Fisheries Management Scenarios Research Articles

MANAGING IN FISHERIES BY USING INDIVIDUAL TRANSFERABLE QUOTAS

The aim of this paper is to present possible fisheries management scenarios and detailed analysis of individual transferable quotas as a potential solution for negative trend in fisheries caused by insufficient elaborated and non-integrated management policy. The application of management policy in a variety of environments, together with application results, is also considered.

Indirect Effects of Conservation Policies on the Coupled Human-Natural Ecosystem of the Upper Gulf of California

High bycatch of non-target species and species of conservation concern often drives the implementation of fisheries policies. However, species- or fishery-specific policies may lead to indirect consequences, positive or negative, for other species or fisheries. We use an Atlantis ecosystem model of the Northern Gulf of California to evaluate the effects of fisheries policies directed at reducing bycatch of vaquita (Phocoena sinus) on other species of conservation concern, priority target species, and metrics of ecosystem function and structure. Vaquita, a Critically Endangered porpoise endemic to the Upper Gulf of California, are frequently entangled by finfish gillnets and shrimp driftnets. We tested five fishery management scenarios, projected over 30 years (2008 to 2038), directed at vaquita conservation. The scenarios consider progressively larger spatial restrictions for finfish gillnets and shrimp driftnets. The most restrictive scenario resulted in the highest biomass of species of conservation concern; the scenario without any conservation measures in place resulted in the lowest. Vaquita experienced the largest population increase of any functional group; their biomass increased 2.7 times relative to initial (2008) levels under the most restrictive spatial closure scenario. Bycatch of sea lions, sea turtles, and totoaba decreased > 80% in shrimp driftnets and at least 20% in finfish gillnet fleets under spatial management. We found indirect effects on species and ecosystem function and structure as a result of vaquita management actions. Biomass and catch of forage fish declined, which could affect lower-trophic level fisheries, while other species such as skates, rays, and sharks increased in both biomass and catch. When comparing across performance metrics, we found that scenarios that increased ecosystem function and structure resulted in lower economic performance indicators, underscoring the need for management actions that consider ecological and economic tradeoffs as part of the integrated management of the Upper Gulf of California.

Theory, consequences and evidence of eroding population spatial structure in harvested marine fishes: a review

In marine populations, spatial structure arises over a wide range of scales and forms hierarchical aggregations. Changing spatial structure can alter the demographic and life history trait variation within populations and subject individuals to both novel environmental conditions and interspecific interactions. Thus, changes in the spatial structure of marine populations can be a prelude to further changes in abundance and can affect the resilience and recovery potential of populations following anthropogenic and environmental perturbations. These observations under - score the importance of studying the spatial ecology of marine fish populations in order to (1) understand the underlying mechanisms that can lead to rapid alterations in population abundance and community interactions, (2) provide indicators of stock health, and (3) characterize the conse- quences of changing spatial patterns on population susceptibility to exploitation and environmen- tal variability. Here, we synthesize the interacting factors that influence the formation, mainte- nance and erosion of spatial structure in marine fish populations and identify the further con sequences of such erosion at the population and community levels. We emphasize human driven changes of population spatial structure for 3 levels of population genetic aggregation that are common in fisheries management scenarios, namely sympatric populations, metapopulations and panmictic populations. Case studies are presented for each level of aggregation. Throughout our review, we both summarize the factors that link spatial and temporal dynamics in marine populations and highlight the management and conservation implications of such linkages.

A comparative multi-fleet analysis of socio-economic indicators for fishery management in SE Brazil

