基于渔获物统计的中国近海鱼类营养级结构变换及其与捕捞作业的关系

为了解我国东部海域(渤海、黄海和东海)和南海的鱼类生态结构和渔业资源变化特征,本研究在1983—2013年中国海洋渔船渔获统计数据的基础上,首先将渔获物中的鱼类按照营养级归类,然后计算其平均营养级(TL)和Fi B指数,并结合海洋捕捞作业方式,对鱼类的营养级结构长期变化进行分析。结果表明,在东部海域捕捞的25种主要鱼类渔获中,31年间TL呈现下降趋势,低营养层级鱼类比例增长了60%,中营养层级鱼类比例增长了129%,高营养级鱼类则下降了近51%;而在南海,31年间TL变化不明显,低营养级鱼类比例下降了6%,中营养级鱼类下降了43%,高营养级鱼类增长198%。东部海域和南海的渔获物鱼类生态结构变化说明,就营养级水平而言,东部海域近海渔业资源呈现明显的衰退现象,而南海则还未出现这种现象。     

Ecosystem structure and trophic dynamics of an exploited ecosystem of Bay of Bengal,Sundarban Estuary,India

A trophic structure model for commercial fisheries of Sundarban Estuary in the northern Bay of Bengal (BoB) is developed using the mass balance modeling software Ecopath (Version 6.4.10992.0). In this model, we simulated 15 functional groups spread across an area of 17,049 km². The mean trophic level of the present study area is 2.716. The ecotrophic efficiency of the present studied ecosystem is in the range of 0.424 of medium demersals and 0.961 of medium pelagics. Penaeid prawn, small pelagics, and medium pelagics are the most exploited groups of this ecosystem. The coastal northern BoB food web is mainly detritivorous and planktivorous; phytoplankton and detritus positively affected almost all the functional groups, and top predators are essentially absent in the system. The zooplankton and benthos have negative impacts on themselves because of cannibalistic behavior. The average catch per net primary production, i.e. the gross efficiency of the system is around 0.001. The system is low trophic and efficient. Proper ecosystem-based management practice can improve the efficiency of this overexploited ecosystem.     

Catch trend of bigeye tuna <Emphasis Type="Italic">Thunnus obesus</Emphasis> by purse seine using fish aggregating devices,by flag states and area of operation in tropical regions of the Western and Central Pacific Ocean

Seventeen members and cooperating non-members (CCMs) of the Western and Central Pacific Fisheries Commission (WCPFC) were responsible for 86% of the total catch of bigeye tuna Thunnus obesus by purse seine fishing from 2012 to 2014. We categorize the CCMs into an eastern, western and “other” group based on their main fishing areas. We found significant differences in the bigeye tuna catch per fish aggregating device (FAD) between the eastern group and the western group. We also estimated that the eastern group achieved a higher catch of bigeye tuna because of their increased fishing effort using FAD in the eastern area where there is a higher catch per unit effort for FAD. The regression analysis found significant correlations between the annual catch of bigeye tuna and the number of FAD sets. The average catch of bigeye tuna per single FAD set, estimated from the slope of the regression line, was 7.1 t in the eastern area and 2.7 t in the western area. An impact and risk plot composed of the slope of the regression line and the catch of bigeye tuna by each individual CCM was developed to improve management measures. Appropriate measures for the sustainable use of tuna resources in the region are discussed.     

Ecosystem structure and functioning of Lake Taihu (China) and the impacts of fishing

