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Density-dependent population dynamic models strongly influence many of the world's most important harvest policies. Nearly all classic models (e.g. Beverton-Holt and Ricker) recommend that managers maintain a population size of roughly 40–50 percent of carrying capacity to maximize sustainable harvest, no matter the species' population growth rate. Such insights are the foundational logic behind most sustainability targets and biomass reference points for fisheries. However, a simple, less-commonly used model, called the Hockey-Stick model, yields very different recommendations. We show that the optimal population size to maintain in this model, as a proportion of carrying capacity, is one over the population growth rate. This leads to more conservative optimal harvest policies for slow-growing species, compared to other models, if all models use the same growth rate and carrying capacity values. However, parameters typically are not fixed; they are estimated after model-fitting. If the Hockey-Stick model leads to lower estimates of carrying capacity than other models, then the Hockey-Stick policy could yield lower absolute population size targets in practice. Therefore, to better understand the population size targets that may be recommended across real fisheries, we fit the Hockey-Stick, Ricker and Beverton-Holt models to population time series data across 284 fished species from the RAM Stock Assessment database. We found that the Hockey-Stick model usually recommended fisheries maintain population sizes higher than all other models (in 69–81% of the data sets). Furthermore, in 77% of the datasets, the Hockey-Stick model recommended an optimal population target even higher than 60% of carrying capacity (a widely used target, thought to be conservative). However, there was considerable uncertainty in the model fitting. While Beverton-Holt fit several of the data sets best, Hockey-Stick also frequently fit similarly well. In general, the best-fitting model rarely had overwhelming support (a model probability of greater than 95% was achieved in less than five percent of the datasets). A computational experiment, where time series data were simulated from all three models, revealed that Beverton-Holt often fit best even when it was not the true model, suggesting that fisheries data are likely too small and too noisy to resolve uncertainties in the functional forms of density-dependent growth. Therefore, sustainability targets may warrant revisiting, especially for slow-growing species. [ABSTRACT FROM AUTHOR]

In this article, we have analyzed the effect of prey apprehension on a modified Leslie–Gower predator–prey fishery model with Allee effect on the prey population. We investigate the predator–prey dynamics for linear, Holling type II, and Holling type III functional responses of the predator and observed that the systems undergo a sudden change in dynamics from the coexistence steady state to the prey-free steady-state when the level of prey apprehension and the amount of harvesting effort surpass some threshold value. At a low intrinsic growth rate of the predator, the system with type II functional response exhibits a transcritical bifurcation when the harvesting effort crosses the threshold value. We study the dynamic optimization of the harvesting policy by employing Pontryagin's maximum principle under the three different functional responses of the predator and obtain the harvesting yields corresponding to the dynamic reference point OSY. We also examine the existence of the bionomic equilibrium corresponding to the open access (OA) scenario and compare the combined harvesting yield with the yields obtained from the static reference point MSY and the dynamic reference point OSY. We observe that OSY provides the maximum economic benefit to the fishery compared to MSY and OA. [ABSTRACT FROM AUTHOR]

The abundance dynamics of short-lived marine species often exhibit large-amplitude fluctuations, potentially driven by unknown but important species interactions and environmental effects. These complex dynamics pose challenges in forecasting and establishing robust reference points. Here, we introduce an empirical dynamic modeling (EDM) framework using time-delay embeddings to recover unspecified species interactions and environmental effects, and use walk-forward simulations with varying harvest rates to estimate maximum sustainable yield (MSY). Firstly, we apply our framework to simulated data under various dynamics scenarios and demonstrate the statistical robustness of EDM-based MSY. Secondly, we apply our framework to abundance and catch time series (>30 years) of federally managed brown shrimp stocks in the US Gulf of Mexico. We identify nonlinear signals and achieve high prediction accuracy in the empirical dynamics of brown shrimp. Lastly, based on the EDM of brown shrimp dynamics, we obtain MSY for timely and effective management. Our results highlight the utility of EDM in deriving reference points for short-lived species, particularly in situations where stock abundance and catch dynamics are influenced by unobserved species interactions and environmental effects in a complex ecosystem. [ABSTRACT FROM AUTHOR]

Maximum sustainable yield reference points (MSY-RPs) are usually calculated assuming spawner-recruitment relationships (SRR) and population dynamics of the stock. However, due to the difficulty of estimating SRR, the uncertainty in MSY-RPs is often too large to be put into practice. Therefore, based on the concept of maximum–minimum yield (MMY), fishing mortality (F) that gives %SPR (spawner biomass per recruitment [SPR] at a given F relative to SPR in the absence of fishing) of 30–50% (F30-50%SPR) is often used as a proxy of FMSY (F that maximizes the long-term catch). In this study, we estimated F % SPR MMY (F expected to produce %SPR at MMY) for 30 stocks of Japanese fishery resources based on the life-history parameters of the stocks and steepness assumptions derived from meta-analysis. Our results showed that %SPRMMY ranged from 23% to 62% (excluding 86% of Scomberomorus niphonius), depending on the stock and the assumed steepness scenario. If the fish were caught under F % SPR MMY , at least 70% of the MSY could be expected in Japanese fishery resources. When compared with the %SPRMSY for the 15 stocks estimated through Japanese fishery stock assessment, %SPRMMY were similar, or often larger. %SPRMMY can be considered a precautionary value, reflecting the uncertainty of SRR. [ABSTRACT FROM AUTHOR]

