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21.
《Marine Policy》2017
Comments are provided on several points in the 2016 State of the World Fisheries and Aquaculture produced by the Food and Agriculture Organization of the United Nations (FAO). It is shown that data assembled by FAO from submissions by countries suggest a “stable” trend mainly because the declining catches of a number of countries with reliable statistics is compensated for by unreliable statistics from countries where reporting increasing catches may be politically expedient, e.g., China, Myanmar. Also, concerns are raised as to why FAO chose to ignore the well-documented data ‘reconstruction’ process, which fills the gaps that exist in data reported by countries to FAO. It is being ignored despite its importance for governance and resource conservation being well known. This process and its findings could be used by FAO to encourage countries to improve their data reporting, including retroactive corrections. This is important in view of successive analyses of the status of fisheries resources undertaken by FAO (published in current and past SOFIAs) and also in modified form by the Sea Around Us. This suggests a degradation of marine fisheries, and, if trends continue, a crisis by mid-century. Finally, comments are presented on the proposition that aquaculture will overtake wild capture fisheries in terms of food production, notably because current aquaculture requires huge quantities of wild-caught fish as feed. Indeed, this emphasis on aquaculture-as-substitute for fisheries raises issues of food security and malnutrition in developing countries, from which much of the fish used as feed originates. 相似文献
22.
《Marine Policy》2017
Pacific bluefin tuna (PBF) (Thunnus orientalis) is commercially important in the North Pacific Ocean. Although its stock has been relatively low for decades, international discussions on a long-term management framework, including the definition of a limit reference point (LRP), have only recently started. This paper argues that an LRP for PBF could be developed by determining a biomass level that would prevent recruitment overfishing. First, it reviews the development of LRPs for various tuna species and demonstrates that most of these limits are not necessarily based on biological information on the respective species. Then, the current management of PBF is also reviewed as background information for considering an LRP for PBF. Finally, a variety of simple analyses of the stock–recruitment relationship of PBF are conducted to find a biomass level that would prevent recruitment overfishing—i.e. an LRP below which stocks should not fall. It is concluded that, for the first time to our knowledge, defining such an LRP for a tuna species is possible (about 30 thousand tonnes or 5% of estimated unfished spawning stock biomass in our calculation). Not only is the LRP based on actual experience, but also the logic behind it would be easier for stakeholders to understand than the theoretical LRPs used elsewhere. This LRP should be useful in future in more comprehensive management framework, such as one through management strategy evaluations, in which stakeholder involvement in decision-making is crucial. 相似文献
23.
We analyzed recent food web and fish stock changes in the central Chile marine ecosystem, comparing the roles of jumbo squid (Dosidicus gigas) as predator, the environment, and fishing. To accomplish this we used food web modeling and the Ecopath with Ecosim software (EwE). The principal fish stocks have experienced wide decadal fluctuations in the past 30 years, including stock collapses of horse mackerel (Trachurus murphyi) and hake (Merluccius gayi), and there was a large influx of jumbo squid during the mid-2000s. We used two EwE models representing the food web off central Chile to test the hypothesis that predation by jumbo squid has been significant in explaining the dynamics of the main fishing resources and other species in the study area. Results indicate that predation by jumbo squid on fish stocks is lower than that of other predators (e.g. hake) and the fishery. Long-term fluctuations (1978–2004) in the biomass of the main fish stocks (as well as other components of the food web) seem to be related to fishing and to variation in primary production, rather than to predation by jumbo squid alone. Jumbo squid seems to play a role as predator rather than prey in the system, but its impacts are low when compared with the impacts of other predators and fishing. Therefore, we conclude that jumbo squid predation on its prey was not the primary force behind the collapse of important fish stocks off central Chile. Future efforts should be directed to better understanding factors that trigger sudden increases in jumbo squid abundance off central Chile, as well as modeling its trophic impacts. 相似文献
24.
Fish hatchery programs commonly are used to enhance depleted fish populations. While these programs are highly valued by the public, most likely due to their nonrestrictive approach to restoring a fishery, the effectiveness of these programs has been often questioned. This study investigates economic and ecological effectiveness of the Albemarle Sound/Roanoke River (AR) striped bass stocking program from 1981 to1996 as a case study. 相似文献
25.
