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1.
Illegal, unreported and unregulated (IUU) fishing can lead to irreversible ecosystem changes; however, it is also one of the most difficult forms of fishing to manage and deter. In northern Australia over the past decade there has been a large increase in small-scale IUU fishing. We suggest that this small-scale fishing has arisen because of long-term fisheries over-exploitation in South East Asia. This IUU fishing forms part of the expansion-and-displacement cycle that can rapidly reduce biomass and alter the trophic structure of local ecosystems. With increasing human populations in the region, the pressure to fish illegally is likely to increase. Regional responses are required to deter and monitor the illegal over-exploitation of fisheries resources, which is critical to secure ecosystem stability as climate change and other destructive human activities threaten food security.  相似文献   

2.
The social and economic importance of small‐scale fisheries is frequently under‐valued, and they are rarely effectively managed. There is now growing consensus on how these fisheries could be managed for sustainability and to minimize the risks of crossing undesirable thresholds. Using a concept developed in health care, these approaches have been referred to as primary fisheries management. By encouraging the use of best‐available information in a precautionary way, the approaches will facilitate sustainable use and should therefore be encouraged, but they accept high scientific and implementation uncertainties as unavoidable because of limited management and enforcement resources and capacity. It is important to recognize that this limitation will result in social costs, because application of a precautionary approach in the face of high uncertainties will require forgoing potential sustainable benefits. Acceptance of primary fisheries management as a final and sufficient goal could therefore add a further constraint on the possibility of fishing communities escaping the poverty trap. Primary fisheries management should be seen as a first and minimum target for fisheries where there is currently no or inadequate management, but the longer‐term goal should still be well informed and adaptive management that strives for optimal benefits, referred to here as tertiary management.  相似文献   

3.
Forage fish occupy a central position in marine food‐webs worldwide by mediating the transfer of energy and organic matter from lower to higher trophic levels. The lesser sandeel (Ammodytes marinus) is one of the ecologically and economically most important forage fish species in the North‐east Atlantic, acting as a key prey for predatory fish and sea birds, as well as supporting a large commercial fishery. In this case study, we investigate the underlying factors affecting recruitment and how these in turn affect productivity of the North Sea sandeel using long‐term data and modelling. Our results demonstrate how sandeel productivity in the central North Sea (Dogger Bank) depends on a combination of external and internal regulatory factors, including fishing and climate effects, as well as density dependence and food availability of the preferred zooplankton prey (Calanus finmarchicus and Temora longicornis). Furthermore, our model scenarios suggest that while fishing largely contributed to the abrupt stock decline during the late 1990s and the following period of low biomass, a complete recovery of the stock to the highly productive levels of the early 1980s would only be possible through changes in the surrounding ecosystem, involving lower temperatures and improved feeding conditions. To that end, we stress the need for ecosystem‐based management accounting for multiple internal and external factors occurring within the broader context of the ecosystem in which forage fish species, such as sandeel, play an important and integral part.  相似文献   

4.
刘勇  程家骅  陈挺 《水产学报》2022,46(2):298-309
海洋捕捞渔船现为属地化管理,但其海上生产具有跨地区管辖水域作业特点.传统上,各地渔船因在近岸水域沿袭地方捕捞经验与传统捕捞习惯,均具显著的地方特性.但随着捕捞渔船的钢质化、大型化,海洋捕捞的作业空间不断扩展,了解与掌握当前海洋捕捞是否具有区域特征差异,对于渔业抽样统计调查研究和精准渔业管理有着重要的科学理论指导意义.本...  相似文献   

5.
Pre-spawning adult samples of long tailed hake, Macruronus magellanicus, were obtained from fisheries vessels in one location in the southeast Pacific Ocean and three in the southwest Atlantic Ocean, at different latitudes. Population structure was determined based on six nuclear hypervariable microsatellite loci and on mitochondrial DNA sequence variation at the locus COI. Paired tests of genic differentiation for microsatellite loci indicate the existence of genetic population structure for this species, where significant differences exist between some southern and northern samples. Multivariate analysis (factorial correspondence analysis) of microsatellite variation showed differentiation between the Pacific and the Atlantic populations. Analysis of the mitochondrial variation confirmed the microsatellite analysis of population structure, and revealed some additional differentiation between northern and southern Atlantic samples and exclusive haplotypes in each region. These findings suggest that the species should be managed as north–south separate stocks in the Atlantic Ocean.  相似文献   