This study features the estimates of MSY (Maximum Sustainable Yield) of the commercial high-priced Spotted croakers (Protonibea diacanthus, Sciaenidae) of Pakistan by evaluating year-wise catch and effort data. Catch and effort data analysis (CEDA) and a surplus production model incorporating covariates (ASPIC) was applied to analyze data from 24 years (1986 to 2009) of catch and effort. The MSY was assessed using the initial proportion (IP) value of 0.9 because the starting catch was about 90% of the maximum catch. The calculated MSY values for the Fox model with three error assumptions of least square, log-transfer, and gamma were 4481 MTs, 4215 MTs, and 4443 MTs. In contrast, the results of MSY were the same in Schaefer and Pella-Tomlinson models as 7265 MTs and 7373 MTs, respectively. Except for Fox models, the gamma error assumption was presented with minimization failure for all models. The calculated MSY results from ASPIC analysis with the two surplus production models of Fox and Logistic were 4609 MTs and 8445 MTs when using an IP value of 0.9. The estimated output values of the Fox model from the CEDA packages, which were lower than the recent catch, indicate that the stock is in over-fished condition, but other analyses from Schaefer and Pella Tomlinson showed higher values than the recent catch indicate safer stock. Similarly, the MSY estimated values from the Logistic model were greater than the current catch. In contrast, from the Fox model of ASPIC analysis, they were also higher than the recent catch, revealing the stock is not under control. However, it is necessary to initiate specific managerial measures to maintain the current fishing effort of this species in Pakistani waters to protect the decreasing trend of the existing stock of P. diacanthus. [ABSTRACT FROM AUTHOR]

Natural ecological communities exhibit complex mixtures of interspecific biological interactions, which makes finding optimal yet sustainable exploitation rates challenging. Most fisheries management advice is at present based on applying the Maximum Sustainable Yield (MSY) target to each species in a community by modelling it as if it was a monoculture. Such application of single‐species MSY policies to strongly interacting populations can result in tragic overexploitation. However, the idea of 'maximising the yield from each species separately' can be extended to take into account species interactions. This leads to a form of Nash Equilibrium, where the yields of each species are simultaneously maximised. Here we present 'nash', an R package that streamlines the computation of Nash equilibrium reference points for fisheries and other systems represented by a user‐defined multispecies or ecosystem model. We present two real‐world fisheries management applications alongside performance benchmarks. Satisfactory search results are shown across models with an approximate factor 7 increase in performance when compared to the expensive round‐robbing sequential optimisation algorithms used by other authors in the literature. We believe that the nash package can play an instrumental role in fully implementing ecosystem‐based management policies worldwide. [ABSTRACT FROM AUTHOR]

Copyright of Marine Fisheries: Jurnal Teknologi & Manajemen Perikanan Laut is the property of IPB University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Jurnal Ilmu dan Teknologi Kelautan Tropis is the property of IPB University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The concept of maximum sustainable yield (MSY), and the underlying Schaefer model, remain relevant in fisheries management today in spite of past difficulties. However, this model is often applied without the consideration of the spatial structure or dynamics of fishing activities. We expand the Schaefer model to account for multiple fishing sites and fishing activities (effort) that follow an ideal free distribution (IFD, a form of Nash equilibrium) driven by exploitation. We explore this conceptual model using both analytical and numerical solutions. MSY across the fishery is unaffected by the spatial structure when fishing is allocated independently within sites. However, in other cases IFD effort dynamics depress MSY and modify the values of associated reference points. The game theoretic aspect of fleet dynamics should be considered in the use of MSY as a management reference point or during the application of the Schaefer model to data‐limited fisheries. Recommendations for Resource Managers: Fisheries where fishing activities move among spatially distinct stocks should be examined for the presence of ideal free effort dynamics.When fishing activities follow an ideal free distribution the maximum sustainable yield (MSY reference point may be less than that estimated without considering effort dynamics, but this depends upon the spatial scale of both effort and fish dynamics.Fishery models used to provide quantitative estimates of MSY should consider spatial effort dynamics when there is empirical evidence for equalization of profitability among sites fished (IFD dynamics). [ABSTRACT FROM AUTHOR]

Larger and older fish contribute disproportionately to spawning and play an important role in the replenishment of exploited stocks. Fishing often removes specific size‐ and age‐classes, with direct impacts on stock productivity and population resilience. Despite this, fisheries advice is commonly based on estimates of spawning stock biomass (SSB) and fishing mortality (F) and makes little reference to the importance of size and/or age structure. Consequently, there is a need for indicators of size and/or age structure to better inform fisheries management and help assess global sustainability goals. Here, we introduce a new age‐based indicator ABIMSY that monitors age structure relative to the equilibrium age structure at FMSY. We apply this new indicator to 72 commercially important stocks in the Northeast Atlantic, covering 26 species, which collectively contributed 86% of all commercial catches in the region in 2019. We estimate that 62% (45 stocks) currently have proportionally fewer older fish relative to FMSY conditions, whereas 38% (27 stocks) have proportionally more older fish; we also note patterns with respect to geographic area and taxonomic family. Simulation testing demonstrated that ABIMSY is responsive to overfishing and generally tracks (with high sensitivity and specificity) a common measure of stock depletion, SSB relative to BMSY. Throughout, we show that ABIMSY provides information on the age structure of exploited stocks that is complementary to conventional reference points for SSB and F. Further, the framework used to estimate ABIMSY make it well placed for integration into current advisory frameworks on fisheries management. [ABSTRACT FROM AUTHOR]

