Maximum Sustainable Level Research Articles

Enhancing Sustainability and Conservation of White Shrimp Penaeus schmitti in Northeast Brazil: Insights Into Life History, Reference Points, and Management Strategies for Beach Seining

ABSTRACTArtisanal 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.

Assessment of the utilization status of fourfinger threadfin (Eleutheronema tetradactylum) in the waters of Dumai City, Riau Province

One of the local fish species exploited in the waters of Dumai is fourfinger threadfin (Eleutheronema tetradactylum). The purpose of this research is to analyze the maximum sustainable yield, optimal efforts, and utilization levels of fourfinger threadfin. Data on catches and efforts were collected from the annual reports of the Department of Fisheries Dumai City over a period of ten years. The results of the analysis using the Walter-Hilborn model indicate that the maximum sustainable yield of fourfinger threadfin is 234 ton year-1, and the optimal effort (Eopt) is 404 unit year-1. The average utilization rate of fourfinger threadfin from 2014 to 2023 is 28 percent. The resource is currently moderately exploited (25-75%), indicating that the stock has been harvested close to its maximum sustainable yield value. It is advisable to increase fishing efforts without compromising the sustainability of fourfinger threadfin in the waters of Dumai City.

Biological life‐history and farming scenarios of marine aquaculture to help reduce wild marine fishing pressure

AbstractAquaculture (freshwater and marine) has largely supplemented fisheries, but in theory could help reduce fishing pressure on wild stocks. Although not the sole factors, some potential benefits depend on aquaculture pressures on fished species, including collection of wild ‘seed’ material—earlier to later life stages—for rearing in captivity and the capacity of aquaculture to increase. Here we first classify 203 marine (saltwater and brackish) animal species as being produced by either open‐cycle capture‐based aquaculture (CBA) or closed‐cycle domesticated aquaculture (DA)—based on their likely reliance on wild seed—and assess the extent to which these forms of aquaculture could support seafood production and greater wild biomass. Using a data‐limited modelling approach, we find evidence that current aquaculture practices are not necessarily helping reduce fishing to sustainable levels for their wild counterparts—consistent with emerging scientific research. However, if some wild capture species (87 equivalent spp.) were instead produced through CBA, almost a million extra tonnes could theoretically be left in the wild, without reducing seafood production. Alternatively, if reliance on wild seed inputs is further reduced by shifting to DA production, then a little less than doubling of aquaculture of the overexploited species in our study could help fill the ‘production gap’ to support fishing at maximum sustainable levels. While other ecological (e.g. escapes), social and economic considerations (e.g. market substitution) are important, we focused on a critical biological linkage between wild fisheries and aquaculture that provides another aspect on how to improve management alignment of the sectors.

An exploratory assessment of the Bering-Chukchi-Beaufort Seas stock of bowhead whales using a stochastic population dynamics model

The stochastic population dynamics model used by Aboriginal Whaling Management Procedure developers is revised to correct weaknesses related to uncertainty parameterisation and replacement yield estimation. Two variants of this model, along with the standard deterministic version, are used to assess the Bering-Chukchi-Beaufort Seas stock of bowhead whales. The variants differ with respect to the magnitude and complexity of the stochastic variation they introduce into natural mortality and birth/calf survival processes. An allowable catch statistic, E (Q0), is defined for appropriate use with stochastic model assessments. Using the same assessment methods, likelihood and priors as IWC (1999a), 5th percentiles of E (Q0) were found to be 117, 106 and 91 for the deterministic, simpler stochastic and extreme stochastic models, respectively. Bayes factor results show that there is no evidence suggesting that either stochastic model should be favoured over any simpler alternative, and the deterministic model yielded the best fit overall. The E (Q0) estimates confirm and strengthen past IWC Scientific Committee inference that under current bowhead subsistence hunting levels the stock should continue to increase towards stabilisation above its maximum sustainable yield level.

