Comparative assessment of soil quality dynamics using SQI modelling approach: a study in rice bowl of West Bengal, India.

The study attempted to evaluate the agricultural soil quality using the Soil Quality Index (SQI) model in two Community Development Blocks, Ausgram-II and Memari-II of Purba Bardhaman District. Total 104 soil samples were collected (0-20 cm depth) from each Block to analyse 13 parameters (bulk density, soil porosity, soil aggregate stability, water holding capacity, infiltration rate, available nitrogen, available phosphorous, available potassium, soil pH, soil organic carbon, electrical conductivity, soil respiration and microbial biomass carbon) in this study. The Integrated Quality Index (IQI) was applied using the weighted additive approach and non-linear scoring technique to retain the Minimum Data Set (MDS). Principal Component Analysis (PCA) identified that SAS, BD, available K, pH, available N, and available P were the key contributing parameters to SQI in Ausgram-II. In contrast, WHC, SR, available N, pH, and SAS contributed the most to SQI in Memari-II. Results revealed that Ausgram-II (0.97) is notably higher SQI than Memari-II (0.69). In Ausgram-II, 99.72% of agricultural lands showed very high SQI (Grade I), whereas, in Memari-II, 49.95% of lands exhibited a moderate SQI (Grade III) and 49.90% showed a high SQI (Grade II). Sustainable Yield Index (SYI), Sensitivity Index (SI) and Efficiency Ratio (ER) were used to validate the SQIs. A positive correlation was observed between SQI and paddy ( R2 = 0.82 & 0.72) and potato yield (R2 = 0.71 & 0.78) in Ausgram-II and Memari-II Block, respectively. This study could evaluate the agricultural soil quality and provide insights for decision-making in fertiliser management practices to promote agricultural sustainability.

Estimating the growth parameters, exploitation rate, biomass and maximum sustainable yield of long whisker catfish Mystus gulio (Hamilton, 1822) in the coastal waters from southwestern Bangladesh.

The research provides a comprehensive analysis of Mystus gulio including growth pattern, growth parameters, recruitment patterns, mortality rates, biomass, exploitation rate (E), and the estimation of maximum sustainable yield (MSY) within the southwestern coastal waters of Bangladesh. From January to December 2017, fishers provided around 1200 specimens. FAO-ICLARM Stock Assessment Tool and Excel-add-in-solver were used to assess stock status through length-frequency data. Indeed, the research findings indicated that the population of M. gulio displayed negative allometric for both individuals (b = 2.53 for male, b = 2.50 for female), as demonstrated by the calculated allometric coefficient value. Nonetheless, the population's dynamic characteristics revealed an asymptotic length (L∞) of 19.34 cm, 23.28 cm and growth coefficient (K) 0.94 year-1 and 0.81 year-1 for male and female M. gulio. The growth performance indexes (Ø') of 2.55 and 2.64 for male and female and maximum lifespan (tmax) 3.20 years and 3.70 years respectively. This study revealed that the slightly variations in the natural mortality rate (M) for both specimens at 1.55 year-1 and 1.59 year-1. The fishing mortality rate (F) 2.75 year-1 and 1.98 year-1and total mortality rate (Z) 4.30 year-1 and 3.57 year-1 for male and females, respectively. The maximum permissible exploitation rate (Emax = 0.421) was lower than the actual exploitation rate (E = 0.63). The MSY was calculated at 67.968 metric tons. Without a doubt, overfishing stands out as the most critical threat to the wild stock. Therefore, it is clear that the existing fishing approach was not efficiently managed the standing stock in a sustainable manner. The findings would be useful for established proper fishing regulations in coastal waters and the surrounding ecosystems.

Effect of boron fertilization on productivity and sustainability of rice-wheat cropping system in Tarai region, North-West India.