Copyright of Revista de Derecho Comunitario Europeo is the property of Centro de Estudios Politicos y Constitucionales and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Cirrhinus reba (Hamilton, 1822), commonly known as Reba carp, is an economically important freshwater species with high demand for its taste. It has been listed as vulnerable and near threatened species in India and Bangladesh, respectively. This study presents a pioneer assessment of the lengthweight relationship and population dynamics of Reba carp using a length-based approach over a threeyear period in the Indian part of the Atrai River. Fish specimens ranged from 50 to 237 mm in length and from 0.90 to 184.19 g in weight. Results indicate positive allometric growth, with a unimodal continuous recruitment pattern peaking between June and August. Population parameters, including asymptotic length (L8 = 250.95 mm), growth coefficient (K = 0.44 year-1), growth performance index (f' = 4.442), length at first capture (Lc = 83.77 mm), and size at first sexual maturity (Lm = 110 mm), were computed. This study revealed a higher fishing mortality rate compared to natural mortality, with the mean current exploitation rate (E = 0.63) surpassing Emax = 0.541, and the highest exploitation rate observed in 2022. Consequently, the annual yield exceeded the Maximum Sustainable Yield limit, underscoring the urgent need to mitigate fishing pressure, especially during the breeding season, to promote stock replenishment and ensure sustainability. [ABSTRACT FROM AUTHOR]

We present a bioeconomic fishery model with variable price based on supply and demand. The model considers three variables: resource biomass, fishing effort, and market price. Rapid price changes classify the fishery system as a slow–fast system. Two main cases arise: catastrophic equilibrium (CE) with overexploitation and fish extinction, and a sustainable fishery equilibrium. We aim to determine conditions for maximum sustainable yield by optimizing cost per unit of fishing effort. Additionally, we explore conditions to prevent extinction and restore sustainable fishing. Marine protected areas (MPAs) can restore fish stocks by destabilizing the CE and maintaining a stable positive equilibrium. A model incorporating an MPA and fish movement is proposed, suggesting a small carrying capacity-to-surface area ratio in the fishing zone. Optimal total catch can be achieved by selecting the appropriate MPA surface area. [ABSTRACT FROM AUTHOR]

Statistical estimates for the exploitable stock of giant grenadier are determined, by fishing zones in the Russian Far East, and interannual dynamics of the species biomass is considered using historical data on catches and abundance. The assessments relationship with reference points of the biomass dynamic models is examined for the first time. With using the Bayesian approach, a priori assumptions about virgin biomass, which were made earlier on results of scientific surveys extrapolated to unsurveyed areas, are accounted in JABBA model; some errors in the catch and abundance indices are revealed. The parameters of instantaneous rate of recruitment and initial depletion of population are determined. Overfishing is not detected yet in any fishing zone, but a negative trend of the biomass dynamics is noticed for the Western Bering Sea fishing zone since 2015 (if the stock estimations based on surveys are realistic). The decline is reasoned by implementation of too high target for exploitation rate of vulnerable biomass (φF = 0.10) that is higher than such target for other fishing zones (< 0.08 or even 0.01 for the stocks exploited with the total allowable catch limits). That’s why annual catches exceeded the surplus production in the Western Bering Sea fishing zone in 2012 and since 2015 to nowadays. The sum of median estimations for the maximum sustainable yields in all fishing zones is about 47.4 . 103 t that exceeds the values of total annual catch. The instantaneous rate of recruitment is almost equal in the neighboring fishing zones in the western Bering Sea and at East Kamchatka (0.086–0.085 by median, with 95 % credible intervals from 0.05 to 0.14) and is much higher at Kuril Islands with the maximum in the North-Kuril fishing zone. The latter case is possibly conditioned by partially external recruitment. Therefore, population structure of giant grenadier should be clarified for correct modeling of the recruitment; until then, the stocks assessments by fishing zones are available.

Of the types of fishery models that use time series of removals, fishing effort, and indices of abundance, two-stage-structured models are less prevalent, especially in developing the maximum sustainable yield (MSY) benchmarks, in part because of ignorance of how to calculate those benchmarks. To fill this gap, this study aims to derive analytical expressions for calculating MSY benchmarks associated with a continuous delay-differential model, given that the recruit stage relates to the spawning-stock biomass (SSB) according to a stock–recruit relationship (SRR) and that the SRR parameters are combined with the components of the composite (two-stage-structured or age-aggregated) yield per-recruit model CYPR14. The focus is on analytical expressions of the fishing mortality producing MSY (FMSY), considering that the equilibrium yield comes from either the equilibrium SSB at the start of fishing regimes or the equilibrium average SSB during fishing regimes. The expressions obtained are versatile for all two-stage-structured models. Derivations employing the fished equilibrium average SSB are recommended for use because they produce precautionary MSY benchmarks and because they are consistent with their counterparts in contemporary age-structured stock assessment models. [ABSTRACT FROM AUTHOR]

Fish stocking in inland fisheries involves a prey–predator interaction model so that the number of fish stocked affects optimal and sustainable yields. It is very important to make mathematical modeling to optimize inland fisheries management which is part of the blue economy. Currently, studies that focus on predator–prey mathematical modeling in inland fisheries, especially those related to insurance are lacking. The bibliometric database was taken from Google Scholar, Dimensions, Science Direct, and Scopus in the 2012–2022 research years. After further processing, it is displayed on the PRISMA diagram and visualized on VOSviewer to display the update of this research topic. As blue economy sustainability, the management of fisheries sector needs to be reviewed deeply. In this study, the assumptions of the predator–prey mathematical model are made to obtain the equilibrium point, maximum sustainable yield (MSY), and catch per unit effort (CPUE) values. These results can be used to calculate fisheries insurance as a strategy for optimizing sustainable fishermen's income. [ABSTRACT FROM AUTHOR]

