Gear-based management of a tropical artisanal fishery based on species selectivity and capture size

The population density, species composition and lengths of fish landed by artisanal fishermen using six types of gear: large and small traps, gill nets, hand lines, spears and beach seines were studied in the multi‐species fishery of southern Kenya. Selectivity and catch composition among gears were determined by studying the species richness, diversity, size and mean trophic level of the catches for each gear type, to develop gear‐based management recommendations for this artisanal reef lagoon fishery. One hundred and sixty‐three reef and reef‐associated species from 37 families were recorded in the catch. Beach seines and small traps accounted for the highest number of fish landed (34–35 individuals per fisherman per day). These gears also caught smaller fish than big traps, spears and gill nets. Beach seines caught the highest number of species (14 ± 7 species per day) while most other gears caught four to five species per day with no differences between gears. Predatory species with a mean trophic level of 3.6 dominated catches from hand lines, while the mean trophic level of the other gears was low and ranged from 2.6 to 2.9 with no differences between the gears. The high diversity and small size of fish caught in beach seines indicates that its selectivity overlapped most with large traps and gill nets. Spears and small traps also showed high similarity in species selectivity and small traps captured the smaller mean size of fish, indicating that they are likely to pre‐empt the resource of spears. Large traps, hand lines and spears catch the largest individuals and the species composition of the catch differed sufficiently such that their selectivity should overlap the least and may, therefore, be the preferred mix of gears. The elimination or reduction of beach seines and small traps should reduce the catch of small fish and overlap in selectivity among the existing gears.     

Fishing profiles of Danish seiners and bottom trawlers in relation to current EU management regulations

Danish seines and bottom trawls operate differently and have different catching processes. Both gears belong to the same legislative category in European fisheries, but different management strategies in other countries and criticism by fishers on grouping Danish seines and trawls together indicate disagreement on current gear classification. This study compared both gears in terms of their fishing characteristics and catches of commercial species based on 16 years of observer data. Danish seining is a specialised fishing method that targeted few species but with higher total catch rates than bottom trawlers. Bottom trawling is a more all‐purpose fishing method that targets a larger number of species, and bottom trawlers use larger engines than Danish seiners. A generalised additive mixed model indicated that catch rates of flatfish are generally higher for Danish seines, and catch rates of roundfish species are higher for trawlers. The results do not directly suggest a separation of the gears in terms of legislation as the quantities of fish below current minimum size were similar, but for example future survival studies may reach different conclusions. Additional factors were found to be important in determining catches of both gears.     

Changes in life history and ecological characteristics of coral reef fish catch composition with increasing fishery management

Abstract Length, life history and ecological characteristics of landed fish communities were studied over a 10‐year period to test theories of fishing disturbance during a time of increased gear and closure management in heavily utilised fisheries. It was predicted that with greater management restrictions: (1) the earliest and fastest responses in the fishery will be seen in those species with faster turnovers, or relatively lower vulnerabilities to fishing; (2) the fishery would transition to a landed catch with higher mean trophic levels, and greater mean body lengths. In addition, the removal of a non‐selective, small‐mesh seine nets should benefit the catch of gears that previously had the greatest species selectivity overlap with the seine net. Many predictions were supported, although maximum lengths and lengths at maturity responded more rapidly than anticipated. The response to eliminating the non‐selective seine net was a more rapid increase in sizes caught by gears with a larger overlap in size (hook and lines) than species selectivity (gill nets). The simultaneous comparison of management systems over time indicates that open‐access fishing grounds can benefit from restrictions imposed in adjacent fishing grounds. The study indicated that multi‐species coral reef fisheries management objectives of maximising yields, as well as maintaining the fish community’s life‐history diversity, require management trade‐offs that balance local socio‐economic and biodiversity needs.     

Changes in a coral reef fishery along a gradient of fishing pressure in an Indonesian marine protected area

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Comparative analysis of artisanal and recreational fisheries for Dentex dentex in a Marine Protected Area

The common dentex, Dentex dentex (L.), is an iconic marine coastal fish in the Mediterranean Sea. This study was performed in the Bonifacio Strait Natural Reserve (BSNR), (NW Mediterranean Sea). The aims were to: (1) evaluate temporal variation of the artisanal fishing of common dentex (2000–2012); (2) compare and quantify catch rates, fishing techniques and catch composition for artisanal and recreational fisheries, and determine the influence of management measures by both activities; and (3) estimate the production of both artisanal and recreational fisheries. Fishery data were collected from different artisanal fishing surveys (onboard fishing vessels and landings) and recreational fishing surveys (roving). The gears with the highest rates of exploitation were longline (3554 g per 100 hooks) and Trolling (351 g boat^?1 h^?1 ±SE), respectively, for artisanal and recreational fishing. This study showed that catches by both activities were quantitatively higher in partially protected areas than outside them. Production estimations suggest that the recreational fishery contributes significantly to fishing mortality and that it can magnify the negative effects of artisanal fisheries. Specific measures are needed for the sustainable fishery management of common dentex.     