A Bayesian stock assessment of the eastern Pacific gray whale using abundance and harvest data from 1967-1996

Abundance and harvest data since 1966/67 were used to assess the eastern Pacific stock of gray whales. A Bayesian statistical method was used to estimate probability distributions for the parameters of both a simple and an age and sex structured population dynamics model, as well as output quantities of interest. Model comparisons using the Bayes Factor provided conclusive evidence that an additional parameter should be used to account for unexplained variation in the abundance time series. Incorporating the additional variance parameter decreased the precision of the estimates of the other parameters. Point estimates of carrying capacity ranged from 24,640-31,840 for the different models, but the posterior distributions from the selected models were very broad and excluded few values. The current depletion level (population size as a fraction of carrying capacity) was estimated to be about 0.75, with a lower 2.5th percentile of 0.36. The probability that the population was still below one-half of its carrying capacity was estimated to be 0.21, with a corresponding probability of 0.28 that the population was still below its maximum sustainable yield level. Quantities from which catch limits could potentially be calculated were estimated, including current replacement yield, maximum sustainable yield and the quantity Q1 (described in Wade and Givens, 1997).

Public debt sustainability in a target zone model with heterogeneous agents

Relying on the assumption of perfect information and agent homogeneity, previous interest rate target zone models could well account for situations of government debt stability (‘honeymoon’) or instability (‘divorce’). In those models, however, the transition from one state to another could only occur with a discrete change in the interest rate and thus could not account for the gradual transition from ‘honeymoon’ to ‘divorce’ that occurred in the months leading up to the euro area crisis of 2011–12. The assumption of heterogeneous agents made in this interest rate target zone model, on the other hand, allows that graduality to be represented. Heterogeneous agents are assumed to be characterized by normally distributed beliefs about the maximum sustainable level of the debt-to-GDP ratio. When public debt increases due to an assumed process of stochastic shocks, therefore, the percentage of agents sharing the belief that they have entered a region of instability also increases, thus leading to the gradual transition from ‘honeymoon’ to ‘divorce,’ observed in the euro area crisis of 2011–2012.

Population status of the eastern North Pacific stock of gray whales in 2009

An age- and sex-structured population dynamics model is fitted using Bayesian methods to data on the catches and abundance estimates for the Eastern North Pacific (ENP) stock of gray whales. The prior distributions used for these analyses incorporate revised estimates of abundance for ENP gray whales and account explicitly for the drop in abundance caused by the 1999–2000 mortality event. A series of analyses are conducted to evaluate the sensitivity of the results to different assumptions. The model fits the available data adequately, but, as in previous assessments, the measures of uncertainty associated with the survey-based abundance estimates are found to be negatively biased. The data support the inclusion of the 1999–2000 mortality event in the model, and accounting for this event leads to greater uncertainty regarding the current status of the resource. The baseline analysis estimates the ENP gray whale population to be above the maximum sustainable yield level (MSYL) with high probability (0.884). The posterior mean for the ratio of 2009 (1+) abundance to MSYL is 1.29 (with a posterior median of 1.37 and a 90% probability interval of 0.68–1.51). These results are consistent across all the model runs conducted. The baseline model also estimates the 2009 ENP gray whale population size (posterior mean of 20,366) to be at 85% of its carrying capacity (posterior mean of 25,808), and this is also consistent across all the model runs. The baseline model estimate of the maximum rate of increase, λmax, is 1.062 which, while high, is nevertheless within the range of estimates obtained for other baleen whales.

Population characteristics and stock assessment of European anchovy (Engraulis encrasicolus L., 1758) in coastal waters of the south-eastern Black Sea of Turkey

AbstractThis study was carried out throughout 10 fishing seasons between 2002 and 2018 to monitor the population and stock variations of Engraulis encrasicolus (L., 1758) on the south-eastern Black Sea coast of Turkey. Asymptotic length (L∞), growth constant (K) and growth performance indexes (φ) were calculated to be between 12.86 and 15.79 cm, 0.69 and 0.99, 2.10 and 2.29, respectively. Theoretical birth ages were determined to range between (to) −0.15 and −0.27, the maximum ages (tmax) ranged between 3.03 and 4.35, total mortality rates (Z) between 2.19 and 2.66, natural mortality rates (M) between 0.93 and 1.26, the fishing mortality rate (F) between 0.93 and 1.47, and the optimum fishing mortality rate (Fopt.) between 0.37 and 0.62. Fishing mortality rates (F) were estimated to be higher than the optimum fishing mortality rates (Fopt). Z/K ratios were determined to range between 1.91 and 3.43. Current exploitation rates (Ecurr.) were calculated to range between 0.42 and 0.62. The first recruit lengths (Lr) and first capture lengths (Lc50) were estimated to range between from 5.25–7.75 and from 7.66–8.74 cm, respectively. The first maturity lengths (Lm50) of E. encrasicolus ranged between 8.57 and 10.53 cm. The maximum sustainable exploitation levels (Emax) were determined to range between 0.72 and 0.83. These data indicate that if current levels of fishing pressure continue, anchovy stocks will collapse in the near future.

