Optimal Fishery Management Research Articles

Optimal fisheries management and the response to price changes

The literature on how price changes affect optimally managed fisheries is mostly concerned with how fish stocks and harvest rates are affected in steady state. There is little published on how prices affect optimal harvest rates at stock levels outside of steady state. Here we show the effect of an unanticipated and permanent price increase. It is shown that in a model of a pure schooling fishery, if the stock is below the steady state, it is optimal to harvest less if the price goes up and vice versa. It is also shown that in a model with stock dependent harvest costs, the optimal response to a price increase is to reduce the harvest rate for low stock levels even if the optimal harvest rate increases close to the steady state. Empirical relevance is demonstrated by illustrating the theoretical results in an estimated model.

Sustainable Harvests under Different Bio-economic Scenarios of Chilika Wetland’s Fisheries

The primary goal of fisheries management is to control overfishing and unregulated fisheries to protect stocks and boost the value of fish resources. In this study, we compare harvesting and fishing efforts in the maximum economic yield (MEY), maximum sustainable yield (MSY), and open access (OA) scenarios using Gordon-Schafer’s bioeconomic model to examine the economic status of Chilika’s fisheries. This paper also measures the effectiveness of Chilika Lake’s restoration measures. An independent sample t-test with bootstrap confidence intervals indicates the results’ robustness and concludes that the fisheries’ output has increased in the post-restoration period (2003–04 to 2020–21) in a statistically significant way. The estimated measures serve as the focal points for designing sustainable and optimal fisheries management strategies. They add to the ongoing research on stock evaluation, which helps determine harvesting effectiveness and strengthens the fishing stock to avoid exhaustion. Therefore, the expectation is that the outputs in the forms of optimal extraction and an enhanced management tool will improve livelihood opportunities and enhance other socioeconomic components of the fisheries sector. As a result, the findings will aid policymakers and other interested parties in creating a suitable harvesting strategy to attain economic optimality.

Influence of El Niño‐Southern Oscillation on bigeye and yellowfin tuna longline catch per unit effort in the equatorial Pacific

AbstractBigeye tuna (BET) and yellowfin tuna (YFT) are economically important target species of pelagic fisheries worldwide, especially for tropical Pacific nations whose economies and food sources are heavily affected by commercial and sustenance tuna fishing. The El Niño‐Southern Oscillation (ENSO) has a strong effect on the oceanographic conditions in the equatorial Pacific, including BET and YFT equatorial habitat and fishing grounds. For optimal fisheries management, the effects of environmental variability such as ENSO on the stocks and on the performance of fisheries must be known and predictable. However, besides some model predictions, the effects of ENSO on these two tuna species are not well understood. In this study, I investigate the statistical relationships between past ENSO conditions and equatorial fisheries using the Multivariate ENSO Index, sea surface temperature (SST), and catch and effort records from the longline fisheries in the region. Results of this study indicate that El Niño events have both delayed and concurrent positive effects on BET and YFT catch per unit effort (CPUE). The delayed positive ENSO effect on CPUE is hypothesized to be the result of enhanced recruitment acting via different mechanisms in the west than in the east. The concurrent positive effects on CPUE could be due to catchability, abundance, and/or vertical distribution of BET and YFT relative to fishing gear and require further investigation. Further exploration of the mechanisms that may underlie the results presented here could lead to predictability of CPUE of these two tuna species.

Productivity and Management of Renewable Resources: Why More Efficient Fishing Fleets Should Fish Less

This article analyses the effect of productivity improvements on optimal fisheries management. It is shown that when harvest costs are independent of resource stock and the stock is below its steady state level, then for any given stock it is optimal to reduce harvest levels in response to a productivity increase unless optimal harvest rate is already zero. If harvest costs are stock dependent this result is modified; for stock dependent harvest costs there exists an interval of stock sizes below the steady state where it is optimal to reduce the harvest rate for any given stock size whereas if the harvest rate is close to an economically optimal steady state it is optimal to increase the harvest rate.

