Uncertainty in the depletion level arises because the model can account for the same removals by either estimating low productivity (e.g., low natural mortality) and high carrying capacity or high productivity and a low carrying capacity, and by estimating different relationships between productivity and depletion level, which are strongly controlled by the stock–recruitment relationship. Therefore, estimates of depletion are particularly sensitive to uncertainty in the biological processes related to natural mortality and the stock–recruitment relationship and to growth when length composition data are used. In addition, depletion-based reference points are highly dependent on the stock–recruitment relationship and need to account for recruitment variability, particularly autocorrelation, trends, and regime shifts. Future research needs to focus on estimating natural mortality, the stock–recruitment relationship, asymptotic length, shape of the selectivity curve, or management strategies that are robust to uncertainty in these parameters. Tagging studies, including close-kin mark-recapture, can address some of these issues. However, the stock–recruitment relationship will remain uncertain. [ABSTRACT FROM AUTHOR]

False killer whales, striped dolphins, and Pacific white-sided dolphins have been targeted by dolphin fisheries in the coastal waters off Japan. Annual catch quotas are allocated on the basis of past abundance estimates, but those estimates were unpublished or more than 30 years old. Here, we reanalyzed the line-transect data collected from the sighting survey on the Pacific coast of Japan from 1985 to 2021 and estimated the past and latest abundances of those three species using a standard distance sampling approach. The surveys were conducted as part of the JAFRACSS-SC (Japan Fisheries and Education Agency Cetacean Sighting Survey-Small Cetacean Survey Program). This program mainly targets other fishery-targeted cetacean species and, thus, covers only a part of the above three species' distribution ranges. As a result, we obtained the latest abundance estimates of 4105 false killer whales, 84,657 striped dolphins, and 28,052 white-sided dolphins. Considering the current estimates represent only a part of the entire population size and that annual catch records did not largely exceed potential biological removals calculated based on these abundances, the current harvest level will not lead to a severe depletion or extinction for these three species. [ABSTRACT FROM AUTHOR]

Forecasting the recruitment of fish populations with skill has been a challenge in fisheries for over a century. Previous large‐scale meta‐analyses have suggested linkages between environmental or ecosystem drivers and recruitment; however, applying this information in a management setting remains underutilized. Here, we use a well‐studied database of groundfish assessments from the West Coast of the USA to ask whether environmental variables or ecosystem indicators derived from long‐term monitoring datasets offer an improvement in our ability to skilfully forecast fish recruitment. A secondary question is which types of modelling approaches (ranging from linear models to non‐parametric methods) yield the best forecast skill. Third, we examine whether simultaneous forecasting of multiple species offers an advantage over generating species‐specific forecasts. We find that for approximately one third of the 29 assessed stocks, ecosystem indicators from juvenile surveys yields the highest out of sample predictive skill compared to other covariates (including environmental variables from Regional Ocean Modeling System output) or null models. Across modelling approaches, our results suggest that simpler linear modelling approaches do as well or better than more complicated approaches (reducing out of sample Root Mean Square Error by ~40% compared to null models), and that there appears to be little benefit to performing multispecies forecasts instead of single‐species forecasts. Our results provide a general framework for generating recruitment forecasts in other species and ecosystems, as well as a benchmark for future analyses to evaluate skill. The most promising applications are likely for species that are short lived, have relatively high recruitment variability, and moderate amounts of age or length data. Forecasts using our approach may be useful in identifying covariates or mechanisms to include in operational assessments but also provide qualitative advice to managers implementing ecosystem based fisheries management. [ABSTRACT FROM AUTHOR]

The management and conservation of tuna and other transboundary marine species have to date been limited by an incomplete understanding of the oceanographic, ecological and socioeconomic factors mediating fishery overlap and interactions, and how these factors vary across expansive, open ocean habitats. Despite advances in fisheries monitoring and biologging technology, few attempts have been made to conduct integrated ecological analyses at basin scales relevant to pelagic fisheries and the highly migratory species they target. Here, we use vessel tracking data, archival tags, observer records, and machine learning to examine inter- and intra-annual variability in fisheries overlap (2013–2020) of five pelagic longline fishing fleets with North Pacific albacore tuna (Thunnus alalunga, Scombridae). Although progressive declines in catch and biomass have been observed over the past several decades, the North Pacific albacore is one of the only Pacific tuna stocks primarily targeted by pelagic longlines not currently listed as overfished or experiencing overfishing. We find that fishery overlap varies significantly across time and space as mediated by (1) differences in habitat preferences between juvenile and adult albacore; (2) variation of oceanographic features known to aggregate pelagic biomass; and (3) the different spatial niches targeted by shallow-set and deep-set longline fishing gear. These findings may have significant implications for stock assessment in this and other transboundary fishery systems, particularly the reliance on fishery-dependent data to index abundance. Indeed, we argue that additional consideration of how overlap, catchability, and size selectivity parameters vary over time and space may be required to ensure the development of robust, equitable, and climate-resilient harvest control rules.

ABSTRACT Sustainable management of recreational fisheries requires balancing angler attitudes and behaviour with fisheries' biological potential. Herein, we investigated the balance in the sea‐run brown trout (Salmo trutta) fishery around the Swedish island of Gotland using data collected through a creel survey, test fishing, and spawning returns to selected streams. Anglers accurately anticipated catches of large fish but underestimated the role of natural reproduction in supporting the stock. Female sea trout entering spawning streams and post‐spawn sea trout caught on the coast were significantly larger than spawning males and non‐spawned fish, and were particularly important for the fishery. Larger sea trout also faced a higher level of harvest pressure than other sizes. Small changes to angler preferences, harvest rates, or regulations could significantly influence characteristics and sustainability of this fishery. The scale and direction of these changes merit further investigation. [ABSTRACT FROM AUTHOR]

