Flow through nets and trawls of low porosity

In trawls intended for harvesting marine zooplankton the mesh size and twine thickness may be as small as O(10⁻⁴ m), the porosity less than 0.5 and the appropriate Reynolds number O(10⁰−10²). The flow locally through the meshes varies strongly with the Reynolds number in this range, and the entire flow field, filtered volume and drag of such nets therefore depend strongly on the net parameters and towing velocity.This paper presents a simplified model for the flow through and forces on inclined permeable screens based on pressure drop considerations. For conical nets the model provides simple expressions for the filtration efficiency and drag as functions of twine diameter, mesh opening, porosity, taper angle and flow (towing) velocity. Comparisons with test tank measurements of typical plankton nets show good agreement.     

北方农牧交错区草原利用与禁牧政策的关键问题研究

草原作为我国最大的陆地生态系统,对生态安全、生物多样性、畜牧业等具有重要的意义,但草原生态承载力有限,随着人口和社会经济压力的不断增加,对草原的过度利用导致草原生态破坏严重,草原生态系统面临巨大威胁。为了恢复和保护草原生态系统,2002年前后国家在草原破坏严重的地区实施禁牧政策。政策实施以来,草原得到很大程度的恢复,生态效果明显,但政策实施过程中也出现了一些新的问题。探索北方农牧交错区草原利用效率和存在的问题可为进一步制定相关政策提供依据,对北方农牧交错区的生态环境修复和可持续发展有重要的意义。本文通过对相关文献的综述和典型禁牧区的研究,从禁牧政策的效益、问题和农户支持度等方面,进行了研究和论述,主要结论包括：（1）北方农牧交错区草原生态承载力低,生态赤字严重。（2）禁牧政策虽对生态环境的改善起到很大作用,但在一些禁牧区,当地政府不能因地制宜实施禁牧政策,再加上配套实施和基础设施滞后,草场界限模糊以及政策宣传和监管力度不够等问题导致了新的草原退化,草原生态恢复大打折扣。（3）禁牧政策实施对农户的生产和生活造成一定的影响,部分农户无法顺利完成生计方式的转型,又因生态补偿标准低和补偿有失公平等问题无法弥补禁牧造成的经济损失,导致农户生活水平有所下降,加深了生态环境与农户生计之间的矛盾,部分农户对禁牧政策的支持度较低。     

Distribution and abundance of anthropogenic marine debris along the shelf and slope of the US West Coast

As marine debris levels continue to grow worldwide, defining sources, composition, and distribution of debris, as well as potential effects, becomes increasingly important. We investigated composition and abundance of man-made, benthic marine debris at 1347 randomly selected stations along the US West Coast during Groundfish Bottom Trawl Surveys in 2007 and 2008. Anthropogenic debris was observed in 469 tows at depths of 55-1280 m. Plastic and metallic debris occurred in the greatest number of hauls followed by fabric and glass. Mean density was 67.1 items km⁻² throughout the study area but was significantly higher south of 36°00′N latitude. Mean density significantly increased with depth, ranging from 30 items km⁻² in shallow (55-183 m) water to 128 items km⁻² in the deepest depth stratum (550-1280 m). Debris densities observed along the US West Coast were comparable to those seen elsewhere and provide a valuable backdrop for future comparisons.     

The EU landing obligation and European small-scale fisheries: What are the odds for success?

A landing obligation was formally implemented in the European Union (EU) for the first time, as part of the recent reform of the EU Common Fisheries Policy (CFP). Given the reasonable success of the landing obligation in some countries such as the Faroe Islands, Iceland and Norway, this policy is seen as a viable approach to tackle the long-recognized discarding problem in EU waters. However, there has been some debate on whether there is sufficient evidence to support the feasibility of such a measure in the EU-CFP. The EU landing obligation will implicitly include all small-scale fisheries (SSF) provided the species captured are subject to catch limits or minimum sizes (in the case of the Mediterranean). SSF were included irrespective of the fact that the discarding problem in the EU has been historically associated with medium- to large-scale fleets (in particular largely mixed species trawl fisheries). Additionally, past experiences with a discard ban policy are still limited to specific countries and/or specific fisheries. This paper examined the appropriateness and feasibility of the recently implemented EU landing obligation in SSF. The effects in the long-term are unpredictable, but available evidence suggests that in the short to medium-term a landing obligation is likely to bring more negative social, economic and ecological impacts than benefits.     