Lake Taihu is the third largest freshwater lake in China and has provided local communities with valuable fisheries for centuries. However, we have only a limited knowledge of its ecosystem. In this study, a trophic model was constructed for the Lake Taihu ecosystem. This model was used to evaluate and analyze the food web structure and other properties of this ecosystem using data covering the period from 1991 to 1995. Using the model, we evaluated the impacts on local fisheries of various management scenarios comprising two basic management regimes: (1) setting fishing mortality for the top predator (large culters, Erythroculter mongolicus and Erythroculter ilishaeformis) to 0, 0.3, 0.6, 0.9 and 1.2, and (2) adjusting overall fishing effort to 0.25, 0.5, 0.75 and 1.25 times the current level. For both scenarios, fishery profit and cost were evaluated to provide an understanding of how components of the ecosystem interact. We identified possible causes of fishery overexploitation in the lake ecosystem and described the necessity of developing ecosystem-based management. The results showed that Lake Taihu had six theoretical trophic levels (TLs), with the trophic flows primarily occurring through the first five TLs. System properties such as transfer efficiency, Finn's index, Finn's mean length, connectance index, system omnivory index, primary production/respiration ratio, and net primary production all indicated that Lake Taihu was an immature, fairly simple ecosystem in which a relatively low fraction of total primary production was utilized. At the same time, the ecosystem was also experiencing high fishing pressure. Yet despite this, the low ascendency index (25.9%) and high system overhead ratio (74.1%) indicated that the system was highly developed and relatively stable, a condition that might result from the high degree of recycling in the system. Among the harvesting strategies considered, a strategy of either decreasing the fishing mortality of the top predator (large culters) to 0.3 or, alternatively, reducing the overall effort on the system by a factor of 0.75 appeared to be most effective at increasing the efficiency of the fisheries.     

Growth rate and mortality of Australian bass, Macquaria novemaculeata, in four freshwater impoundments in south-eastern Queensland, Australia

Abstract  Growth and total mortality of Australian bass, Macquaria novemaculeata Steindachner, were studied in four freshwater impoundments using data from a cooperative angler tagging programme. Growth was modelled using the computer program GROTAG. Annual growth increments varied among impoundments, ranging from 5.0 to 7.8 cm yr⁻¹ among fish 20-cm total length (TL) and 1.7 to 4.9 cm yr⁻¹ among fish 30 cm TL, but exceeded previous estimates for the species. Annual total mortality rates, based on the decrease in recapture rate with time, ranged from 0.03 to 0.07 and were lower than for other comparable species, presumably because of the prevalence of catch and release fishing in the impoundments studied.     

Can fishermen allocate their fishing effort in space and time on the basis of their catch rates? An example from Spermonde Archipelago,SW Sulawesi,Indonesia

Spatial and temporal patterns in catch rates and in allocation of fishing effort were analysed for the coastal fishery in Spermonde Archipelago, Indonesia, to assess whether fishermen can optimise their strategy from catch information, or whether they fish under great uncertainty and merely minimise risks. On average 517 fishing units operated in the 2800 km² area, catching 21 t fish day⁻¹. Major gear categories were hook and line (59% of total effort and 5% of total catch), and lift nets (16% of total effort and 70% of total catch). The size of individual resource spaces varied with gear type and was smaller in unfavourable weather conditions. Although spatial patterns in catch rates at the scale of the whole archipelago were evident, fishermen could not differentiate between locations, as catch variance within their individual resource spaces was high relative to the contrasts in spatial patterns. The aggregated distribution of fishing effort in Spermonde must be explained by factors such as the small scale of operations, rather than fish abundance.     

Selectivity of hooks in the handline fishery of the Saya de Malha banks (Indian Ocean)

Experimental handline fishing trials were conducted on the coral-reefs of the Saya de Malha banks with different hooks within a size range difference of 96% between the biggest and the smallest ones. The major species of fish captured was Lethrinus mahsena representing about 90% of the total catch. For a given population, no effect of modifying the size of tooks and baits on selectivity under varying fishing conditions was identified. The relative abundance of larger fish catch, however, obtained in preference to smaller fish indicates the existence of competition among fish of different sizes.     

