IFQs and total factor productivity changes: The case of the Gulf of Mexico red snapper fishery     

《Marine Policy》2015

This study investigates changes in the total factor productivity (TFP) and identifies the main sources of TFP growth following the adoption of an individual fishing quota (IFQ) program in the Gulf of Mexico red snapper commercial fishery. Utilizing an unbalanced panel of 722 vertical line vessels Malmquist indices were derived from an output-oriented stochastic distance frontier. The analysis shows that the IFQ program had a positive impact on the productivity of the fleet and that most of the productivity gains were due to improvements in technical efficiency. The study also finds that changes in technical efficiency were time variant suggesting that the exit of the less efficient vessels and easing of command and control regulations such as trip limits and short fishing seasons were responsible for most of these gains. Changes in the exploitable biomass of red snapper were found to have a moderate impact on productivity growth whereas the impact of technological progress was minimal.  相似文献   

内蒙古阿拉善呼口塞勒铜矿床Ⅱ号矿体原生叠加晕特征          下载免费PDF全文

李国庭 《山东国土资源》2015,31(2):7-11

研究了内蒙古阿拉善呼口塞勒铜矿床Ⅱ号矿体100线剖面原生叠加晕特征,结果表明,100线剖面+1 308~1 141m标高的轴向分带序列(由上到下)为W-Ni-As-Pb-Mo-Cu-Co-Au-Zn,有明显的相互叠置特征,地球化学参数在中段逐渐减小,可以确定矿体是多个成矿阶段叠加形成的。2个主成矿阶段形成的矿体部分叠加,矿体上部经过较强的剥蚀,但还有一定的延深。此次原生叠加晕的研究为下一步钻探施工提供了依据,明确了在该区继续进行原生晕研究的方向。  相似文献   

北京市中心城区网络RTK加密控制测量的方法与实践     

张学  陈廷武 《北京测绘》2012,(5):70-71,99

简要总结了原城区导线网复测、更新状况,以及采用传统测量方法维护、更新城市导线网点存在的主要问题。采用GNSS RTK技术对中心城区加密控制网进行重新设计、布网和观测,根据相关改算公式对满足要求的点位进行改正,以满足加密控制测量的精度要求。通过实际应用,采用GNSS RTK施测方法进行城区加密控制测量是可行的。  相似文献   

New evidence for a glacioeustatic influence on deep water circulation, bottom water ventilation and primary productivity in the South China Sea     

L. Lwemark  S. Steinke  C.-H. Wang  M.-T. Chen  A. Müller  L.-J. Shiau  S.-J. Kao  S.-R. Song  H.-L. Lin  K.-Y. Wei 《Dynamics of Atmospheres and Oceans》2009,47(1-3):138-153

We provide new evidence for the development of a stable estuarine circulation characterized by stagnating water bodies, nutrient recycling and increased primary productivity in the South China Sea (SCS) during glacial intervals. This circulation was caused by the closure of the shallow and narrow straits connecting the SCS in the south and west. Our main evidence is derived from newly measured Mn concentrations and Mn/Al ratios in two sediment cores from the northern and southeastern SCS covering the last 500 ky. Concentrations and Mn/Al ratios of the redox sensitive element Mn show clear glacial–interglacial cycles with maxima during interglacial periods and minima during glacial periods. These cycles indicate ventilation cycles of the bottom water, and are connected to the glacial–interglacial changes in sea level. In contrast, total organic carbon (TOC) concentrations display an opposite pattern with pronounced maxima during glacial times, especially in the southern part of the basin. The variations in TOC can be ascribed to two factors. Firstly, variations in primary productivity are controlled by variations in the intensity of the winter monsoon. Secondly to the degree of preservation of TOC controlled by variations in ventilation, which in turn is ultimately controlled by sea level. Consequently, variations in TOC represent a superimposition of primarily sea level influenced preservation control and winter monsoon driven variations in primary productivity intensity. The decrease in Mn correspond to times when sea level dropped 40–60 m below the present level. The larger amplitude of the variations in TOC and Mn in the southern part of the basin compared to the northern site suggest that oxygen depletion and nutrient recycling was stronger in the parts of the basin situated the furthest away from the only remaining opening to the open Pacific, the Luzon Strait.  相似文献   

一次华南暴雨过程中不同区域降水特征的模拟分析   总被引：6，自引：5，他引：1  

史荟燕  潘晓滨  谢海军  臧增亮  何亿强 《气象科学》2009,29(1):58-63

通过对2005年6月19-20日的一次华南大暴雨过程的诊断分析表明,本次降水过程的水汽来源有两个,一是来自于印度洋上的印度季风,另一个是来自于澳大利亚的东南信风.对不同暴雨中心的分析表明,福建北部的降水带为华南准静止锋锋面上的系统性降水,假相当位温的经向垂直剖面呈明显的Ω型结构,而广东河源附近的暴雨中心为暖区对流性降水,低层为强的不稳定.利用ARPS模式对这次暴雨过程进行了数值模拟,结果表明,锋面雨带主要来自于网格降水的贡献,而对流性降水主要来自于次网尺度降水的贡献.  相似文献   