6.
Abstract  Lough Neagh produces over 500 t of grown eel annually and employs 300 people fishing yellow and silver eel. Glass eel are transported upstream and stocked into the Lough. Since glass eel returns crashed in the 1980s, additional glass eel seed has been purchased from other fisheries. The fishery now faces ecological, social and economic pressures. Prices for the product have fallen; recruitment to the fishery has declined, and seed has decreased in availability and increased in price. Fishers are less inclined to take up the hard work required to make a living fishing eel and the fisher population is ageing. The European Commission has recognised the decline of eel and proposed emergency measures, which may further affect the viability of the fishery. The sustainability of the fishery is examined, based on the relationship between glass eel input and grown eel outputs over a period of 45 years, set against increasing environmental, socio-economic, and natural resource pressures. Spawning escapement of silver eel is estimated by mark–recapture experiments.  相似文献   

7.
Abstract The factors important in determining fishing power in the Lake Kariba sardine, Limnothrissa miodon (Boulenger, 1906), fishery were identified using data from the major fishing area of the lake, the Kariba basin, for the periods 1980–1982 and 1988–1990. Comparisons were carried out using fishing power calculated from the mean catch of some standard vessels. Three methods were used for identification of the important attributes. Analysis of variance (ANOVA) was carried out for each component to compare the mean fishing power at all levels within each variable. Multiple regression analysis was used to build predictive models and to determine the factors which best predict fishing power. Factor analysis was used to ordinate vessel types and examine any vessel groupings related to fishing power. Factor analysis showed that vessel and net size were the most important variables. Vessels without engines for propulsion, of low value and without radios had less fishing power than the other vessels in the fleet. Vessels from the same company had similar fishing power, suggesting that some unmeasured variable such as quality of management linked to the fishing companies had a significant effect on catch. The factors which were important in determining catch were length of vessel, depth of the net, presence and absence of echo sounder, mobility, the type of light, number and wattage of the underwater lights in the 1988–1990 fishing period. Vessel length and net category were most important in the period 1980–1982. The models accounted for between 37.6 (1981) and 61.2% (1988) of the variation in fishing power. During the development of the fishery, there has been a change from purse seine to lift nets, and increases in the use of echo sounders, engines for the propulsion of vessels and radios, all of which could have increased effective fishing effort.  相似文献   

8.
Although small‐scale fisheries (SSF) play an important socio‐economic role in developing nations, overfishing seems to be increasing the risk of stock vulnerability. This study aims to quantify the pressure of SSF on fish stocks in Sunda Strait (Indonesia) using several biological indicators that are important in quantifying fishing pressure. Data on these indicators were collected monthly for three years (2012–2014) in one of the main fishing ports of the area. The results provide evidence that, although SSF would appear to be the most environmentally sustainable of all the fishing techniques being used today in the coastal waters of Indonesia, the impact of SSF fishing on juvenile fishes in certain areas such as the Sunda Strait must not be underestimated. The results also show the need to protect immature fish of species that are not only commercialised but are also important in subsistence fisheries. Although further studies are needed to assess the impact of SSF on fish stocks in the area, it is suggested management recommendations that include the implementation of marine‐protected areas in nursery grounds and establishing minimum landing sizes well above the size‐at‐maturity for each species, are needed.  相似文献   

9.
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.  相似文献   

10.
The allocation of effort among fishing gears is as important as controlling effort with respect to both sustainable yield and ecosystem management. Differences in age‐specific vulnerability to the fishing method can modify the maximum sustainable yield (MSY) that is obtainable from a fish stock. Different gears or methods are more or less selective for the species targeted, and MSY is rarely, if ever, attainable simultaneously for all species. The different fishing methods capture different types of nontarget species. Some methods will often be more profitable than others, and different user groups will prefer different methods. In many fisheries, it is unlikely that fishing can be limited to a single gear or method, so compromises among them will be required. Global MSY is discussed as a possible reference point for fisheries management. The yellowfin tuna fishery in the eastern Pacific Ocean (EPO) shows all the above characteristics and is used to illustrate effort allocation among fishing methods.  相似文献   

11.
An age-structured model of the Australian pilchard’s population has been adapted to simulate recovery from the mass mortality suffered during the herpesvirus epidemics of 1995 and 1998/1999. The model generates a vigorous recovery even when levels of mortality are very high, which accords with observations. In spite of this strong recovery, the model indicates that stock is sensitive to increased fishing pressure. Healthy stocks of juvenile pilchards play a key role in the vigorous post-epidemic recovery.  相似文献   

12.
1. Economic development in arid regions is closely linked to efficient use of limited water resources. As such, management and conservation of these water resources requires concurrent optimization of the interrelationships between supply quantity and resource quality. 2. Multiple uses of water resources generate conflicting needs within management, with different uses requiring objective characterization of quality for different management scenarios and goals. 3. A sound management programme needs close interactions between water policy makers, managers, users, engineers and limnologists, and thus needs a common language that can transcend the boundaries of the individual fields. 4. This paper describes a system of water quality indices and standards designed for conservation and sustainable management of Lake Kinneret (Sea of Galilee), Israel, based on observed variability in various chemical and biological parameters during a 25‐year period (1969–1992). Such a system can form a common language which can then be used as a tool for optimal management. 5. This system of water quality indices (a) includes both traditional limnological parameters (plant nutrients, chlorophyll, primary production) and engineering parameters (coliform bacteria, turbidity), (b) is acceptable to all parties involved in lake management, and (c) is easily adaptable to different management scenarios and to management‐induced changes in ecosystem functioning. 6. Analysis of variability in these water quality parameters in Lake Kinneret during 1994–1999 when the lake was showing signs of destabilization highlights the usefulness and limitations of this system. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