The development of fisheries at Bornholm,Denmark (Baltic Sea) during 1880s–1914

For centuries the abundance of fish in the Baltic Sea has had an important role in the economy of Bornholm, Denmark. This study examines the development of Bornholm fisheries between approximately 1880s and 1914 on the basis of the first officially recorded Danish fisheries data. Several species were caught, but prior to 1914 especially herring, salmon and cod were economically most important. In the late 19th and early 20th century, the catch composition changed fundamentally due to complex interactions between biological, technological and economical factors. During the late 19th century the catches of herring increased, while the catches of salmon and cod decreased. This development coincided with the introduction of new technologies and fishing practices, including motorization of fishing vessels and the exploitation of herring in previously unexploited areas (i.e., expansion of fishing areas). In addition, the salmon fishery diminished after the introduction of driftnets, which caught large numbers of small salmon. The high catches of small salmon, in combination with other factors, probably contributed to the decline in catches of larger salmon. Each of the fisheries for the three species required different types of vessels and gear, and when catches began to drop in the salmon fishery, Bornholm fishermen were faced with two options. They could either specialise in the growing herring fishery, thereby hoping to maintain their income level, or they could pursue a strategy of risk minimization, by acquiring an income outside the fishing industry, while continuing to work part-time in the salmon and cod fisheries. This dual tendency was intensified further as marine engines and new types of vessels were introduced, raising the costs of fishing.     

闽南-台湾浅滩渔场单船拖网作业调查与分析

根据2009—2010年闽南-台湾浅滩渔场单船拖网作业监测调查资料和生产统计数据,阐明单船拖网作业的渔业地位、渔场分布、网具类型,着重分析该作业渔获种类组成及主要捕捞对象的资源动态。结果表明:单船拖网作业产量位居闽南-台湾浅滩渔场各种海洋捕捞作业的首位,大吨位、大功率渔船数量连续多年不断增长;渔具型式以有翼单囊网具为主;部分渔船使用的拖网网囊尺寸远远低于国家标准;带鱼、二长棘鲷幼鱼损害现象较为严重;秋季8—10月蓝圆鲹和鲐鱼群体绝大多数个体可达到最小可捕规格。调查研究结果还表明,2002年以来单船拖网渔业资源结构已发生较大变化,生命周期短、营养级较低的蟹类、枪乌贼类、乌贼类和虾类资源渔获比重显著增长;原优势种类绿布氏筋鱼资源已出现严重衰竭;二长棘鲷资源量逐年减少,渔获群体明显趋向小型化、低龄化。     

The decline of fisheries on the Madeira River,Brazil: The high cost of the hydroelectric dams in the Amazon Basin

Despite being considered beneficial by providing a clean and renewable source of energy, the construction of hydroelectric dams has extremely negative implications for Amazonian fisheries. This study investigated the impacts of the Santo Antônio and Jirau hydroelectric dams on the fishery stocks of the Madeira River. This investigation was based on fish catch data from the Z‐31 fishing colony, located in the municipality of Humaitá, in Amazonas State, Northern Brazil. Data were collected daily and provided information on the date of return from each trip, the fish species targeted, and the total catch (kg) between January 2002 and September 2017. The results indicated reductions of 39% in the mean annual catch and 34% in the mean monthly catches. These results highlight the high price paid by local fish communities for the development of hydroelectric power in the Amazon basin.     

Eel, Anguilla anguilla L., stock and yield in Polish lakes

Abstract. Details of mean annual slocking rate and catch of eels in a random sample of 68 Polish lakes over a period of 36 years are presented. Multiple correlation and curvilinear regressions are used to assess the effectiveness of stocking. Maximum stocking rate of 275 elvers/ha/year and maximum catch of 5.2 kg/ha were determined. Yields per recruit were highest in the lakes in which the greatest catches of other fish were made and stocking was most effective in lakes of depth less than 5 m.
The theoretical maximum catch of 5.2kg/ha was very much less than maxima observed elsewhere. Two possible contributory factors are the Polish practice of using relatively large-meshed seines for fishing, permitting the escape of eels of less than 50cm and the relatively small number of potential competing fish species in fisheries such as that of Lough Neagh in Ireland.     