Extensive global dependency on rice and wheat crops has necessitated the adoption of intensive cultivation practices, thereby compelling to closely monitor the potential yield-limiting factors, among which, boron (B) deficiency stands out to be a prime concern. The present study explores the effects of B fertilization strategies within the Rice-Wheat Cropping System (RWCS) in the Tarai region of North-West India. A comprehensive six-year field experiment was conducted (2013-2019) at G.B. Pant University of Agriculture and Technology, Uttarakhand, India. The experiment tested graded B doses (0.5, 1.0, 1.5, and 2.0 kg ha-1) at varied frequencies (single, alternate, and annual) in a factorial design. The study revealed significant impacts of alternate B application at 1.5 kg ha-1 on crop yields and the Sustainable Yield Index (SYI). The System Rice Equivalent Yield (SREY) exhibited an increase of 6.7% with B supplementation over B-deprived plots, highlighting the pivotal role of B fertilizer in enhancing productivity within the RWCS. The economic optimum B dose was found to be 1.422 kg ha-1 using a linear plus plateau model, resulting in a calculated annual SREY of 9.73 t ha-1 when applied alternately to the cropping system. Continuous application and higher B rates demonstrated substantial increases in various B fractions, while the mobility factor remained within 10%, depicting safe ecological limits. The distribution of fractions in B-treated plots on average followed the order: residual B > organically-bound B > oxide bound B > specifically adsorbed B > readily soluble B. Similarities in the distribution patterns of B fractions between B-treated plots and the control indicated potential influence of biotic or abiotic processes on B fraction dynamics, even in the absence of external B application. To sum up, B application in alternate years at 1.5 kg ha-1 was most sustainable in enhancing the SREY, SYI, available soil B, and B fractions and lowering the environmental hazards.

Phytohormones unlocking their potential role in tolerance of vegetable crops under drought and salinity stresses.

Globally, abiotic stresses are drastically reducing the productivity of vegetable crops. Among abiotic stresses, drought and salinity are more challenging constraints for the sustainable production of vegetables. A great variety of vegetables are facing dry and hot summer spells, poor water availability, and higher salinity mainly due to irrigation with brackish water. Vegetables are considered higher water-dependent crops, requiring water for proper growth and yield. Drought and salinity impair plant metabolism. The disruption in plant metabolism leads to a reduction in growth, developmental processes, and ultimately crop yield. Appropriate management measures are needed to cope with the adverse effects of drought and salinity. Different agronomic and molecular approaches contributed to improving tolerance. Therefore, the present review significantly explores the impact of phytohormones on vegetable crops under drought and salinity stresses. Phytohormones (salicylic acid, melatonin, jasmonates, Brassinosteroids, ascorbic acid, and numerous others) can be sprayed for improvement of plant growth, yield, and photosynthetic pigments by modulation of physiological and biochemical processes. In this manner, these phytohormones should be explored for sustainable production of vegetable crops growing under abiotic stress conditions.

Stock assessment of landlocked ayu Plecoglossus altivelis altivelis in Japan through length-based models.

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.

Square root identities for harvested Beverton-Holt models.

We introduce the term net-proliferation rate for a class of harvested single species models, where harvest is assumed to reduce the survival probability of individuals. Following the classical maximum sustainable yield calculations, we establish relations between the proliferation and net-proliferation that are economically and sustainably favored. The resulting square root identities are analytically derived for species following the Beverton-Holt recurrence considering three levels of complexity. To discuss the generalization of the results, we compare the square root result to the optimal survival rate of the Pella-Tomlinson model. Furthermore, to test the practical relevance of the square root identities, we fit a stochastic Pella-Tomlinson model to observed Barramundi fishery data from the Southern Gulf of Carpentaria, Australia. The results show that for the estimated model parameters, the equilibrium biomass levels resulting from the MSY harvest and the square root harvest are similar, supporting the claim that the square root harvest can serve as a rule-of-thumb. This application, with its inherited model uncertainty, sparks a risk sensitivity analysis regarding the probability of populations falling below an unsustainable threshold. Characterization of such sensitivity helps in the understanding of both dangers of overfishing and potential remedies.

