Comparison Between Maximum Sustained Yield Proxies and Maximum Sustained Yield

Ricker's stock-recruitment equation, including the multivariate ENSO index (MEI) as an environmental variable, was fitted to data of the Pacific sardine (Sardinops sagax caerulea) fishery from Magdalena Bay, Baja California Sur, Mexico. The equation was then incorporated into an age-structured, bioeconomic model. Uncertainty was incorporated by using environmental fluctuations; seven-year projections, equivalent to one sardine generation, were computed. Five management options were considered in the projections: open access, effort at maximum sustainable economic yield (fMSE), catch at maximum sustainable yield (CMSY), equivalent effort level applied in the year 2004 (f2004), and an arbitrary catch quota of 40000 tons (CQ40000). Projection results were summarised by the indicator Net Present Value (NPV) of the fishery for the modelled period. The strategies that involved some regulation in the effort level (fMSE and f2004) yielded the largest NPV. On the other hand, the strategies that involved regulation of the catch predicted—in addition to a lower NPV—a substantial increase in the effort to achieve the desired catch level. This study is the first bioeconomic approach for a sardine fishery management plan in this region.

Foresters often claim that the goal of good forest policy is to have a sustained forest yield, or even a maximum sustainable yield. They also claim that people wish to save a few extra trees for their children. This bequest motive is not modelled in the standard approach to the optimal rotation problem. In this paper, we present a standard version of an overlapping generation model augmented with a simple tree technology. We show in particular that the market equilibrium can be dynamically inefficient, and that a bequest motive in terms of trees can correct for the overaccumulation of capital that causes the inefficiency. The bequest motive also enables us to account for a harvesting intensity varying with age (young people typically cut more than elderly people) in spite of a perfect capital market.

A structured one-page mail questionnaire was used to evaluate present and future management goals of state recreational fisheries management personnel. Recreational fisheries management goals evaluated were (1) maximizing sustained yield, (2) maximizing catch, (3) establishing trophy fisheries, (4) maximizing fishing license sales, (5) maximizing angler-trips, (6) maximizing angler-days, (7) maximizing angler hours, (8) minimizing angler crowding, and (9) minimizing angler complaints. Respondents indicated that maximum sustained yield is currently the dominant goal being used in recreational fisheries management. Future fisheries management goals were likely to be similar to current goals. No significant differences were found between manager's educational levels for the current and future list of top-ranked goals. Significant differences were found between a manager's years of work experience and his anticipated future fisheries management objectives: more experienced managers tended to anticipate a change in goals away from yield toward angler-oriented goals. However, the total number of recreational fisheries managers favoring maximum sustained yield and catch as realistic goals is not likely to change in the future. Comparison of the “desires” of the angling public for a multifaceted fishing experience to the managers' heavy orientation towards yield suggests a concerning disparity.

The population dynamics of Rastrelliger kanagurta from the northwestern coastal waters of Sri Lanka were studied based on the length frequency data collected from October 1993 to September 1994. The resource is mainly exploited by gillnets and beach seines. The length frequency distributions ofRastreIliger kanagurta for the two gear types were similar with two prominent peaks at 13.5-15.5 cm and 20.524.5 cm (total length) length ranges. In addition, smaller individuals with total lengths varying from 7.5-10.5 cm were also observed among the beach seine catches.Population parameters were estimated using the FiSAT software package. The asymptotic length, growth constant and the growth performance index were estimated to be 28.0 cm (total length), 1.5 year -1 and 3.07 respectively. The estimated value for the natural mortality coefficient using the Pauly's empirical formula was 2.37 year-1. The fishing mortality coefficient for the combined fishery was estimated at 2.62 year-1 while the estimated values for the total mortality coefficient and the exploitation rates were 4.99 year-1 and 0.53 respectively. The recruitment was continuous with two peaks per year.The length based Thompson and Bell model was used in the bio­economic prediction. Of the possible scenarios, increasing the gillnet effort while maintaining that of the beach seines at the present level appeared to be the most realistic in accordance with the existing social and legal framework. The maximum sustainable yield and maximum sustainable economic yield for the combined fishery were estimated at 207 MT and 200 MT respectively. As the corresponding effort levels were 3 and 1.6 times the present effort, it is reasonable to conclude that the stocks are not over­exploited at present.