Are the exploitation pressures on the Nile perch fisheries resources of Lake Victoria a cause for concern?

Abstract Lake Victoria is one of the African Great Lakes, and an important source of affordable protein food in the form of fish. It provides employment, income, and export earnings to the riparian communities. Despite this importance there are major concerns about the status and exploitation of the fisheries. This study assesses if current extraction rates/yield of Nile perch, Lates niloticus (L.), from Lake Victoria are sustainable for the foreseeable future. The paper reviews trends in catch and effort in the Nile perch fishery and models the expected scenarios using ECOPATH. The fishery exhibits, classic indicators of intensive fishing, erring towards overexploitation, including: (i) decline in total estimated catch of Nile perch in recent years from the peaks in the 1990s. This is coupled with a shift in contribution of catches from higher trophic level species (Nile perch) to lower trophic level (dagaa) species. (ii) Three major trends in the fishing effort are evident: (a) almost doubling of the number of fishers and fishing boats between 1990 and 2000, and the even greater expansion between 2000 and 2002; (b) a large scale increase in the number of gears operational in the lake; and (c) the propensity for use of ‘illegal’ gears. (iii) Catch‐per‐unit‐effort has declined from about 80 to 45 kg per boat day. (iv) Predictive modelling (ECOSIM) of the future of the Nile perch fisheries under a scenario of increased fishing effort suggests that the fisheries are unsustainable and will decline in the long term. It appears that the Nile perch stocks in the three riparian countries are under intense fishing pressure, and unless concerted action is taken, the potential for degradation of the resources is prevalent. In view of the importance of these fisheries, it is recommended that a precautionary approach to further intens‐ification of the fisheries is adopted until such time empirical evidence shows that the fisheries are capable of further expansion and intensification. The main options for management are devolvement of responsibilities for the fisheries to the communities, enforcement of existing regulations, improved monitoring and data collection processes, reducing post‐harvest losses and increasing the value of the products to the export market.     

珠江口浅水域小型虾拖网渔获组成分析

拖虾是广东省沿海捕捞渔业的主要作业方式之一。为了查明小型虾拖网的渔获组成及其对渔业资源的影响，2006年10～11月对在珠江口浅水域进行捕虾作业的虾罟网渔船进行了海上渔获组成抽样调查。研究结果表明，珠江口浅水域虾罟网的渔获种类多、组成复杂，幼鱼和副渔获的比例高；主要渔获种类是周氏新对虾Metapenaeus joyneri（18．57％）、矛形梭子蟹Portunus hastatoides（15．48％）、脊尾白虾Exopalaemoncarinicauda（11．50％）和斑节对虾Penaeusmonodon（11．16％），刀额新对虾Metapenaeus ensis、脊尾白虾、白姑鱼Argyrosomus argentatus、海鳗Muraenesocidae和银鲳Pampusargenteus渔获100％为幼鱼，凤鲚Coiliamystus和棘头梅童鱼CoUichthys lucidus幼鱼比例分别高达87．65％和96．15％；周氏新对虾、脊尾白虾、斑节对虾为主捕对象，鱼类和蟹类是主要的副渔获种类；虾罟网捕捞对渔业资源造成一定程度的破坏。     

Trap modification opens new gates to achieve sustainable coral reef fisheries

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2014年江苏沿海定置张网渔业生产时空分布特征

本研究基于 2014 年江苏沿海定置张网渔船的大样本随机抽样调查数据, 对渔船捕捞产量及渔获物结构的时空分布特征进行了初步分析。研究结果显示: 江苏沿海渔船捕捞具有显著的空间特征, 多数在近海生产、少有渔船远赴外海生产, 除个别月份, 少有渔船在长江口航道中生产, 长江口近岸北侧常年有该类渔船生产, 在江苏近岸 20 m 等深线附近水域形成了一条连贯、且相对高产的水道走廊。渔船生产具有季节性, 在水温偏低的冬季, 渔船趋于向外、向南扩展生产, 而在水温偏高的夏季则趋于向北扩展生产。渔获物结构比较分析发现, 主捕对象存在季节变化, 分别出现虾类(1—4 月和 10—11 月)、毛虾(2—3 月、5 月和 11—12 月)、梭子蟹(9—11 月)等渔获比例相对较高的情况, 而杂鱼杂虾除 1—4 月和 11 月比例相对偏小外, 其余月份比例均较高, 虾类资源与其他杂鱼杂虾资源之间呈现显著负向关系。文献比较分析发现, 渔获物中的杂鱼杂虾与经济鱼类幼鱼之间有对应关系。基于研究结果, 建议定置张网伏休时间提前一个月、并加强伏休后渔船捕捞网目尺寸的管理, 以确保足量补充群体维持渔业资源的可持续利用。     