There is evidence that the European hake is one of the main target species of demersal fisheries in the Western Mediterranean and has been widely exploited for decades; the potential for overfishing is very high. The purpose of this study was to evaluate the stock assessment and the age validation of European hake (Merluccius merluccius Linnaeus, 1758) in the GFCM/GSA 04 (Algerian eastern coast) in order to provide a management strategies and effective control measures. A total of 662 hake specimens were sampled from commercial landings from January 2021 to December 2021. The sex ratio was in favor of females (54.8%) but there were no differences in mean lengths between sexes. The estimated total mortality rate (Z) and the natural mortality (M) were 1.48 year− 1 and 0.41 year− 1, respectively. The estimated instantaneous rate of fishing mortality (F) was calculated as 1.06 years− 1, with an exploitation ratio of 0.72, which suggests that the stock in GSA 04 area could be overexploited (E > 0.5). The fishing mortality rate F = 1.06 is higher than the fishing mortality for maximum sustainable yield (Fmax = 0.43) corresponding to the fisheries mortality rate factor that maximizes equilibrium yield per recruit; hence the hazard ratio of the stock is being overfished. To limit the risk of stock collapse, adjustment of the Fcurrent fishing effort factor to F0.1 (0.29) is essential, it should be reduced by 77% the fishing effort to increase by long term exploitable biomasses of hake stock and allow the renewal of the resource. The findings reported here provide new key instruments for the stock assessment of this species and thus contribute to it conservation. [ABSTRACT FROM AUTHOR]

The optimal management and utilization of natural resources is eventually important, due to increase in the consumption of natural resources and in view of this, the main aim of fisheries is to maintain the marine organisms at levels that produces maximum sustainable yield (MSY). In this study, the one step numerical approximations schemes are developed to find the solution of such bioeconomic fisheries models whose analytical solution is not possible. In the proposed work, the explicit Runge-Kutta scheme based on fourth order tetra geometric mean is established and this method solve fishery management models of Schaefer and Gordon-Schaefer. The models analyze bioeconomic growth rate, carrying capacity, total and marginal costs and revenues. In solving, the models through proposed tetra geometric mean Runge-Kutta method, it is obtained that the method is easy to implement. The results obtained are much better as compared to other methods when compared in terms of errors and central processing unit (CPU) time. [ABSTRACT FROM AUTHOR]

To address the issue of overfishing, sustainability and its effect on marine fishers' income, this study was taken up in Mumbai, India. Greater Mumbai was studied at micro level. Primary data on capital costs, operating costs and returns to mechanized fishing were collected. Secondary data on marine fish landings, landings from the trawlers and total effort of trawlers was collected from 2000 - 2018. The Gompertz-Fox Model was used, and results showed that Maximum Sustainable Yield (MSY) was at 1,04,099 tonnes of fish and effort level corresponding to MSY (EMSY) at 43,363 fishing trips against the current 1,31,118 tonnes and 33,466 trips. Maximum Economic Yield (MEY) was calculated to be 1,03,030 tonnes, while the estimated value of effort (EMEY) was 37,429 trips. Therefore, the current fishing yield was found to be both biologically and economically unsustainable. The study concluded that the catch and income of fishers may be sustainably enhanced by following the MSY and MEY approach. Fishing at MEY will yield increased income in real terms as well as saved catch will ensure minimisation of environmental damage. Reducing the input costs will enable savings on wasteful operational costs, resulting in increased savings, which in other words, is income, since averted loss is income earned. [ABSTRACT FROM AUTHOR]

Excessive fuelwood harvest is a major cause of deforestation in developing countries. To mitigate this, various preventive measures have been introduced in different countries. The availability of affordable substitutes to the community dependent on the forest for domestic energy consumption may prevent further forest degradation. A stock-dependent optimal control model of fuelwood harvest from a natural forest is presented here and comparative statics has been used to show that the presence of a fuelwood substitute will reduce its harvest and increase the forest stock. The model indicates that the availability of cheaper and high-energy content alternatives for fuelwood can substantially reduce fuelwood extraction from a forest. Also, a lower discount rate and higher cultural and spiritual values (CSV) will keep the optimal forest stock close to its carrying capacity and reduce fuelwood harvest. The model reveals that the maximum sustainable yield of forest stock and the ratio of energy content per unit mass of fuel plays a central role in the fate of forest stock and the level of fuelwood harvest. An empirical example of the Southeast Asian Forest growth model along with Liquid Petroleum Gas (LPG) as a substitute has been used to illustrate the results. The outcomes of this study can be incorporated into forest conservation policies.

Climate change is projected to affect the productivity of global fisheries. Management based on maximum sustainable yield (MSY) has been effective at eliminating overfishing in many regions. However, continuing to use yield‐maximizing targets under climate‐driven changes in productivity can result in higher anthropogenic pressure on populations subject to climate‐related stress than maintaining status quo management targets. We demonstrate this effect using a theoretical example and case studies from snow crab in the eastern Bering Sea and a global marine fisheries database. In these examples, the conservation gain (i.e. biomass in the ocean) of maintaining status quo management targets is larger than the small gain in harvest made through climate adaptation in MSY‐based management. The aggregate conservation gain of maintaining management targets increases as the harmful impacts of climate change on productivity worsen. Instead of climate‐adaptive MSY‐based targets, new management tools are needed to balance conservation and food production in ecosystems of populations displaying non‐stationary productivity. [ABSTRACT FROM AUTHOR]