利用HOG-LBP自适应融合特征实现禁令交通标志检测

针对我国圆形禁令交通标志,提出一种快速、稳定的标志自动检测方法。首先,基于RGB空间对标志图像进行颜色分割,针对三通道差值的固定阈值分割方法对图像亮度的适应性较差的问题,提出基于基础通道选择的相对通道差值计算及阈值曲线拟合的方法进行自适应颜色分割,并针对标志与背景同色的情况,提出梯度过滤的方法将标志与同色背景分离;然后对分割图像进行边缘提取,基于标志椭圆特征,用最小二乘椭圆拟合后验偏差估计法来对边缘进行筛选,并提取最终标志边缘。实验表明,该方法能快速准确地对自然环境下不同亮度的圆形禁令标志自动检测,具有实时性和鲁棒性,在智能交通中具有良好的应用前景。     

2×339KW综合节能渔船底拖网试验报告

根据农牧渔业部水产局下达的“294.2千瓦综合节能渔船”项目网具节能课题的要求,新设计了一项低阻底拖网,并进行了网模水池试验和海上实测及一周年商业性捕鱼生产,获得了很好的效果。试验和捕鱼生产结果充分证明:新设计的拖网网口高、阻力小、渔获量高,是一种较为理想的节能型双船底拖网网型,具有增产节能兼优的经济效益和社会效益。     

强对流风暴新一代雷达产品特征分析

利用濮阳、三门峡新一代天气雷达产品,结合卫星、探空、天气图、地面雨量等资料对2006年6月25日发生在河南省北部、西部和中部的强对流风暴过程进行分析发现:(1)此次强对流风暴表现为多个处于不同发展阶段的的强对流回波单体组成长80～400km、宽40km的NE-SW向中β对流回波带即飑线;(2)强对流风暴在发展旺盛期间,其前沿有雷暴出流边界;(3)低层强NW风推动对流回波带向前发展成弓型带状回波;(4)在强对流风暴前侧,紧挨雷暴出流边界内侧产生了一条弧线窄带速度线,随着雷暴出流边界远离强对流风暴主体,该弧线窄带速度线也远离大片的速度区,并逐渐消失;(5)不同性质的强对流天气,其基本反射率、回波顶高、垂直液态积分含水量时有差异.北部雷雨大风伴短时强降水的强对流天气,强中心基本反射率在53～63dBz,回波顶高9～14km,垂直液态积分含水量在38～48kg*m-1之间;而西部中部的雷雨大风伴随局部冰雹和短时强降水的强对流天气,强中心基本反射率在53～65dBz,回波顶高度11～16km,对应垂直液态积分含水量在48～63kg*m-1之间;(5)在强对流风暴发展旺盛时期一直有中气旋伴随,中气旋出现在强对流单体前侧或前侧的入流槽口处.强对流风暴的新一代雷达产品特征是强对流天气监测预警的重要参考依据.     

From Moral to Markets: The Rhetoric of Responsibility and Resource Management in European Union Fisheries Policy

Ecological, economic, and social sustainability has been prioritized by the European Union in its proposal for a reformed Common Fisheries Policy (CFP), but it is recognized that there is a lack of knowledge concerning the objectives of these three aspects. Addressing the issue of how these objectives are given meaning as policy is being articulated, two Swedish seminars where fisheries’ stakeholders discuss the proposal for a reformed CFP are analyzed. The analysis shows how fish become defined as a specific kind of resource and how their status as a resource is framed as a moral issue. Once morally charged the resource is subjected to valorization through economic modeling. As a result, the potential for sustainability in fisheries becomes conditional upon the creation of new markets.     

南海底拖网方、菱目网囊选择性研究

1997年 6月～ 1 998年 7月 ,使用 3种网目尺寸的方形网目网囊和一种网目尺寸的菱形网目网囊 ,在南海北部珠江口以外海域水深 3 5～ 96m拖网渔场进行了总共 2 6个有效网次的捕鱼对比试验 ,获得了关于蛇鲻、绯鲤、金线鱼 3种鱼种的选择性参数。结果表明 ,方形网目网囊比菱形网目网囊具有更好的选择性能 ,对于保护南海幼鱼资源是有效的     

Does the relationship between fishermen and enforcers impact regulatory compliance?

The focus of US fisheries regulations has changed from expanding fishing effort to protecting resources for current and future use. Regulations, enforcement, and compliance have changed and grown over the last forty years. Members of both the enforcement and commercial trawl fishing communities speculate and complain about regulatory compliance, often from opposite perspectives. A small research project in Oregon studied the relationship between these communities and regulation compliance. Although a difference was noted in the relationships between the varied levels of enforcement and trawl fishermen, this did not constitute a shift in compliance; compliance remained high with participants from both communities reporting that the fishermen have “little choice but to follow the rules.” What varied was communication within and between these communities, and the amount of control participants’ felt they had in regulation development. A small glimpse into the relationships within and between these communities offers insights into the factors that may impact fisheries, regulation development and enforcement, and communication within and between these interdependent, occupational communities.