One-dimensional stock cutting problems can be encountered at the production stage of many areas of engineering as well as in shipbuilding and coastal structures. In this paper, a novel approach is proposed to solve the problem directly by using the cutting patterns obtained by the analytical methods at the mathematical modeling stage. By minimizing both the number of different cutting patterns and material waste, the proposed method is able to capture the ideal solution of the analytical methods. The main advantage of the method comes from the fact that an integer solution is guaranteed. However, in analytical methods it is not always possible to produce integer solutions and the linear programming algorithm must be run repeatedly to select integer solutions from the alternatives to get practical results. The proposed nesting algorithm is a low-cost and efficient tool. Minimizing the number of cutting patterns contributes to time and material savings. Also, by using this method trim loss is minimized and stock usage is maximized. The efficiency of the proposed method is demonstrated by extensive numerical results. 相似文献
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27.
The chemically peculiar (CP) stars of the upper main sequence are perfect tracers for several astrophysical processes. Their study especially in open clusters further helps to establish their evolutionary status. The latter is most important to understand the origin and evolution of the CP phenomenon, i.e. the connection between diffusion and a stellar magnetic field. There are two important topics, we cover with this paper. First of all, we investigate the reliability of the CCD Δa photometry for fainter objects in open clusters. The latter method is able to detect CP stars very efficiently, but still a spectroscopic verification is needed to verify the photometric candidates. On the other hand, already published spectral classifications on the basis of photographic plates and prism technology have tobe tested with modern instruments. Classification resolution spectroscopy is presented for thirty five bona‐fide CP candidates. Twenty six of them are located within the boundaries of fourteen open clusters, for which we also investigated their membership probabilities. Apart from five objects, they seem tobe members of the respective clusters. The objects were classified in the framework of a refined Morgan‐Keenan system with the extension of well established CP star spectra. We confirm the CP nature of all but one target. The results of Δa photometry and the spectral classifications are in excellent agreement. For the cluster members we find a continuous sequence of CP stars from 10 to 850 Myr, the whole range of investigated cluster ages (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
28.
随着人类活动对于海洋资源的开发和利用不断深化,许多渔业资源的开发速度已经超过其再生能力的上限,渔业资源衰退趋势愈发显著。因此,渔业资源亟待科学合理的理论指导来保护和利用有限的渔业资源。Ecopath生态通道模型是一种研究生态系统特征与变化的经典模型,除了可用于分析生态系统结构与功能以及评估生态系统的成熟稳定程度外,该模型还可以评估物种的生态容量,为增殖放流活动等渔业资源保护措施提供科学依据,因此被广泛应用于渔业资源生态容量研究。本文综述了Ecopath模型的原理、建立和调试方法,归纳了生态容量的概念以及国内基于生态通道模型评估渔业资源生态容量的进展以及不同水域生态系统下的特征参数对比,最后提出了模型的限制性以及发展前景。本综述重点归纳了不同水域生态系统下的物种生态容量评估研究,旨在为不同生态环境下的增养殖活动提供科学参考。 相似文献
29.
《Marine Policy》2014
This brief note is an update to the authors' "The Expansion, Limit and Decline of the Global Marine Fish Catch," published in the September 2012 issue of Marine Policy. That paper examined the steady increase in the world's catch from 1950 to 1989, its slight decline and rise to a final peak in 1996. This limit has been followed by a steady decline to 2010. Since there have been improvements in the technology of fishing and no reason to believe that there has been a reduction in fishing effort, then the apparent limit and subsequent decline in the catch suggests a reduction in the supply of fish and invertebrates in the world's oceans. The earlier paper also noted the geographic shift in the world's catch to Asia and the rise of China to become the world's largest catcher of fish. 相似文献
30.
《Marine Policy》2014
Attributional LCA, which monitors specific production systems in steady state conditions, is increasingly used in fisheries to assess the environmental profile of fleets and seafood supply chains. However, this approach is not pertinent to assess the environmental consequences of (large scale) policies. In contrast, consequential LCA (CLCA) has been successfully implemented in other sectors to assess the expected changes in environmental impacts of a given production system and other (marginal) production systems that may be affected in response to changes driven by policy or strategic decisions. CLCA commonly combines LCA with economic models to simulate the interactions occurring between the analysed systems. However, the use of these models may not be the most appropriate approach to follow for fisheries. Hence, it seems feasible that CLCA should be combined with stock prediction tools rather than with economic models, to determine how changes in stock sizes and quota restrictions may cause variations in the environmental impact of fishing fleets. 相似文献