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1.
Gillnet selectivity parameters for the Atlantic sharpnose, Rhizoprionodon terraenovae, blacknose, Carcharhinus acronotus, finetooth, Carcharhinus isodon, and bonnethead, Sphyrna tiburo, sharks were estimated from fishery-independent catches in multi-panel gillnets with stretched mesh sizes ranging from 8.9 to 14.0 cm in steps of 1.3 cm, with an additional size of 20.3 cm. Mesh selectivities were estimated using a maximum-likelihood model, which fits a gamma distribution to length data for each mesh size using the log-likelihood function. The Atlantic sharpnose and finetooth shark exhibited the broadest selection curves. Peak selectivities for the Atlantic sharpnose were reached from 750 mm FL for the 8.9 cm mesh to 1150 mm FL for the 14.0 cm mesh in 50 mm FL increments per mesh. Peak selectivity for the finetooth shark was reached at 550 mm FL for the 8.9 and 10.2 cm meshes, increased to 650 mm FL for the 11.4 mesh, and 750 mm FL for the 12.7 and 14.0 cm meshes. Selectivity was highest at 1150 mm FL for the 20.3 cm mesh. The bonnethead and blacknose shark exhibited narrower selection curves, with peak selectivity occurring at 450 mm FL for the 8.9 cm mesh, 750 mm for the 12.7 cm mesh in 100 mm FL increments per mesh. Maximum selectivity for the 20.3 cm mesh was 950 and 1050 mm FL for bonnethead and blacknose shark, respectively. The θ1 values for blacknose and finetooth shark were most similar (140.58 and 141.25), whereas the value calculated for Atlantic sharpnose was the highest (211.95) and that for the bonnethead (131.77) was the lowest. Values calculated for θ2, a parameter that describes the variance of sizes by mesh, ranged from 27,259 for the bonnethead to 189,873 for the finetooth shark. Although gillnets used in this study were not directly constructed for use in estimation of gillnet selectivities, information on mesh selectivities estimated herein has direct applicability to commercial gillnets with meshes of similar sizes.  相似文献   

2.
This paper presents the scientific basis for changes in the minimum mesh size in gill nets, from 28 to 30 mm, introduced by fishery management in Poland to limit the catch of undersized perch (those less than 17 cm total length). Experimental fishing with six different mesh sizes was performed in accordance with commercial fisheries practice. A bi-normal selection curve was fitted to the data by including the between-set variation in the model. The locations of the primary and secondary modes of the bi-normal curve on the transformed length scale (length/mesh) were estimated to be 6.95 and 7.41, respectively. The results indicated that a minimum mesh size in gill nets of 28 mm should be sufficient to ensure a low level of discards as well as protecting the interests of fishermen.  相似文献   

3.
不同尺寸网目与缩结系数对许氏平鲉的选择性   总被引：1，自引：0，他引：1  
为探究不同尺寸网目及缩结系数对许氏平鲉(Sebastesschlegelii)的选择性,本研究基于实验水槽中的套网法试验,测得许氏平鲉的生物学特征参数,采用Logistic模型曲线拟合得到不同尺寸网目及缩结系数对许氏平鲉的选择性曲线,并用极大似然法估算选择性参数。结果表明:网目尺寸为63 mm、82 mm、93 mm时,许氏平鲉的50%选择性体长(L50)分别为18.49 cm、23.90 cm、25.12 cm,选择范围(SR)分别为3.18、3.6、3.85,选择因素(SF)分别为2.93、2.91、2.70,随着网目尺寸的增大,许氏平鲉的L50、SR逐渐增大, SF逐渐减小;当82 mm网目的缩结系数(Et)分别为0.5、0.6、0.707时,许氏平鲉的50%选择性体长(L50)分别为21.47 cm、23.90 cm、22.02 cm,选择范围(SR)分别为3.23、3.6、3.38,选择因素(SF)分别为2.65、2.91、2.68,随着网目缩结系数的增大,许氏平鲉的L50、SR、SF先增大后减小,在Et为0.6时均达到最大。为保护许氏平鲉幼鱼资源,建议在鱼礁区使用网目规格为70 mm, Et为0.6的笼壶渔具进行采捕。  相似文献   

