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1.
采用套网法对双船底拖网不同网目尺寸(40、50、60、65 mm)的方形目和菱形目网囊捕捞东海区小黄鱼(Larimichthys polyactis)进行选择性实验,对不同网囊网目结构、不同网囊网目尺寸的选择性数据进行了比较分析。结果表明:(1)网囊网目尺寸小于50 mm,小黄鱼的逃逸率极低,网目结构选择性差异不明显。大于50 mm时,方形目网囊逃逸率均略高于菱形目结构,但方形目与菱形目逃逸率差异并不显著(P0.05)。(2)网目尺寸为50 mm、60 mm和65 mm时,方形目网囊的50%选择体长(L_(0.5))分别比菱形目网囊的L_(0.5)大28.5%、16.8%和7.3%,方形目网囊对于小黄鱼具有较好的选择性。(3)根据小黄鱼的50%选择体长(L_(0.5)),结合现行可捕体长标准以及不同阶段渔获物体型特征,建议菱形网目尺寸为60 mm或者方形网目尺寸为55 mm,二者具有相同的选择性和渔获率。  相似文献   

2.
为探究坛子网网囊网目形状和尺寸对小黄鱼(Larimichthys polyactis)选择性的影响,分别设计了3种规格菱形网目(内径30 mm、40 mm、50 mm)和方形网目(内径20 mm、30 mm、40 mm)网囊,采用套网法,于2020年秋季在黄海海州湾海域开展了12次海上试验;在分析渔获物组成和小黄鱼幼鱼逃逸率基础上,应用Logistic选择性模型,分析网目形状和网目尺寸对小黄鱼选择性的影响。结果显示:试验渔获物中共包含不同种类63种;小黄鱼体长范围为80~134 mm,平均体长为106 mm;在菱形网目和方形网目网囊中其渔获量占总渔获量的比例分别为41.45%和36.83%;相同网目尺寸条件下,方形网目网囊小黄鱼幼鱼释放效果优于菱形网目,网目尺寸为40 mm时,方形网目尾数和质量逃逸率比菱形网目分别高34.53%和34.39%;网目尺寸为30 mm和40 mm的方形网目网囊的50%选择体长(L50)比对应的菱形网目选择性分别高5.93%,18.84%;渔获物组成中,小黄鱼的幼鱼比例非常高,超过90%,基本全为幼鱼。基于上述试验结果,综合考虑海州湾小...  相似文献   

3.
为评价南海北部拖网方形和菱形混合网目网囊对主要渔获物的网目选择性,使用套网法,开展混合网目网囊(试验网)和传统菱形网目网囊(对照网)的对比选择性试验,结合Logistic和Richards曲线拟合选择性曲线,分析2种不同网目结构网囊对南海北部蓝圆鲹的选择性能。试验结果显示:试验网中数量逃逸率和质量逃逸率均高于80%的渔获种类有8种,而对照网只有5种;蓝圆鲹作为2种网囊中渔获质量最高的渔获种类,试验网中蓝圆鲹的数量逃逸率和质量逃逸率分别为25.35%和20.98%,而对照网中分别为16.39%和15.48%。选择性结果表明,试验网和对照网2种网囊Richards曲线拟合更好,模型残差和赤池信息指数更小,其拟合的蓝圆鲹的50%选择叉长分别为14.31 cm和13.60 cm。因此,方形和菱形混合网目网囊对多种副渔获的释放率较高,使用该网囊可以有效提高拖网的选择性能,保护渔业资源的可持续利用。  相似文献   

4.
单桩张网菱形、方形网目网囊选择性研究   总被引:3,自引:0,他引:3  
近年来,一种利用帆布作为扩张装置的新型单桩张网渔具在吕四渔场得到了快速发展。为了改善这种张网对主要渔获对象的尺寸选择性,进而评价其渔获性能以及对渔业资源的影响,使用套网试验法开展了不同网目尺寸(25 mm、35 mm和45 mm)的菱形和方形网目网囊尺寸选择性试验。通过对黄鲫(Setipinnataay)和小黄鱼(Pseudosciaena polyactis)渔获体长数据的选择性分析,结果显示,无论是菱形还是方形网目网囊,其50%选择体长L50和选择范围SR都随着网目尺寸的增大而增大(L50呈线性增长)。对比菱形和方形网目的选择性发现,对于黄鲫,50%选择体长L50差异不大,但菱形网目的选择范围SR大于方形网目;对于小黄鱼,方形网目具有更好的选择特性,即具有较大的L50(8%)和较小的SR(52%),但差异均不显著。菱形和方形网目对于不同体型鱼类的选择性差异以及渔民对方形网目网囊的抵触情绪等都使得在张网渔业中推广方形网目网囊值得商榷。  相似文献   

