Optimizing competitive uses of water for irrigation and fisheries

Choosing the appropriate reservoir water management strategy can be difficult when the water has multiple uses. This study examines this problem for reservoir managers where water use involves irrigation and fisheries. A stochastic dynamic programming (SDP) model is developed to facilitate reservoir management, using a case study illustration for southern Vietnam. The model includes the response of rice and fish yields to key factors including reservoir water levels, the timing and quantity of water release, and climatic conditions. The model also accounts for variation in rainfall patterns, irrigation requirements, and the demand for low water levels during the fish harvest season. Three production scenarios are examined where the reservoir's water is used for: only producing rice (scenario 1), only producing fish (scenario 2), and producing rice and fish (scenario 3). Key findings are: (1) for scenario 1, adequate water should be released to meet rice growing water requirements and residual water should be stored as a source of water in case of low rainfall, (2) for scenario 2, sufficient water needs to be released prior to the fish harvest to maximize this harvest; and (3) for scenario 3, water should be released prior to fish harvest, but sufficient water should remain to satisfy the water requirements of rice. When the reservoir is managed for joint production of rice and fish, net benefits are 6% greater than when the reservoir is managed solely for rice production. The SDP model developed in this paper could be adapted and applied to other multiple-use resources such as forests, river basins, and land.     

从文化渔业的角度谈休闲渔业发展的新路径

休闲渔业是实现现代渔业转型发展的重要途径,然而我国雨后春笋般出现的休闲渔业产业如出一辙的模式使休闲渔业发展陷入瓶颈期,本文试图从“文化学”角度探讨,重新整合运用现有资源,尝试为休闲渔业的发展寻找新的突破口.     

Human behaviour: the key source of uncertainty in fisheries management

There is broad consensus that the main problem facing fisheries globally is too many boats chasing too few fish. Unfortunately it is also possible to argue that there are too many proposed solutions and not enough practical answers to improving fisheries management. There is a deepening divide between those who propose alternative regulatory controls on fishers, including establishing large areas permanently closed to fishing, and those who argue for better alignment of incentives combined with broad participation of resource users in fishery management decisions (in simple terms, between top down and bottom up systems of governance). However despite the choice of policy instruments used, a consistent outcome is that resource users behave in a manner that is often unintended by the designers of the management system. Hence whilst uncertainty is broadly recognized as a pervasive feature of fisheries management, to date most of the attention has focussed on only part of that uncertainty – scientific uncertainty about the status of exploited resources. The effect of uncertainty generated on the human side of fisheries science and management has received much less attention. However, the uncertainty generated by unexpected resource user behaviour is critical as it has unplanned consequences and leads to unintended management outcomes. Using empirical evidence of unexpected resource user behaviour and reviewing current responses to unexpected management outcomes, we identify different approaches that both improve prediction of human behaviour in fisheries systems and identify management measures that are more robust to these sources of uncertainty. However, unless the micro scale drivers of human behaviour that contribute to macro scale implementation uncertainty are communicated effectively to managers and considered more regularly and in greater depth, unanticipated responses to management actions will continue to undermine management systems and threaten the sustainability of fisheries.     

Developing socioeconomic indicators for an ecosystem-based fisheries management approach: An application to the Korean large purse seine fishery

Developing socioeconomic indicators for ecosystem-based fisheries management is particularly important. This is because socioeconomic factors have direct effects on ecosystems, and ecosystems have direct effects on socioeconomic factors. Therefore, it is imperative that socioeconomic indicators are developed and evaluated in order to predict changes in ecosystems and to provide advice for effective fisheries management. In this study, socioeconomic indicators have been developed to be combined with biological and ecological indicators, in order to conduct the ecosystem-based fisheries assessment. In terms of socioeconomic indicators, five socioeconomic criteria were considered as important attributes of socioeconomic changes. These were economic production, business conditions, levels of income, the state of the market, and levels of employment. In order to establish reference points for the evaluation of indicators, target reference points and limit reference points were set through a comparison with other industries or other fisheries rather than by using the Traffic Light System (TLS) method, which has been used in many previous studies. In addition, on the basis of the application of developed indicators and reference points to the Korean large purse seine fishery, the socioeconomic conditions of the fishery and the usefulness of the indicators were evaluated and management implications were discussed.     