13.
Individual transferable quota (ITQ) programmes have been incorporated into many marine fisheries management strategies for 30 years, but their implementation and utility remains controversial. This study provides an overview of the global status of ITQ programmes, the reasons they have been adopted and the changes in stock biomass after their implementation. Eighteen countries currently use ITQs to manage several hundred stocks of at least 249 species. ITQs were adopted in these countries for many reasons: overcapitalization, economic gains, safety concerns for fishers and political change. The implementation of ITQs does not translate into consistent changes in stock biomass. Improvements in 12 of 20 stocks after ITQs were introduced suggest that ITQs can be an effective component of fisheries management strategies, but eight of the stocks continued to decline after ITQs were introduced. This suggests that alternative or complementary measures are needed to sustain those fisheries, such as combining ITQs with more effective total allowable catches, better enforcement and monitoring, and implementing aspects of ecosystem-based fisheries management.  相似文献   

14.
A bio‐economic model was developed to evaluate aspects of proposed quota‐based constraints vs the current effort control regulations for the tropical rock lobster, Panulirus ornatus, Fabricius, fishery in the Torres Strait (Australia/Papua New Guinea). The analysis integrates across biological, economic and social considerations. Model performance indicators have been chosen to reflect higher level policy objectives. The model simulation results indicate important trade‐offs. There is lower overall fleet total profit (across all the subfleets), lower fishery total value added and lower total employment if the fishery is quota‐constrained. This is due to an assumed rationalisation driven by incentives and current utilisation of capacity. The simulated re‐allocation of quota from the commercial non‐indigenous fleet allowing for greater potential indigenous fisher participation results in predicted increases in indigenous employment and would meet social objectives; however, due to limited capacity in the indigenous fleet, the simulated predicted lower catches led to lower total fishery profits and decreased total fishery value added within the supply chain. Investment in capacity could potentially offset this result.  相似文献   

15.
Abstract –  Fishing is a potent ecological force. In Lake Victoria, East Africa, Nile perch , Lates niloticus contributes to a multi-million dollar fishing industry but is threatened by over-exploitation. We quantified spatial and temporal trends in the distribution, diet and size of Nile perch in Lake Nabugabo, Uganda, a satellite of Lake Victoria. From 1995 to 2007, we detected a decline in catch per unit effort of Nile perch, a shift in their distribution and diet, and a decrease in their body size. A greater proportion of Nile perch were found near wetland ecotones than in the 1990s. This may reflect intensive size-selective fishing in open waters, and encroachment of Vossia cuspidata , an emergent macrophyte that has expanded across the lakeshore. Results highlight the strength of fishing in inducing phenotypic changes in target stocks as well as large-scale changes to the aquatic community and are of value in understanding changes in Lake Victoria.  相似文献   

16.
Scientists feel discomfort when they are asked to create certainty, where none exists, for use as an alibi in policy‐making. Recently, the scientific literature has drawn attention to some pitfalls of simulation‐based fisheries management‐strategy evaluation (MSE). For example, while estimates concerning central tendencies of distributions of simulation outcomes are usually fairly robust because they are conditioned on ample data, estimates concerning the tails of distributions (such as the probability of falling below a critical biomass) are usually conditional on few data and thus often rely on assumptions that have no strong knowledge base. The clients of scientific advice, such as the European Commission, are embracing the mechanization of the evaluation of proposed Harvest Control Rules against the precautionary principle and management objectives. Where the fisheries management institutions aim for simple answers from the scientists, giving ‘green/red light’ to a proposed management strategy, the scientists are forced into a split position between satisfying the demands of their advisory role and living up to the standards of scientific rigour. We argue against the mechanization of scientific advice that aims to incorporate all relevant processes into one big model algorithm that, after construction, can be run without circumspection. We rather encourage that fisheries advice should be a dynamic process of expert judgement, incorporating separate parallel concurrent, lines of scientific evidence, from quantitative and qualitative modelling exercises and factual knowledge of the biology and the fishery dynamics. This process can be formalized to a certain degree and can easily accommodate stakeholder viewpoints.  相似文献   

