青岛斋堂岛海域春季双桩竖杆张网网囊网目的选择性

2014年春季,采用平行作业法,以2a=16 mm(a为目脚长度)的菱形目网囊为对照网(CN),选取30 mm菱形目网囊和20 mm、30 mm、40 mm的方形目网囊(分别以30D、20S、30S和40S表示)作为实验网囊,对青岛斋堂岛附近海域的双桩竖杆张网进行了不同网目形状的网囊和不同网目尺寸方形目网囊的选择性比较试验。以多元统计分析方法进行种间选择性分析,以Logistic曲线作为选择性模型、采用极大似然估算法进行种内选择性分析。结果显示,与对照网相比,所有实验网囊均能有效释放玉筋鱼(Ammodytes personatus)、舒氏海龙(Syngnathus schlegeli)等低值渔获以及经济鱼类的幼体。比较不同网目形状网囊的渔获数据发现,方形目网囊较菱形目网囊具有更好的选择性,其中30S网囊对玉筋鱼和舒氏海龙的释放率(以尾数计)分别比30D网囊高4.61%和16.80%,对六丝钝尾虾虎鱼(Amblychaeturichthys hexanema)和日本枪乌贼(Loigo japonica)的50%选择体长(胴长)L50分别比30D网囊大38.47%和61.29%。比较不同网目尺寸方形目网囊的渔获数据发现,当实验网为20S和30S时,六丝钝尾虾虎鱼的L50分别为6.58 cm和7.20 cm,选择范围(SR)分别为3.02 cm和0.87 cm;当实验网为20S、30S和40S时,日本枪乌贼的L50分别为2.88 cm、4.03 cm和10.49 cm,SR分别为0.74 cm、0.52 cm和2.67 cm;不同尺寸的方形目网囊对这2种渔获物的L50随着网目尺寸的增大而增大。根据实验海区各种渔获物的经济价值、低值鱼类和幼鱼的释放比例以及分拣渔获物的劳动力投入等综合分析认为,30 mm方形目网囊在保护渔业资源的同时对渔业生产不会造成显著影响,建议予以推广。     

Evaluation of codends with sorting grids, exit windows, and diamond meshes: Size selection and fish behaviour

This paper presents the results of an experiment aimed at improving the size selection of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in the Nordic bottom trawl fishery. Three systems simulating commercial conditions were tested: a 135 mm diamond-mesh codend fitted with a 55 mm sorting grid (Sort-V); a 135 mm diamond-mesh codend fitted with two lateral exit windows; and a codend built entirely of 155 mm diamond mesh. The selectivity curves showed similar selection ranges (SR) for the three systems. For cod, the mean SRs were around 8 cm, while for haddock, they were around 6 cm. All the estimated l₅₀ values were far above the minimum landing sizes (MLS). For cod, the mean l₅₀s were 56.1, 53.9, and 60.7 cm for the sorting grid, exit windows, and diamond-mesh configurations, respectively, while for haddock, they were 50.2, 50.6, and 49.9 cm, respectively. Underwater observations revealed that most of the fish escaped from the grid and exit-window codends as soon as they reached the vicinity of the sorting device. In contrast, fish remained inside the diamond-mesh codend for a longer time, and consequently were more exposed to physical damage before escape. In addition, many fish escaped from this codend during haul back and these fish were not likely to survive due to the rapid changes in pressure. Thus, the selectivity results obtained with this type of codend should be interpreted carefully.     

帆式张网网囊网目选择性能研究

分别对规格为４０、５０、６０、７０和８０ｍｍ网目的帆式张网网囊进行各４０网次的选择性试验,分析不同网囊规格的网目选择性能,探讨东海区帆式张网网囊的最小网目尺寸。结果表明,选择规格５５ｍｍ的网囊网目尺寸较为适宜。     

Square‐mesh codend length and selectivity in southeastern Australian stow nets

Abstract The relationship between the amount of square mesh in codends and selectivity was investigated for an Australian penaeid stow‐net fishery. Three lengths (3, 2 and 1 m) of square‐mesh codend made from 27‐mm mesh hung on the bar were alternately tested with a conventional 34‐mm diamond‐mesh design during two covered‐codend experiments. Compared with the conventional codend, the square‐mesh configurations incrementally selected school prawns, Metapenaeus macleayi (Haswell) across narrower selection ranges (SR) and mostly at greater sizes at 50% retention (L₅₀), while retaining fewer fish. Irrespective of the mesh configuration or square‐mesh codend length, there were significant differences between experiments (attributed to water flow) and impacts of catch weight on the selectivity of school prawns. Both variables had a negative relationship with L₅₀, while water flow similarly affected SR. This study reaffirms the utility of square‐mesh codends as a key input control for managing the selectivity of penaeid‐catching gears.     