Game-theoretical model for the sustainable use of thermal water resources: the case of Ischia volcanic Island (Italy).

The Island of Ischia, one of the Italian active volcanoes, is a famous tourist resort for spa treatments. Spas are supplied by withdrawals from groundwaters which are characterized by a wide range of chemical compositions, salinity and temperature. In natural conditions, the hydrogeological system is recharged by rainfall and by deep fluids; the discharge is towards the sea and the springs. During the peak of the tourist season, when approximately 240 wells are operating simultaneously, a significant additional recharge of the aquifers derives from seawater and from upwelling increase in deep fluids. Although this does not compromise the availability of groundwater, the pumping often determines variation in composition and temperature of groundwater over time. Conversely, the maintenance of a stable quality of thermal waters represents one of the requirements for their therapeutic use in the spas. The study aims to establish game-theoretical modeling of the optimal sustainable exploitation of the groundwater resources of the island by competing users (spas) falling in the same flow tube of the aquifer. In the game the spas are the players, the strategy of a player consists of a fixed pumping rate and daily time durations of pumping, and the player's utility or payoff is proportional to the total quantity of withdrawn thermal water in a given time period. A special constrained Pareto optimal strategy choice is obtained, considered as a cooperative solution of the game. Pareto optimality means that there is no other strategy choice that makes one player better off without making some other player worse off.

Production, Optimization, Characterization and Drought Stress Resistance by ß-Glucan-Rich Heteropolysaccharide From an Endophytic Fungi Colletotrichum alatae LCS1 Isolated From Clubmoss (Lycopodium clavatum).

Endophytic entities are ubiquitous in nature with all-square bioactivity ranging from therapeutic effects toward animals to growth promoting attributes and stress tolerance activities in case of green plants. In the present study, the club moss Lycopodium clavatum for the first time has been subjected for the isolation of endophytic fungi. An exopolysaccharide (EPS) extracted from Colletotrichum alatae LCS1, an endophytic fungi isolated from L. clavatum Linn., was characterized as a ß-glucan heteropolymer (composed of mannose, rhamnose, arabinose, glucose, galactose, and fucose) which plays a pivotal role in obliterating the drought stress in rice seedlings (Oryza sativa) when applied at an amount of 20, 50, and 100 ppm. The fresh weight contents of rice tissue (39%), total chlorophyll (33%), proline (41%), soluble sugar content (26%) along with antioxidant enzymes such as catalase, peroxidase, and super-oxide dismutase increased (in comparison to control of non-EPS treated seedlings) while malondialdehyde content had reduced markedly after 30 days of regular treatment. The drought resistance of rice seedling was observed at peak when applied at 50 ppm dosage. Vital parameters for EPS production like fermentation duration (5 days), medium pH (6), nutrient (carbon (glucose-7 g%/l), nitrogen (yeast extract-0.4 g%/l), and mineral (NaCl-0.10 g%/l) sources, oxygen requirements (O2 vector or liquid alkane-n-hexane, n-heptane, n-hexadecane), and headspace volume (250 ml Erlenmeyer flask- 50 ml medium, 200 ml-headspace volume) were optimized to obtain an enhanced EPS yield of 17.38 g/L-59% higher than the preoptimized one. The present study, for the first time, reported the ß-glucan rich heteropolysaccharide from Colletotrichum origin which is unique in structure and potent in its function of drought stress tolerance and could enhance the sustainable yield of rice cultivation in areas facing severe drought stress.