Ability of Thermal Work Limit (TWL) to Assess Sustainable Heat Stress Exposures.

Thermal Work Limit (TWL) recommends a maximum metabolic rate for a given environmental condition, clothing ensemble, and acclimatization state so that thermal equilibrium can be sustained at or below the limiting metabolic rate. The purpose of this paper was to assess the ability of TWL to recommend maximum sustainable levels of heat stress using an existing database of progressive heat stress trials using four levels of clothing (woven clothing, particle barrier, water barrier, and vapor barrier), three levels of relative humidity, and three levels of metabolic rate. Each trial had a compensable and an uncompensable observation plus and observation at the transition point from compensable to uncompensable. Each observation was classified as a case (steady increase in rectal temperature) or non-case (steady rectal temperature). The data were used to compare the difference between the observed metabolic rate (Mobs) and the limiting metabolic rate of TWL (i.e., ∆LimitTWL = Mobs - TWL), where ∆LimitTWL > 0 was above the TWL limit. The sensitivity and specificity for each of the four clothing ensembles were about 0.96 and about 0.20, respectively. Logistic regression for all the data found that ∆LimitTWL, clothing, metabolic rate, and water vapor pressure were significant predictors of outcome. The ln(odds) equations for each clothing ensemble predicted a probability of an uncompensable exposure. The probability of an uncompensable outcome (case) when ∆LimitTWL = 0 was 0.14 for work clothes and particle barrier, and 0.22 for water barrier and vapor barrier. The probability of a case at ∆LimitTWL = 0 was greater than the probability of a case for the wet bulb globe temperature-based exposure limits where the probability of a case was 0.01. That is, the TWL was less restrictive than WBGT but with higher risk.

This is what we know: Assessing the stock status of the data-poor common sole on the Iberian coast

In the Iberian Coast region, the common sole (Solea solea) is considered a very relevant species due to its high commercial value. Despite its importance, the current status of this stock is still poorly known due to the scarcity of available data to apply formal assessment methods. In data-poor situations length-based methods have been widely applied to estimate biological parameters and to understand the dynamics of marine stocks. In this study we evaluate the status of common sole in the Iberian Coast region using the following three different length-based methods: (1) the length-based indicators, (2) the length-based spawning potential ratio and (3) the mean length-based mortality estimators. Overall, the three methods agree that this stock appears to be exploited at the maximum sustainable yield level, the immatures are well preserved whereas the proportion of large mature individuals is relatively low, although it has been increased in the last years. Assessing the status of this valuable stock through data-limited methods is the first step towards designing and implementing effective management measures.

Sale price flexibilities of Mediterranean hake and red shrimp

The formation of ex-vessel price of two important Mediterranean fisheries products (hake and red shrimp) was studied through an inverse demand approach, using data from the Catalonia bottom trawl fishery (NW Mediterranean). In both species, the landings by commercial category (proxy for fish size) and total landings determined the daily price fetched at the auction, as summarized by the quantity and scale coefficients (“flexibilities”) derived from the inverse demand model. In general, quantity flexibilities were between −0.1 and − 0.6, indicating that a 1% increase in the landings of one category (for a given species) would reduce the average daily ex-vessel price by 0.1–0.6%. Scale flexibilities were generally lower than − 1, showing that these species tend to behave non-homothetically, especially for the large size categories. These results imply that changes to the quantities landed and the size composition of landings, resulting for instance from fisheries management measures, will affect sale prices. Simulations of sale price for scenarios of reduced landings, in line with fishing at maximum sustainable levels, showed that losses in revenue would be much less than the losses projected with constant prices. Similarly, higher landings resulting from rebuilt stocks would yield lower revenues from these stocks because of the generally negative flexibilities.

