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11.
ABSTRACT: The demersal multispecies trawl fishery in the western Mediterranean Sea has a poor selectivity; large numbers of juvenile fish are caught when using the legislated 40-mm diamond mesh cod end. The selectivity of a flexible sorting grid with 20-mm bar spacing (BS20) installed in front the conventional trawl cod end was investigated. The standard covered cod end method was used. Data was adequate for analyzing the selectivity of European hake Merluccius merluccius , poor cod Trisopterus minutus , greater forkbeard Phycis blennoides and Norway lobster Nephrops norvegicus . The selectivity of the 20-mm sorting grid was compared with the performance of 40-mm diamond (DM40) and square mesh (SM40) cod ends. The effect of a guiding funnel on the performance of the grid (BS20-f) was also explored. Finally, the potential changes in yield per recruit (Y/R) and biomass per recruit (B/R) after implementing a sorting grid were explored. An overall improvement in the 50% selection length ( L 50 ) with all four species was substantial when comparing the BS20 to the DM40. Higher improvement in L 50 s was achieved when the grid was equipped with the guiding funnel. When comparing the performance of the BS20-f to the SM40, there was no marked difference in L 50 s. The Y/R and B/R, however, are substantially higher with BS20-f for poor cod and about the same for European hake. BS20 compared to SM40 achieved lower Y/R and B/R for all four species; the smallest difference was observed for Norway lobster. Further development is required if the sorting grid is to be introduced into commercial fisheries. 相似文献
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在2012 年8 月进行的南海北部虾拖网海上调查的基础上,对虾蟹类渔获的种类组成、生物学特征和幼
体比例等进行了分析。结果显示,渔获种类一共71 种,其中虾蟹类15 种,但其产量却占总产量的82.34%;虾类优势
种为日本囊对虾(Marsupenaeus japonicus)、刀额新对虾(Metapenaeus ensis)、近缘新对虾(M. affinis)和周氏新对虾(M.
joyneri);蟹类优势种为红星梭子蟹(Portunus sanguinolentus)、三疣梭子蟹(P. trituberculatus)和远海梭子蟹(P.
pelagicus);刀额新对虾的幼虾比例为73.36%,三疣梭子蟹的幼蟹比例为78.79%。最后,探讨了促进南海虾蟹类资源
合理利用的措施。 相似文献
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Trawling for cephalopods off the Portuguese coast—Fleet dynamics and landings composition 总被引:1,自引:0,他引:1
Tereza Fonseca Aida Campos Manuel Afonso-Dias Paulo Fonseca Joo Pereira 《Fisheries Research》2008,92(2-3):180-188
Fleet dynamics was addressed for three cephalopod taxa of commercial interest, the squid Loligo vulgaris, the octopuses Octopus vulgaris and Eledone cirrhosa, and the cuttlefish Sepia officinalis, for 48 trawlers of the fish trawling fleet. Landing profiles (LP) were identified based on the species composition of the landings using hierarchical cluster analysis. Four out of a total of 12 different LP were related to cephalopods and other species associated with them.The effects on the landing proportions of a number of variables, year, season and vessel, are analysed for each of the species studied using generalized linear models (GLM). The factor “vessel”, including an ensemble of technical characteristics as well as the abilities of individual skippers, explained most of the model deviance, strongly reinforcing the existence of a fleet component dedicated to catch cephalopods. However, time also explains much of the variation found in the data.Seasonal alternation between landings of octopodidae and cuttlefish was observed within a small group of old trawlers operating mainly off the south coast, following the abundance cycles of these species. For a larger group of more modern trawlers, operating off the western coast, inter-annual shift between octopus and squid was found, together with a well marked seasonal pattern between the catches of cephalopods and horse mackerel.Spatial patterns of activity were identified using vessel monitoring system (VMS) data available for trawlers in Portugal, demonstrating the existence of cephalopod targeting strategies in Portuguese fish trawling activities. 相似文献
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本文报道了1986 ̄1992年期间对441kW渔船使用的1顶度拖网网口高度的海上实测结果。结果表明:网口高度是网口拉直周长的5.5 ̄7.3%。两者的关系可用经验公式表示为:H=0.2609L^0.7344。 相似文献
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首先对诱鱼光场进行计算,并分析其对光诱鱿鱼浮拖网作业的影响,据此合理配置了灯光强度及其布局,探讨了一套较有效的诱导渔方法。根据鱿鱼的趋光习性及浮拖网的特点,设计了适应在较深渔场作业的光诱浮拖网渔具,并成功地试验了光诱鱿鱼浮拖网柔性网板;取得了良好的社会生态效益和经济效益。 相似文献
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板梁系是桥梁中常用的结构形式。本文根据板梁系的比拟板理论,用三次B样条函数之积来逼近挠曲面,在正交坐标系下,写出正交异性板的总势能。通过正交坐标系和斜交坐标系之间的变换,导出斜交坐标系下的总势能。然后再应用变分原理,在文献的基础上,利用现有的表格形成斜板单元的刚度方程。和通常有限元相比,本法具有计算量少,节省机时、提高精度等特点。 根据本文的刚度方程,编制了FORTRAN计算程序,在IBM微机上即可运行。计算成果与文献中的实例相当符合。由于本文采用了比拟板理论,所以不论板梁结构纵横梁的数目有多少,都可以用该程序计算。因此,该程序在实际使用上是很方便的,具有一定的通用性。 相似文献