5.
南海区拖网网囊最小网目尺寸选择性研究   总被引:19,自引:2,他引:17       下载免费PDF全文
为了科学地确定南海区拖网网囊的结构和适宜网目尺寸,于2000年11月25日-12月20日在南海北部珠江口以外海域,水深36-70m拖网渔场,对4种不同网目尺寸的方形网目网囊进行了2个航次34网次的网囊套网式捕鱼选择性试验。4种网囊的网目尺寸(Mex)分别为30.3mm、35.2mm、39.4mm和43.6mm。结果表明,蓝圆参(Decapterus maruadsi)、多齿蛇鲻(Saurida tumbil)和条尾绯鲤(Upeneus bensasi)仍是南海拖网渔获中常见的鱼种;4种方形网目网囊的数量平均逃逸率均高于重量平均逃逸率;网囊渔获的优势体长总是大于套网渔获的优势体长;方形网目网囊有利于释放纺锤形鱼类和圆体形鱼类(如蓝圆参、多齿蛇鲻、条尾绯鲤)的幼鱼;3种主要鱼种的50%选择长度(L0.5)与Mex之间的线性回归方程为:蓝圆参L0.5=57.98 1.80Mex;多齿蛇鲻L0.5=72.71 1.64Mex;条尾绯鲤L0.5=37.62 1.66Mex。经综合分析认为,南海区拖网最好使用方形网目网囊,最小网目尺寸不应小于40mm。  相似文献   

6.
杨炳忠  晏磊  李杰  王腾  张鹏 《中国水产科学》2023,30(10):1271-1281
大网目拖网是我国海洋渔业捕捞带鱼的重要渔具。为提高拖网网囊选择性, 本研究在南海区采用套网法对双船大网目拖网 4 组网目尺寸(30、35、40 和 45 mm)的网囊进行实验, 在双重拔靴法的架构下, 拟合选择性参数、比较选择性的差异、估算捕捞方式指标。结果表明, 随着网目尺寸的增大, 网囊对带鱼的 50%选择体长增大, 对带鱼幼鱼个体的选择率显著下降, 带鱼幼鱼的渔获比例也呈下降趋势。结合带鱼最小可捕规格(23.0 cm)管理规定, 结果还表明网目尺寸为 40 mm 的网囊选择性较差, 其对带鱼的抛弃率大于 93%。为了进一步提高带鱼拖网渔业的资源养护水平, 还需要开展更多的选择性实验。  相似文献   

7.
为了让地笼网在人工鱼礁区进行捕捞许可提供科学依据,2018年4月在渤海莱州湾海域采用套网法进行地笼网不同网目尺寸(20、30、40、50、60 mm)的渔获物调查,探讨不同网目尺寸地笼网的渔获性能。对试验结果从相对重要性指数(IRI)、渔获量、主要渔获物优势体长、尾数和重量逃逸率、经济品种渔获量和口虾蛄体长分布进行分析。结果显示,试验共捕获渔获物37种,其中优势种8种;渔获物的数量与种类逃逸率随着网目尺寸增加而增加,40~60 mm网目种类逃逸率达80%左右,尾数逃逸率超过90%,质量逃逸达50%以上,表明40~60 mm网目具有明显的释放效果;经济品种渔获量占比与网目尺寸呈正相关;以主要渔获种类口虾蛄分析,使用50 mm网目捕捞未达到可捕体长的口虾蛄占比最少,为10.3%;经综合分析,50 mm网目尺寸地笼网的渔获性能较好,符合生产和生态的要求,因此推荐在海洋牧场海域使用50 mm网目地笼网。  相似文献   

8.
南海北部拖网35.2与30.3mm方目网囊渔获选择性比较   总被引:1,自引:0,他引:1  
根据1997年10月和2000年11~12月的拖网网囊网目选择性试验资料,对网目内径35.2mm方目和30.3mm方目网囊的渔获选择性进行了比较和分析。对比试验结果表明,35.2mm方目网囊渔获尾数总逃逸率为39.28%、重量总逃逸率为16.18%,高于30.3mm方目网囊的28.40%和7.47%,35.2mm方目网囊的渔获选择性有所提高;2种规格方目网囊及其套网中出现的渔获种类较为相似,具有释放鱼类种类少、数量低的共同特点,且在渔获选择性能上的差别还不明显,对渔获种类数量的释放效果都相当有限;作为优势释放种类,大头狗母鱼、条尾绯鲤和多齿蛇鲻在2种规格方目网囊中的尾数逃逸率和重量逃逸率分别在42.9%~65.8%和24.2%~45.0%之间;其中条尾绯鲤和多齿蛇鲻的50%选择体长均未达到最低可捕标准。总体来看,2种规格方目网囊对渔获的总体释放效果还不理想,要实现负责任捕鱼,需进一步放大拖网方目网囊的网目尺寸。  相似文献   