One of the problems in an ecosystem approach to fisheries management is the lack of economic analyses which clearly define the performance of different fishing fleets within the system. We describe a comparative multi-fleet analysis of socio-economic indicators applicable for inclusion into ecosystem modeling and management. Based on a survey of different industrial fishing fleets in São Paulo, Southeastern Brazil, an inter-fleet comparison of economic attributes such as investment, fixed costs, effort, labour, sailing-related costs and profits, as well as a set of performance indicators, was conducted. Costs varied between fleets with fuel being the largest component on average, representing almost 37% of total costs. Similarities between fleets were driven by fuel costs, gross incomes and profits. In general, the best economic performance was associated with indicators of profitability and economic efficiency. Bottom-longliners and both surface and bottom-gillnet fleets showed the best economic performance per fishing trip due to their low percentage of variable costs. Purse-seiners and pink-shrimp trawlers had the lowest average rate of return and economic efficiency because of their high variable costs and relatively low catch values, and were considered economically net losers. However, in terms of jobs generated, purse-seiners had the greatest value creating about 49% of total jobs by all fleets. The sea-bob-shrimp fleet had the lowest crew size per vessel but generated the second highest total number of direct jobs (23%), with high economic viability as a whole. The inter-fleet cost and socio-economic performance analysis revealed that additional attention should be given to the poor profitability and overcapacity of fleets, fishing impacts, and open-access related issues, while social indicators may also be considered. This study provides information useful for evaluating different fisheries management scenarios and fleet size optimization in the South Brazil Bight, for ecosystem modeling policy optimization routines, and for a pragmatic ecosystem approach to fisheries management.

A trophic model of the coral reef ecosystem of La Parguera, Puerto Rico: synthesizing fisheries and ecological data

A BSTRACT. — La Parguera, Puerto Rico, a well-studied Caribbean reef system, is showing signs of overfishing and thus, is a good candidate to evaluate fishery policy scenarios using ecosystem modeling. The first steps taken to build a plausible ecosystem model of the La Parguera reef system using Ecopath with Ecosim software included synthesizing fisheries and ecological data then balancing and analyzing trophic relationships for the year 2000. The model is centered around species of commercial and ecological importance in the ecosystem, grouped by habitat preferences. Model construction identified gaps in available data (e.g., diet compositions, metrics of fishing effort, incomplete landings) and balancing raised interesting ecological questions. Some groups, such as parrotfish are so underutilized as prey that the accuracy of biomass estimates and our understanding of predator-prey relationships are questioned. Apparent shortcomings in estimates of primary production relative to consumer biomass generated questions of whether estimates are inaccurate or whether the system is highly subsidized by importation from outside ecosystem boundaries. Although details are not directly comparable because of different structures, a similar Carribean model built for the 1970-1980s estimated total biomass 5.6 times higher than the present model. Changes of this magnitude, if found to be accurate, point out the need for further study of the roles fishing and environmental change have played in reshaping this system over the last 30-40 years. This modeling effort defined future data needs, generated hypotheses for further coral reef research, and provided a starting point towards evaluation of fishery management scenarios in an ecosystem context.

A spatial ecosystem and populations dynamics model (SEAPODYM) – Modeling of tuna and tuna-like populations

An enhanced version of the spatial ecosystem and population dynamics model SEAPODYM is presented to describe spatial dynamics of tuna and tuna-like species in the Pacific Ocean at monthly resolution over 1° grid-boxes. The simulations are driven by a bio-physical environment predicted from a coupled ocean physical–biogeochemical model. This new version of SEAPODYM includes expanded definitions of habitat indices, movements, and natural mortality based on empirical evidences. A thermal habitat of tuna species is derived from an individual heat budget model. The feeding habitat is computed according to the accessibility of tuna predator cohorts to different vertically migrating and non-migrating micronekton (mid-trophic) functional groups. The spawning habitat is based on temperature and the coincidence of spawning fish with presence or absence of predators and food for larvae. The successful larval recruitment is linked to spawning stock biomass. Larvae drift with currents, while immature and adult tuna can move of their own volition, in addition to being advected by currents. A food requirement index is computed to adjust locally the natural mortality of cohorts based on food demand and accessibility to available forage components. Together these mechanisms induce bottom-up and top-down effects, and intra- (i.e. between cohorts) and inter-species interactions. The model is now fully operational for running multi-species, multi-fisheries simulations, and the structure of the model allows a validation from multiple data sources. An application with two tuna species showing different biological characteristics, skipjack ( Katsuwonus pelamis) and bigeye ( Thunnus obesus), is presented to illustrate the capacity of the model to capture many important features of spatial dynamics of these two different tuna species in the Pacific Ocean. The actual validation is presented in a companion paper describing the approach to have a rigorous mathematical parameter optimization [Senina, I., Sibert, J., Lehodey, P., 2008. Parameter estimation for basin-scale ecosystem-linked population models of large pelagic predators: application to skipjack tuna. Progress in Oceanography]. Once this evaluation and parameterization is complete, it may be possible to use the model for management of tuna stocks in the context of climate and ecosystem variability, and to investigate potential changes due to anthropogenic activities including global warming and fisheries pressures and management scenarios.