Adaptability of quinoa genotypes to altitudes and population densities in Colombia / Adaptação de genótipos de quinoa em altitudes e densidades de plantio na Colômbia

This work aimed at evaluating and comparing agronomic characteristics of 15 quinoa (Chenopodium quinoa Willd) genotypes cultivated in two altitudes and sowing densities. The experiment initiated by individual plant selection in Brasília, DF, followed by progeny evaluation in Colombia, at 1,100 m and 1,850 m altitude and population densities of 30 and 12 plants m-1, with row spacing of 0,50 m. Eleven progenies and four commercial cultivars were tested. The progenies were obtained by selecting individuals in BRS Syetetuba based on plant height, grain and dry matter yield, harvest index and 1,000 grain weight. The genotypes with the highest grain yield were BRQ 8 (2,283 kg ha-1), Aurora (2,121 kg ha-1) and BRQ 4 (2,043 kg ha-1). In general, the genotypes had early plant cycle, from emergence to physiological maturity of 100-110 days at high plant density for the two altitudes. It is concluded that exploring variability in progenies originated from natural crosses is effective in the adaptation of quinoa to tropical environments. Moreover, genotypes tested in the Cerrado (Brazilian Savannah) maintain the same response relation when evaluated in Colombia. (AU)

Este trabalho teve por objetivo avaliar e comparar características agronômicas e biométricas de 15 genótipos de quinoa (Chenopodium quinoa Willd), cultivados em duas altitudes e densidades de semeadura. O experimento iniciou por seleção individual em Brasília, DF, seguido por avaliação agronômica em duas altitudes (1,100 m e 1,850 m), e duas densidades de semeadura (30 plantas m-1 e 12 plantas m-1) na Colômbia. O experimento foi constituído por 11 progênies e quatro cultivares comerciais em uso na Colômbia. Na seleção, consideraram-se altura de plantas, produção de grãos e massa seca, índice de colheita e peso de 1000 grãos. Os genótipos que se destacaram para rendimento foram BRQ 8 (2,283 kg ha-1), Aurora (2,121 kg ha-1) e BRQ 4 (2,043 kg ha-1). Em geral, os genótipos apresentaram precocidade, com ciclo (emergência-maturação) entre 100 e 110 dias, com densidade ótima de 30 plantas m-1 nas duas altitudes. Conclui-se que a exploração de variabilidade em progênies oriundas de cruzamentos naturais, mostra-se efetiva na adaptação de quinoa a ambientes tropicais. Ademais, genótipos selecionados no Cerrado mantêm as mesmas relações de resposta quando avaliados na Colômbia. (AU)

Sustainable agronomic practices for enhancing the soil quality and yield of Cicer arietinum L. under diverse agroecosystems.

Sustainable agronomic practices are being implemented worldwide to promote the cleaner and planet friendly crop production. Therefore, in the present study, we investigated the effect of agro-waste derived biochar and vermicompost on soil quality and yield in Cicer arietinum L. Field experiment was carried out at three different agro-climatic regions (Varanasi, Sultanpur and Gorakhpur) of Uttar Pradesh, India and periodic soil and crop sampling were done accordingly. Experimental results proven that a significant increase (p < 0.01) in total organic carbon, available N, P and K content was observed under vermicompost followed by biochar amendment at each site. Similarly, irrespective of the experimental site, a significant increase (p < 0.01) in microbial biomass carbon was recorded under vermicompost amendment. Furthermore, the addition of vermicompost increased the grain yield (28-39%) than biochar (23-36%) addition whereas the higher microbial and soil respiration (2-6%) found in former field than the biochar added field (1-3%). Significant correlation (R2= 0.61-0.99) was found between the sustainable yield index and soil fertility factors at each site. Assessment of agricultural soil sustainability indicators (ASSI) suggests that the biochar was more effective in enhancing the soil carbon stock (21 ± 1.31 Mg C ha-1) and higher glomalin activity (62%). The study also confirmed the increased alkaline phosphatase (two fold) and ß-glucosidase activity (one fold) along with enhanced urease (45%), soil dehydrogenase activity (36%) under vermicompost amendment followed by biochar. Present study highlights the significance of sustainable agronomic practices for improving the soil quality and agricultural yield while reducing adverse impact.

Balancing maximum sustainable yield and ecological resilience in an exploited two-predator one-prey system.