The external dependence of ecological products: Spatial-temporal features and future predictions

The instability of international trade can threaten the resource security of resource-importing countries, while international trade helps address spatial mismatches between regional populations, economies, and resources. Ecological products are the basis for human survival and development, in which agri-livestock products are especially sensitive to trade fluctuation and closely related to human well-being. The external dependence is an important indicator to reveal the external supply risk of regional resources. Scientific understanding the external dependence of ecological products can reveal the potential risks of trade fluctuations to human well-being and ecological sustainability. In this study, the global status and trend of countries' external dependence of agri-livestock ecological products are investigated. The results showed that nearly 80% (141) of countries relied on imports to meet ecological product demands in 2018, in which Asian-African-Latin countries accounted for about 78%, which indicated that the instability of international trade would threaten the ecological resource security in 80% of the world's countries, especially for underdeveloped countries. Even worse, 68% of countries are increasing their external dependence of ecological products. Even if the intensity of ecological resource exploitation reaches the maximum sustainable utilization level, 60% (113) of countries are expected to need imports for meeting their ecological product demands in 2050. Moreover, even considering the agricultural technological upgrade and the consumption transformation, more than 50% (94) of countries are still net importers of ecological products. Therefore, trade liberalization is still one of the important means to reduce resource security risks caused by trade instability. More notably, half of the countries in the world may sacrifice ecological sustainability to meet basic human well-being in the future under deglobalization.

Trade-offs among spatio-temporal management actions for a mixed-stock fishery revealed by Bayesian decision analysis

Abstract Management and conservation of populations that are harvested simultaneously present a unique set of challenges. Failure to account for differences in productivity and spatio-temporal abundance patterns can lead to over-exploitation of depleted populations and/or loss of potential yield from healthy ones. Mixed-stock fisheries (where a stock may comprise one or more populations of reared or wild origin) harvest multiple stocks, often in unknown proportions, and lack of tools for estimation of stock-specific harvest rates can hamper status evaluations and attainment of management goals. We present a method for evaluating stock-specific impacts of alternative harvest strategies, using coastal trap net fisheries for Atlantic salmon (Salmo salar) in the Baltic Sea as a case study. Our results demonstrate a large variation among stocks in coastal mixed fishery harvest rates, as well as large differences in harvest rates relative to stock-specific maximum sustainable yield (MSY) and recovery levels. Bayesian decision analysis showed that spatio-temporal management actions, such as delayed fishery opening and closed areas may be effective in improving probabilities of meeting management objectives for Baltic salmon. However, stocks did not respond uniformly to different management actions, highlighting the potential for trade-offs in reaching stock-specific targets that must be considered by managers.

Determination of the optimum effort for small scale fisheries in Bulukumba regency

This study aims to determine the catch per unit effort (CPUE) or abundance, maximum sustainable yield (Cmsy), optimum effort (Emsy), catch quota, utilization level, and effort of yellowfin tuna (Thunnus albacarez) for small scale fisheries in Bulukumba Regency, using a surplus production method, as well as time-series data for 11 years. According to the results, the CPUE or abundance average, Cmsw, Emsw, and catch quota, were about 4.4284 tons/unit, 720 tons, 184 units of hand line, and 576 tons, respectively. Meanwhile, the sustainable production with actual production showed overfishing, except for 2010 and 2015, while the production data for 2016 – 2020 were unavailable. In addition, the average MSY utilization, catch quota, and average effort levels were 61.9512 %, 77.4397 %, and 86.8352%, respectively. Theoretically, the MSY utilization levels for all years were about 100%, except for 2010 (1.4449 %) and 2015 (23.7581%), as well as 2012, where the value exceeded 100% (364.7357%), while the catch quota for all years was above 100 %, except for 2010 (1.8062 %) and 2015 (29.6976 %). However, the two production data values were unavailable for 2016 – 2020. Also, the effort levels fluctuated while almost all the half values were below 100 %.

Can we live within environmental limits and still reduce poverty? Degrowth or decoupling?

Can we live within environmental limits and still reduce poverty? Degrowth or decoupling?