4.
A study was undertaken on the northwestern coast of Portugal to evaluate the selectivity effect of both tooth spacing and mesh size on the catch of the white clam (Spisula solida). Two typical clam dredges, equipped with different tooth spacing and mesh size, were towed side by side. Three tooth spacing (20, 40 and 60 mm) and three mesh sizes (35, 40 and 50 mm) were investigated. The dredge selectivity experiments were performed by attaching a cover bag with a 20 mm mesh to the gear. Individual hauls were analysed by the SELECT model. The Fryer’s mixed model of between-haul variation was also applied to data. The results showed that the space between teeth does not have an effect on selectivity. Tooth length was directly related to the dredge’s capture efficiency. The only factor that contributed to dredge size selection was mesh size. The 50% retention lengths estimated for mesh sizes 30, 40 and 50 mm were 25.68, 26.35 and 31.94 mm, respectively. For all mesh sizes, very narrow selection ranges were observed. The most appropriate mesh size to be enforced within the Portuguese northwestern S. solida fishery should be 40 mm.  相似文献   

5.
Abstract  The selection properties of three experimental mesh sizes were examined in the lampara net fishery for eastern sea garfish, Hyporhamphus australis (Steindachner), in New South Wales, Australia. The sizes of fish retained in 25-, 28- and 32-mm mesh nets were compared with those retained in a control 12-mm mesh net. The 25-mm mesh net retained significant numbers of immature H. australis , the 28-mm mesh net retained predominantly only mature fish and the 32-mm mesh had very low catch rates. Catch rates decreased linearly with increasing mesh size and there was a significant linear relationship between mesh size and the 50% selection size ( L 50 ). Given this species is being overfished, the 28-mm mesh size is recommended as the most appropriate for use in the fishery.  相似文献   

6.
ABSTRACT:   The size selectivity of a trammel net for herded oval squid Sepioteuthis lessoniana in Tateyama Bay, Chiba Prefecture, was estimated by comparison between the mantle length frequency distributions of oval squid caught by a trammel net and by a set net. The measured mesh sizes of the inner net of the trammel net and of the final section of the set net were 85.3 and 11.3 mm, respectively. In the trammel net fishery where oval squid are herded into the net, most of the oval squid are caught in the bag-shaped inner net. Hence, the logistic function was employed for the size selectivity curve of the trammel net. The 'share each length's catch total' (SELECT) model was implemented for the estimation of the selectivity curve. The size selectivity r ( l ) of the trammel net for the oval squid was expressed as a logistic function of the mantle length l : r ( l ) = exp(−18.57 + 0.88  l )/[1 + exp(−18.57 + 0.88  l )]. From these logistic parameter estimates, the 50% selection mantle length and selection range ( L 75– L 25) were calculated as 21.07 and 2.49 cm, respectively. The selection probability of oval squid whose mantle girth was equivalent to the mesh perimeter of the inner net was 0.09. Accordingly, oval squid of a girth smaller than the mesh perimeter were likely to pass through the mesh to escape from the net.  相似文献   

7.
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   

8.
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   

9.
In 2008, Korean flounder (Glyptocephalus stelleri) was designated by the Korean Ministry for Food, Agriculture, Forestry and Fisheries as a species for restoration in the coastal waters of Korea. However, there are currently no regulations regarding the minimum landed size of flounder, or the minimum legal mesh size used by the coastal gillnet and trammel net fisheries. Selectivity experiments for gillnets and trammel nets were conducted using commercial vessels in several areas off the eastern coast of Korea between October 2006 and June 2009. The selectivity analysis required an adaption of the SELECT method because trammel net mesh sizes were altered part-way through the experiment. Gillnet and trammel net selectivity was best described using a bi-modal selection curve. The two gears were found to have different selection curves for a given mesh size. The length of maximum retention was similar for the two gears, but the selection curve of the trammel net was substantially wider than that of the gillnet. For the largest size of mesh used in the commercial fishery (8.5 cm stretched), 50% relative retention was estimated to occur at a length of 20.4 cm for the trammel net, and 22.5 cm for the gillnet. In comparison, the length of 50% maturity for this species is approximately 26 cm. As there are currently no size restrictions on landings of Korean flounder, these results suggest that use of these gears may pose a serious threat to local stocks of this species.  相似文献   

10.
青岛斋堂岛海域春季双桩竖杆张网网囊网目的选择性   总被引：3，自引：1，他引：2  
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。  相似文献   

