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1.
Concern over illegal, unreported and unregulated (IUU) fishing has led to a number of policy, trade and surveillance measures. While much attention has been given to the impact of IUU regulation on industrial fleets, recognition of the distinct impacts on small‐scale fisheries is conspicuously lacking from the policy and research debate. In this paper, we outline three ways in which the application of IUU discourse and regulation undermines small‐scale fisheries. First, the mainstream construction of “illegal,” “unreported” and “unregulated” fishing, and also the categorical use of “IUU” in an all‐inclusive sense, disregards the diversity, legitimacy and sustainability of small‐scale fisheries practices and their governing systems. Second, we explore how the recent trade‐related measures to counter IUU fishing mask and reinforce existing inequalities between different sectors and countries, creating an unfair burden on small‐scale fisheries and countries who depend on them. Third, as IUU fishing is increasingly approached as “organized crime,” there is a risk of inappropriately targeting small‐scale fisheries, at times violently. Reflecting on these three trends, we propose three strategies by which a more sensitive and ultimately more equitable incorporation of small‐scale fisheries can be supported in the global fight against IUU fishing.  相似文献   

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3.
Quantifying the mortality of marine fishes is important for understanding spawner–recruit relationships, predicting year‐class strength, and improving fishery stock assessment models. There is increasing evidence that pelagic predators can exert a top‐down influence on prey, especially during critical early life‐history stages. The objective of this study was to quantify predation by North Pacific albacore on Northern anchovy in the California current system (CCS). I estimated the abundance of juvenile albacore in the CCS from 1966–2005 using stock assessment models and spatially explicit catch‐per‐unit‐effort time series. Anchovy abundance (1966–93), both recruitment and total biomass, was obtained from a stock assessment model. Annual rates of anchovy consumption by albacore were calculated using diet studies of albacore in the CCS, an age‐structured bioenergetics model, and regional estimates of albacore abundance. The range of estimates was large: albacore may remove from less than 1% to over 17% of anchovy pre‐recruitment biomass annually. Relationships between predation and recruitment biomass were consistent with expectations from top‐down effects, but further study is required. This is the first attempt to quantify a specific source of mortality on anchovy recruits and to demonstrate potential top‐down effects of predation on anchovy.  相似文献   

4.
Acoustic telemetry was used to investigate the longitudinal and lateral movements and distribution of adult common bream, Abramis brama (L.), over 43 months in a heavily modified lowland river in eastern England. A positive relationship between activity and temperature was found, with bream moving greater cumulative distances during the warmer months and distributed over a greater longitudinal proportion of the main channel. The occupancy of tributaries was related to temperature, with bream entering shallow tributaries during rising temperatures in the spring, whilst a deeper, slow‐flowing tributary was used more frequently during the cooler autumn/winter months. During the autumn, occupancy of this deeper tributary was positively related to flow rate in the main channel, suggesting that bream use this tributary for flow refuge. The functions of these behaviours are discussed along with potential management of heavily modified lowland rivers.  相似文献   

5.
光照强度对沉水植物生长和光合作用影响的研究进展   总被引:2,自引:0,他引:2  
沉水植物作为重要的初级生产者,在水生生态系统中有着非常重要的作用。沉水植物的生长和分布受到诸多环境因子的影响,其中水下光照强度、水温和矿质元素等是重要的因子。本文综述了光照强度对沉水植物生长和光合作用影响的研究进展,总结了沉水植物对弱光在形态和生理上的适应机制,并对目前研究中存在的问题和今后的研究方向进行了展望,以期为进一步开展沉水植物生理生态学研究及受损生物群落的恢复提供科学参考。  相似文献   

6.
Abstract– Historical and contemporary fish collections were used to examine the influence of agricultural land use on fish communities in the central Chattahoochee River, USA. In-stream habitat data were also collected to examine the relationship between agricultural land use and stream habitat structure. We found a significant positive relationship between agricultural land use and in-stream sediment ( r 2=0.43, P =0.01). Stream depth heterogeneity decreased significantly with increased sediment ( r 2=0.39, P =0.02). Mainstream reaches draining agricultural lands had significantly lower levels of fish diversity than forested reaches ( r 2=0.47, P < 0.01). Agriculture also explained significant variation in mainstream species abundances but was not a significant predictor of species diversity or species abundances in headwater reaches. Most pool species that use coarse substrates decreased in relative abundance with increasing agriculture in the watershed. Our results suggest that mainstream environments and their associated communities are more susceptible than headwater reaches to the effects of agriculture. This finding has important consequences for conservation, since mainstream reaches are reported to function as species refugia during pulse disturbance events (e. g., floods, droughts).  相似文献   