Estimates of Abundance and Harvest Rates of Female Black Bears Across a Large Spatial Extent

ABSTRACTAmerican black bears (Ursus americanus) are an iconic wildlife species in the southern Appalachian highlands of the eastern United States and have increased in number and range since the early 1980s. Given an increasing number of human‐bear conflicts in the region, many management agencies have liberalized harvest regulations to reduce bear populations to socially acceptable levels. Wildlife managers need reliable population data for assessing the effects of management actions for this high‐profile species. Our goal was to use DNA extracted from hair collected at barbed‐wire enclosures (i.e., hair traps) to identify individual bears and then use spatially explicit capture‐recapture methods to estimate female black bear density, abundance, and harvest rate. We established 888 hair traps across 66,678 km2 of the southern Appalachian highlands in Georgia, North Carolina, South Carolina, and Tennessee, USA, in 2017 and 2018, arranged in 174 clusters of 2–9 traps/cluster. We collected 9,113 hair samples from those sites over 6 weeks of sampling, of which 1,954 were successfully genotyped to 462 individual female bears. Our spatially explicit estimator included a percent forest covariate to explain inhomogeneous bear density across the region. Densities ranged up to 0.410 female bears/km2 and regional abundance was 5,950 (95% CI = 4,988–7,098) female bears. Based on hunter kill data from 2016 to 2018, mean annual harvest rates for females were 12.7% in Georgia, 17.6% in North Carolina, 17.6% in South Carolina, and 22.8% in Tennessee. Our estimated harvest rates for most states approached or exceeded theoretical maximum sustainable levels, and population trend data (i.e., bait‐station indices) indicated decreasing growth rates since about 2009. These data suggest that the increased harvest goals and poor hard mast production over a series of prior years reduced bear population abundance in many states. We were able to obtain reasonable population abundance and density estimates because of spatially explicit capture‐recapture methods, cluster sampling, and a large spatial extent. Continued monitoring of bear populations (e.g., annual bait‐station surveys and periodic population estimation using spatially explicit methods) by state jurisdictions would help to ensure that population trajectories are consistent with management goals. © 2021 The Wildlife Society.

Aspects of Stock Assessment of Klunzinger's Mullet, Planiliza klunzengeri (Day, 1888) from Northwest Arabian Gulf, Iraq

The stock assessment of Klunzinger's mullet, Planiliza klunzengeri was conducted, to estimate its some aspects viz. growth, mortality, recruitment, yield-per-recruit and virtual population analysis in Iraqi marine waters, northwest Arabian Gulf, Iraq, from February 2020 and January 2021. The population parameters were analyzed by the FiSAT software using monthly length-frequency data collected by the Shaheen dhow and from the artisanal fishermen at the fish landing site in Al-Fao city to derive information required for their management. A total of 3319 individuals of P. klunzingeri ranged from 11.0 to 27.0 cm have been collected. Length-weight relationship was calculated as W= 0.026L2.716. The asymptotic length (L∞), growth rate (K) and the growth performance index (Ø') were 29.8 cm, 0.34 and 2.48, respectively. The rates of annual instantaneous of total mortality (Z), fishing mortality (F), natural mortality (M) and present exploitation (Epresent) were 1.19, 0.84, 0.36 and 0.30, respectively. The recruitment pattern of P. klunzingeri was continuous throughout the year, with one peak during May. The results of virtual population analysis revealed that the majority of P. klunzingeri were harvested between 14 cm and 19 cm. The length at first capture (L50) in the current study was higher than the length at first maturity (Lm) of the species in the region. The Epresent was below the biological target reference points (E0.1= 0.770 and Emax= 0.903), referred to the stock of P. klunzingeri is underexploited. Therefore, the harvest level should increase to its maximum sustainable yield level by increasing fishing effort level with monitoring surveys and evaluate the risk associated with fishing effort increases as fishing precautionary approaches.

Индикаторная оценка состояния популяции рыбца в условиях дефицита биологической информации в Азовском море методом LBI

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

The impact of climatic and environmental changes on the sustainable yield of the Saudi’s capture fisheries

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.

Boosting fiscal space: the roles of GDP-linked debt and longer maturities

SUMMARYThis paper assesses how issuance of GDP-linked debt and longer-maturity debt, in comparison to short-term debt, can help boost fiscal space for a given path of primary balances. By explicitly linking debt service to repayment capacity, GDP-linked debt helps to stabilize the debt ratio under growth uncertainty and reduces default risk through risk sharing with investors. Longer-maturity nominal debt also helps reduce default risk via state-contingent variation in the market price of debt. Reduced default risk in both cases lowers borrowing costs and results in higher maximum sustainable debt levels (and fiscal space given initial debt) for a given path of primary balances. Simulation results suggest sizable gains in fiscal space from the introduction of these instruments, though debtor moral hazard could militate against these benefits.