海州湾秋季坛子网网目选择性研究

2018年秋季,利用囊网内径网目为25、35、45、55 mm的坛子网在黄海海州湾渔场N 35°02.335′,E 119°24.842′附近海域进行了11网次试验。从Logistic选择性模型、坛子网不同网目对主要渔获物小黄鱼的选择性曲线、渔获物组成、幼鱼比例及选择性分析等方面,研究坛子网网囊的选择性。试验结果显示,坛子网九月主要渔获物为小黄鱼、带鱼和三疣梭子蟹;随网囊网目尺寸的增加,渔获物质量逃逸率及尾数逃逸率均迅速增加,网目尺寸为55 mm时其值均超过80%,且质量逃逸率及尾数逃逸率的值比较接近;渔获物组成中,小黄鱼、银鲳和三疣梭子蟹幼体比例非常高,基本全为幼体,带鱼幼鱼比例也超过70%;根据小黄鱼的可捕体长,获得坛子网针对小黄鱼的最适网囊网目尺寸,为(40.59±3.19)mm。研究结果可为我国海州湾渔具管理以及渔业资源的可持续发展与管理提供科技支撑。     

肖四海湖五种渔具的鳜渔获结构特征及其对鳜资源的影响

为评估不同渔具对鳜资源的影响,于2007年5月和12月对长江中游浅水湖泊肖四海湖刺网、延绳钓、网簖、电拖网和电捕仪5种渔具捕获的鳜渔获物结构特征进行了调查分析.结果发现,共采集鳜样本359尾,全长分布范围为92 ～600 mm,优势全长集中于251～350 mm;体质量分布范围为10～3 380 g,优势体质量集中于300 ～500 g.种群由5个年龄组构成,2～3龄为优势龄组,占总数的74.6％.刺网、延绳钓和网簖对鳜有较强的捕捞选择性,网目大小为80 mm和100 mm刺网的鳜渔获物中2龄及以上成熟个体占总数的93.3％,个体平均体质量466 g,“标鳜”(0.4 ～0.75 kg)个体占总数量的57.0％;延绳钓捕获的鳜渔获物中2龄及以上成熟个体占总数的86.9％,“标鳜”个体占总数量的43.5％;网簖捕获的鳜渔获物中90％以上为1龄的未成熟个体.电拖网和电捕仪捕获的鳜全长范围明显较大,其渔获物以1龄和2龄个体为主.综合分析表明,刺网适于作为鳜捕捞的主要渔具,延绳钓可以作为一种鳜捕捞的辅助渔具.网簖对鳜补充群体有较大危害,不适于作为鳜的捕捞网具.电拖网和电捕仪均属于违法渔具,对鳜资源危害巨大,应该加大监管力度,严禁使用.     

The effect of a closed area and beach seine exclusion on coral reef fish catches

Fish landing data from the Mombasa Marine National Park (MNP) and a marine reserve exploited by various gears were studied over a 5‐yr period to determine the influence of the closed area and different gears in fisheries. The number fishing and boats per landing site was constant, but total and catch per unit effort progressively declined in all sites on an annual basis irrespective of the existence of a marine reserve, exclusion of the beach seines or use of gear. Differences between landing sites were most pronounced when analysed on a catch per area as opposed to the more standard catch per fisherman, suggesting compensation in human effort when catches decline. A marine reserve next to a closed area that excluded beach seines had the highest catch per area (5.5 kg ha^?1 month^?1) despite having the highest density of fishermen (0.07 ± 0.02 fishermen ha^?1 month^?1). The annual rate of decline in the catch was lower than the other sites at around 250 g day^?1 compared with 310–400 g day^?1 in the other sites. One landing site, which excluded beach seine landings for more than 20 yrs, had a high catch per area (～5.3 kg ha^?1 month^?1), but after experiencing a doubling in the effort of other gears (line, speargun and trap), the catch per fisherman and area were reduced. Environmental or habitat degradation and excessive effort remain the most likely explanation for the overall declines in catch from 1995 to 1999. Closed areas and beach seine exclusion have the potential to increase catch rates, but the first often reduces the total fishing area and possibly leads to a loss of total catch, at least on a time scale of less than 10 yrs. The exclusion of beach seines can lead to an increase in other gear types that can also cause reductions in catch.     