In this paper, we consider a two-predator one-prey system to determine the feedback of exploitation in individual as well as joint population levels. As balancing yield with resilience is highly essential for the conservation of species in the marine ecosystem, here we measure both the maximum sustainable yield (MSY) and resilience simultaneously. Then we investigate both the trade-offs and synergies among maximum yield, conservation, and resilience that emerge from different harvesting plans. It is found that for single species harvesting, a prey species-oriented system is capable of producing more yield in compare to any predator-oriented system but for resilience, a prey species-oriented system is far behind the others. In the case of joint harvesting of all the species, it is observed that the first predator-oriented system has a better ability to absorb the disturbances than the other cases. The correlation between yield and resilience at the MSY level is studied in all the cases. It is further observed that the increase of intraspecific competition in the predator decreases the risk of sustainability. In this way, this study may be helpful for fishery management to fulfill their goals without affecting the ecosystem's health in the long run.

Proportional threshold harvesting in discrete-time population models.

Threshold-based harvesting strategies tend to give high yields while protecting the exploited population. A significant drawback, however, is the possibility of harvesting moratoria with their socio-economic consequences, if the population size falls below the threshold and harvesting is not allowed anymore. Proportional threshold harvesting (PTH) is a strategy, where only a fraction of the population surplus above the threshold is harvested. It has been suggested to overcome the drawbacks of threshold-based strategies. Here, we use discrete-time single-species models and rigorously analyze the impact of PTH on population dynamics and stability. We find that the population response to PTH can be markedly different depending on the specific population model. Reducing the threshold and allowing more harvest can be destabilizing (for the Ricker and Hassell map), stabilizing (for the quadratic map), or both (for the generalized Beverton-Holt map). Similarly, management actions in the form of increasing the threshold do not always improve population stability-this can also be due to bistability. Our results therefore emphasize the importance of a rigorous analysis in investigating the impact of PTH on population stability.

What is multispecies MSY? A worked example from the North Sea.

The concept of an optimum yield at intermediate levels of fishing (the so called maximum sustainable yield or MSY) has been with us since the 1930s and is now enshrined in legislation as a key objective of fisheries management. The concept seems intuitively reasonable and is readily applicable to a single stock treated in isolation and assuming a constant environment. However, translating this concept into a mixed and multispecies fishery, where there are complex trade-offs between fleets and stocks and in general no simple optimum solution, has been problematic. Here I introduce a framework for thinking about multispecies MSY in terms of an integrated risk of stock depletion and expected long-term yield. Within this framework I consider the performance of a set of simple harvest control rules based upon a single-limit fishing mortality rate (F) which is common to all stocks and a target biomass which is a set fraction of a stock's virgin biomass. Using a multispecies management strategy evaluation, I compare expected outcomes for a set of these harvest control rules with alternative scenarios, in which each stock has its own F based on the assessment process. I find that the simple framework can produce outcomes that are similar to those from the more sophisticated estimates of F. I therefore conclude that achieving multispecies MSY may depend more upon setting reasonable biomass targets and faithfully applying a harvest control rule approach rather than determining the best possible Fs for each stock.

Meeting Yield and Conservation Objectives by Harvesting Both Juveniles and Adults.

Sustainable yields that are at least 80% of the maximum sustainable yield are sometimes referred to as "pretty good yields" (PGY). The range of PGY harvesting strategies is generally broad and thus leaves room to account for additional objectives besides high yield. Here, we analyze stage-dependent harvesting strategies that realize PGY with conservation as a second objective. We show that (1) PGY harvesting strategies can give large conservation benefits and (2) equal harvesting rates of juveniles and adults is often a good strategy. These conclusions are based on trade-off curves between yield and four measures of conservation that form in two established population models, one age-structured model and one stage-structured model, when considering different harvesting rates of juveniles and adults. These conclusions hold for a broad range of parameter settings, although our investigation of robustness also reveals that (3) predictions of the age-structured model are more sensitive to variations in parameter values than those of the stage-structured model. Finally, we find that (4) measures of stability that are often quite difficult to assess in the field (e.g., basic reproduction ratio and resilience) are systematically negatively correlated with impacts on biomass and size structure, so that these later quantities can provide integrative signals to detect possible collapses.