In the context of the general overexploitation of South Pacific reef fisheries, there is a global push to precisely define fishery parameters such as fishing effort, annual landings, and exploitation levels. In Bora-Bora, several surveys were performed to define the fishing grounds and the fishing effort of the reef fishery for the first time. Maps of the fishing grounds under different fishing pressures were created for the Bora-Bora reef fishery. The average fishing effort throughout the lagoon was 40 trips week−1 km−2. Annual landings were estimated following two different methods: school participatory surveys and landing based on the catch per unit effort. These estimations were used to determine that the maximum sustainable yield of the island's fisheries was 6.5 tons km−2 year−1. the reported annual yield in 2022 was 5.35 tons km−2 year−1, under the estimated maximum sustainable yield. The level of exploitation of the fisheries was also estimated based on the catch size composition of the ten most fished species. This revealed that fishing is responsible for more than 50% of fish mortality in six of the ten studied species, and that catch length could be increased to optimize both catches and biomass. Overall, the Bora-Bora reef fishery may be experiencing growth overfishing (i.e., the catching of fish that are too small to maximise biological sustainability and economical yield), which can endanger stock recruitment in the future if no actions are taken.

Ayu Plecoglossus altivelis altivelis is a key commercially and culturally important freshwater osmeroid in Japan. Its native population is mostly an amphidromous form migrating between rivers and the sea, and not only native but also artificially landlocked forms are found in lakes and dam reservoirs. This study was undertaken to execute population feasibility and maximum sustainable yield (MSY) analysis of an artificially landlocked form of ayu during January 2018 to December 2020 in the Haidzuka reservoir and its connected Tabusa River, western Japan. FAO-ICLARM Stock Assessment Tools-II and empirical models were employed to estimate the growth function and population parameters. The estimated asymptotic length was 19.50 cm, and the growth coefficient was 0.73 year−1 with a growth performance index of 2.443. The length at first maturity and length at optimum yield were calculated as 10.77 cm and 12.63 cm, respectively, which were lower than the length at first capture (Lc = 13.15 cm), suggesting the mesh size of fishing gear favoring the sustainability of the reproductive potential of this population. The calculated total, natural, and fishing mortalities were 2.45, 1.19, and 1.26 year−1, respectively. The recruitment pattern was continuous round the year with two pulses where the peak was during July. The current level of exploitation (0.51) was slightly higher than the maximum exploitation rate (0.45), indicating a little overharvesting. The MSY of ayu in the Haidzuka reservoir was estimated to be 211 metric tons if the recommended Lc is maintained. Results of this study illustrate the first information on population characteristics of landlocked ayu and will help the development of suitable management policies for ayu fishery in lakes and dam reservoirs. [ABSTRACT FROM AUTHOR]

This work presents a model of a harvested population in a multisite environment. Locally it has the shape of the Gordon-Schaefer model. This model gives rise, placing us in the case of a fishery, to an equilibrium of the stock and the fishing effort and, therefore, of the yield that is obtained per unit of time. Considering that the management of the fishery can act on the fishing costs, the yield is optimized as a function of the cost. The objective of the work is to compare the maximum obtained yield in two extreme cases: unconnected sites and connected sites with rapid movements of both the stock and the fishing effort. The analysis of the model, first in an environment with two sites and later with any number of them, makes it possible to establish the conditions for one of the two cases to be more favorable from the point of view of the yield. In this way, it is proposed towards which of the two compared cases management should be directed. [ABSTRACT FROM AUTHOR]

The International Council for the Exploration of the Sea (ICES) has provided scientific stock advice based on reference points to manage fisheries in the North Atlantic Ocean and adjacent seas for decades. ICES advice integrates the precautionary approach with the objective of achieving maximum sustainable yield. Here, we examine ICES reference point evolution over the last 25 yr and provide a comprehensive empirical review of current ICES reference points for data-rich stocks (Category 1; 79 stocks). The consistency of reference point estimation with the ICES guidelines is evaluated. We demonstrate: (1) how the framework has evolved over time in an intergovernmental setting, (2) that multiple precautionary components and sources of stochasticity are included, (3) that the relationship and historical context of stock size and recruitment are crucial for non-proxy reference points, (4) that reference points are reviewed frequently, taking into account fluctuations and multiple sources of variability, (5) that there are occasional inconsistencies with the guidelines, and (6) that more comprehensive and clearer documentation is needed. Simplifying the stock-recruit typology and developing quantitative criteria would assist with this critically important classification. We recommend a well-documented, transparent, and reproducible framework, and periodic syntheses comparing applications across all stocks. [ABSTRACT FROM AUTHOR]

Three species of lobsters including Panulirus penicillatus, P. homarus and P. longipes are harvested simultaneously by traps in Gunungkidul waters, Indonesia. The management restriction for only one species of lobster can be dangerous for the other species. A multi-species assessment was conducted to investigate the stock status indicators and to develop the management tools. Time-series catch and effort data for the three aggregated lobsters were used to apply a surplus production model to forecast the stock rebuilding scenarios. The recent fishing effort was higher than the effort at maximum sustainable yield and the recent aggregated stock biomass was less than the optimal biomass. Growth overfishing and recruitment overfishing were detected based on the multi-species yield per recruit and the spawning potential ratio analysis. In this multi-species fishery, P. penicillatus has the lowest spawning stock biomass, thus it could be considered as the weakest stock to develop the lobster fishery management in Gunungkidul waters. For the sustainability of multi-species fishery in Gunungkidul waters, a 29% reduction of recent effort, applying the TAC (Total allowable catch) to be 26,145 kg and setting the optimal mesh size should be taken into consideration as rational fisheries management tools.