9.
多囊桁拖网选择性研究中对照网囊网目尺寸的选择   总被引:2,自引:1,他引:1  
张健  石建高  张鹏  孙满昌 《水产学报》2010,34(1):160-168
对比作业法是拖网渔具选择性研究中重要的试验方法之一,而对比试验中对照网囊网目的选择至关重要。研究利用多囊桁拖网不同网目尺寸(20、30、35和40mm)网囊捕获的哈氏仿对虾、小黄鱼和棘头梅童鱼渔获体长分布数据,应用几何相似原理,分析过滤性渔具的选择性,并按不同假设条件下(假设1:符合几何相似原理对渔获具有一定的选择性;假设2:对渔获种类没有选择性),探讨如何合理选择对照网囊网目尺寸。结果表明,对照网网囊网目尺寸为20mm,在上述2种假设下,对选择性模型的拟合、简化及对其它网囊的选择性参数没有显著的影响;在考虑了桁拖网渔具各网囊具有相同相对作业强度,以及桁拖网渔具与普通拖网渔具选择性分析方法上的差异等因素后,认为在此项研究中,将小于20mm网目尺寸的网囊视为没有选择性的对照网囊是可行的。  相似文献   

10.
东海张纲张网网囊网目选择性研究   总被引:2,自引:0,他引:2  
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。  相似文献   

11.
ABSTRACT:   Selectivity experiments of diamond and square mesh codends with different mesh size (30, 35, 40 and 45 mm) for hairfin anchovy Setipinna taty were carried out using the covered codend method in Chinese stow net fisheries. In the present study, 5151 specimens were subsampled and asymmetric and symmetric selectivity curves (Richards and Logistic curves) were fitted to the catch data, using the maximum likelihood method according to the SELECT model. The results show that the Richards curve gives a better fit to the selectivity curve for diamond mesh codends with 30, 35 and 40-mm mesh sizes, whereas the logistic curve gives a better fit for the diamond mesh codend with 45 mm mesh size and square mesh codends with 30, 35, 40 and 45-mm mesh size. With the exception of 45-mm mesh size codends, the L 50 of diamond mesh codends were insignificantly larger than those of square mesh codends. However, the selectivity curves of square mesh codends were steeper than those of diamond mesh codends, except the 30-mm mesh size codends. As for diamond mesh codends, according to the linear relationship between the L 50 and mesh size, 36.5-mm mesh size codends could release 50% juvenile hairfin anchovy (below 1-year old). However, diamond mesh codends with such a mesh size are not selective for other species.  相似文献   

12.
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.  相似文献   

13.
Abstract The relative efficiencies and selectivities of conventional and modified codends were examined in a demersal trawl fishery targeting several species, including eastern king prawns, Penaeus plebejus (Hess), whiting, Sillago spp. and cephalopods. The modifications to codends included: (i) reducing the circumference; (ii) increasing the mesh size in conventional diamond‐mesh designs; and (iii) orientating meshes on the bar so that they were square shaped. The codends were tested against a fine‐meshed control in paired comparisons onboard three commercial trawlers. The conventional codend comprised 41‐mm diamond‐shaped mesh attached to an anterior extension section at a ratio of 150 to 100 meshes and was demonstrated to be non‐selective for the targeted species. Reducing codend circumference to 100 meshes and increasing the size of mesh to 45 mm both improved selection for eastern king prawns, but the lateral mesh openings were estimated to be insufficient to allow juveniles of the other key species to escape. By contrast, codends made from 35‐ and 41‐mm mesh hung on the bar improved the size selection for eastern king prawns and selected stout whiting, Sillago robusta (Stead) (the smallest commercial‐sized fish) across narrow selection ranges and at 50% sizes of retention (L50s) that were closely correlated to the transverse morphology of fish and the maximum mesh opening. With the exception of a reduction in catches of octopus, Octopus spp., by the 41‐square codend, there were no other impacts on commercial catches by the square‐mesh designs. It was concluded that diamond‐mesh codends are inappropriate for use throughout this multispecies fishery and that a modified design comprising at least 35‐mm mesh hung on the bar is required to minimise the fishing mortality of unwanted sizes of the key target species. The results are discussed in terms of the utility of these types of modifications for closely regulating selection in penaeid‐shrimp trawls.  相似文献   