Optimal Fisheries Management and the Response to Price Changes

Optimal Fisheries Management and the Response to Price Changes

Robust, ecological–economic multispecies management of Central Baltic fishery resources

Abstract The Baltic fisheries are in distress. In the Central Baltic, fisheries management is challenged by reduced cod stock productivity, and altered species interactions. Here, we use an age-structured, ecological–economic multispecies model, which includes latest biological and economic knowledge, to advance our understanding of optimal fisheries management and related trade-offs between user groups under such altered conditions. We contribute to the scientific discussion (i) by showing that the economic importance and optimal stock size of cod largely decreased under prevailing conditions, while clupeids increased in importance. (ii) We challenge the current MSY management objective in a multispecies setting (MMSY) and suggest that an economic multispecies management objective (MMEY) might be more useful for setting future management targets. (iii) We identify new trade-offs and synergies by including a consumer perspective: There is a win–win situation for ecological conservation, and profits in the fishery, while fishery management faces trade-offs between these two on the one hand, and consumer surplus on the other hand. (iv) Finally, we suggest an easy to implement new management approach, called robust management, which is capable of better dealing with variability and time-trends in recruitment, as observed for cod, in order to safeguard the Central Baltic fishery resources.

Lifetime residency of capelin (Mallotus villosus) in West Greenland revealed by temporal patterns in otolith microchemistry

Capelin (Mallotus villosus) is a marine fish species that spawns along the shorelines of Greenlandic fjords during late spring/early summer, but its migration patterns from hatching to spawning are largely unknown. This prohibits optimal fisheries advice and management of the stock. In this study, we examine spatial population structure through the lifetime of capelin in West Greenland using otolith microchemistry of 421 individual fish, caught while spawning at 16 different localities. In order to investigate the life-time residency of each fish, otolith core-to-edge measurements of Ba, Li, and Pb concentrations are classified to either of two West Greenland regions (north/south of ~68° N). Classifications suggest that West Greenland capelin reside mostly within one region throughout their life. Secondly, examination of Pb profiles indicate local residency on a smaller geographical scale. Otolith Pb levels, which most likely reflect bioavailable Pb derived from local geological and anthropogenic sources, vary between localities, but are found to be largely consistent throughout otolith chronologies of individual fish. Fish from neighboring localities are in some cases found to have contrasting otolith Pb levels, which suggests the existence of locally segregated populations with little or no connectivity. Significant Pb increases are observed towards the otolith edge, which indicates relatively high Pb exposure during the spawning period, where the fish enter shallow waters. These findings are in stark contrast to what is seen in other North Atlantic capelin stocks, such as those spawning in the Barents Sea, around Iceland and off East Canada, which exhibit long-distance migrations between spawning, feeding and overwintering areas. The information presented here has implications for West Greenland capelin stock management, which should be fitted within a high spatial resolution framework that takes locally segregated populations into account to avoid local collapses.