ABSTRACT Artisanal fishing significantly not only contributes to socioeconomic development of numerous countries but also exerts pressure on natural populations. The white shrimp (Penaeus schmitti) is a key species in Brazilian artisanal fisheries, yet it is currently classified as data‐deficient. Conducting comprehensive studies on its population dynamics is essential to establish reference points that guarantee sustainable fishing. Therefore, we estimated population parameters to assess status of the white shrimp stock captured by beach seining in Northeast Brazil. Monthly samples of white shrimp were collected using a beach trawl. Based on population parameters, the white shrimp population in the study area, the sex ratio was 1 male to 1.29 females, with females larger and heavier than males. Weight–length relationships revealed positive allometric growth for males, females, and grouped sexes, with no significant difference between sexes. Asymptotic length, t_achor, and growth performance index also did not differ between sexes; however, the growth coefficient was higher for females. Beach trawling in northeastern Brazil predominantly targeted adult white shrimp, with carapace length at first capture (Lc50) averaging 2.12 cm for females and 2.19 cm for males. Mortality and exploitation rates were below maximum sustainable levels, so the stock was classified as underexploited. Overall, beach‐seine fishing was less harmful to this stock (F = 1.42) than motorized fishing and can be considered a sustainable fishing activity for the white shrimp population. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has emerged as a highly sensitive and efficient tool for the biomonitoring of aquatic ecosystems. In this study, we investigated fish and benthic species communities using eDNA techniques in a medium-sized reservoir (about 3 square kilometers) in Anhui, China. A total of 12 water samples and 11 sediment samples were analyzed by 12S and 18S primers, respectively. We analyzed the composition of species diversity and the effect of seven environmental factors using the Mantel test. A total of 42 fish taxa were present in the water samples, and 188 benthic taxa in the sediment samples. Species composition was different in disparate stations. We found that water temperature and salinity are pivotal factors influencing the composition of fish communities, while chlorophyll-a is a primary environmental determinant for benthic species assembly structures across different zones. Biodiversity information generated by eDNA techniques can be used to reflect the resource status of this reservoir. The relevant results will provide important scientific reference information for the development and exploitation of medium-sized reservoirs. [ABSTRACT FROM AUTHOR]

In a state-space framework, temporal variations in fishery-dependent processes can be modeled as random effects. This modeling flexibility makes state-space models (SSMs) powerful tools for data-limited assessments. Although SSMs enable the model-based inference of the unobserved processes, their flexibility can lead to overfitting and non-identifiability issues. To address these challenges, we developed a suite of state-space length-based age-structured models and applied them to the Korean chub mackerel (Scomber japonicus) stock. Our research demonstrated that incorporating temporal variations in fishery-dependent processes can rectify model mis-specification but may compromise robustness, which can be diagnosed through a series of model checking processes. To tackle non-identifiability, we used a non-degenerate estimator, implementing a gamma distribution as a penalty for the standard deviation parameters of observation errors. This penalty function enabled the simultaneous estimation of both process and observation error variances with minimal bias, a notably challenging task in SSMs. These results highlight the importance of model checking and the effectiveness of the penalized approach in estimating SSMs. Additionally, we discussed novel assessment outcomes for the mackerel stock. [ABSTRACT FROM AUTHOR]

The value of no-take marine protected areas (MPAs) in providing fisheriesindependent information to evaluate the status of adjacent fish stocks is increasingly being recognised. However, to ensure robust assessments of fisheries using this approach, MPAs need to be representative of the wider fished area and sampling should include multiple MPA and fished locations spanning the area of interest. The spiny lobster Jasus edwardsii fishery in Aotearoa New Zealand's Hauraki Gulf has been in decline since the late 1990s, but latest stock estimates suggest a dramatic recovery following catch reductions in 2018. We compared J. edwardsii populations on shallow reefs (<20 m depth) in three marine reserves with six fished locations across the Hauraki Gulf to provide a fisheries-independent assessment of this important fishery and the degree of recovery following catch reductions. Region-wide surveys found that J. edwardsii populations within protected areas were dominated by large, legal-size individuals, whereas lobster in fished locations were mostly below or around legal-size. Total, vulnerable, and spawning stock biomass was 12-43 times higher within MPAs compared to fished locations. Overall, biomass at fished locations was <10% of that in reserves and there was little evidence of recovery following catch reductions. Our fisheries-independent data suggest that recent stock assessments have severely overestimated the recovery and state of lobster populations in the Hauraki Gulf and that populations on shallow reefs remain depleted. These findings highlight the critical need for fisheries-independent data and the value of MPA monitoring data in evaluating population status and recovery following fisheries management actions. [ABSTRACT FROM AUTHOR]

Most baleen whale populations are increasing after the end of industrial whaling, but their recovery patterns challenge long‐standing assumptions about density dependence.It has long been assumed that population growth rates will decline with recovery, until reaching equilibrium ('carrying capacity', K). Indeed, the International Whaling Commission assumes that growth rates will slow long before K is reached, with maximum productivity at 0.6K. This 0.6K population level is used as an international benchmark that forms the basis of whaling regulations and decisions about whether baleen whale populations are declared depleted.We fit models to four long‐term data sets for baleen whales with multiple abundance estimates that span the range from low to high abundance, finding strong evidence that increase rates remain at near‐maximal levels across a wide range of abundance levels, and only decline as the population nears K. As a result, maximum productivity occurs at 0.69–0.87 of K across these populations, which predicts more rapid recovery for baleen whale populations than currently assumed. The overall mean of these values (0.8K) would be a more sensible default choice than the 0.6K currently assumed.Synthesis and applications. Estimated recovery rates imply that management thresholds currently used are lower than actual maximum productivity and that populations can increase rapidly even at high abundance. However, if population models continue to assume that maximum productivity is at 0.6K, they will estimate abundance relative to K to be lower than it is, providing conservative assessment results. Our results should stimulate further discussion about the role of maximum sustainable yield as a fundamental concept in fisheries and wildlife management. [ABSTRACT FROM AUTHOR]

Marine protected areas (MPAs) can allow some fish populations to rebuild within their borders in areas impacted by overfishing, but the effectiveness of reserves is highly dependent on how effectively fishing mortality is controlled, which in turn depends on the level of fishery management implementation. In Cuba's Gardens of the Queen MPA, the largest in the Caribbean, a variety of fishery management measures have been implemented to ensure the social, economic, and political viability of protecting such a large area. Here, we evaluate the biological response, in terms of fish density and the biomass of commercially valuable and ecologically important reef fish species, to a spatial gradient of fishery management enforcement, in terms of fish density and biomass, of commercially valuable and ecologically important reef fish species. The enforcement gradient is characterized by the level of protection, fishing effort, patrolling effort, distance to the nearest fishing port, and fishing intensity. Fish density and biomass were estimated from visual scuba surveys. Areas with higher levels of enforcement support higher levels of average biomass (up to 1378 kg/ha) and density (up to 2367 indv./ha) of commercially important fishes in comparison to areas with very low or no enforcement (estimates of 757 kg/ha average biomass and 1090 indv./ha average density, respectively). These fish density and biomass levels can serve as proxies in the development of harvest control rules that adjust fishing pressure according to the ratio of fished density or biomass to unfished density or biomass, through the use of the MPA Density Ratio method. [ABSTRACT FROM AUTHOR]