Abstract We point out problems with the article Productivity beyond density: A critique of management models for reindeer pastoralism in Norway by Marin and co-workers published in Pastoralism in 2020. In our opinion, there are several misleading claims about the governance of the reindeer pastoralist system in Norway, the Røros model for herd management and density dependence in reindeer herds in their article. We point out the errors in their empirical re-evaluation of previous work on the relationship between reindeer densities and the productivity and slaughter weights in herds. These errors have a significant bearing on their conclusions. We agree that weather variability has a substantial impact on reindeer body mass growth, fecundity and survival, but disagree with Marin et al. when they argue that reindeer densities are of minor importance for reindeer productivity and animal welfare.

Small-scale fisheries often operate under conditions of regulated open access; that is, the fishery is subject to natural or regulatory constraints on fishing technology, including regulations of fishing gear and fishing practices, but typically there is no direct regulation of catches. We study how an increase in harvesting efficiency changes the different components of welfare—consumer surplus and producer surplus—in such a regulated open-access fishery, taking t the feedback of harvesting on stock dynamics, i.e. the dynamic common-pool resource externality into account. We find that both components of welfare change in the same direction. If, and only if, initial efficiency is low enough so that there is no maximum sustainable yield (MSY) overfishing, an improvement of harvesting efficiency increases welfare. [ABSTRACT FROM AUTHOR]

In this paper, we propose to study a fishery model with variable price. We assume that the price evolves much faster than the rest of the system. Under certain assumptions, this makes it possible to consider the fishery system as a slow–fast system, on two time scales, and to study it with a reduced model of dimension two. Two main cases can occur. The first one which we called catastrophic equilibrium corresponds to over-exploitation leading to fish extinction and a booming price. The second case corresponds to a sustainable fishery equilibrium which is stable. The possible effects of the creation of marine protected areas (MPAs), sites where fishing is prohibited, on the fish stock and fishery are evaluated. We show that MPAs can have a positive effect on the restoration of depleted fish stocks by destabilizing the catastrophic equilibrium and keeping only one positive equilibrium which will be globally asymptotically stable. This problem is addressed by proposing a model with MPA for the fish dynamics. Fish are assumed to move between MPA and fishing area and are subject to harvesting through fishing. We show that to avoid the extinction of the stock and stabilize the fishery in the long term, it is necessary to define a fishing zone such that the ratio of its carrying capacity to its surface is small enough. We further show that with a judicious choice of the surface area of the MPA, it is possible to optimize the total capture. [ABSTRACT FROM AUTHOR]

This study aimed to describe the characteristics and cultivation conditions of Thunnus albacares in Pelabuhan Perikanan Pantai (PPP, shore-port fisheries) of Labuhan Lombok, East Lombok. Data was collected by a simple random sample using a questionnaire for 30 fishing boats. Primary data was collected by interview with respondents and field observation, while secondary data was obtained from records of PPP in Labuhan Lombok, BPS and DKP, East Lombok. Results showed that East Lombok has a high potential for T. albacares cultivation as well as eco-friendly fishery cultivation; this is practiced by local fishermen who commonly use traditional boats sized 4-7 GT complete with fishing utilities, including handline rods and trolling rods. From a biological aspect, there was open access to T. albaceros in 2006, followed by biological overfishing in 2007, and economic overfishing in 2005, 2008, 2009, 2010 and 2011. The maximum sustainable yield (MSY) reached 922,518.18 kg per year (MSY level 3,313 per year). The resource optimization of T. albaceros reached the peak of maximum economic yield (MEY) valued at IDR 24,693,982,361, with fish haul efforts from 2,063 annual trips yielding 791,270.90 kg of tuna per year.

Small-scale fisheries (SSFs) and the foods they produce are extremely important, contributing 25–50% of global seafood landed for direct consumption. In some cases, SSFs provide seafoods with an exceptionally low carbon footprint, but like all food, it is important to understand the factors that regulate that footprint in the face of increasing demand and a worsening climate-ecological crisis. We utilize long-term fisheries monitoring data from Northwest Mexico to generate novel stock assessments and, subsequently, test the relationship between underlying fishery biomass and fuel intensity observed among several motorized SSFs. Using fuel data from over 4,000 individual fishing trips, in combination with estimated biomass data for 19 regional stocks, we show that the fuel footprint per kilogram of seafood increases sharply as the stock’s underlying annual biomass (B) falls below its estimated biomass at Maximum Sustainable Yield (BMSY). We find an inverse relationship between B/BMSY and fuel intensity using a test for simple correlation between the two (r= -0.44), a linear regression analysis (R2adj. = 0.17), and a mixed-effects model with gear type, year, and genus modelled as random effects. These results indicate that efforts to end overfishing, rebuild fishery stocks, and/or minimize intensive fishing practices will help to decrease the carbon emissions generated by motorized wild-catch fishing. We anticipate that this study will contribute an important “missing link” to discussions on how best to secure climate-resilient fisheries and, ideally, help SSF stakeholders garner recognition and support for SSFs in this context.