17.
Abstract  – Brown trout ( Salmo trutta L.) and Arctic charr ( Salvelinus alpinus (L.)) use whitefish ( Coregonus lavaretus (L.)) as their main prey in the subarctic Lake Muddusjärvi. Brown trout dwelled in littoral and pelagic habitat, whereas Arctic charr lived only in epibenthic habitat. Both species shifted to whitefish predation at a length of 20–30 cm. At this size, brown trout fed on larger whitefish than Arctic charr. Whitefish occur in three sympatric forms, differing in their habitat, ecology and morphology. Both the predators preyed primarily upon the small-sized, densely rakered whitefish form (DR), which was the most numerous whitefish form in the lake. DR used both epibenthic and pelagic habitat, whereas two sparsely rakered whitefish forms dwelled (LSR and SSR) only in epibenthic habitat: LSR in littoral and SSR in profundal areas. Sparsely rakered whitefish forms had minor importance in predator diet.  相似文献   

18.
The world's fisheries are under severe pressure. Yet, according to the marine trophic index, the health and stability of marine ecosystems vary greatly across countries. The argument developed and tested in this article holds that some of the sources of this variation can potentially be derived from differences in the character of two fundamental relationships in society – a horizontal one between resource users and a vertical relationship between the government and the resource users. The empirical analysis focuses on sub‐Saharan Africa and finds that levels of ethnic and linguistic heterogeneity and levels of democracy in the year that each country declared its exclusive economic zone have a close relationship with ensuing marine exploitation patterns.  相似文献   

19.
Numerical response experiments were conducted using three strains of the Brachionus plicatilis species complex. They are commonly used in aquaculture, and could also coexist in nature although this has not been studied yet. Brachionus plicatilis sensu stricto (s.s.), B. ‘Cayman’ and B. ‘Nevada’ were cultured at different concentrations of Nannochloropsis oculata (0-40 mg C l− 1). Growth rate, egg female ratio (EF), fecundity and percentage of ovigerous females were determined at each food concentration. From the growth rate and EF, the egg development time and mortality rate were estimated using the Paloheimo equation. Monod curves with a threshold for zero growth described the relationship between growth rate and food concentration. The three strains had different growth rates at low (< 0.04 mg C l− 1) and high (> 5.0 mg C l− 1) food concentrations, but were similar at intermediate food levels. B. ‘Cayman’ had the highest maximum growth rate (1.57 ± 0.07 d− 1), whereas B. plicatilis s.s. had the less negative minimum growth rate and the highest maximum EF (0.96 ± 0.02 eggs ind− 1). These differences were attributed to the lowest egg development time of B. ‘Cayman’ (5.95 ± 0.24 h) and the higher starvation resistance of B. plicatilis s.s. (84 ± 12 h), respectively. B. ‘Nevada’ was the inferior competitor at high and low food concentrations due to the higher investment in body growth rather than reproduction. The outcome of competition in hatcheries is predicted to favor B. ‘Cayman’ under high food concentrations, whereas the three species may coexist under moderate food limitation.  相似文献   

20.
Otter-trawl catch rates and population structure of the prawn Melicertus kerathurus were studied at the fishing ground of Thermaikos Gulf (North Aegean Sea, Eastern Mediterranean), where the stock is exploited both by otter-trawlers and the artisanal local fleet. Sampling was conducted on board commercial trawlers on a monthly basis in two consequent open fishing seasons (October to May 2000–2001 and 2001–2002) resulting to a total of 70 hauls. Samples were also obtained through experimental trawling (24 hauls) during the closed season. The main trawling ground is located near the border between the outer and the inner gulf, and along the western and northeastern coasts of the outer gulf in depths ranging from 35 to 70 m (most frequently at 40–50 m). Catch per unit effort (CPUE) varied significantly with month but not with fishing season (mean CPUE 3.18 and 1.78 kg/h for the 2 successive years) or depth. Catches were at maximum (up to 7.5 kg/h) at the beginning of the open season in autumn and decreased sharply as the season proceeded (<2.5 kg/h), which is likely to be due to induced fishing mortality in the preceding months, to prawn dispersal and/or to its tendency for longer burrowing. Commercial fishing trips consisted of multiple, short efforts when catches were high, whereas low yields during winter–spring led to less hauls of longer duration: ln CPUE = 2.974 − 2.047 ln HD, r = −0.57. Prawn size ranged from 17 to 60 mm CL, showing a consistent difference in favor of females. A weak recruitment to the fishery was observed from autumn through winter, while, as shown by experimental trawling, the main recruitment pulse to the fishery occurs just prior to the season's opening. The delayed arrival of the prawns on the fishing ground during the second fishing season, accompanied by smaller prawn size and shallower exploitation depth, was possibly related to decreased autumn rainfall. In both years, sex ratio showed a temporal pattern, which seems to be the result of sex-related differences in fishing vulnerability, in timing of inshore migration and in mating mortality.  相似文献   

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