基于RegCM4.6的中国地区云对地表太阳辐射的影响研究     

郭子嘉  刘鑫  陈勇航  辛渝  张蕾  秦艳  陈春美  刘平平  周海江 《沙漠与绿洲气象(新疆气象)》2020,14(6):107-113

使用RegCM4.6区域气候模式，选取Emanuel和Mix（Grell+Emanuel）两种积云对流参数化方案，以2016年为例，分别对中国地区云短波辐射强迫及其涉及的物理量进行数值模拟，揭示其时空分布特征，并探究两种积云对流参数方案模拟效果的差异及其原因。结果表明：从季节平均来看，全国地表云短波辐射强迫均为负值，云对地表为冷却效应，冬季最小，春夏季较大。塔里木盆地四季均为辐射强迫低值区，夏季冷却效应最弱，辐射强迫绝对值低于40 W·m-2；全天空地表净短波辐射分布也呈显著季节差异，除夏季外均呈由南向北逐渐递减的分布趋势；晴空地表净短波辐射在横断山脉处和塔里木盆地处均比较低，其中春季最为明显；两个方案所得的季节空间分布特征大致相同，但在数值上存在差异。春季时全国大部分地区全天空地表净短波辐射通量差异最大，在55 W·m-2左右，晴空地表净短波辐射通量在青藏高原处差异在60W·m-2左右。  相似文献   

石油和天然气运移、聚集的特征   总被引：8，自引：0，他引：8  

李明诚 《地球物理学进展》1994,9(1):120-124

虽然石油和天然气都是流体矿产，但它们的物理性质有很大不同，诸如：密度、粒度、溶解度、表面张力、扩散性等等，从而引起它们在运移和聚集特征上也有很大不同，这些不同的特征决定了天然气勘探的时空领域比石油更广阔，然而却比石油更难于保存下来。  相似文献   

Variation of phytoplankton biomass and primary production in Daya Bay during spring and summer   总被引：11，自引：0，他引：11  

Song X  Huang L  Zhang J  Huang X  Zhang J  Yin J  Tan Y  Liu S 《Marine pollution bulletin》2004,49(11-12):1036-1044

Environmental factors, phytoplankton biomass (Chl a) and primary production of two water areas in Daya Bay (Dapeng'ao Bay and Aotou Bay) were investigated during the transition period from spring to summer. Chl a ranged from 3.20 to 13.62 and 13.43 to 26.49 mg m(-3) in Dapeng'ao Bay and Aotou Bay respectively, if data obtained during red tides are excluded. Primary production varied between 239.7 and 1001.4 mg Cm(-2) d(-1) in Dapeng'ao Bay. The regional distribution of Chl a and primary production were mostly consistent from spring to summer in both bays. Seasonal transition characters have been found in Daya Bay from spring to summer, including high values of DO, nitrate and silicate. Size structures of phytoplankton and its primary production do not change very much from spring to summer, with micro-phytoplankton dominating and contributing about 50% of the whole. In Daya Bay, phytoplankton is limited by nitrogen in spring, and by phosphate in summer. Artificial impacts are evident from high temperature effluent from nuclear power stations, aquaculture and sewage. During the investigation, a red tide occurred in Aotou Bay, with a maximum Chl a of 103.23 mgm(-3) at surface and primary production of 2721.9 mg Cm(-2) d(-1) in the red tide center. Raised water temperature and nutrient supply from land-sources help to stimulate annual red tides.  相似文献   

近30年乌鲁木齐地区自然植被净第一性生产力变化分析   总被引：3，自引：0，他引：3  

张山清普宗朝  买买提江 《沙漠与绿洲气象(新疆气象)》2005,28(5):7-8,44

利用周广胜、张新时提出的自然植被净第一性生产力模型，估算分析了乌鲁木齐地区近30年自然植被净第一性生产力（NPP）的时空变化。结果表明，除后峡地区的NPP呈递减趋势外，其它各地的NPP总体上呈递增趋势；中山带的NPP最高，亚高山、高寒、低山和山前荒漠地带依次降低；气候变暖除对高寒地带的自然植被的NPP有一定的正效应外，对其它地区的NPP均产生较明显的负效应；年降水量的增加对提高自然植被净第一性生产力具有积极作用。  相似文献   

阻塞过程的正、斜压涡度拟能场诊断研究   总被引：1，自引：0，他引：1       下载免费PDF全文

黄昌兴  李维京 《应用气象学报》2005,16(3):304-311

应用正、斜压涡度拟能方程，对1998年6月3～11日发生在鄂霍次克海的一次阻塞环流进行诊断。结果表明:阻塞区内总涡度拟能和正压涡度拟能具有显著的变化，它清楚地揭示了阻塞过程中酝酿、维持和崩溃阶段中的不同特征，而正、斜压动能所显示的阻塞过程的变化特征则不明显。正、斜压涡度拟能场相互转换及阻塞区内外正、斜压涡度拟能场的净通量机制是鄂霍次克海阻塞环流建立和维持的两项主要因子。其过程是:首先通过斜压涡度拟能净通量机制，使斜压涡度拟能增长；又通过正斜压涡度拟能场的转换机制将增长的斜压涡度拟能转为正压涡度拟能；与此同时，通过正压涡度拟能净通量机制使正压涡度拟能增长。这两种不同的机制相互结合，从而使正压涡度拟能增长和维持，形成阻塞环流。而斜压涡度拟能增长甚微。  相似文献