Equilibrium yields and biomasses in relation to fishing mortality were generated for a wide range of life‐history traits (LHTs), which included growth parameters, natural mortality, maturity, selectivity and steepness of the Beverton and Holt stock–recruitment relationship. For each combination of LHTs, the fishing mortality expected to produce maximum sustainable yield (Fmsy), its selected proxies (F0.1, F40%, F40%SSB and Fmax) and mean length at Fmsy (Lmsy) were estimated. Next, linear models combining the estimated Fmsy and Lmsy with the traits were fitted (R2 >.95). Almost all of the LHTs were statistically significant, and the largest effect on Fmsy was from steepness, while natural mortality and growth rate had smaller effects. In the case of Lmsy, however, the largest effect in the fitted model was from the growth rate, while steepness influenced Lmsy only slightly. The Fmsy proxies were evaluated, and F40%SSB appeared to be a generally conservative Fmsy proxy, while Fmax always overestimated Fmsy, generally to a large extent. F0.1 and F40% may be used as Fmsy proxies or conservative proxies mainly for steepness values of 0.6 and higher; for lower steepness, they may markedly overestimate Fmsy. The ratio of biomass at Fmsy to virgin biomass was on average 0.34, and for a steepness of 0.9, some values were lower than 0.2. The analysis indicates that the use of the mean length of a catch in relation to Lmsy for evaluating stock status should be done with caution, especially for species with a high growth rate. [ABSTRACT FROM AUTHOR]

The global overfishing scenario of the historically exploited marine stocks have generated concern and encouraged the search for new potentially exploitable fisheries resources. In this sense, shrimps are potential alternative resources to be exploited, given their high diversity and stock resilience. This study had an objective to estimate life-history traits and analyse yield and abundance fishing levels to see whether Plesionika edwardsii shrimp is vulnerable to overexploitation or not in the mid-North Atlantic (Azores region, ICES Subdivision 10a2). The females showed larger L8 (asymptotic length) and k (coefficient of growth; L8 = 27.3 mm, k = 0.75 year-1) than did males (L8 = 24.58 mm, k = 0.73 year-1). The mortality rates of males (Z = 1.00 year-1; M = 0.84 year-1) and females (Z = 0.92 year-1; M = 0.85 year-1) were very similar. In terms of longevity, the males (3.47 year-1) survived longer than did females (3.34 year-1). Depletion experiments showed a fast and straightforward decline of CPUEs (3, 5 and 9 days), confirming a low mobility and vulnerability to high fishing efforts. The maximum sustainable yield (MSY) estimates (5.4-10.7 tonnes (Mg) year-1) showed a low annual sustainable catch. These values combined with the life-history characteristics indicated that this stock is less resilient and highly vulnerable to overfishing. [ABSTRACT FROM AUTHOR]

Sharks (class Chondrichthyes, subclass Elasmobranchii) typically have a long lifespan, slow growth rate and low fecundity, leading to low productivity and hence relatively high vulnerability to fishing. Information for managing fisheries catches of elasmobranchs is often lacking, because elasmobranchs are usually non‐target species, often with low abundance. It is more feasible to develop management reference points for elasmobranchs based on their life‐history information than through traditional stock assessments. The natural mortality rate (M) is the leading life‐history parameter (LHP) required by many methods for developing reference points and is itself often derived indirectly from other LHPs. In this paper, we evaluate nine M estimators, using 15 shark stocks in the Western and Central Pacific Ocean as examples. We then compare four methods for developing fishing mortality reference points Fmsy, including empirical modelling, the Euler‐Lotka equation, an M‐productivity‐based method and the spawning potential rate converted method. Our analyses show that popular M estimators developed mainly from teleost data resulted in large deviations from the average and were not suitable for elasmobranchs. All four methods for estimating Fmsy performed similarly. However, the empirical method is very simple and cost‐effective and tended to produce smaller deviations from the average than the other three methods. Nonetheless, it is recommended that multiple methods should be used to minimize possible bias and reflect uncertainty, if the required LHPs are available. [ABSTRACT FROM AUTHOR]

The fishery of the sea cucumber Isostichopus fuscus was the most important one in the early 2000s in the Galapagos Marine Reserve. Its overexploitation leads to its total closure from 2016 to 2021. At the end of this period, if the co-management system of the Galapagos Marine Reserve decides to open this fishery, a total allowed catch must be established using the methodology of Wolff, Schuhbauer, and Castrejón (2012). The objective of this paper is to evaluate this methodology and improve the total allowed catch calculation. We replicated Wolff et al.‘s methodology that uses the Cadima equation of Maximum Sustainable Yield (in Troadec, 1977). We determined the age and growth parameters of I. fuscus to estimate total mortality and improved the calculation of the area of fishing and habitat of this species in Galapagos to estimate its abundance. We found inconsistences in Wolff et al.‘s estimations of mortality and abundance and we recommend that the Maximum Sustainable Yield be used not as the total allowed catch, but as a limit reference point for this fishery. We propose, instead, to use a dynamic abundance model that is capable of estimating a variety of reference points, including the fishing mortality for optimal fishing that is recommended to use to establish a total allowed catch. In addition, for the first time, the age and growth parameters of I. fuscus for Galapagos and the eastern-central region of the Pacific Ocean are determined (L∞ = 42.5 cm; K = 0.21/year).

Abstract A new way to study the harvested predator–prey system is presented by analyzing the dynamics of two-prey and one-predator model, in which two teams of prey are interacting with one team of predators and the harvesting functions for two prey species takes different forms. Firstly, we make a brief analysis of the dynamics of the two subsystems which include one predator and one prey, respectively. The positivity and boundedness of the solutions are verified. The existence and stability of seven equilibrium points of the three-species model are further studied. Specifically, the global stability analysis of the coexistence equilibrium point is investigated. The problem of maximum sustainable yield and dynamic optimal yield in finite time is studied. Numerical simulations are performed using MATLAB from four aspects: the role of the carrying capacity of prey, the simulation about the model equations around three biologically significant steady states, simulation for the yield problem of model system, and the comparison between the two forms of harvesting functions. We obtain that the new form of harvesting function is more realistic than the traditional form in the given model, which may be a better reflection of the role of human-made disturbance in the development of the biological system.

