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1.
LYNDA D. RODWELL EDWARD B. BARBIER CALLUM M. ROBERTS TIM R. McCLANAHAN 《Natural Resource Modeling》2002,15(4):453-486
ABSTRACT. The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. In this paper we examine the contribution of fully protected tropical marine reserves to fishery enhancement by modeling marine reserve‐fishery linkages. The consequences of reserve establishment on the long‐run equilibrium fish biomass and fishery catch levels are evaluated. In contrast to earlier models this study highlights the roles of both adult (and juvenile) fish migration and larval dispersal between the reserve and fishing grounds by employing a spawner‐recruit model. Uniform larval dispersal, uniform larval retention and complete larval retention combined with zero, moderate and high fish migration scenarios are analyzed in turn. The numerical simulations are based on Mombasa Marine National Park, Kenya, a fully protected coral reef marine reserve comprising approximately 30% of former fishing grounds. Simulation results suggest that the establishment of a fully protected marine reserve will always lead to an increase in total fish biomass. If the fishery is moderately to heavily exploited, total fishery catch will be greater with the reserve in all scenarios of fish and larval movement. If the fishery faces low levels of exploitation, catches can be optimized without a reserve but with controlled fishing effort. With high fish migration from the reserve, catches are optimized with the reserve. The optimal area of the marine reserve depends on the exploitation rate in the neighboring fishing grounds. For example, if exploitation is maintained at 40%, the ‘optimal’ reserve size would be 10%. If the rate increases to 50%, then the reserve needs to be 30% of the management area in order to maximize catches. However, even in lower exploitation fisheries (below 40%), a small reserve (up to 20%) provides significantly higher gains in fish biomass than losses in catch. Marine reserves are a valuable fisheries management tool. To achieve maximum fishery benefits they should be complemented by fishing effort controls. 相似文献
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《数学学报(英文版)》2014,(9)
<正>Submission Authors must use LaTeX for typewriting,and visit our website www.actamath.com to submit your paper.Our address is Editorial Office of Acta Mathematica Sinica,Academy of Mathematics and Systems Science,Chinese Academy of Sciences,Beijing 100190,P.R.China. 相似文献
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In this paper we use martingale techniques to derive upper bounds for the probability of ruin for a risk process. The important difference between our results and previous results in this area is that our model for the risk process explicitly allows for delay in claims settlement. 相似文献
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K. E. Zimen 《Angewandte Chemie (International ed. in English)》1971,10(1):1-11
In this article the world's potential energy reserves are summarized on the basis of available estimates, and the future energy consumption is estimated with the aid of a working hypothesis relating to the growth of the world's population (P) and the energy consumption per capita (γ). According to this estimate, the energy requirements in 30 years will be about seven times and in 80 years about fifty times as high as they are today, and all the concentrated energy sources will be exhausted in about 120 to 160 years. – The energy requirements in the steady state (Pγ = const.) could be of the order of 1013 MWh per year and could be met out of magmatic rocks (U,Th) and sea water (U,D). High priority should be given to research and development work on the construction, reliability, and safety of breeder and fusion reactors, the chemical treatment and final disposal of radioactive waste, the extraction of uranium, thorium, and deuterium from the “primitive” raw materials, the relevant problems relating to protection of the environment, and the worldwide control of the excess birthrate. 相似文献
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S. Thore S. L. McDonald R. Gonzalez N. P. Ritchey T. W. Ruefli K. K. Sinha 《Annals of Operations Research》1996,68(3):409-422
The gradual exhaustion of existing deposits of a depletable non-renewable resource such as oil tends to shift the supply price curve of the resource upwards, increasing its marginal cost. Advances in technologies for exploration and production act as a brake on such upward shifts. Thus, there is a tug-of-war between the gradual exhaustion of existing deposits and technological progress. Using a recently developed constrained least-squares regression technique, we demonstrate that technological progress was the dominant force of the two during the first part of this century, causing a secular drop in marginal costs, but that this situation eventually was reversed, and that the gradual exhaustion of deposits gained the upper hand, causing marginal costs to increase. The turning point occurred around 1971–72. We also discuss the forecasting of the possible current upward drift of marginal costs. 相似文献
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MAARTEN J. PUNT HANS‐PETER WEIKARD EKKO C. VAN IERLAND 《Natural Resource Modeling》2013,26(2):164-193
Abstract Marine protected areas (MPAs) are gaining momentum as tools within fisheries management. Although many studies have been conducted to their use and potential, only few authors have considered their use in the High Seas. In this paper, we investigate the effects of fish growth enhancing MPAs on the formation of regional fisheries management organisations (RFMOs) for highly migratory fish stocks. We argue that in absence of enforcement MPAs constitute a weakest‐link public good, which can only be realized if everyone agrees. We combine this notion with a game theoretic model of RFMO formation to derive potentially stable RFMOs with and without MPAs. We find that MPAs generally increase the parameter range over which RFMOs are stable, and that they increase stability in a number of cases as compared to the case without MPAs. They do not necessarily induce a fully cooperative solution among all fishing nations. In summary, results of this paper suggest a positive role for MPAs in the High Seas. 相似文献
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面对突发事件导致的巨大物资需求,实物储备往往体现出应对能力不足。而对于生产时间较短的重要应急物资,生产能力储备是缓解这一压力的有效途径。对此,本研究构建了一个物资企业双储备形式下的应急物资采购模型,分析研究了在物资企业可以选择生产形式(常规生产和加急生产)的情况下,政府的最优支付决策和物资企业的双储备决策。推导分析结果显示,物资企业的生产能力约束和政府的支付水平对政企合作形式起到决定性作用。本研究进一步通过数值分析验证模型的有效性和契约合作的优势,并讨论了若干重要外生参数对政企最优决策的影响。 相似文献
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SIV REITHE 《Natural Resource Modeling》2006,19(2):221-242
ABSTRACT. This paper explores the effects of using marine reserves as a measure to control bycatch that is of no commercial value, under different assumptions regarding the ecological interactions between targeted species and that taken as bycatch. Three cases are examined: (1) no ecological interactions between the two species, (2) targeted and bycatch species exist in a predator‐prey relationship and (3) species compete. Targeted species is assumed to consist of two sub‐populations that are discretely distributed in space, but linked through density dependent migration while bycatch species is assumed to consist of one uniformly distributed stock only. In each case the equilibrium stock levels of targeted and by‐catch species, effort and harvest are numerically calculated and compared, assuming pure open access and open access in combination with a reserve. It is of special interest to identify circumstances that allows for a win‐win situation, that is, both harvest of the targeted species and biomass of the bycatch species increase. It is shown that the ecological interactions between the two species influence the possibility of actually protecting the bycatch species through the use of a reserve, the possibility a win‐win situation, and the issue of what patch to close. 相似文献