Estimating trends and magnitudes of bycatch in the tuna fisheries of the Western and Central Pacific Ocean

Minimising the unintended capture of fish, marine mammals, reptiles, seabirds and other marine organisms is an important component of responsible fisheries management and for stabilising declines and rebuilding populations of threatened species. The analyses presented were designed to establish the first quantitative baseline of historical catches, catch rates and species composition for the dominant tuna fisheries operating in the western and central Pacific, the world's largest in terms of tuna catch. Using records from 612,148 fishing events collected by independent ‘at sea’ observers, estimates for finfish, billfish, elasmobranchs, marine mammals and sea turtles show that the composition and magnitude of catches varied considerably by fishery type and practice for the period 2003–2019. Simulations indicated that precision in longline estimates would be improved by monitoring a proportion of fishing sets from all fishing trips rather than full coverage from a proportion of all fishing trips. While attributing reasons for temporal trends in estimated bycatch was difficult due to the confounding impacts of changing abundances and fishing practices, the trends identified the nature of potential relationships for species that are not accurately quantified, or not covered, by fishing vessel logbooks. The trends in catch estimates, and the catch rate models, have utility in identifying species which may require targeted additional analyses and management interventions, including species of conservation interest (either due to their threatened status or vulnerability to fishing) such as elasmobranchs and sea turtles. Moreover, the estimates should support future evaluations of the impact of these industrial-scale fisheries on bycatch species.     

A framework for adaptive gear and ecosystem‐based management in the artisanal coral reef fishery of Papua New Guinea

• 1. Artisanal fishing on coral reefs in Papua New Guinea is an important livelihood activity that is managed primarily at the level of local communities. Pockets of overexploitation exist and are expected to increase with plans for increased commercialization.
• 2. This paper provides a current assessment of the artisanal multi‐species coral reef fishery by examining selectivity of the dominant gear, namely line fishing, spearguns, and gill nets. Each gear has its own strengths and weaknesses in terms of use and conservation of resources, with no clear problem gear.
• 3. The three gears utilize different resources but there was moderate overlap in the species caught, particularly between gill nets and line fishing and marginally between lines and spearguns. Gill nets have the disadvantage of being destructive to coral and the advantage of catching commercial species. Line fishing catches an intermediate number of species but mostly large‐bodied and predatory species that could potentially reduce predation and the mean trophic level of the fishery. Spearguns catch the highest numbers of species, including many non‐commercial and herbivorous fish and could reduce the diversity of fish and encourage algal growth.
• 4. This information could be used in combination with scientific monitoring and traditional ecological knowledge to develop an adaptive management framework that uses local restrictions on the various gears to restore or balance the fishery and ecosystem. Restrictions could be selectively imposed: on gill nets when coral cover is low, line fishing when large‐bodied predators are depleted, and spearguns when biodiversity is reduced and algal abundance high.

Copyright © 2008 John Wiley & Sons, Ltd.     

Recreational charter fishery attributes and variation in key species catches and discards: Resource management considerations

Strategic long‐term sampling programmes that deliver recreational catch, effort and species demographic data are required for the effective assessment and management of recreational fisheries and harvested organisms. This study used a spatially and temporally stratified observer programme to examine variation in the rates, quantities and lengths of retained and discarded catches of key species in a recreational charter fishery. Geographic region, but not season, significantly influenced catch rates of key demersal species, being driven by temporally persistent latitudinal clines in environmental conditions influencing species distributions. There was considerable trip‐to‐trip variation in catch rates that were attributed to localised differences in fishing operations, locations, environmental conditions and client preferences. Broad trends in retained and discarded catch rates were nevertheless, similar across different fishing effort standardisations (per‐trip, per‐hour, per‐client, per‐client/fished hour), demonstrating that the coarsest unit of effort could be used in fishery assessments. Discard rates of organisms were variable and driven by a combination of mandated legal lengths, individual client and operator preferences for particular species and sizes of organisms, and not due to attainment of catch quotas or high‐grading. This study has identified important fishery attributes that require consideration in assessing charter fisheries and stocks of recreational fish species.     

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.