The Norway lobster (Nephrops norvegicus) is one of the most important fishery items for the EU blue economy. This paper describes a software architecture based on neural networks, designed to identify the presence of N. norvegicus and estimate the number of its individuals per square meter (i.e. stock density) in deep-sea (350–380 m depth) Fishery No-Take Zones of the northwestern Mediterranean. Inferencing models were obtained by training open-source networks with images obtained from frames partitioning of in submarine vehicle videos. Animal detections were also tracked in successive frames of video sequences to avoid biases in individual recounting, offering significant success and precision in detection and density estimations. [ABSTRACT FROM AUTHOR]

Most fisheries are conducted without any scientific knowledge about the size and productivity of the stocks that support them. This navigation in the dark in most fisheries is a major obstacle in making them sustainable sources of nutrition for people in general and income for fishers and other economic actors along supply chains. Fisheries that have not been assessed generally are data‐intermediate and data‐poor, the latter usually having annual time series of landings as the single piece of data available. A major effort in the last two decades has been directed toward developing 'catch‐only' stock assessment methods, although some of these methods have been tested and found deficient. Here we provide a novel approach to using annual landing time series as the single source of data to qualitatively judge the condition of un‐assessed stocks using frequentist cumulative probability ogives, both in terms of stock biomass and fishing mortality. A meta‐analysis of the FishSource database allowed us to infer statistical patterns from hundreds of assessed fisheries and thousands of annual landings, biomass, and fishing mortality observations. Four stock‐management types were considered separately in the analysis: short‐lived and others (mid‐ to long‐lived) stocks, controlled or not controlled by catch limits. Obtained cumulative probability ogives provide clear evaluations of stock biomass and fishing mortality trends in all four stock‐management types, leading to actionable information on probable current status and future trends. Using these probability ogives, we developed decision trees that lead to qualitative scores on the exploitation status of un‐assessed stocks. [ABSTRACT FROM AUTHOR]

The study investigated the growth, mortality, exploitation rate and recruitment of Fringescale sardinella (Sardinella fimbriata Valenciennes, 1847) found in Malampaya Sound, Palawan, Philippines. A total of 1200 samples were collected from April 2023 to March 2024. The relationship between length and weight was expressed as y = 0.0291 × 2.561 for combined sex, y = 0.0404 × 2.4254 for males, and y = 0.0355 × 2.4856 for females. The resulting b values pinpoint to a negative allometric growth. The calculated regression model showed a significant association during which the p-values were below 0.0000 and the r2 values ranged between 0.76 and 0.79. Estimation using the FISAT II soft ware resulted in an asymptotic length (L∞) = 16.28 cm, growth rate (K) = 0.68 yr-1, maximum length (Lmax) = 15.78 cm, theoretical age at birth (t0) = -0.5515 years and growth performance index (') = 2.256. The estimated average total mortality rate (Z), natural mortality (M), and fishing mortality (F) were 2.69, 1.68, and 1.01 per year, respectively. Recruitment occurs throughout the year and peaks in June. It can be noted that the exploitation is calculated as 0.38, which is considered lightly exploited. To have a sustainable population and avoid overfishing, an optimum total yield (E50) can be set at an exploitation rate of 0.278. The maximum yield (Emax) is at an exploitation rate of 0.421. [ABSTRACT FROM AUTHOR]

Lessepsian Erugosquilla massavensis is one of the three Stomatopod species reported on the Levantine coast of Türkiye. Its natural habitat is the Red Sea and it is the first Red Sea stomatopod species reported from the Mediterranean. This study aims to determine the morphometric relationships, growth parameters, sex ratio, age, mortality, and exploitation rates of non-native E. massavensis in the north-eastern Mediterranean. Samples were collected monthly by commercial trawl surveys between September 2016 and March 2017 in Iskenderun Bay. Relationships between the carapace length (CL)–total length (TL) and the total length (TL)–total weight (TW) were estimated. Negative allometric growth was observed between the CL–TL and TL–TW relationship for females, males, and all. The von Bertalanffy growth parameters (vBGP) were found L∞ = 155.4 mm, K = 0.520 year−1, t0 = −0.199, ø′ = 4.099 for females, L∞ = 157.5 mm, K = 0.600 year−1, t0 = −0.127, ø′ = 4.173 for males. This research provided the first-ever data on the vBGP of E. massavensis. The study found that both sexes had a higher fisheries mortality coefficient than natural mortality (Z = 2.01, M = 0.71, F = 1.3) and were exploited (E = 0.65). [ABSTRACT FROM AUTHOR]

Ensemble model use in stock assessment is increasing, yet guidance on construction and an evaluation of performance relative to single models is lacking. Ensemble models can characterize structural uncertainty and avoid the conundrum of selecting a "best" assessment model when alternative models explain observed data equally well. Through simulation, we explore the importance of identifying candidate models for both assessment and short-term forecasts and the consequences of different ensemble weighting methods on estimated quantities. Ensemble performance exceeded a single best model only when the set of candidate models spanned the true model configuration. Accuracy and precision depended on the model weighting scheme, and varied between two case studies investigating the impact of catch accuracy. Information theoretic weighting methods performed well in the case study with accurate catch, while equal weighting performed best when catch was underreported. In both cases, equal weighting produced multimodality. Ensuring that an ensemble spans the true state of nature will be challenging, but we observed that a change in sign of Mohn's rho across candidate models coincided with the true OM being bounded. Further development of protocols to select an objective and balanced set of candidate models, and diagnostics to assess adequacy of candidates are recommended. [ABSTRACT FROM AUTHOR]

Changing distribution and abundance of small pelagic fishes may drive changes in predator distributions, affecting predator availability to fisheries and surveys. However, small pelagics are difficult to survey directly, so we developed a novel method of assessing the aggregate abundance of 21 small pelagic forage taxa via predator stomach contents. We used stomach contents collected from 22 piscivore species captured by multiple bottom trawl surveys within a vector autoregressive spatio-temporal model to assess trends of small pelagics on the Northeast US shelf. The goal was to develop a spatial "forage index" to inform survey and (or) fishery availability in the western North Atlantic bluefish (Pomatomus saltatrix) stock assessment. This spatially resolved index compared favorably with more traditional design-based survey biomass indices for forage species well sampled by surveys. However, our stomach content-based index better represented smaller unmanaged forage species that surveys are not designed to capture. The stomach-based forage index helped explain bluefish availability to the recreational fishery for stock assessment and provided insight into pelagic forage trends throughout the regional ecosystem. [ABSTRACT FROM AUTHOR]