Environmental Variability and Threshold Model’s Predictions for Coral Reefs

Current models of the future of coral reefs rely on threshold (TM) and multivariate environmental variability models (VM) that vary in how they account for spatial and temporal environmental heterogeneity. Here, a VM based on General Additive Model (GAM) methods evaluated the empirical relationships between coral cover (n= 905 sites pooled to 318 reef cells of the Western and Central Indian Ocean Provinces) and 15 potentially influential variables. Six environmental and one fisheries management variables were selected as significant including SST shape distributions, dissolved oxygen, calcite, and fisheries management. Common predictive variables, including cumulative degree-heating weeks (DHW), pH, maximum light, SST bimodality and rate of rise, and two multivariate metrics were either weak or not significant predictors of coral cover. A spatially-resolved 2020 baseline for future predictions of coral cover within 11,678 reef ∼6.25 km2cells within 13 ecoregions and 4 fisheries management categories using the 7 top VM variables was established for comparing VM and TM coral cover prediction for the year 2050. We compared the two model’s predictions for high and low Relative Concentration Pathway (CMIP5; RCP8.5 and 2.6) scenarios using the four available future-cast SST variables. The excess heat (DHW)-coral mortality relationship of the TM predicted considerably lower coral cover in 2050 than the VM. For example, for the RCP8.5 and RCP2.6 scenarios, the decline in coral for the TM predicted was 81 and 58% compared to a 29 and 20% for the VM among reef cells with >25% coral cover in 2020, if a proposed optimal fisheries management was achieved. Despite differences, coral cover predictions for the VM and TM overlapped in two environmental regions located in the southern equatorial current region of the Indian Ocean. Historical and future patterns of acute and chronic stresses are expected to be more influential than cumulative heat stress in predicting coral cover, which is better accounted for by the VM than the TM.

Population dynamics of Indian river shad Gudusia chapra (Hamilton, 1822) using length frequency analysis for fisheries management in a floodplain wetland of Ganga River Basin, India

AbstractThe small‐scale fisheries sector plays very significant role in Indian fisheries. Fish life history parameters such as growth and morality are considered important factors for their conservation and management. Accordingly, the population parameters of a commercially important freshwater clupeid fish, Gudusia chapra (Hamilton, 1822) of Mathura beel, a tropical oxbow lake in West Bengal were investigated on the basis of primary data using a FiSAT‐II software package. A total of 2062 specimens of both sexes combined, exhibiting a length (TL) range 1.7–15.4 cm and a weight range of 1.14–35.69 g, were collected from different sites of the wetland during October 2017–September 2019. The growth parameters L∞, K and t0 of the species were 16.55 cm, 1.10/year and −0.02, respectively. The growth performance (ϕ) was 2.48. The estimated mortality rates Z, M and F were 2.72, 1.25 and 1.47/year, respectively. The current exploitation ratio (E) was estimated to be 0.54 based on the length‐converted catch curve. Analysis of the relative yield per recruit and relative biomass per recruit model indicated that the current E value is approaching an Emax value of 0.56. The maximum sustainable yield of this species was estimated to be 10.7 t, compared to the present annual yield of 11.5 t. For optimal fisheries management and a reduced risk of over exploitation, the current exploitation rate should be reduced by about 40% to achieve E0.5 as a target reference point. The information generated in the present study will facilitate optimal management of the resources for sustainable fisheries management and conservation of G. chapra.

Defining the stock structures of key commercial tunas in the Pacific Ocean II: Sampling considerations and future directions

Delineating the stock structure of highly-mobile, wide-ranging fishes subject to exploitation is a challenging task, yet one that is fundamental to optimal fisheries management. A case in point are stocks of skipjack tuna (Katsuwonus pelamis), yellowfin tuna (Thunnus albacares), bigeye tuna (Thunnus obesus) and albacore tuna (Thunnus alalunga) in the Pacific Ocean, which support important commercial, artisanal, subsistence, and recreational fisheries, and contribute roughly 70 % of global commercial tuna catches. Although some spatial and temporal structuring is recognised within these stocks, growing evidence from a range of approaches suggests that the stock structure of each tuna species is more complex than is currently assumed in both stock assessment and climate change models, and in management regimes. In a move towards improving understanding of the stock structure of skipjack, yellowfin, bigeye and South Pacific albacore tunas in the Pacific Ocean, an international workshop was held in Nouméa, New Caledonia, in October 2018 to review knowledge about their movement and stock structure in the region, define and discuss the main knowledge gaps and uncertainties concerning their stock structure, and develop biological sampling approaches to support the provision of this information. Here, we synthesise the discussions of this latter component. For each tuna species, we identify several general sampling considerations needed to reduce uncertainty, including i) the need for broadscale sampling in space, ideally covering each species’ distribution, targeting adults in spawning condition and adopting a phased approach; ii) the need for temporally-repeated sampling of the same geographical areas to assess stability in observed patterns over time; iii) the need to resolve patterns in spatial dynamics, such as those resulting from movements associated with the seasonal extensions of poleward flowing currents, from underlying stock structure, iv) the importance of adopting a multidisciplinary approach to stock identification, and v) the need for careful planning of logistics and coordination of sampling efforts across agencies. Finally, we present potential sampling designs that could be adopted to help overcome uncertainties around the initial identification of stocks and the provenance, mixing and proportional contributions of individuals in harvested assemblages, as well as how these uncertainties could be accounted for in fisheries management via the use of management strategy evaluation.