Accounting for indirect effects and non-commensurate values in ecosystem based fishery management (EBFM)

The objective of this study was to determine the maximum sustainable yield (MSY) of the crab fishery in the Gulf of California by applying the catch-MSY method. This fishery occurs in two states—Sonora and Sinaloa, along the mainland coast of the Gulf of California—and involves two species: Callinectes hellicosus and Callinectes arcuatus. The main species supporting the fishery in both states is C. bellicosus, whereas C. arcuatus accounts for 5% of crab catches in Sonora and 20%–30% in Sinaloa. The catch-MSY method uses a set of viable r–k combinations to approximate MSY. The r–k combinations are the carrying capacity k and the maximum rate of population increase r for a given stock in a given ecosystem, which are required in most production models, such as the Schaefer model, to estimate MSY. Prior carrying capacity in this study was set arbitrarily from the maximum catches in a series evaluated to 100 times the maximum catch. This range ensures the real carrying capacity could be determined if catches were at MSY sometime during the period evaluated. Maximum potential could have been realized since 2006 for the Sinaloa stock and since 1996 for the Sonora stock. The evidence for these facts is that the catch per unit of effort decreased, and reductions were observed in the mean size of individuals; these changes occurred in the Sinaloa crab fishery. All methods devoted to management procedures of fisheries stocks entail a number of criticisms, and estimations of carrying capacity and stock biomass are costly; however, because sustainable fisheries are desired and data-poor stocks are common, a simple method like catch-MSY has proved be useful in the management of the crab fishery in the Gulf of California.

Quang Nam is one of the leading provinces in fisheries in Vietnam. Nui Thanh district is an important area where small-scale fisheries on nearshore waters are focused. In recent years, the overfishing status in Nui Thanh district has made the rapid depletion of coastal resources. However, only a few have studied the fisheries management aspect in this area and no quantitative research on sustainable fisheries management has been conducted. This research project was conducted from 2013 to 2015 by surveying 110 fleets to find out reference values for sustainable fisheries management in Nui Thanh district. By using Sustainable Fisheries Models, the results showed that the maximum sustainable yield (MSY) should be 26,500 tons when the fleet capacity reached 80,500 HP (fMSY). To get the maximum economic yield (MEY) estimated VND 864.5 billion, the fleet capacity should be 64,300 HP, the MSY should be 25,500 tons; at that time, the fish stock was estimated about 76,000 tons. Fisheries management polocies and solutions were proposed for Nui Thanh district’s coastal fisheries toward the sustainable development by reducing fleet capacity, building alternative career models, protecting and restoring fish stocks.

There is a global decline in marine fish abundance due to unsustainable harvesting. An effective harvesting policy can protect the overfished population from possible extinction. In this study, we used a mathematical model characterized by density-dependent refuge protection for herbivorous fish, exhibiting an anti-predator response in presence of a generalist invasive fish. The anti-predator behavior entails predator density-dependent reduced fecundity of the herbivorous fish. The model assumes a continuous threshold harvesting policy (CTHP) for the herbivorous fish and uses the catch-per-unit-effort (CPUE) hypothesis for harvesting the invasive fish. The CTHP allows harvesting of the herbivorous fish only when the density of the herbivorous fish exceeds a specified threshold value, thus ensuring the long-term sustainability of the herbivorous fish stock. The existence and stability of steady-state solutions and the bifurcations of the model are investigated. Our study reveals that the level of apprehension of the herbivorous fish and fishing efforts will play a significant role in the stability of the system. We examine the existence of the bionomic equilibrium and then study the dynamic optimization of the harvesting policy by employing Pontryagin’s maximum principle. We discuss different subsidies and tax policies for the effective management of a sustainable fishery. We use numerical simulations to compare the revenues corresponding to the harvest policies based on maximum sustainable yield (MSY), maximum economic yield (MEY), and optimal sustainable yield (OSY) for inferring an ecologically sustainable and economically viable harvesting policy.

