Assessment of catch, effort and species changes in the pair-trawl fishery of southern Lake Malawi, Malawi, Africa

Abstract  Catch per unit effort (CPUE) and species composition in the pair-trawl fishery in commercial Area A of southern Lake Malawi were assessed from 1991 to 2001. CPUE declined from 1.7 t day⁻¹ in 1995 to 0.5 t day⁻¹ in 2001 and the fishery is considered depleted. In 2000/2002, catch composition differed significantly from a 1991 survey, and was dominated by haplochromine cichlids (92% by weight). Of 98 haplochromine cichlid taxa identified in the catch, 18 contributed ≥1% by weight. The artisanal fishery targeted similar species of a similar size. It was recommended that: (1) renewed investment and increased effort in the pair-trawl fishery is not advisable; (2) there was a need for effort limitation in Area A and (3) the pair-trawl fishery should not be managed in isolation of the artisanal fishery.     

智利竹鱼拖网最适网囊网目尺寸探讨

根据拖网网囊网目尺寸与鱼体生物学存在关系 ,对智利竹鱼的优势叉长组成、形体特征、初次性腺成熟时的叉长等进行了分析。通过现场测试得出 2 0 0 0年智利竹鱼的优势叉长为 2 5 0～ 30 0mm ;体高、体宽和体周与叉长存在线性关系 ,分别为 2a =0 .185 8L - 3 .5 2 19,2b =0 .1339L - 4.2 99,c =0 .480 3L - 3 .4794。并对智利竹鱼拖网网囊网目尺寸进行了分析与计算 ,认为智利竹鱼拖网网囊的最适网目内径为 115～ 12 0mm。     

西非海域单船底拖网的试验研究-Ⅰ四片式拖网的设计与试验

以1029 kW六片式拖网为母型,设计四片式拖网,并进行水槽模型试验,分析其水动力性能。研究结果表明:通过改进上下纲结构形式、调整上下纲比例和背侧网比例,四片式拖网的水动力性能得到了较大的提高。当拖速为3.5 kn时,四片式拖网的阻力仅为44.57 kN,网口高度达5.9 m,水动力性能系数为2.32 m2/kN,能耗系数为1.20 kW.h/104m3。     

欧洲地区选择性虾拖网渔具的研究进展

虾拖网渔业是世界上兼捕、抛弃问题最为严重的渔业.为了缓解虾拖网渔业的这一突出问题,世界各国、各组织的研究人员在世界各主要虾拖网渔业中开展了多样而有效的选择性研究.北大西洋北方长额虾Pandalus borealis拖网渔业、东北大西洋和地中海海螯虾Nephrops norvegicus拖网渔业是欧洲开展选择性研究最早、最全面的渔业,作者从上述2种虾拖网渔业及其兼捕、抛弃特点出发,通过对渔业中有关的尺寸选择性和种类选择性研究,特别是兼捕减少装置(BRD)的设计开发进行归纳和总结,结合渔业中有关兼捕减少技术措施的介绍,探讨了这2种渔业中选择性研究的特点及其对其他渔业选择性研究的借鉴意义,为我国今后开展虾拖网渔业选择性研究和渔业立法提供一定的参考依据.     

四片式高口双拖网

本文反映黄海区群众渔业双拖网改进研究取得的一项新成果,报导了设计的依据、改进的特点、网模水池试验及海上实测的验证数据。经三年捕捞试验,取得了比原型网增产40％以上的显著效果。     

广东大鹏湾虾拖网网囊网目选择性研究

虾拖网渔业是南海海域重要的作业方式之一,但尚未有关该渔业网目尺寸选择性的报道。为评价虾拖网渔具的渔获性能、合理利用虾类资源,在广东大鹏湾进行了网目选择性试验。试验采用双支架虾拖网作为试验网具,并使用套网法估算了网目内径为35、40和45 mm的网囊对主捕虾类的选择性。结果显示,虾类渔获中刀额新对虾、须赤虾、周氏新对虾和日本囊对虾渔获数量较多,比较以往资料,刀额新对虾和周氏新对虾优势体长、平均体长均有所下降,其它2种虾类平均体长未见明显变化;选择性分析结果显示,主捕虾类的L50随网目尺寸线性增大。根据试验结果并结合历史资料,笔者认为现阶段35 mm的网囊网目尺寸对于保护上述4种虾类资源是比较合适的。     

136kW渔船鳀鱼变水层拖网的试验研究

本文报道了改进设计的专用鳀鱼变水层拖网1994～1995年期间海上的试验结果。试验结果表明:该网的结构合理,网具性能优良。网口高度达12.6m,拖速提高到3.0～3.8节。拖网阻力比原生产网减少19％,平均网次产量比原生产网增产35.3％。     

Fisheries resource management of the daggertooth pike conger,Muraenesox cinereus,using existing limited datasets in the western Seto Inland Sea,Japan

The daggertooth pike conger, Muraenesox cinereus (Forsskål), has become an important fish resource in the western Seto Inland Sea, Japan, since the 1990s. However, introducing sustainable fisheries resource management for this species is difficult in this region because stock assessments have not been performed, and official fisheries statistics for this stock were discontinued after 2007. This study used existing limited data sets to compile the first report for fisheries resource management for this M. cinereus stock. Yield‐per‐recruit analyses showed that increasing fishing pressure above current levels would provide only a minimal increase in expected catch levels. Hence, the current harvest level is considered to represent the upper limit of fishing pressure. Age composition in a given year could potentially be used to forecast landing abundance for the following 2 years. This study provides a basis for establishing effective fisheries resource management strategies for M. cinereus.     

Can Mediterranean cephalopod stocks be managed at MSY by 2020? The Balearic Islands as a case study

According to the Common Fisheries Policy (CFP), all European fish stocks should be brought to a state where they can produce at MSY by 2015 wherever possible or by 2020 at the latest. Despite the high socio‐economical importance of cephalopods in the Mediterranean and the increased availability of stock assessments during the recent past, only few European cephalopod stocks have been assessed to date. Surplus production models were applied to analyse the exploitation state of octopus and cuttlefish stocks from the Balearic Islands (western Mediterranean) to estimate how far away they were from the MSY target established by the CFP using a long‐term data series (1977–2013). The stocks were overexploited (cuttlefish) or about to be overexploited (octopus) during the late 1970s; this state remains even now and will only recover from overexploitation by 2020 if severe measures are taken.     

渔船拖网绞机恒张力控制系统的设计与仿真

针对拖网捕捞作业中较难保持曳纲张力恒值的问题,设计并搭建了基于模糊PID控制的渔船拖网绞机恒张力控制系统。在对渔船拖网绞机传动原理研究的基础上,建立恒张力控制系统的传递函数,构建模糊PID控制器,通过控制拖网绞机转速而调节曳纲张力。介绍了系统硬、软件的构成,并利用MATLAB进行仿真验证。仿真结果表明,模糊PID控制能在0.8 s内实现曳纲张力恒值,并能在收到干扰后0.7 s内恢复到之前的稳定状态,性能优于传统PID控制和模糊控制。研究表明,基于模糊PID控制的渔船拖网绞机恒张力控制系统具有系统响应快、超调量小、鲁棒性强等特点,能够有效地保持曳纲张力恒值,提高捕捞效率,具有较强实践指导意义。