Managing yield and resilience in a harvested tri-trophic food chain model.

In this article, we compare the two ecological services known as yield and resilience, for a tri-trophic food chain model consisting of a prey, an intermediate predator and a top predator. For this comparison process, we use both analytical and numerical techniques. It is shown that a variety of patterns are possible based on the intensity of efforts distributed among different trophic levels. Thus we may suggest that fishing down the food chain, as suggested by Pauly et al. (1998) is not bound to happen. Our analysis also shows that balancing the harvest between prey, intermediate predator and top predator could give more yield and stabilizing the ecosystem, than the selective harvesting of any one species. This balanced harvesting may not be a win-win situation for yield and resilience, but it could be a most favourable strategy to balance them. This research would help to correlate resilience with yield and determines the desirable selection of two policies, resilience maximizing yield or maximum sustainable yield to safeguard ecological communities.

Harvesting induced stability and instability in a tri-trophic food chain.

Non-equilibrium dynamics in the form of oscillations or chaos is often found to be a natural phenomenon in complex ecological systems. In this paper, we first analyze a tri-trophic food chain, which is an extension of the Rosenzweig-MacArthur di-trophic food chain. We then explore the impact of harvesting individual trophic levels to answer the following questions : a) when a non-equilibrium dynamics persists, b) whether it can locally be stabilized to a steady state, c) when the system switches from a stable steady state to a non-equilibrium dynamics and d) whether the Maximum Sustainable Yield (MSY) always exists when the top predator is harvested. It is shown that searching for a general theory to unify the harvesting induced stability must take into account the number of trophic levels and the degree of species enrichment, the outcomes that cannot be obtained from the earlier reports on prey-predator models. We also identify the situation where harvesting induces instability switching: the non-equilibrium state enters into a stable steady-state and then, upon more intensive harvesting, the steady-state again loses its stability. One of the new and important results is also that the MSY may not exist for harvesting the top predator. In general, our results contribute to biological conservation theory, fishery and ecosystem biodiversity management.

Prospective study of the fishery of the shrimp Plesionika narval (Fabricius, 1787) in the Northeastern Atlantic / Estudo prospectivo da pesca do camarão Plesionika narval (Fabricius, 1787) no Atlântico Nordeste

Abstract Several experimental surveys were carried out in the Northeastern Atlantic, Madeira archipelago from 1991 to 2008 to explore new fisheries resources. This study examined the selectivity of bottom and floating traps and the analysis of yield-per-recruit (YPR) and biomass-per-recruit (BPR) providing helpful insight to the management of the shrimp Plesionika narval. A total of 28,262 specimens were sampled and the analysis of length at first capture returned higher values when using floating traps indicating that these traps are more selective, exerting less pressure on the resource. The YPR and BPR analysis showed that the stock is under exploited for the studied area and suggests that the use of floating traps in the commercial fisheries of P. narval is recommended, which will allow a higher maximum allowable limit of exploitation and greater yield. The results suggest that P. narval has the potential to support a viable and sustainable fishery using floating traps.

Resumo Vários cruzeiros de investigação foram realizados no Atlântico Nordeste, arquipélago da Madeira entre 1991 e 2008 visando a exploração de novos recursos pesqueiros. O presente estudo contemplou a comparação da seletividade de pesca entre armadilhas de fundo e flutuantes e a análise de rendimento por recruta (YPR) e biomassa por recruta (BPR) facultando informação essencial para a gestão do camarão Plesionika narval. Um total de 28,262 especimens foram amostrados e a análise de comprimento de primeira captura retornou valores mais elevados aquando da utilização de armadilhas flutuantes, indicando que essas armadilhas são mais seletivas e exercem menos pressão sobre o recurso. A análise YPR e BPR mostrou que o estoque se encontra sob explorado para a área de estudo e recomenda a utilização de armadilhas flutuantes na pesca comercial de P. narval, que permitirão um limite máximo de exploração com rendimento superior. Os resultados sugerem que P. narval tem o potencial para suportar uma pescaria viável e sustentável mediante a utilização de armadilhas flutuantes.