网线直径和模拟渔获物对拖网网囊水阻力及形态影响

为探究网线直径和渔获物对拖网网囊水阻力及形态的影响,利用上海海洋大学循环动水槽对3顶不同网线直径(1.11mm、0.96mm、0.54mm)的网囊结构在5种流速(0.5m/s、0.6m/s、0.7m/s、0.8m/s、0.9m/s)和2种渔获状态(空网、存在模拟渔获物)下进行试验,比较分析各条件下网囊形态、水阻力和横向缩结系数的变化。结果表明：(1)空网条件下,网囊阻力系数随网线直径的增大而增大;随雷诺数的增加,阻力系数呈减小的趋势。(2)网囊水阻力与流速、网线直径和渔获量呈正相关关系。(3)存在模拟渔获物网囊随着网线直径的增大,中部宽度增大;随着流速的增加,网囊长度的增加较空网网囊更为明显;空网网囊整体形态较饱满。(4)空网网囊横向缩结系数先减小后趋于平缓,而存在模拟渔获物网囊横向缩结系数先减小后增至最大。研究结果可为改善拖网网囊水动力性能,提高渔具的作业特性及选择性提供科学基础依据。     

南海区虾拖网网囊对刀额新对虾的选择性研究

为了研究虾拖网网囊对刀额新对虾(Metapenaeus ensis)的选择性,2014—2017年于南海海域使用套网法和裤网法对2组菱目网囊(D25和D30)和6组混目网囊(S35+D18、S25+D25、S30+D25、S35+D25、S35+D30和S35+D35)进行选择性试验。以SELECT模型为基础框架,以logsitic曲线为模型,使用极大似然估算法估算单网次和联合网次下网囊对刀额新对虾的选择性。结果表明,菱目网囊D25和D30对刀额新对虾的选择性很差,逃逸数量很少;套网法试验中,混目网囊S35+D18、S25+D25、S30+D25和S35+D25对刀额新对虾的平均50%选择体长(L50)分别为51.52 mm、60.84 mm、63.21 mm和64.53 mm,平均选择范围(SR)分别为16.48 mm、14.31 mm、12.84 mm和9.75 mm;裤网法试验中,混目网囊S35+D25、S35+D30和S35+D35对刀额新对虾的平均L50分别为75.43 mm、82.38 mm和95.39 mm,平均SR分别为6.93 mm、6.39 mm和20.44 mm,平均相对作业强度(p)分别为0.51、0.52和0.64。综合南海区刀额新对虾的首次性成熟体长(80 mm)和网囊选择性等多方面因素,认为S35+D30网囊的选择性较好,研究结果可为南海海域虾拖网的渔具管理和刀额新对虾资源的合理利用提供参考。     

Fishery-specific differences in the size selectivity and catch of diamond- and square-mesh codends in two Australian penaeid seines

Abstract  The selectivities and catch compositions of conventional 30-mm diamond-mesh codends and a new square-mesh design made from 20-mm mesh hung on the bar for river and lagoon penaeid seines in south-eastern Australia were compared. The square-mesh design significantly improved the selectivities of the river seine for school prawns, Metapenaeus macleayi (Haswell), and the lagoon seine for greasyback prawns, Metapenaeus bennettae (Racek & Dall), by increasing their carapace length at 50% probability of retention ( L ₅₀) and by decreasing between-haul variability in selectivity. The presence of weed reduced the L ₅₀ for greasyback prawns caught in the conventional diamond-mesh codend during the lagoon-seine experiment. The differences among codend performances are discussed in terms of the differing methods of operation and composition of catches between the seines. These differences highlight the need to develop and manage modifications to improve the selectivity of fishing gears on a fishery-specific basis.     

网囊周长对单桩张网渔具选择性的影响

改变网囊周长是改善过滤性渔具网囊选择性的主要技术措施之一。为了评价网囊周长对中国近海渔业使用的单桩张网网囊选择性的影响,使用套网试验法对不同网目尺寸（25mm和35mm）的传统网囊和减小30％周长的网囊进行选择性试验,并对黄鲫Setipinnataty和小黄鱼Pseudosciaenapolyactis渔获体长数据的选择性进行了分析。结果显示：减小网囊周长可改善对渔获体长的选择性,即减小周长的网囊的50％选择体长（l50）较传统网囊大,而选择范围较小,对于较小的个体,选择性得到较为明显的改善;对比其它文献的研究结果,减小30％周长的网囊的l50要比相同网目尺寸的菱形和方形网目网囊大,但网囊周长对其尺寸选择性影响的具体规律有待于进一步研究。     

东海张纲张网网囊网目选择性研究

张纲张网是我国近海渔业的重要作业方式,当前渔业管理中规定了张纲张网网囊最小网目尺寸,但渔民实际使用的网目尺寸与之差异很大,造成渔获中幼鱼比例大。为了更好地掌握网目尺寸对主要捕捞对象的尺寸选择性,于2012年秋季和2013年春季使用平行作业法开展了不同网目尺寸(35、40、45、50、55 mm)网囊的选择性试验。试验结果显示,网囊对小黄鱼(Pseudosciaena polyactis)、带鱼(Trichiurus haumela)和银鲳(Pampus argenteus)的50%选择体长L50随着网目尺寸的增大而增大,表明放大网目尺寸能有效减少幼鱼渔获,L50与网目尺寸(Me)的线性关系为:小黄鱼L50=2.79×Me-1.45,带鱼L50=4.27×Me-38.28,银鲳L50=1.79×Me+28.66。此次试验不同网目尺寸网囊的L50相比其它研究结果较大,推测试验方法的不同可能是导致这一差异的主要原因。结合当前东、黄海主要捕捞对象的可捕规格,认为目前55 mm的网囊网目尺寸能实现张纲张网对3种主要捕捞对象的管理目标。