Management of crustacean fisheries is often data‐limited, and techniques used in finfish fisheries are often inappropriate for crustaceans due to life‐history differences. Limitations in modeling capacity and data availability make it difficult to determine the status of crustacean stocks using model‐based biological reference points (BRPs), but BRPs are a key component of successful fisheries management. Using crustacean fishery case studies depicting model‐based and empirical management strategies, we synthesized the current state of crustacean fisheries management with respect to data availability and use of management controls. Input and output controls can be successful with supplemental BRPs, but whatever methods are used must explicitly consider species' unique life‐history characteristics. In data‐limited fisheries, output controls can effectively conserve a species under high levels of exploitation. Implementation of discrete BRPs can improve sustainability of both emerging and data‐rich crustacean fisheries, to make these quantitative metrics a valuable tool for crustacean management globally. [ABSTRACT FROM AUTHOR]

The Atlantic pearl oyster, Pinctada radiata (Leach, 1814), is an Indo-Pacific bivalve of the subtidal zone that has colonized habitats all over the Mediterranean. There is a lack of detailed information on the reproductive activity of P. radiata in Hellenic waters, especially following the recent amendment of national legislation aiming to regulate the fishery and prevent illegal fishing and trafficking as a substitute for indigenous oysters. A total of 703 individuals were collected by scuba diving from the southwest part of Evia Island. Gonad microscopic examination indicated that gametogenesis occurs from February to September, with a recovery stage in early autumn. Synchronicity occurs for both sexes, with temperature being the main controlling factor. The annual recruitment pattern indicated two prominent peaks of similar magnitude. Analysis of covariance indicated a significant temperature effect on gonad index above 22 degrees. Onset of sexual maturity (L50) was estimated at 47.2 mm in shell height and 27.09 gr in total weight for the entire population. The sex ratio was in favor of females at 1:1.70, with 7% and 19% of the individuals assessed macroscopically and microscopically identified as hermaphrodites, respectively. Results offer valuable information for the management and conservation of pearl oyster populations. [ABSTRACT FROM AUTHOR]

This study examined the growth patterns of the spotted catfish, Arius maculatus (Thunberg, 1792) in the Thanlwin River Estuary throughout the analysis of standard lengths obtained from observed otolith data and back‐calculated data. Between April 2023 and January 2024, 516 fish ranging in standard lengths from 8.3 to 33 cm were collected. The annual deposition of annuli in otoliths was confirmed using the marginal increment ratio, with ages ranging from 2 to 9 years. The Dahl‐Lea back‐calculation method expanded the length at age data to 2472 records for ages 1–9 years. Growth was characterized using Von Bertalanffy growth curves, revealing the significant differences between the observed data (asymptotic length L∞ = 25.34 cm, growth coefficient K = 0.257 year−1 and growth performance index ϕ′ = 2.02) and the back‐calculated data (L∞ = 36.23 cm, K = 0.087 year−1 and ϕ′ = 2.21). The findings of the study suggested that the back‐calculated otolith data were more dependable for determining growth parameters compared to the observed otolith data. A. maculatus appears to exhibit slow growth characteristics, suggesting that the environmental conditions in the Thanlwin River Estuary may be deficient for this species. The insights gleaned from this research are crucial for guiding and shaping fishery management policies through informed advice and recommendations. [ABSTRACT FROM AUTHOR]

The Southeast Area Monitoring and Assessment Program (SEAMAP) Bottom Longline (BLL) survey was established to provide a nearshore complement to the offshore National Marine Fisheries Service (NMFS) BLL survey. SEAMAP state partners (i.e., Texas, Louisiana, Mississippi, and Alabama) used identical gear and sampling protocol to NMFS; however, temporal window, sampling universe, sampling frequency, and station selection were determined independently by each state based on available resources and capabilities. Although each state collected high quality data, the lack of a unified design complicated the efforts to combine state partner data to develop an index of abundance for stock assessment purposes. To improve the value of the survey and prioritize the quality and utility of the resultant data, the SEAMAP BLL survey was modified to implement a unified design that included consistency in spatial coverage and sampling frequency, and proportional allocation of sampling effort. Data from the early (2008-2014) and modified (2015-2021) SEAMAP BLL surveys, and from the modified SEAMAP and NMFS surveys were compared to determine the effects of this unified design on data precision. Overall catch composition slightly differed between the early and modified SEAMAP BLL surveys; however, taxa with declined abundance under the modified SEAMAP BLL survey were adequately sampled by the complementary NMFS BLL survey. Size composition was compared for three managed species. The size composition of Atlantic Sharpnose Sharks and Blacktip Sharks differed significantly between the modified SEAMAP BLL survey and the NMFS BLL survey, indicating that the modified survey is indeed providing complementary data. Further, implementing the modified design reduced the coefficient of variation for the indices of abundance for both Blacktip Sharks and Red Drum. The evolution of this survey highlights the benefit of unifying survey designs that build upon existing efforts to enhance the utility of survey data for multiple applications.

This study evaluates the stock status of Scomberomorus commerson in the southern Arabian Gulf, particularly in Abu Dhabi waters, using length-based models to address data limitations in fisheries assessments. The findings contribute critical insights into management practices using four length-based models, namely, LBI, LBB, LBSPR, and LIME, to analyze length frequency distributions from commercial catches between 2011 and 2023. The results indicate that the stock is overfished, with low proportions of mature and optimal-sized individuals and an excessive harvest of juveniles, as shown by the model estimates of F/M ratios and SPR values below target levels. From 2011 to 2019, the biomass declined sharply, but signs of recovery were evident by 2023 due to management actions, such as a gillnet ban introduced in 2019. The final-year estimates revealed a B/Bmsy ratio of 1.0 and F/M of 1.2, suggesting ongoing but reduced overfishing pressures. These outcomes underscore the importance of ongoing data-limited assessment methods in monitoring exploited stocks, providing evidence that restrictive measures have positively impacted biomass recovery. The convergence of outputs across methods, such as the indication of overfishing in S. commerson stocks, suggests that implementing multiple models enhances the robustness of management recommendations, including the enforcement of minimum size limits or reductions in fishing efforts or restriction of certain fishing methods. Overall, this study highlights the importance of using multiple models and choosing appropriate priors to improve the quality of stock assessments in data-limited fisheries.