Prospective study of the fishery of the shrimp Plesionika narval (Fabricius, 1787) in the Northeastern Atlantic

Abstract Several experimental surveys were carried out in the Northeastern Atlantic, Madeira archipelago from 1991 to 2008 to explore new fisheries resources. This study examined the selectivity of bottom and floating traps and the analysis of yield-per-recruit (YPR) and biomass-per-recruit (BPR) providing helpful insight to the management of the shrimp Plesionika narval. A total of 28,262 specimens were sampled and the analysis of length at first capture returned higher values when using floating traps indicating that these traps are more selective, exerting less pressure on the resource. The YPR and BPR analysis showed that the stock is under exploited for the studied area and suggests that the use of floating traps in the commercial fisheries of P. narval is recommended, which will allow a higher maximum allowable limit of exploitation and greater yield. The results suggest that P. narval has the potential to support a viable and sustainable fishery using floating traps.

Resumo Vários cruzeiros de investigação foram realizados no Atlântico Nordeste, arquipélago da Madeira entre 1991 e 2008 visando a exploração de novos recursos pesqueiros. O presente estudo contemplou a comparação da seletividade de pesca entre armadilhas de fundo e flutuantes e a análise de rendimento por recruta (YPR) e biomassa por recruta (BPR) facultando informação essencial para a gestão do camarão Plesionika narval. Um total de 28,262 especimens foram amostrados e a análise de comprimento de primeira captura retornou valores mais elevados aquando da utilização de armadilhas flutuantes, indicando que essas armadilhas são mais seletivas e exercem menos pressão sobre o recurso. A análise YPR e BPR mostrou que o estoque se encontra sob explorado para a área de estudo e recomenda a utilização de armadilhas flutuantes na pesca comercial de P. narval, que permitirão um limite máximo de exploração com rendimento superior. Os resultados sugerem que P. narval tem o potencial para suportar uma pescaria viável e sustentável mediante a utilização de armadilhas flutuantes.

Quota implementation of the maximum sustainable yield for age-structured fisheries.

One of the main goals stated in the proposals for the Common Fisheries Policy (CFP) reform was achieving maximum sustainable yield (MSY) for all European fisheries. In this paper, we propose a fishing rights allocation mechanism or management system, which specifies catch limits for individual fishing fleets to implement MSY harvesting conditions in an age-structured bioeconomic model. An age-structured model in a single species fishery with two fleets having perfect or imperfect fishing selectivity is studied. If fishing technology or gear selectivity depends on the relative age composition of the mature fish stock, fixed harvest proportions, derived from catchability and bycatch coefficients, is not valid anymore. As a result, not only the age-structure and fishing technology but also the estimated level of MSY is steering the allocation of quota shares. The results also show that allocation of quota shares based on historical catches or auctioning may not provide viable solutions to achieve MSY.

An explicit solution for calculating optimum spawning stock size from Ricker's stock recruitment model.

Stock-recruitment models have been used for decades in fisheries management as a means of formalizing the expected number of offspring that recruit to a fishery based on the number of parents. In particular, Ricker's stock recruitment model is widely used due to its flexibility and ease with which the parameters can be estimated. After model fitting, the spawning stock size that produces the maximum sustainable yield (S MSY) to a fishery, and the harvest corresponding to it (U MSY), are two of the most common biological reference points of interest to fisheries managers. However, to date there has been no explicit solution for either reference point because of the transcendental nature of the equation needed to solve for them. Therefore, numerical or statistical approximations have been used for more than 30 years. Here I provide explicit formulae for calculating both S MSY and U MSY in terms of the productivity and density-dependent parameters of Ricker's model.