Simulating fisheries management options for the Beibu Gulf by means of an ecological modelling optimization routine

The Beibu Gulf is a semi-enclosed sea surrounded by land territories of China, Vietnam and China's Hainan Island. Historically, the Beibu Gulf supported various commercial, recreational, and artisanal fisheries. Many fisheries are now depleted or had experienced substantial decline in productivity. In this paper, we developed a mass balance model using Ecopath with Ecosim (EwE), to evaluate how the ecosystem may respond to changes in fisheries activities over a period of 20 years. Input data were mainly from the information collected in trawl surveys from October 1998 to September 1999. Four fishery management scenarios, which maximized three independent (fishery profits, employment, and ecosystem) and the combination of the above three objectives were simulated with different vulnerability settings. Results suggested that socioeconomically driven policy caused the ecosystem to be vulnerable whereas maximized ecological stability and the compromise scenarios were generally consistent with different vulnerability settings. To maximize social and economical criteria, the ecosystem structure was shifted to a simplified state where the high trophic level species became depleted and the low trophic level species gained dominance. Therefore, the optimal state (social strategy) had the lowest trophic level, 2.78. When an ecological stability criterion was considered, the model predicted effort should decrease more than 70% for all fishing sectors. A trade-off analysis indicated that ‘Big compromise’ strategy would be optimal to balance fishery and conservation. These results indicate that developing multispecies harvesting strategies is a complex task, and goal functions may be conflicting, while initial model conditions can affect the results.

Models To Compare Management Options For A Protogynous Fish

Populations of gag (Mycteroperca microlepis), a hermaphroditic grouper, have experienced a dramatic shift in sex ratio over the past 25 years due to a decline in older age classes. The highly female-skewed sex ratio can be predicted as a consequence of increased fishing mortality that truncates the age distribution, and raises some concern about the overall fitness of the population. Management efforts may need to be directed toward maintenance of sex ratio as well as stock size, with evaluations of recruitment based on sex ratio or male stock size in addition to the traditional female-based stock-recruitment relationship. We used two stochastic, age-structured models to heuristically compare the effects of reducing fishing mortality on different life history stages and the relative impact of reductions in fertilization rates that may occur with highly skewed sex ratios. Our response variables included population size, sex ratio, lost egg fertility, and female spawning stock biomass. Population growth rates were highest for scenarios that reduced mortality for female gag (nearshore closure), while improved sex ratios were obtained most quickly with spawning reserves. The effect of reduced fertility through sex ratio bias was generally low but depended on the management scenario employed. Our results demonstrate the utility of evaluation of fishery management scenarios through model analysis and simulation, the synergistic interaction of life history and response to changes in mortality rates, and the importance of defining management goals.

Evaluation of current and alternative fisheries management scenarios based on spawning-per-recruit (SPR), revenue-per-recruit (RPR), and yield-per-recruit (YPR) diagrams

Abstract Spawning-per-recruit (SPR) and yield-per-recruit (YPR) analyses are widely used in stock assessments of exploited fish populations. In decision-making for fisheries management, the trade-off between fisheries production (YPR) and stock reproduction (SPR) is important. The general outputs of SPR and YPR analysis, such as single variate plots with contour lines or optimal harvest strategies estimated by numerical optimization, are inappropriate in obtaining an overview of the trade-off. This paper introduces a diagram that expresses graphically the bivariate trade-off between YPR and SPR. The method was applied to chub mackerel (Scomber japonicus) data, and two management scenarios were compared using the SPR–YPR diagram. Differences between YPR and revenue-per-recruit (RPR) were also considered. The results showed that: (i) current estimated fishing mortality is suggestive of growth-overfishing, and there is room for improving SPR and YPR simultaneously; (ii) increasing the age at first capture is more effective than effort control; (iii) management strategies that maximize landing weight or revenue are significantly different. The management strategy that maximizes landing weight, when considered from the viewpoint of maximizing revenue, results in growth-overfishing.