11.
Abstract  Variability in community (richness, diversity and evenness) and population (size structure) attributes of discards was evaluated in a shrimp fishery in Celestun Lagoon, Mexico, in different climatic seasons and hydrological zones. Sampling was conducted using two bottom nets with different mesh size codends: 1.3 cm (used in the fishery) and 2.5 cm. Although the shrimp:discard ratio was 1:1 in both cases, total biomass and abundance with the 1.3-cm mesh size were, respectively, 4.6 and 1.8 times higher than with the 2.5-cm mesh size. This result was consistent in time and space. Discards were dominated by fishes [60% in 1.3-cm mesh size and 96% in 2.5-cm mesh size, mainly Cichlasoma urophthalmus (Günther), Eucinostomus gula (Quoy & Gaimard) and Lucania parva (Baird & Girard)] and shellfishes (40% in 1.3-cm mesh size and 4% in 2.5-cm mesh size, mainly Palaemonetes spp. and Callinectes spp.). The highest discards were registered the nortes season with both mesh sizes. The 1.3-cm mesh size retained significantly smaller sizes than the 2.5-cm mesh size in six of the eight most important species. An increase in mesh size, together with a fishery closure during the nortes season, are suggested to mitigate the impact of the fishery on the discarded fauna.  相似文献   

12.
利用几何相似原理将传统的过滤性渔具选择性曲线转化为选择性曲面。运用选择性方程，并假设不同网目大小的渔具对相同尺寸渔获个体的渔获服从多项分布后，对过滤性渔具的网目选择性建立模型。使用极大似然估计法对模型进行拟合，同时，通过假设检验对模型进行简化。使用平行作业法试验条件下的张网渔具的黄鲫(Setipinrm taty)渔获数据进行模型拟合。结果显示，所建模型可以在没有对照网的情况下估算出各不同网目大小网囊的选择率，并同样适用于套网法试验条件下的选择性分析。模型的建立为今后进行过滤性渔具网目选择性试验方法改革提供了理论参考。通过与SELECT模型比较，认为模型使用选择性方程并区分渔获能力和捕捞努力量使得模型更具普遍性。  相似文献   

13.
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   

14.
为了解东莞生态园湿地水域群落结构特征,探讨2种类型刺网(沉网和浮网)及不同网目网片渔获物组成的差异性,实验利用多网目(1.0、1.25、1.6、2.0、2.5、3.1、3.9、4.8、5.8、7.0、8.6和11.0 cm)单层刺网对该湿地的鱼类进行了调查。研究期间共采集到13种鱼类,相对重要性指数显示,海南似和莫桑比克罗非鱼为优势种,前者密度最高(占84.8%),后者生物量居多(40.2%)。渔获物物种组成沉浮网间差异显著,但单位努力捕捞数量(NPUE)、单位努力捕获重量(BPUE)及物种数与沉浮网间均无显著差异;海南似的NPUE在2种类型刺网间无显著差异,但莫桑比克罗非鱼和尼罗罗非鱼的NPUE浮网显著低于沉网。12个网目网片的渔获物物种聚成2类,1.0～2.0 cm网目网片渔获物聚为1类,海南似为指示种;2.5～11.0 cm片的聚为另1类,莫桑比克罗非鱼和尼罗罗非鱼为指示种。渔获物大小结构聚为2类,1.0～3.9 cm网目网片渔获物聚为1类,4.8～11.0 cm网目网片的聚为另1类。随着网目大小增加,渔获物平均体长线性递增,NPUE呈幂函数式下降。研究表明,为对内陆水域鱼类群落...  相似文献   

15.
ABSTRACT:   Fishing experiments were carried out in Yeongil Bay, Korea using an encircling gill net with four different mesh sizes and two different hanging ratios to measure the mesh selectivity for gizzard shad Konosirus punctatus . Twenty-six trials were conducted giving a total catch of 485 gizzard shad. The 'share each length's catch total' (SELECT) analysis with maximum likelihood method was used to fit the different functional models, the normal, lognormal, and bi-normal model, for a selectivity curve to the catch data. In addition, two cases in which the relative fishing intensity was either estimated or fixed were compared. The bi-normal model with the fixed relative fishing intensity was found to fit the data best. For the selectivity curve on the bi-normal model, the relative length (the ratio of fish length to mesh size) with the maximum efficiency was obtained as 3.70. From this, the focal fish lengths in the commercial encircling gill net, with mesh size ranging from 5.0 to 6.0 cm, were inferred to be 18.5–22.2 cm.  相似文献   

16.
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   

17.