捕捞和环境变化对渤海生态系统的影响

以1982年的渤海Ecopath静态模型为起始状态,设置17个功能群,利用CPUE和渔业相对捕捞强度作为时间强制序列,构建渤海Ecosim模型,模拟1982—2008年渤海生态系统发育的动态变化及捕捞的影响;利用气候环境时间序列数据,分析环境变化对渤海生态系统渔业资源的影响。研究发现,1982—2008年间,只有口虾蛄的生物量保持上升趋势,主要经济鱼种小黄鱼、蓝点马鲛、鳀、花鲈、黄鲫等的生物量均呈下降趋势,虾蟹类、头足类的生物量相对稳定。渤海渔获物的平均营养级在1982—2008年间明显下降,总捕捞产量在1984年之后一直保持上升趋势,两者之间存在显著的负相关;FIB指数的变动与捕捞产量的变动保持一致。Q-90多样性指数在1982—1987年间处于波动状态,从1988—1994年间保持增长趋势,在1994年之后迅速下降,由2.5降至0.5附近,渔业生物多样性下降;渤海海表盐度、海表水温、黄河径流量对捕捞产量影响显著。Ecosim模型终止状态(2008年)与起始状态(1982年)的比较表明,系统成熟度降低,生态系统出现一定程度的退化,渔业捕捞是渔业生态系统出现退化的主要原因,降低了生态系统总体的生物量水平;除捕捞因素外,环境变化也是影响渤海生态系统渔业资源变动的主要因素。     

利用水温垂直结构研究中西太平洋鲣鱼栖息地指数

根据1990~2001年中西太平洋海域(20°N~25°S、175°W以西)金枪鱼围网鲣鱼作业产量和作业次数,结合不同水层的水温及其温差数据(海表温度SST,12.5 m、237.5 m和287.5 m温度,137.5 m与287.5 m温差),以高产频次的相对比值分别建立各因素的栖息地指数SI,建立单因素一元非线形回归模型。采用连乘法、最小值法、最大值法、算术平均法和几何平均法建立综合栖息地指数HSI,并对1990~2001年各月HSI值与实际作业产量进行验证。结果表明,采用连乘法和最小值法时,主要产量分布在HSI<0.5以下的区域;采用算术平均法和几何平均法时,主要产量分布在0.30.7的区域,其产量占总产量的87%。五种模型结果比较,认为最大值法能更好地反映中心渔场分布和符合鲣鱼的分布特征。采用最大值法推算2003年各月HSI值,并与实际产量分布进行实证分析,发现其各月产量主要分布在HSI>0.8的区域,说明利用HSI模型来预测中心渔场是可行的。     

Bycatch and discarding in the South African demersal trawl fishery

Observers aboard commercial trawlers collected data on the total catch composition of 614 and 479 hauls made by vessels operating off the south and west coasts of South Africa, respectively. On the south coast, four fishing areas were identified on the basis of target species and fishing depth. On the west coast, hauls were separated into those targeting hake Merluccius spp. in four depth ranges (0–300, 301–400, 401–500, and >500 m) and those targeting monkfish Lophius vomerinus. For each area, the catch composition was calculated and the species assemblages were investigated using cluster analysis and multi-dimensional scaling. Finally, for each coast, the weight of fish discarded annually was estimated. On the south coast, although hake dominated, between 21% and 47% of the catch was not hake, depending on the fishing area. In comparison, hake dominated west coast catches, the proportion of hake increasing with depth. For each fishery investigated, approximately 90% of the catch was processed and landed. However, estimates of annual discards indicate that the south and west coast fisheries may annually discard 9000 or 10,000 t and 17,000 or 25,000 t, of undersized and unutilizable fish and offal, respectively, depending on the estimation method used. When developing strategies to limit or enhance utilization of bycatch, cognisance should be taken of the differences in catch composition between the south and west coasts and of the importance of bycatch revenue to south coast fishing companies.     