Lessons from the past: investigating historical data from bluefin tuna fisheries

In 1963, the leading fisheries targeting Atlantic bluefin tuna ( Thunnus thynnus ) in the Norwegian Sea and North Sea suddenly collapsed without any warning. Little is known about this collapse and several hypotheses have been put forward, such as changes in migratory routes, recruitment failure or eradication of a sub-population: all of these hypotheses could result from natural causes and/or from overfishing. To help explain this mysterious event, an original data set of the main bluefin tuna fisheries of the 20th century, including total catch and size composition of the catch, has been compiled and analysed. The results reveal a strong and unambiguous link between the Nordic purse seine and Spanish trap fisheries during the 1950s and 1960s. However, this link vanished during the 1970s. In addition, the North-west Atlantic and Mediterranean trap fisheries appeared also to be partially connected to the Nordic fisheries. During the 1950s and 1960s, the main migration routes of bluefin tuna were probably from the Mediterranean spawning grounds and from the West Atlantic coasts to the Norwegian coast and North Sea, which were probably a key feeding ground at that time. The analyses also lead to the conclusion that interactions between environmental, trophic and fishing processes have probably affected bluefin tuna migration patterns which would have finally caused the Nordic fisheries collapse. This retrospective analysis finally leads to an original – albeit more speculative – hypothesis concerning Atlantic bluefin tuna population structure, therein conjectured as an assemblage of at least three sub-populations.     

Improving management advice through spatially explicit models and sharing information

Recent assessments of Chilean shrimp, Heterocarpus reedi, in central Chile have been conducted separately for the northern and southern zones of the fishery and treating them as two separate stocks. However, it is not clear whether H. reedi of the two zones interact with one another or whether they share similar characteristics. Such knowledge is necessary to determine whether they should be modeled as separate “stocks” or as a single stock. This has motivated the use of the Pella–Tomlinson model to test whether there are spatial differences in the population dynamics of H. reedi in the two zones and whether sharing information between the zones improves management advice. We test if it is better, from a stock assessment point of view, to model the stock as one unit in the whole area, or as two separate stocks. In the single-stock model, we sum the catch data of both zones, but each catch-per-unit-of-effort index is fit as a separate data set, using a joint likelihood. Under the single-stock hypothesis, the best model fit was the symmetric production function (i.e. the Schaefer model for which the biomass that supports maximum sustainable yield as a proportion of carrying capacity (B_MSY/B₀) = 0.5), with different catchability coefficients for each CPUE index, but a shared standard deviation of the log-normal likelihood function. Under the two-stock hypotheses, both catch and CPUE data were separated for each zone in the model. In this case, the best model fit is also the one with symmetrical production curve, and the only parameter that differed between the zones was B₀. However, B₀ per unit of habitat was similar for the two zones. Also, the precision of estimated management quantities was improved by modeling the appropriate spatial structure and sharing information among zones. The results suggest that the demographic parameters are similar for the two zones. It appears that the main difference between the two zones is the exploitation history, with the catch in the southern zone being reduced earlier than in the northern zone and consequently the biomass in the southern zone increased earlier than in the northern zone. This implies that local depletion can occur in this stock and that differences in management among zones may require explicitly modeling sub-stocks in the assessment of this and other species.     