ABSTRACT Recent studies demonstrated that integrating allometric scaling could strengthen the relationship between environmental DNA (eDNA) concentration and organism abundance. The finding has been supported mainly by field surveys but has not been verified sufficiently at the individual level in a controlled experimental condition. In addition, it remains unknown whether not only eDNA but also environmental RNA (eRNA) production scales allometrically with body mass. To address the knowledge gaps, we conducted a long‐term rearing experiment using ayu (Plecoglossus altivelis) to monitor the production of their eDNA and messenger and ribosomal eRNA in their growth from larvae to adults. Water samples were collected from the experimental tanks and P. altivelis eDNA and eRNA (eNAs) concentrations in water samples were estimated using a quantitative real‐time PCR with the mitochondrial and nuclear gene markers. In parallel with each water sampling, the number of fish individuals and total biomass in the tank were recorded. Regardless of gene and RNA types, individual‐level P. altivelis eNA concentrations were related to their allometric scaled mass (ASM), with the scaling coefficient (b) = 0.75, more strongly than their mean body mass. The result indicated that a larger individual produces lesser mass‐specific eNA particles, supporting the relevance of the allometric scaling in eDNA production at the population level observed in field surveys. Moreover, the ratios of some eNA concentrations significantly decreased with larger mean fish body mass in the tank. The finding may relate to the changes in intracellular physiology with individual growth and/or aging, having the potential to indicate the population's average body size. Our study offered insights into the production of various eNA particles depending on body size and metabolic rate and implications for a better understanding of the population's ecology and more effective stock management.

Small-scale fisheries account for almost 90 % of global fisheries employment and are responsible for landing >40 % of the world's fish catch. Yet their importance to livelihoods and food and nutrition security in Least Developed Countries are only recently emerging due to the logistical, financial, and capacity challenges of gathering and interpreting data in this diverse, dispersed and informal sector. Peskas was designed as a low-cost solution to tackle this problem, providing a template workflow for ingestion and analysis to a decision dashboard, which can be adapted to different contexts and needs.

Sablefish (Anoplopoma fimbria) of the Northeast Pacific support a highly mobile, valuable fishery resource currently managed as three separate populations. Recent work has shown sablefish to be genetically mixed; have high movement rates; and have synchronous biomass trends, including recent declines. A management strategy evaluation was developed with stakeholders and scientists from three regions to investigate whether spatially structured management paradigms might result in better conservation and economic outcomes. The management strategy evaluation includes a transboundary operating model to represent spatial population dynamics including movement and a delay–difference estimation method with varying spatial complexities and potential stratifications, and harvest control rules. Mismatches in the spatial scale of management and the underlying biological units pose a crucial risk of localized depletion in the southern U.S. West Coast. This study presents one of the first transboundary, spatially-explicit management strategy evaluations conditioned to actual data. These results underscore the importance of spatial management strategy evaluation tools and implications when regional management is conducted in isolation. Future work should incorporate additional spatial hypotheses and investigate the drivers of recruitment patterns range-wide. [ABSTRACT FROM AUTHOR]

Current estimates of the threatened southern distinct population segment of the North American green sturgeon (Acipenser medirostris) combine a plot-sampling density estimator with Dual frequency IDentification SONar (DIDSON) and adaptive resolution imaging sonar (ARIS) sonar data. From 2020 to 2022, we annually collected images of all known green sturgeon aggregations and compared the established method to an N-mixture model using side-scan sonar images. We compared 18 different N-mixture model combinations and chose an overdispersed Poisson model that produced estimated abundances of 742, 1286, and 1208 for 2020–2022, respectively. These numbers are ∼2 times greater than the previous method and, if sustained, would fulfill a key criterion for green sturgeon recovery. N-mixture models are known to be sensitive to violations of assumptions, such as the highly dispersed data from our study that caused serious issues, and we recommend practitioners make judicious use of overdispersion and goodness-of-fit tests and be able to identify parameter confounding between detectability and abundance estimates. For our green sturgeon, we recommend simpler population estimates and to focus future energy on reducing variability in the data collection process. [ABSTRACT FROM AUTHOR]

Mohale, H.P.; Jawahar, P.; Jayakumar, N.; Swapnil, N.; Kadam, R.V.; Prakash, P.; Oli, G.A., and Ravikumar, T., 2024. Fishery, biology, and dynamics of Parapenaeopsis maxillipedo (Alcock, 1905) off the SE coast of Tamil Nadu (India). Journal of Coastal Research, 40(4), 779–791. Charlotte (North Carolina), ISSN 0749-0208. The current study was carried out between September 2022 to September 2023 from SE coast of Tamil Nadu for Parapenaeopsis shrimp. This shrimp, estimated to rank third in shrimp production, landed as 2216, 2032, and 1704 kg from Thoothukudi, Mandapam, and Nagapattinam landing centers, respectively. The catch per unit effort was calculated to check the abundance of this species and ranged from 21.83 to 96.41 kg, averaging 46.33% in both years. The total length of males and females was observed in the range of 5.5 to 10.5 cm and 6.5 to 12.5 cm, respectively. Female shrimp attained first maturity at 6.5 cm, whereas male shrimp were 5.5 cm. The gonadosomatic index was calculated and found to be the highest (5.64–5.78) in March and September and the lowest in April and October for both years. The absolute fecundity for P. maxillipedo was recorded and ranged from 38,500 to 1,32,000 ova per female. The highest index of relative importance was observed in October and April for both male (57.04) and female (73.82) shrimp. To estimate von Bertalanffy's growth equation in P. maxillipedo, the asymptotic length and growth coefficient (K) growth parameters were combined for both sexes and analyzedas 13.55 cm and 1.5 y–1, respectively. The total mortality and natural mortality (M) were observed as 3.04 and 2.86 y–1, respectively. Hence, fishing mortality was 0.18 y–1, and the exploitation rate (E) was 0.06. The length at first catch per length (LC/L) and M/K values were calculated using the Y/R model as 0.52 and 1.2 for males and 0.48 and 1.3 for females, respectively. E was observed as 0.06, which was lower than the maximum E of 0.4, which showed that the P. maxillipedo fisheries along the SE coast of Tamil Nadu were at unexploited conditions. [ABSTRACT FROM AUTHOR]