14.
单船框架拖网(俗称弓子网)是渤海海区常见的作业渔具,对底栖渔业生物选择性差,作业过程中产生大量副渔获物。为改善网囊网目的选择性,2017年9月在莱州湾海域采用“套网法”对网囊网目尺寸分别为15、25、35、45和55 mm的5种网囊进行了选择性实验。结果显示,弓子网对渔获物种类的选择能力较差,具有捕获栖息于作业海域绝大多数底栖种类的能力。随网囊网目尺寸的增加,渔获物质量、尾数逃逸率和产值损失率逐渐增大,短吻红舌鳎(Cynoglossus joyneri)、口虾蛄(Oratosquilla oratoria)、鹰爪虾(Trachypenaeus curvirostris)和日本鼓虾(Alpheus japonicas)的选择性参数(L0.5、SR)呈线性增加。口虾蛄和鹰爪虾的50%选择体长(L0.5)与网目尺寸(m)的线性回归方程分别为L0.5=1.472m+12.63(R2=0.934)和L0.5=1.394m+0.724(R2=0.920)。在目前的渔业资源状况下,为保护口虾蛄和鹰爪虾等经济渔获物资源,兼顾生产效益和幼鱼资源保护,建议将弓子网最小网目尺寸放大至45 mm。  相似文献   

15.
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.  相似文献   

16.
设计并研制了一种内、外圆环形刚性框架和柔性六角形网片组合而成的桁杆虾拖网选择性装置。所研制选择性装置在东海区近海桁杆虾拖网中,采用对比试验法开展了海上选择性试验,并针对试验期间主要渔获品种哈氏仿对虾,以Logistic曲线为选择性模型,对六角形网目水平缩结长度分别为D1=31.00 mm,D2=27.50 mm,D3=21.25 mm三种规格选择性装置的选择性效果进行分析。结果表明,3种规格选择性装置均具有选择性效果,其中安装六角形网目水平缩结长度为31.00 mm和27.50 mm的选择性装置的目标网囊内哈氏仿对虾的优势体长均为75~95 mm,相应非目标网囊内哈氏仿对虾的优势体长分别为25~45 mm和35~55 mm,具有较显著的差异性;而安装六角形网目水平缩结长度为21.25 mm的选择性装置的目标网囊内哈氏仿对虾的优势体长35~55 mm,相应非目标网囊内哈氏仿对虾的优势体长同为25~45 mm。六角形网目水平缩结长度31.00 mm的选择性装置对哈氏仿对虾的50%选择体长L50最大,为48.89 mm,而选择性范围SR最小,为16.75 mm,在试验规格范围内的选择性效果最显著。  相似文献   

17.
Two experiments, done in a south-eastern Australian trawl fishery targeting school whiting (Sillago flindersi: Sillaginidae), examined the relative efficiencies and selectivities of five codends and extension sections made from double-twine, 90-mm (inside stretched length) mesh netting. All extension sections were made from 3-mm diameter twine and were 100 meshes long and 100 meshes in circumference, while the codends were 25 meshes in length. The first experiment tested three codends made from 4-mm diameter twine: one with a circumference of 100 meshes and two of 200-mesh circumference, with one of the latter incorporating two cross-sectional joins in its extension piece. The second experiment compared two 200-mesh circumference codends, one constructed from 3-mm diameter twine and the other from 5-mm diameter twine. The codends were alternately fished with a small-meshed control. The results showed a general trend of reduced selection by the 200-mesh circumference and thicker twined codends, and especially by the industry-preferred 200-mesh circumference codend constructed from 5-mm diameter twine. Experiment 1 found that the 100-mesh codend caught significantly fewer school whiting, retained catch and total catch than did the two 200-mesh codends, and the 200-mesh codend with the modified extension section caught significantly fewer school whiting and retained catch than did the 200-mesh codend with the straight extension. In the second experiment, the 200-mesh 5-mm twine codend caught significantly more total and retained catch, school whiting, and longspine flathead (Platycephalus longispinis: Platycephalidae) than did the 200-mesh 3-mm twine codend. Across all codends, the smallest lengths at 50% probability of retention (L50) were estimated for longspine flathead, redfish (Centroberyx affinis: Berycidae) and longfin gurnard (Lepidotrigla argus: Triglidae) in the 5-mm 200-mesh codend. The limited size range of school whiting resulted in unreliable estimation of selectivity in the 200-mesh 5-mm twine codend, but this design was the only one that retained a substantial proportion of individuals below the minimum marketable length (15 cm fork length). While the 200-mesh 5-mm twine codend retained commercial quantities of school whiting, it seems far from optimal. It is suggested that a more efficient design comprising possibly smaller, square-shaped meshes should be developed and used in conjunction with temporal, spatial and catch restrictions.  相似文献   

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