Modelling South Pacific jack mackerel spatial population dynamics and fisheries

Since the 1970s, South Pacific jack mackerel (Trachurus murphyi) is one of the world's most important commercial exploited fish stock. The peak in the catch was achieved in the 1990s, after which the catch for all fleets steadily decreased due to strong fishing mortality and potentially unfavourable environmental conditions. An application of the ecosystem and fish population model SEAPODYM was developed for this species in the South Pacific Ocean to determine the extent of environmental and fisheries drivers on the stock dynamics. We combined publicly available fishing data, acoustic biomass estimates and expert knowledge to optimise fish population dynamics parameters (habitats, movements, natural and fishing mortality). Despite a large proportion of missing catch over the simulation period, the model provides realistic distributions of biomass, a good fit‐to‐data and is in agreement with the literature. The feeding habitat is predicted to be delineated by water temperature between 15°C for the first cohorts and 8.5°C for the oldest and dissolved oxygen concentration above 1.8 ml/L. Optimal spawning temperature is estimated to 15.57°C (S.E.: 0.75°C). The core habitat is predicted off Central Chile which is also the main fishing ground. There are other areas of higher fish concentration east of New Zealand, in the eastern part of the southern convergence and off Peru and northern Chile. However, there is a clear continuity between these different large sub‐populations. Fishing is predicted to have by far the highest impact, a result that should be reinforced if all fishing mortality could be included.     

Minimizing the impact of fishing

Minimizing the impact of fishing is an explicit goal in international agreements as well as in regional directives and national laws. To assist in practical implementation, three simple rules for fisheries management are proposed in this study: 1) take less than nature by ensuring that mortality caused by fishing is less than the natural rate of mortality; 2) maintain population sizes above half of natural abundance, at levels where populations are still likely to be able to fulfil their ecosystem functions as prey or predator; and 3) let fish grow and reproduce, by adjusting the size at first capture such that the mean length in the catch equals the length where the biomass of an unexploited cohort would be maximum (L_opt). For rule 3), the basic equations describing growth in age‐structured populations are re‐examined and a new optimum length for first capture (L_{c_opt}) is established. For a given rate of fishing mortality, L_{c_opt} keeps catch and profit near their theoretical optima while maintaining large population sizes. Application of the three rules would not only minimize the impact of fishing on commercial species, it may also achieve several goals of ecosystem‐based fisheries management, such as rebuilding the biomass of prey and predator species in the system and reducing collateral impact of fishing, because with more fish in the water, shorter duration of gear deployment is needed for a given catch. The study also addresses typical criticisms of these common sense rules for fisheries management.     

Trap modification opens new gates to achieve sustainable coral reef fisheries

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中东大西洋中部海域中上层鱼类资源结构与渔场分布

为了解中东大西洋中部海域中上层鱼类资源结构与渔场分布,对2007-2014年入渔FAO34渔区3.11和1.32小区(毛里塔尼亚专属经济区)从事中上层鱼类捕捞的7艘国内渔船的生产数据进行了分析。结果表明,我国入渔船只数量、入渔渔船总产量和作业渔船平均日产量均呈现先增加、后减少的趋势,且在2011年入渔渔船总产量和作业渔船平均日产量到达最大值,2012年入渔船只数量到达最大值。渔获种类主要包括沙丁鱼(Sardina pilchardus)、短体小沙丁鱼(Sardinella maderensis)、金色小沙丁鱼(Sardinella aurita)、日本鲭(Scomber japonicus)和竹筴鱼(Trachurus trachurus),各渔获种类的渔获量年际间波动较为明显。月均产量在17.2~23.6 t/haul,最高值和最低值分别出现在12月和8月;月均总产量在1 279.0~2 414.2 t,最高值和最低值分别出现在1月和8月,12月至次年3月为渔汛旺期。渔场季节变化现象明显,夏秋季向北移动,冬春季向南移动,20.0°~20.8°N、17.4°~18.0°W区域为高产量海域。该海域中上层鱼类洄游现象明显,这可能主要与该海域的不同洋流在不同月份的强弱变化有关,该海域整体渔业资源呈现一定衰退现象。建议渔船入渔该海域从事中上层鱼类捕捞持谨慎态度,加强该海域渔业资源的研究与保护。     

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.     