The marine fisheries of Bangladesh have experienced an uncontrolled expansion of fishing over the last few decades. Consequently, most fish stocks became vulnerable to overfishing. Similar to many other fisheries, catch of white sardine (Escualosa thoracata) is rapidly declining. Therefore, three data‐limited approaches (length‐based Bayesian biomass analysis, LBB; length‐based spawning potential ratio, LB‐SPR; and Froese's length‐based indicators, LBIs) were used to estimate growth, mortality, and fisheries reference points to evaluate stock status of the white sardine fishery. Results revealed that the fishery is being overfished: F/M = 1.32 years−1 in LBB and 6.67 years−1 in LB‐SPR. However, the stock biomass is still good with B/B0 = 0.43 and B/BMSY = 1.20. Stock indicators revealed that the fishery was mainly targeting mature fishes, most of which were mega‐spawners (older, larger fish), which suggested stocks were recruitment overfished. Harvesting an optimum size range (6.57 to 8.03 cm) and reducing fishing mortality to a sustainable level (F = M) would sustain a healthy stock biomass. [ABSTRACT FROM AUTHOR]

Objective: The common whelk Buccinum undatum is of great commercial and ecological importance, but little information is known regarding the gear selectivity of the fishery. Understanding gear selectivity is key for the long‐term sustainability of a stock and has applications in stock assessments and fishery management. Methods: We investigated the effect of gear (pots) on the selectivity of catch within the common whelk commercial fishery through a mark–recapture study and comparative gear trials across Wales. The size composition of the population in the water was estimated by dividing the numbers at size brought onboard by the selectivity of the pots. The selectivity of experimental pots (commercial pots that were modified to catch a wider size range) was estimated by comparing the size composition of whelks caught in the experimental gear to the estimated size composition of the population. Result: Peak selectivity of commercial pots occurred around the current minimum landing size (65 mm total shell length) for common whelks, with selectivity sloping off gradually for larger individuals and rapidly for undersized individuals. Across regions, less than 30% of the catch from baited lay‐down pots was discarded. Experimental pots were found to have a more variable but generally dome‐shaped selectivity curve similar to that of the commercial pots. Conclusion: The fishery appears to be well designed, with gear successfully targeting the legal‐sized catch, which is promising for the conservation of the stock if discards have a high survival rate. Experimental gear is ideal for stock assessment purposes, and methods developed to estimate the selectivity of the experimental pots reduce the need for further intensive mark–recapture studies as fishing gear evolves over time. Impact statementThe common whelk is regarded as a data‐poor stock; other than total landings, little information is currently known about the fishery. This study used mark–recapture surveys and comparative gear trials to estimate the selectivity of whelk pots and to determine the composition of whelks in the population. Our findings will facilitate the ongoing development of management strategies for this commercially important species. [ABSTRACT FROM AUTHOR]

Japanese flounder Paralichthys olivaceus is one of the most important coastal fish species in Japan. However, its catch in the southwestern Sea of Japan has been decreasing. Therefore, there is a need to improve the accuracy of stock assessment. Catch-at-age, which is the basis for stock assessment, is calculated based on the length–frequency distribution using age-length keys. It is recommended that this basic information is revised annually. However, the information for this species has not been updated for a relatively long period. In this study, growth curves were estimated and compared with those recorded from other areas. A multinomial logistic age-length key was generated and compared with the classical catch-at-age calculation method to examine potential errors. On the basis of the results obtained, a sex-specific von Bertalanffy growth curve was selected using the Bayesian information criterion. A model of sex and season was chosen for the multinomial logistic age-length key. The relative error was smaller and the estimated age composition was more accurate with the multinomial logistic age-length key, even when data with missing values were used. The improved accuracy of catch-at-age achieved due to the superior characteristics of the multinomial logistic age-length key is expected to be useful for the advancement of stock assessment. [ABSTRACT FROM AUTHOR]

Despite continued calls for the application of ecosystem‐based fisheries management, tactical fisheries management continues to be heavily reliant on single‐species stock assessments. These stock assessments rarely quantitatively integrate the effects of ecosystem processes on fish stock productivity. This lack of integration is ultimately driven by the complexity of interactions between populations, ecosystems and fisheries, which produces uncertainty when defining which processes to include and how to include them. Models developed using a structured hypothesis testing framework would allow formalizing uncertainties while underscoring the importance of incorporating different population and ecosystem processes to explain non‐stationary stock productivity. Here, we develop a conceptual framework for extending and comparing population dynamics models of increasing complexity. We illustrate the utility of the framework by investigating the population and ecosystem processes that most likely affected the differential recovery of two flatfish populations (American plaice and yellowtail flounder) on the Newfoundland Grand Banks over the past three decades. We found that yellowtail flounder population dynamics were primarily driven by recruitment variability, which was negatively affected by warmer climatological conditions, as indicated by an integrated regional climate index. Meanwhile, American plaice population dynamics were affected by a combination of temporal variability in recruitment and natural mortality, where natural mortality increased during colder than average conditions. By exploring hypotheses about the effects of population and ecosystem processes on population dynamics, this modelling framework will improve understanding about the drivers of shifts in population productivity while serving as a transparent and robust approach to support ecosystem‐based fisheries management. [ABSTRACT FROM AUTHOR]

This paper outlines the principal challenges confronting fisheries resources and their management in the South China Sea through summarizing resource characteristics in each fisheries zone. It is evident that the South China Sea stands as China's most productive sea in terms of fisheries resources. Nevertheless, economically significant species in the northern fisheries zone are currently facing a critical issue of resource over-exploitation. Conversely, there is substantial development potential in the outer sea. In the South China Sea's current fisheries management, the fishing moratorium system has restored major economic species before reopening. Yet, its impact is limited, necessitating additional research and survey data to conclusively assess its effectiveness. Future studies are imperative for a comprehensive evaluation of the moratorium system's ability to sustain fisheries resource rehabilitation. The management and conservation of fishery resources face substantial challenges due to human activities, climate warming, ocean acidification, reliance on outdated stock assessment methods, etc. Achieving sustainable use of fishery resources in the South China Sea is of great significance, and this can be accomplished through developing reasonable measures for the conservation and management of fishery resources, conducting comprehensive resource surveys, and employing appropriate methods for stock assessment. [ABSTRACT FROM AUTHOR]