Ecological-economic sustainability of the Baltic cod fisheries under ocean warming and acidification

Human-induced climate change such as ocean warming and acidification, threatens marine ecosystems and associated fisheries. In the Western Baltic cod stock socio-ecological links are particularly important, with many relying on cod for their livelihoods. A series of recent experiments revealed that cod populations are negatively affected by climate change, but an ecological-economic assessment of the combined effects, and advice on optimal adaptive management are still missing. For Western Baltic cod, the increase in larval mortality due to ocean acidification has experimentally been quantified. Time-series analysis allows calculating the temperature effect on recruitment. Here, we include both processes in a stock-recruitment relationship, which is part of an ecological-economic optimization model. The goal was to quantify the effects of climate change on the triple bottom line (ecological, economic, social) of the Western Baltic cod fishery. Ocean warming has an overall negative effect on cod recruitment in the Baltic. Optimal management would react by lowering fishing mortality with increasing temperature, to create a buffer against climate change impacts. The negative effects cannot be fully compensated, but even at 3 °C warming above the 2014 level, a reduced but viable fishery would be possible. However, when accounting for combined effects of ocean warming and acidification, even optimal fisheries management cannot adapt to changes beyond a warming of +1.5° above the current level. Our results highlight the need for multi-factorial climate change research, in order to provide the best available, most realistic, and precautionary advice for conservation of exploited species as well as their connected socio-economic systems.

Accounting for tourism benefits in marine reserve design.

Marine reserve design often considers potential benefits to conservation and/or fisheries but typically ignores potential revenues generated through tourism. Since tourism can be the main source of economic benefits for many marine reserves worldwide, ignoring tourism objectives in the design process might lead to sub-optimal outcomes. To incorporate tourism benefits into marine reserve design, we develop a bioeconomic model that tracks tourism and fisheries revenues through time for different management options and location characteristics. Results from the model show that accounting for tourism benefits will ultimately motivate greater ocean protection. Our findings demonstrate that marine reserves are part of the optimal economic solution even in situations with optimal fisheries management and low tourism value relative to fisheries. The extent of optimal protection depends on specific location characteristics, such as tourism potential and other local amenities, and the species recreational divers care about. Additionally, as tourism value increases, optimal reserve area also increases. Finally, we demonstrate how tradeoffs between the two services depend on location attributes and management of the fishery outside marine reserve borders. Understanding when unavoidable tradeoffs will arise helps identify those situations where communities must choose between competing interests.

Stable isotopic composition of otoliths in identification of stock structure of small yellow croaker (Larimichthys polyactis) in China

Oxygen and carbon isotope ratios (δ 18O and δ 13C) in otoliths were used to identify the stock structure of small yellow croaker, Larimichthys polyactis. Otoliths were collected from fish at five locations across the Yellow Sea and the Bohai Sea representing most of their distributional range and fisheries areas. The significant differences in the isotopic signatures showed that the five locations could be chemically distinguished and clearly separated, indicating stock subdivision. Correlation of δ 18O and δ 13C values suggested that population of L. polyactis could be divided into the Bohai Sea group, the southern Yellow Sea group and the central Yellow Sea group. Discriminant analysis of δ 18O and δ 13C values demonstrated a high significant difference with 85.7% classification accuracy. The spatial separation of L. polyactis indicated a complex stock structure across the Yellow Sea and the Bohai Sea. These results indicate that optimal fisheries management may require a comprehensive consideration on the current spatial arrangements. This study has provided further evidence that measurement of the stable isotopes ratios in otolith can be a valuable tool in the delineation of fishery management units.