稻渔综合种养技术研究进展

稻渔综合种养可使农业从单一经营转变为复合经营,从平面生产转变为立体生产,是农业转方式、调结构的重要发展方向。为进一步促进稻渔综合种养研究的深入开展和稻渔综合种养模式的推广应用,综述了中国稻渔综合种养技术的发展概况,阐明了稻渔综合种养模式的增产增效作用及与之配套的稻田工程技术、安全植保技术、安全施肥技术、鱼病防治技术、水质管理技术的实施过程,指出了稻渔综合种养模式对产业的支撑作用,展望了稻渔综合种养模式的发展前景,并提出了稻渔综合种养模式的重点研究方向。     

Overlooked impacts and challenges of the new European discard ban

Discards are the portion of animal and plant material in the catch that is dumped back at sea. The Common Fisheries Policy plan proposed by the European Commission for 2014–2020 presents a controversial goal: to enforce the landing of fishing discards as a measure to encourage their reduction. This historical and political decision will shape the future of the fishing exploitation in European Seas. Discards generated by European fleets are not negligible, and its reduction is an ecological, socioeconomical and moral imperative. However, it must be achieved through the reduction in discards at source and the promotion of selective and non‐destructive gears. We argue it is doubtful that this discard ban will result in an effective reduction of discards. The proposed measure may, in fact, negatively affect ecosystems at all levels of biological hierarchy by disregarding the Ecosystem‐Based Approach to Fisheries and the Precautionary Principle. It could negatively impact several species by increasing fishing mortality, also commercial species if discards are not accounted in the total allowable catch. Communities preying on discards will likely be affected. The role discards currently play in the energy turnover of current ecosystems will be modified and should be fully evaluated. The landing of discards will likely generate new markets of fishmeal due to the growing demands for marine living resources. The ban will require substantial public investment to deal with technical problems on board and to control and enforce. Therefore, this measure should be only implemented after rigorous scientific and technical studies have been developed.     

The role of CITES in the conservation of marine fishes subject to international trade

All possible tools need to be marshalled for marine fish conservation. Yet controversy has swirled around what role, if any, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) should play for marine fishes. This paper analyses the relevance and applicability of CITES as a complementary tool for fisheries management. CITES currently regulates the international trade of very few marine fish species, by listing them in its Appendices. After the first meeting of the Parties (member countries) in 1976, no new marine fish taxa were added to the CITES Appendices until 2002, when Parties agreed to act to ensure sustainable and legal international trade in seahorses (Hippocampus spp.) and two species of sharks. Progress has continued haltingly, adding only one more shark, humphead wrasse (Cheilinus undulatus) and sawfishes by 2012. Parties voice concerns that may include inadequate data, applicability of CITES listing criteria, roles of national fisheries agencies, enforcement challenges, CITES' lack of experience with marine fishes, and/or identification and by‐catch problems. A common query is the relationship between CITES and other international agreements. Yet all these arguments can be countered, revealing CITES to be a relevant and appropriate instrument for promoting sound marine fisheries management. In reality, Parties that cannot implement CITES effectively for marine fishes will also need help to manage their fisheries sustainably. CITES action complements and supports other international fisheries management measures. As CITES engages with more marine fish listings, there will be greater scope to analyse its effectiveness in supporting different taxa in different contexts.     

Biomass management targets and the conservation and economic benefits of marine reserves

The establishment of no‐take marine reserves has been increasingly promoted as a key measure to achieve conservation and sustainability goals in fisheries. Regardless of the wide range of benefits cited, the effectiveness of reserve establishment depends critically on fisheries management outside the reserves. We construct a bioeconomic model of a fishery that allows for the establishment of a no‐take marine reserve and evaluate how the choice of the off‐reserve management target influences the effectiveness of reserve establishment. We evaluate two biomass targets: (i) B_MSY or the biomass that produces the maximum sustainable yield (MSY) and (ii) B_MEY or the biomass that maximizes the net present value of the returns to fishing. The parameterized model shows that, for a wide range of scenarios, the fishery will be better off in terms of both conservation and economic objectives when the no‐take reserve is established in conjunction with the B_MEY target rather than with the B_MSY target. Model results further show that the opportunity cost of securing additional fish biomass, in both deterministic and stochastic environments, is lower when the reserve size is increased under the B_MEY target. This finding is important because marine reserves have been established as a key measure to restore depleted fish stocks, and the results suggest that this objective can be achieved with lower economic costs in a B_MEY managed fishery.