Optimal impulsive harvesting on non-autonomous Beverton–Holt difference equations

We developed a new type of generalized depletion model adapted to the rapid life cycle of Octopus vulgaris and the data collection framework put in place in its co-managed small-scale fishery (SSF) in Asturias, northwest Spain. The model uses weekly data from 19 seasons to estimate annual recruitment and female spawners emigration out of the vulnerable stock to attend to their broods. The matched annual spawners-recruitment (SR) magnitudes are then used as observations in a non-Bayesian hierarchical inference framework. The Shepherd SR model was selected among three alternatives. The stock has a high degree of density-dependence, leading to overcompensation. The estimated SR model has an unstable equilibrium point, driving the stock to deterministic cyclic fluctuations under small disturbances. Under those conditions the maximum sustainable yield (MSY) is not applicable, lending further credence to Sidney Holt’s opposition to the MSY as a basis for the elaboration of fishery management objectives, with potentially wide relevance to the management of SSF and cephalopod fisheries. We argue that harvest rates based on mean latent productivity, a concept that includes the MSY as a special case, are more adequate and sustainable for fluctuating stocks.

Consideration of economic outcomes is commonplace in most fisheries management systems globally, although only a few jurisdictions have adopted an economic objective as the primary target for fisheries management. Such an objective has been adopted for Australia's federally managed fisheries, with maximum economic yield (MEY) identified as the primary management objective. Correspondingly, target reference points defined in terms of biomass (i.e., BMEY) are used in harvest control rules. In the absence of explicit BMEY estimates, proxy estimates based on maximum sustainable yield (i.e., BMSY) are used. Identifying BMEY in multi-species fisheries is complicated as most stock assessments are undertaken at the individual species level, but economic activity occurs across species. This is further complicated when different fishing activities using different fishing gears and targeting practices (i.e., métiers) are present in a fishery. We employ an age-structured bioeconomic model to estimate BMEY for key species in a multi-species, multi-métier fishery. We find that optimal biomass levels are substantially higher than those assumed under the current proxy-based system, and that the economic targets are sensitive to prices and fishing costs, both of which change over time.

Information about potency and utilization of Skipjack Tuna in Bone Bay region will support regionalmanagement of fisheries resources in Indonesiabased on characteristic and carrying capacity of marine waters,espcially in Bay region. The aims of this study were to estimate potency of Skipjack Tuna and the level of theirutilization in Bone Bay region and to estimate the primary productivity produced by euphotic zone (Pp).Analysis methods used in this study were catch per unit effort(CPUE) and maximum sustainable yield (MSY),vertically generalized production model (VGPM) which required data of photosynthetically active radiationanddepth of euphotic zone, fish production model by considering energy transfer efficiency among trophic level.This study was conducted for eight months in Luwu Regency.The result of the study showed that the utilization ofthe Skipjack Tunawas bigger than the MSY,.The Ppeu was in the range of 483.3143to 1306.027 mgC m. The Skipjack Tuna biomass estimation was in the range of 97.87 to264.47tonnes Keywords : Skipjack Tuna, utilization, potency, fisheries management, Bone Bay

Stock assessment of Hooghly Croaker Panna heterolepis in the Bay of Bengal (Southern Bangladesh): implications for sustainable management

The Application of ANN-Linear Perceptron in the Development of DSS for a Fishery Industry

This research aimed to determine utilization level and effort level of scad mackerel (<i>Decapterus spp</i>) in the North Bolaangmongondow waters. One of the approach in the management of the fisheries resources is by mathematics modelling. In this research using Surplus Production Model with 5 estimator methods, that are: Schaefer, Fox, Schnute, Walter-Hilborn, and Clarke Yoshimoto Pooley. The analysis was performed aiming to get the best estimated for the surplus production model to determine the maximum sustainable yields (MSY), utilization level, and effort level of scad mackerel. The criteria of the best model (estimator) are: sign suitability of regression equation, values of coefficient determination, validations value (residual), and significance of regression coefficients. From the best model by using the formula can be determined the maximum sustainable yields (MSY), utilization level, and effort level. The data of catch and fishing effort scad mackerel collected from the Marine and Fisheries Service of the North Bolaangmongondow Residence and the North Sulawesi Province from 2009 – 2021. The best Surplus Production Model, which is used to assess the potential of scad mackerel is <i>Fox Model</i>. Optimal effort (E<SUB>MSY</SUB>) of 83 trips per year, with catches of optimal C<SUB>MSY</SUB> 287.679 kgs per year. The effort level for 2021 is 63.86%, which shows the quite efficient of effort, the utilization level of 95.93%, showing the production nearly optimum.