Relationships between Stocking and Anglers' Catches in Draycote Water Trout Fishery

The trout fishery at Draycote Water was investigated during the 1980 fishing season. Fish stocked were batch-marked according to the date of introduction by freeze branding, and catch data were obtained by the cooperation of anglers. Population estimates were made at the end of the fishing season using gill nets and mark-recapture techniques. Of the 32,960 marked brown and rainbow trout stocked, 69.8% were caught and declared by anglers. Returns of rainbow trout were better (78.1%) than those of brown trout (44.2%). Over 90% of all fish caught were taken within 45 days of stocking. Catch per unit effort fluctuated widely but was closely associated with stockings of fish. Catchability (Q) of stocked fish was found to diminish rapidly with time after stocking. At the end of the fishing season the estimated population of marked trout was 4045 (2 × SE = 250), compared with a theoretical number (stock less total catch) of 10,802, giving a mean daily apparent natural mortality, made up of the true natural mortality plus the undeclared catch, of 1.36%.     

Temporal dynamic and economic valuation of recreational fisheries of the lower Cuiabá River,Brazilian Pantanal

Fisheries are the most common ecosystem service that fish provide to human populations, yet recreational fisheries are often overlooked when evaluating such services. Here, the socioeconomic profiles of fishers, the composition of their catches and catch per unit effort (CPUE) are described, to estimate the economic value of the recreational fishery on a stretch of the Cuiabá River in the Brazilian Pantanal. Questionnaires were used to obtain socioeconomic information and fishing yield from fishers for 2013 and 2014. Additionally, a census on the number of fishers and fishing platforms along the sampled region was conducted in 2018. This recreational fishery mostly involves middle class adult males, based mostly in the Cuiabá city metropolitan region. They invested, on average, US$41.1 (SD = US$16.5, median = $35.2) per fishing visit, catching around 19 fish species. Overall, mean CPUE from the recreational fishery was 42.20 fish/fisher.day (17.4 kg/fisher/day). Annual economic value of this recreational fishery was estimated at around US$1.8 million, which highlights the importance of this activity to the local economy. Greater environmental conservation efforts are recommend to ensure the long-term viability of this ecosystem service.     

Recruitment abundance index of Pacific bluefin tuna using fisheries data on juveniles

ABSTRACT:   The recruitment abundance index of Pacific bluefin tuna Thunnus orientalis was estimated from 1980 to 2003 fishing year by using the troll fishery data in Nagasaki Prefecture, western Japan. It has been shown that the troll fishery in Nagasaki Prefecture operates with good time–area coverage of the species habitat, and that the fishing power slightly changed during the period analyzed, based on fisheries statistics, published information, and interviews with the fishers. Average catch per unit effort (CPUEs) were standardized by a generalized linear model (GLM) considering the effects of fishing year, season and landing area. Standardized CPUE of age-0 bluefin tuna showed larger fluctuations year by year than the nominal CPUE combined for all ages. High CPUEs in fishing years of 1981, 1994, 1996 and 1999 were observed. Data from these years agreed with the higher recruitments estimated by virtual population analysis (VPA) or higher catch of age-0 fish reported for the Pacific side. The age-specific standardized CPUE of age-0 bluefin tuna in this study was judged to be a useful indicator of recruitment.     

Population size estimation of the pond smelt Hypomesus nipponensis in Lake Kasumigaura and Lake Kitaura,Japan

We estimated the population size of the pond smelt Hypomesus nipponensis at the beginning of the fishing season in Lake Kasumigaura and Lake Kitaura, Japan using two DeLury methods and cohort analysis. A growth curve was estimated on the basis of monthly standard length. The relationship between standard length and weight was utilized for calculating the mean weight on the survey day in a particular month. Total monthly catches in Lake Kasumigaura and Lake Kitaura were calculated using partial monthly pond smelt catch obtained from processing plants located near the lakes between July and December. The total monthly catch was calculated from the total monthly catch weight and the monthly mean weight. The number of boats operating each month, compiled by the Kasumigaura-Kitaura Fisheries Office of Ibaraki Prefecture, was also employed. The estimated initial population sizes were compared with the population level index (PLI) estimated from survey data before the start of the fishing season. No significant differences were detected among the initial population sizes estimated by DeLury method, cohort analysis and PLI. The estimates ranged from 7.4 million to 410 million in Lake Kasumigaura, and from 7.7 million to 44 million in Lake Kitaura.     

Mesh selectivity of encircling gill net for gizzard shad Konosirus punctatus in the coastal sea of Korea

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.