A perspective on needed research, modeling, and management approaches that can enhance Great Lakes fisheries management under changing ecosystem conditions

Abstract The Great Lakes Fishery Commission sponsored a 2-day workshop that sought to enhance the ability of Great Lakes agencies to understand, predict, and ideally manage fisheries production in the face of changes in natural and anthropogenic forcings (e.g., climate, invasive species, and nutrients). The workshop brought together 18 marine and freshwater researchers with collective expertise in aquatic ecology, physical oceanography, limnology, climate modeling, and ecosystem modeling, and two individuals with fisheries management expertise. We report on the outcome of a writing exercise undertaken as part of this workshop that challenged each participant to identify three needs, which if addressed, could most improve the ability of Great Lakes agencies to manage their fisheries in the face of ecosystem change. Participant responses fell into two categories. The first identified gaps in ecological understanding, including how physical and biological processes can regulate early life growth and survival, how life-history strategies vary across species and within populations, and how anthropogenic stressors (e.g., nutrient runoff, climate change) can interact to influence fish populations. The second category pointed to the need for improved approaches to research (e.g., meta-analytic, comparative, spatial translation) and management (e.g., mechanistic management models, consideration of multi-stock management), and also identified the need for improved predictive models of the physical environment and associated ecosystem monitoring programs. While some progress has been made toward addressing these needs, we believe that a continued focus will be necessary to enable optimal fisheries management responses to forthcoming ecosystem change.

Optimal Fishery Management with Regime Shifts: An Assessment of Harvesting Strategies

This paper compares outcomes from informed and uninformed harvesting strategies for a fish stock with switching dynamics where the probability of switching is influenced by climate. Using data on sea-surface temperature anomalies, the impacts of climate on the conservation and the welfare that can be extracted from the stock are investigated. Results indicate that an informed management policy leads to stock biomass and resource rents that are up to 2.7 and 2 times higher, respectively, than under an uninformed policy. Also, the fishery is open 54 % longer under the informed policy. The magnitude of these effects depends on the choice of the discount rate indicating that when the future is highly discounted gains from the informed policy dissipate.

Incentives for optimal management of age-structured fish populations

We characterize optimal fishery management in an age-structured, bio-economic model where two age groups are harvested with costly and imperfect selectivity. We show that a system of tradable fishing permits, each allowing to harvest a specific number of fish that differs with age group, implements optimal age-structured harvesting, while traditional biomass quotas fail to solve the problem of growth overfishing. With our system, gear restrictions (such as mesh-size prescriptions) become obsolete. We apply our model to the Eastern Baltic cod fishery and quantify the benefits of optimal age-structured management.

Does the Optimal Size of a Fish Stock Increase with Environmental Uncertainties?

We analyze the effect of environmental uncertainties on optimal fishery management in a bio-economic fishery model. Unlike most of the literature on resource economics, but in line with ecological models, we allow the different biological processes of survival and recruitment to be affected differently by environmental uncertainties. We show that the overall effect of uncertainty on the optimal size of a fish stock is ambiguous, depending on the prudence of the value function. For the case of a risk-neutral fishery manager, the overall effect depends on the relative magnitude of two opposing effects, the ‘convex-cost effect’ and the ‘gambling effect’. We apply the analysis to the Baltic cod and the North Sea herring fisheries, concluding that for risk neutral agents the net effect of environmental uncertainties on the optimal size of these fish stocks is negative, albeit small in absolute value. Under risk aversion, the effect on optimal stock size is positive for sufficiently high coefficients of constant relative risk aversion.