The China government has introduced many strategies in fisheries management of the Yellow Sea and the Bohai Sea, the most stringent of which is the summer fishing moratorium. Whether the summer fishing moratorium can restore fishery resources has always been a concern. In this study, we selected eight representative commercial fish species the Yellow Sea and Bohai Sea, including Pampus argenteus, Trichiurus lepturus, Scomberomorus niphonius, Ilisha elongata, Thamnaconus modestus, Scomber japonicus, Engraulis japonicus and Larimichthys polyactis, and used the JABBA method to study their historical exploited dynamics and current stock status. We evaluated the effectiveness of the summer fishing moratorium based on the increments of biomass and catch after its implementation and adjustments. P. argenteus and S. niphonius stocks were in the healthy status in 2022, the other six fisheries stocks were overexploited. The summer fishing moratorium had a strong conservation effect, especially after the first implementation in 1995, with the biomass of six fish species increased and the catch of seven species increased, and the total average biomass and catch increments were 21.22 % and 89.72 %. This positive effect was also reflected after the first adjustment in 2003. Although the moratorium duration was continuously extended after the second and third adjustment, the conservation effect was offset by the flooding of fishing efforts immediately after the moratorium. For the six overexploited stocks, we suggest that the allowable catch of E. japonicus, T. lepturus, L. polyactis, S. japonicus, I. elongata and T. modestus is at most 527.91 kt, 147.51 kt, 93.43 kt, 81.51 kt, 1.25 kt and 4.95 kt in the Yellow Sea and Bohai Sea, respectively.

European pilchard (Sardina pilchardus), herein referred to as “sardine” or “European sardine”, is the most productive and economically important small pelagic fish in the Northwest African waters. Thus far, very little is known about its stock status in the West African region despite the rapid decadal increase in its catch production. The present study provides avenues vital to improving guidance for sustainable species management. In this region, sardine is divided administratively into three stocks (northern: stock N, central: stock A + B, and southern: stock C). Thus, the present study used two Surplus Production Models (SPM) to evaluate sardine's stock status. Sardine's catch and scientific survey biomass data obtained from FAO-CECAF's (Fishery Committee for the Eastern Central Atlantic (CECAF)) latest reports were used in this analysis to fit the SPMs and investigate the effectiveness of the available catch-per-unit-effort (CPUE) trends in setting the total allowable catch (TAC) for sustaining the different sardine stocks in the region. Results from the SPMs indicate that the sardine stock in the north is fished at optimum levels. Meanwhile, the SPMs output based on the scientific survey biomass indices indicated a healthy state for the central and southern sardine stocks. Similarly, the fishery CPUE indices for the central and southern stocks showed similar biomass trends compared to the survey biomass index, indicating healthy stock status. Therefore, in cases where survey biomass index data is unavailable to run stock assessments, this study suggests that sardine fishery CPUEs could be used in SPMs to monitor biomass trends over time and may also provide stock status proxies. Additionally, with rapid climate and other environmental changes, sardine stocks must be regularly monitored with consistent and comparable scientific methodologies and updated fisheries time series data.

Abstract This study examined the growth patterns of the spotted catfish, Arius maculatus (Thunberg, 1792) in the Thanlwin River Estuary throughout the analysis of standard lengths obtained from observed otolith data and back‐calculated data. Between April 2023 and January 2024, 516 fish ranging in standard lengths from 8.3 to 33 cm were collected. The annual deposition of annuli in otoliths was confirmed using the marginal increment ratio, with ages ranging from 2 to 9 years. The Dahl‐Lea back‐calculation method expanded the length at age data to 2472 records for ages 1–9 years. Growth was characterized using Von Bertalanffy growth curves, revealing the significant differences between the observed data (asymptotic length L∞ = 25.34 cm, growth coefficient K = 0.257 year−1 and growth performance index ϕ′ = 2.02) and the back‐calculated data (L∞ = 36.23 cm, K = 0.087 year−1 and ϕ′ = 2.21). The findings of the study suggested that the back‐calculated otolith data were more dependable for determining growth parameters compared to the observed otolith data. A. maculatus appears to exhibit slow growth characteristics, suggesting that the environmental conditions in the Thanlwin River Estuary may be deficient for this species. The insights gleaned from this research are crucial for guiding and shaping fishery management policies through informed advice and recommendations.

The study investigated the growth, mortality, exploitation rate and recruitment of Fringescale sardinella (Sardinella fimbriata Valenciennes, 1847) found in Malampaya Sound, Palawan, Philippines. A total of 1200 samples were collected from April 2023 to March 2024. The relationship between length and weight was expressed as y = 0.0291 x 2.561 for combined sex, y = 0.0404 x 2.4254 for males, and y = 0.0355 x 2.4856 for females. The resulting b values pinpoint to a negative allometric growth. The calculated regression model showed a significant association during which the p-values were below 0.0000 and the r2 values ranged between 0.76 and 0.79. Estimation using the FISAT II software resulted in an asymptotic length (L∞) = 16.28 cm, growth rate (K) = 0.68 yr-1, maximum length (Lmax) = 15.78 cm, theoretical age at birth (t0) = –0.5515 years and growth performance index (ɸ’) = 2.256. The estimated average total mortality rate (Z), natural mortality (M), and fishing mortality (F) were 2.69, 1.68, and 1.01 per year, respectively. Recruitment occurs throughout the year and peaks in June. It can be noted that the exploitation is calculated as 0.38, which is considered lightly exploited. To have a sustainable population and avoid overfishing, an optimum total yield (E50) can be set at an exploitation rate of 0.278. The maximum yield (Emax) is at an exploitation rate of 0.421.

Widas Reservoir is situated in an area of 570 ha in the Pajaran Village, Madiun Regency, East Java Province, Indonesia, playing an essential role in fisheries, with the average fish catch per year of about 283 tons/year. This study explores the standing stock, growth parameters, mortality, and exploitation rates of several dominant fishes in Widas Reservoir. This study was carried out from February to November 2019. Fish stocks were estimated using acoustic tools, fish catch records, and sizes collected by local enumerators. Fish length frequency sampling was conducted on several dominant fish species, such as Oreochromis niloticus, Barbonymus gonionotus, and Osteochilus vittatus. Based on the length-frequency data, estimating fish population dynamics, the fish population dynamics (infinitive length (L∞) and growth coefficient (K)) estimation was run in a time series using the Fish Sock Analysis Tool, II (FISAT II) program package. Moreover, the estimation of natural mortality parameters, the fishing mortality parameter, and the exploitation rate was also performed. The approximated overall fish stock in the Widas Reservoir was about 79,848 kg, which lowered with the increase in water depth. Of particular concern, in the surface layer at a depth between 1–5 m, the fish stock reached 58,813 kg, while in the deeper zone (> 15 m), the value significantly lowered by about 98%, reaching 1,219 kg. These results indicate an overfishing in the Widas Reservoir. The value of the exploitation rate (E) of B. gonionotus was 0.748, O. niloticus 0.8, and O. vittatus 0.7, respectively, proving the overfishing states occurred in the study area. Therefore, regulations governing the number of catches and the use of fishing gear are crucial in Widas Reservoir, particularly the use of lift and gill nets with a mesh size of less than 2 cm.