This study evaluates the impacts of mesh size of the net, fishing depth and season on the catches of target, non-target and discarded species for short mackerel Rastrelliger brachysoma gillnet fishery in the vicinity of Pattani Bay, Gulf of Thailand. The catches were examined for species composition, catch efficiency and size of catch. Samples were obtained monthly from February 2019 to February 2020 at three fishing depths (2.0, 4.0 and 6.0 m) using gillnets with three different mesh sizes (3.0, 4.0 and 4.5 cm). Including the target species, 112 species were collected, the majority of which were non-targeted fishes and crustaceans. The target species, Rastrelliger brachysoma, contributed only 6.0% by number and 8.76% by weight to the total catches. The 111 non-target species were classified into five categories based on potential sale prices. A total of 18 species, equivalent to 3.04% by weight of the total catches, were considered to be of negligible value and discarded or sold for the production of fish meal. Temporal variability was observed for number of individuals and biomass of total catches; the compositions of the catches clustered to two distinct seasons from December to March and from April to November, respectively. Spatial variability in this study focused on the depth profile which was found to significantly influence species richness and sizes of some fish species. For 12 species, mesh sizes of the gillnets significantly affected the number of individuals caught, as well as their weight and sizes. The novel findings of this study provide essential information that can be used for the sustainable management of the Rastrelliger brachysoma fishery in the Gulf of Thailand.

  相似文献   

18.
网目尺寸对金枪鱼围网沉降性能及网具形态的影响   总被引：1，自引：0，他引：1  
根据以往的研究结果和海上网具性能实测,并在听取生产第一线船长意见的基础上,把上海开创远洋渔业有限公司现行金枪鱼围网主网衣下部约三分之一网衣的网目尺寸放大50%,即从260 mm增大到390 mm,以探讨改进围网渔具的沉降性能。实验应用田内准则换算并制作成模型网,在日本下关西日本日网公司专业围网动水槽进行模型试验,比较了侧流、背流、顺流(流速8 cm/s,相当实物网0.20 m/s)3种相对流向的放网模式下放网以及无流(0 cm/s)海况下放网,网目尺寸改变前后围网的沉降性能、网具形态和闭合效果。结果显示,主网衣下部网目尺寸从30 mm (对照网,相当于实物网网目尺寸260 mm)放大到45 mm (试验网,相当于实物网网目尺寸390 mm),网具的沉降深度和沉降速度分别提高1.6%和1.1%;试验网的收绞时间比对照网缩短14.3%,且能保持较好的形态;有流时的3种放网模式下,试验网和对照网浮子纲在放网结束时刻的初始包围面积基本相同;在收绞结束时,试验网浮子纲包围面积为对照网的1.33倍,绞纲结束前6 s,试验网沉子纲包围面积为对照网的1.79倍,说明增大网目尺寸有利于网具包围面积的增大,改善了被围鱼群的活动空间。  相似文献   

19.
Codend selectivity for the jack mackerel Trachurus japonicus and the whitefin jack Kaiwarinus equula were evaluated based on data from trouser trawl experiments carried out in the East China Sea, using a test codend of 60 mm diamond mesh and a control codend made of minnow net with a square mesh of 9 mm bar length. Between-haul variations in parameters and the mean selection curves were tested with the catch data in the SELECT approach, and then the model of between-haul variation in the split parameter with the mean selection curve was chosen as the best fit using Akaike’s information criterion model selection. The 50% retention lengths and the selection ranges were 11.4 and 3.36 cm for jack mackerel and 8.83 and 0.93 cm for whitefin jack, respectively. The selection curve for whitefin jack was sharp, whereas that for jack mackerel was relatively wide. As the estimated split parameters indicated, about 80% of the whitefin jack entered the control codend, but 85 and 90% of the jack mackerel entered the control codend in the second and third hauls, respectively. The inequality in the split parameter is discussed from the viewpoint of the animal’s swimming behavior and water movement based on underwater video observations.  相似文献   

20.
Little is known about the size selectivity of cod in static fishing gears such as pots and traps. In this field study, floating fishing pots were equipped with 40, 45 and 50 mm square mesh escape windows in order to estimate the size selectivity of cod at different mesh sizes. Relationships between selectivity parameters and mesh size, as well as an optimal mesh size for the escape window with respect to current minimum landing size of cod in the Baltic Sea were sought. The results show that the floating pot is not only species selective when used in the Baltic Sea cod fishery, the implementation of an escape window reduced the proportion of undersized bycatch in the pots by more than 90%. The estimated length at 50% retention was found to be a direct function of fish body length (girth) and mesh size of the escape window, while the estimated selection range remained unchanged regardless of mesh size. Optimal mesh size, with respect to the length at 50% retention and current minimal landing size of 38 cm in the Baltic, was determined to be 45 mm. Strong indications (significant on the 0.01 probability level in the case of 50 and 40 mm escape windows) suggested that the relative fishing power of the pots increased with the implementation of an escape window. This result could be explained as a “saturation effect”, i.e. the probability of cod entering the pot is likely to be negatively dependent on cod density in the pot. The high species selectivity and the low catch rate of undersized fish have consolidated the floating pots position as a highly benign fishing method and the foremost alternative gear for the future coastal cod fishery in the Baltic Sea.  相似文献   

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