Integrating habitat restoration and fisheries management : A small-scale case-study to support EEL conservation at the global scale

The aim of this work was to develop a methodological framework for the management of local eel stocks that integrates habitat restoration with optimal fishery management. The Bolsena lake (Viterbo, Italy) and its emissary, the river Marta, were taken as a reference system. The river flows in the Mediterranean sea but its course is fragmented by a number of dams built in the past century preventing eel migration from and to the sea. Eel fishery in the Bolsena lake is thus sustained by periodic stocking of glass eels caught at the Marta river estuary. A detailed demographic model was applied to simulate fishery yields and potential spawner escapement under different recruitment and management scenarios. It was estimated that the high exploitation rates occurring in the nineties reduced the potential spawner escapement from the Bolsena lake to less than 1 t; under current harvesting rates, the potential spawner escapement is estimated in about 12 t while in pristine conditions (i.e. high recruitment and no fishing) estimated spawner escapement is about 21 t. This analysis thus showed that current fishery management would comply with the 40% spawner escapement requirement of the EU regulation 1100/2007 if the connections between the Bolsena lake emissary and the sea were fully re-established. This confirms the opportunity of an integrated approach to management at the catchment area level scale for eel populations, that shall hopefully contribute to the conservation of the global stock.

Stock structure of blue threadfin Eleutheronema tetradactylum across northern Australia as inferred from stable isotopes in sagittal otolith carbonate

Abstract Stable isotopes of δ18O and δ13C in sagittal otolith carbonates were used to determine the stock structure of the polynemid Eleutheronema tetradactylum (Shaw) across tropical northern Australia, where this species is an important component of inshore commercial and recreational fisheries. Stable isotopes from the sagittal otolith carbonate of 470 fish from 11 discrete locations across western, northern and eastern Australia were sampled between 2007 and 2009. Analysis of these stable isotopes revealed different location-specific signatures, indicating strong population subdivision. The significant differences in the isotopic signatures of E. tetradactylum demonstrated that there is unlikely to be substantial movement of fish between these locations. The spatial separation of these populations indicates a complex fine spatial scale stock structure across northern Australia, with at least 11 stocks or management units present. The population subdivision of E. tetradactylum was evident along expansive stretches of open beach systems and within coastal embayments with no physical barriers such as headlands. These results indicate that optimal fisheries management will require a review of the current spatial arrangements, particularly the potential for localised depletion of stocks on small spatial scales.

Variation in stable isotope (δ 18O and δ 13C) signatures in the sagittal otolith carbonate of king threadfin, Polydactylus macrochir across northern Australia reveals multifaceted stock structure

Otoliths of king threadfin, Polydactylus macrochir were collected from 2007 to 2009 at nine locations across northern Australia representing most of their distributional range and areas where fisheries are active. Measurement of the stable isotope ratios of δ 18O and δ 13C in the sagittal otolith carbonate from assemblages of P. macrochir revealed location-specific signatures and indicated that adult fish sampled from representative sites across their range were significantly different. The significant differences in the isotopic signatures of P. macrochir demonstrated that population subdivision is evident and there is unlikely to be substantial movement of fish among these distinct adult assemblages. The stable isotopic signatures for the fish from the different locations were persistent through time, and therefore it could be concluded that they comprise separate stocks for many of the purposes of fisheries management. The spatial separation of these populations indicates a complex stock structure across northern Australia with stocks of P. macrochir associated with large coastal beaches and embayments on a fine spatial scale. These results indicate that in order to achieve optimal fisheries management, the current spatial management arrangements need to be reviewed, particularly the potential for localised depletion of stocks on small spatial scales. This study has provided further evidence that measurement of the stable isotopes ratios in teleost sagittal otolith carbonate can be a valuable tool in the delineation of fishable stocks or fishery management units of adult fish and that widely distributed fish can nonetheless show strong localised population structure.