Background. Despite the importance of inland fishery, assessments of exploited inland stocks have relied on data-deficient databases, mainly in developing countries. In this paper, we employed two distinct analytical methods to evaluate the stock status of Prochilodus nigricans Spix et Agassiz, 1829, the most important fish in the Amazonian freshwater landings. In this study, we intended to test the sustainability of small-scale fisheries comparing two different methods. Materials and methods. The population dynamic of P. nigricans was studied using length and weight data for fish caught in Manacapuru Lake and the lower stretch of the Solimões River. Estimates of maximum sustainable yield and corresponding fishing mortality for 2012 and 2013, using Beverton–Holt curve, indicated an overfishing status for both years. At the same region, fishers were interviewed and their knowledge on the P. nigricans stock status was assessed using a stock assessment methodology based on fishers’ knowledge, known as ParFish. Results. Both yield per recruit curves employed to assess the stock status of P. nigricans in 2012 and 2013 and ParFish approach indicate an overfishing status, but ParFish also found a high uncertainty level around 47%. Conclusion. The use of ParFish algorithm and traditional knowledge can provide qualitatively similar results to conventional models, such as the Beverton–Holt approach. The ParFish approach shows the advantage including confidence intervals to its estimates.

Nile tilapia Oreochromis niloticus is a commercially important fish species in the Lake Tana fishery and contributes to 65% of the total annual catch. This study estimated the maximum sustainable yield (MSY) and effort at maximum sustainable yield (fMSY) for the O. niloticus fishery using the Thompson and Bell yield prediction model. Catch and effort data from four representative landing sites were collected daily from June 2016 to May 2017 and used to estimate the total mortality coefficient (Z) using catch curve analysis, natural mortality (M) using Pauly's empirical formula, and fishing mortality (F) as F = Z − M. Population abundance was evaluated using the Jones length-based cohort analysis model. The estimated Z, M and F values were 1.1, 0.52, and 0.49 per year, respectively. In total, 5 077 tons of O. niloticus were produced, which exceeds the MSY of 4 904 tons per year that could be obtained from the fishery at an F0.1. Consequently, the recommendation is to reduce the fishing effort by 15%. Collection of catch-and- effort data from more landing sites, over an extended period, could improve the yield estimates and this should be considered in conjunction with a bioeconomic analysis in future. [ABSTRACT FROM AUTHOR]

We point out problems with the article Productivity beyond density: A critique of management models for reindeer pastoralism in Norway by Marin and co-workers published in Pastoralism in 2020. In our opinion, there are several misleading claims about the governance of the reindeer pastoralist system in Norway, the Røros model for herd management and density dependence in reindeer herds in their article. We point out the errors in their empirical re-evaluation of previous work on the relationship between reindeer densities and the productivity and slaughter weights in herds. These errors have a significant bearing on their conclusions. We agree that weather variability has a substantial impact on reindeer body mass growth, fecundity and survival, but disagree with Marin et al. when they argue that reindeer densities are of minor importance for reindeer productivity and animal welfare. [ABSTRACT FROM AUTHOR]

The Straits of Malacca provides half of Malaysia's total marine fish and seafood supply. Due to depleted fish stock, the Malaysian Government has established a comprehensive legal framework to reduce overfishing in the Straits over the last five decades. However, there are limited scientific studies on the current status of stock recovery. This paper aims to use bioeconomic approach to determine the current trawl fishery status in the Straits. Various statistical tests showed that the Clarke-Yoshimoto-Pooley model was better than the Schnute model in predicting and thus used to estimate the crucial bioeconomic parameters. The current yield and standardised effort of 239,692 tonnes and 931,692 standard fishing days were very close to the estimated biological maximum sustainable yield (239,915 tonnes) and above 18 % of the standardised effort (763,649 standard fishing days) to achieve it. The maximum economic yield was estimated at 201,542 tonnes while the corresponding standardised effort was 396,799 standard fishing days indicating serious economic overfishing in the Straits. If the current effort can be reduced by 57 %, fish biomass and economic rent will increase by 97 % and 835 %, respectively. A price sensitivity analysis predicted that demand-pull fish price inflation could exacerbate the overfishing problem, particularly under unrestrained environment. A 50 % increase in price could lead to a 132 % increase in fishing effort from the base case. The findings of this paper provide valuable insights for fishery managers to refine their existing fishery management program to achieve sustainable fishery for the future. [ABSTRACT FROM AUTHOR]

Saudi Arabia aims to enhance the productivity of fish production and culture of consumption of fish products and increase the export of fish products through implementing the National Transformation Program. This study aimed to identify the current status of marine fish production and most critical climatic and environmental factors affecting the production of natural fisheries and estimate the maximum sustainable yield in Saudi Arabia by focusing on the primary fisheries in the Arabian Gulf and the Red Sea during the period 2000–2019. We found that the most important economic, climatic, and environmental factors affecting marine fish production in Saudi Arabia were the number of industrial fishing boats, number of fishers, and wind speed. There was a significant positive relationship between the quantity of fish production in Saudi’s fisheries and the number of industrial fishing boats and fisher numbers. In contrast, there was an inverse relationship between wind speed and fish production in these fisheries. The total output elasticity was 0.10, which is less than 1, indicating that fish production in these fisheries is in the second production stage, which is called the economic production stage. In contrast, there is an opportunity to increase the production variables with diminishing returns. Schaefer’s model analysis confirmed the ability to increase production in most of the study period in both the Arabian Gulf and the Red Sea with fishing production not exceeding the maximum sustainable level.