Pampus argenteus and Pampus chinensis form the high-value demersal Pomfret fishery of Bangladesh. But, due to a monotonic decline in catches over the last five years, it is essential to explore the current stock status concerning the removal rate to ensure the sustainability of this fishery. Therefore, given the reliability and minimal data requirements, this study employed an extended Bayesian State-Space Surplus Production Model, JABBA (Just Another Bayesian Biomass Assessment), to assess the stock rigorously. The results revealed that the stock biomass of the Pomfret fishery in the final year of the time series is significantly lower than BMSY, the biomass required to produce MSY. Consequently, this study recommends a yearly catch limit (TAC) of 10,000 metric tons to prevent further depletion of the stock biomass. Furthermore, to avoid growth overfishing by allowing all immature fishes to reproduce at least once before being caught, this study also calculated the optimum length (Lopt) for catch for both species at which biologically maximum yield and revenue can be obtained. The estimated Lopt is 25 cm for P. argenteus and 30 cm for P. chinensis, and not to capture fishes with lengths lower than these limits, this study further calculated the minimum mesh size limits for gill and set bag nets is 7.5 cm. Though the mesh size regulation was estimated using length-based reference points derived from an empirical equation, this regulation can be used as an associate reference point when TAC is applied to assure the sustainability of this fishery.

Accurate estimation of fish stock abundance and exploitability is critical for effective fishery management; however, fishery-dependent data are often affected by temporal and spatial heterogeneities due to the seasonal migration of fish, posing challenges for refined stock management. Previous studies have largely ignored these spatio-temporal dynamics, assuming static populations. This study develops a seasonal spatio-temporal model for Japanese sardine (Sardinops melanostictus) in the Northwest Pacific Ocean (NPO), using fishery-dependent data from 2014 to 2022. Seasonal standardized abundance indices (spring, summer, autumn, and an overall average) were generated and integrated with the abundance maximum sustainable yield (AMSY) method for stock assessment. The performance of the AMSY method using a spatio-temporal index was compared with the conventional model-based index, showing the superiority of the spatio-temporal approach. Results indicate a gradual increase in sardine abundance, with a significant shift in the center of gravity toward the northeast. The stock is in a sustainable state with a 94.8–99% probability of recovery. Although the stock is recovering, careful management is advised to prevent future declines. This framework offers a novel approach for assessing distant water and coastal fishery resources.

Stock depletion level is an important concept in the assessment and management of exploited fish stocks because it is often used in conjunction with reference points to infer stock status. Both the depletion level and reference points can be highly dependent on the stock–recruitment relationship. Here, we show how depletion level is estimated in stock assessment models, what data inform the depletion level, and how the stock–recruitment relationship influences the depletion level. There are a variety of data that provide information on abundance. In addition, to estimate the depletion level, unexploited absolute abundance needs to be determined. This often means extrapolating the abundance back in time to the start of the fishery, accounting for the removals and the productivity. Uncertainty in the depletion level arises because the model can account for the same removals by either estimating low productivity (e.g., low natural mortality) and high carrying capacity or high productivity and a low carrying capacity, and by estimating different relationships between productivity and depletion level, which are strongly controlled by the stock–recruitment relationship. Therefore, estimates of depletion are particularly sensitive to uncertainty in the biological processes related to natural mortality and the stock–recruitment relationship and to growth when length composition data are used. In addition, depletion-based reference points are highly dependent on the stock–recruitment relationship and need to account for recruitment variability, particularly autocorrelation, trends, and regime shifts. Future research needs to focus on estimating natural mortality, the stock–recruitment relationship, asymptotic length, shape of the selectivity curve, or management strategies that are robust to uncertainty in these parameters. Tagging studies, including close-kin mark-recapture, can address some of these issues. However, the stock–recruitment relationship will remain uncertain.

Spatial scales are important for examining health of exploited fishery stocks and guiding management actions. However, information about the optimal spatial scale is still unclear for assessment of transit fisheries, such as elver fisheries of the American eel Anguilla rostrata. We applied a generalized depletion model to assess catch and effort data from three nearby rivers (within 50 km) to test the hypothesis that modeling on pooled and separate data from nearby rivers would give similar estimates of abundance and exploitation rate. Overall, pooling data from rivers within 50 km did not result in large differences (<20% in relative difference) in estimates of abundance and exploitation rate with close mean abundance estimates and similar temporal trends in abundance, exploitation rate, and relative escapement. Pooling nearby river systems can greatly reduce modeling effort, at the cost of ignoring fine‐scale variability in elver recruitment and having coarser spatial scale for the management. When only an index of annual recruitment and exploitation rate are of interest, pooling data may be practical from different locations up to 50 km. [ABSTRACT FROM AUTHOR]

Environmental DNA and RNA (eDNA and eRNA; collectively eNA) analyses have the potential for non-invasive and cost-efficient biomonitoring compared with traditional capture-based surveys. Although various types of eNA particles, including not only mitochondrial eDNA but also nuclear eDNA and their transcripts, are present in the water, performances of eNA detection and quantification have not yet been evaluated sufficiently across multiple mitochondrial and nuclear genes. We conducted a tank experiment with ayu (Plecoglossus altivelis) to compare the detection sensitivity, yields per water sample, and quantification variability between replicates of each type of eNAs. The assay targeting the multi-copy nuclear gene exhibited a higher sensitivity than the assay targeting the mitochondrial gene, and both the target eDNA and eRNA concentrations per water sample were higher for the nuclear gene. On the contrary, variation in eRNA quantifications per sample does not necessarily correspond to that in eDNA, and the intra-sample quantification variability (represented as the CVs between PCR replicates) tended to be larger for eRNA than eDNA. Our results suggested that, even if suitable to the sensitive detection of species occurrence, the use of eRNA particularly derived from multi-copy nuclear gene may not be necessarily appropriate for the reliable assessment of species abundance. The findings in this study would help optimize eNA analyses for making biomonitoring and stock assessment in aquatic environments more efficient and reliable. [ABSTRACT FROM AUTHOR]