7.
Fish assemblages in six reaches of the Hawkesbury–Nepean River were studied to identify the effects of two types of riparian vegetation; well‐vegetated banks supporting complex flora dominated by trees and shrubs, and grassed banks, that have been colonised only by grasses after historical deforestation. The fish assemblages showed both spatial and temporal differences and habitats adjacent to grassed banks supported more individuals and more fish species than well‐vegetated banks. Three small species of fish, firetail gudgeon, Hypseleotris galii (Ogilby), flathead gudgeon, Philypnodon grandiceps (Krefft), and empire gudgeon, Hypseleotris compressa (Krefft), occurred in greater abundances adjacent to grassed banks, but freshwater mullet, Myxus petardi (Castelnau), were less abundant near grassed banks than beside well‐vegetated banks. Differences were also shown in the size frequencies of the four larger fish species between riparian vegetation types. The observed differences in the distributions of fish species appeared to be related to the greater abundance aquatic macrophytes near grassed banks, probably an effect of shading of macrophytes near well‐vegetated banks.  相似文献   

8.
A GIS model of the littoral bathymetry and substrate composition of Lake Taupo was created using ArcInfo. Littoral substrates were mapped by aerial photography and confirmed by ground-truthing. Water depths were determined by echosounding linked to a differential GPS. These data were imported into ArcInfo where a 3D GIS model was used to calculate the total area of smelt, Retropinna retropinna Richardson, spawning habitat (i.e. clean sand between depths of 0.5–2.5 m) at each of five lake levels. There was little change in area over the first 50 cm below the natural maximum lake level, but spawning habitat decreased rapidly over the next 1.4 m such that a 30% reduction occurred at the natural minimum level. Anecdotal information on inter-annual variations in lake level and smelt abundance supported the notion that high lake levels in spring result in high recruitment of smelt. The GIS model also predicted effects of lake level change on areas of macrophyte cover and on other littoral substrates, and could be used to assess effects of lake level changes on the habitats of other biota.  相似文献   

9.
We investigated how stream fragmentation affects local fish species persistence and extinction from three Rio Grande systems (Texas, USA) stream reaches with different levels of natural fragmentation. We examined species–volume (SV) relationships of fish assemblages in 42 pools across the watersheds and predicted greater fragmentation would correspond to an increase in the slope of the SV relationship due to decreased within‐reach rescue effects. In addition, we examined relationships among tributary‐specific nested subset patterns, local habitat features and spatial position of the reaches relative to the Rio Grande mainstem to better understand the importance of local and regional processes on fish species richness patterns in the stream reaches. Slopes of the SV curves did not differ among the stream reaches, but the intercepts of the SV curves were significantly different. These results indicated rescue effects among habitats within a stream reach were not apparent; however, rescue effects from the mainstem largely determined the species richness of a given stream reach. The nested subset patterns in all stream reaches were related to several local environmental factors, and large, deep pools provided important aquatic refugia in all three systems. We suggest declines in mainstem and tributary flows will likely continue to impact local and regional fish assemblage attributes. High flow events are important for dispersal and can reset tributary fish communities for the next extinction‐driven, successional cycle.  相似文献   

10.
研究湟水流域水生态现状和保护与修复措施,加强湟水流域水生态保护,维持黄河尤其是黄河上游流域及青藏高原和黄土高原-川滇生态屏障生态安全。湟水干流、大通河梯级开发集中,河流纵向连通性遭到严重破坏,且大部分水电站是引水式小水电站,枯水期水电站下游河道脱流现象严重,河流水流连续性及横向连通性遭到破坏,河流生态功能严重下降。根据国家及黄河流域对湟水流域生态保护定位及要求,在湟水流域水生态状况评价及问题识别的基础上,明确各区域(河段)水生态保护目标,提出了湟水上中下游水生态保护与修复总体布局、重要断面生态需水指标及保障措施和重要湿地、重要鱼类栖息地等保护与修复措施体系。  相似文献   

11.
张晶晶 《水利渔业》2011,32(6):66-71
为了分析傀儡湖鱼类对水环境的影响,于2010年1-12月研究了傀儡湖的渔获量、组成比例和主要鱼类食物组成。结果表明,傀儡湖渔获物中,发现有9科、26种鱼类,其中鲤科鱼类最多,有18种,占鱼类种数的69.23%;鱼类组成中,鲢和鳙为优势种,分别占总渔获量的(20.82±8.06)%和(41.58±19.24)%;主要鱼类...  相似文献   

12.
  • 1. Over the last decade the development of small hydropower projects has been one of the most active areas of the energy sector. One of the main environmental challenges faced by such projects is related to fish passage.
  • 2. The impact of 18 small hydropower plants (SHPs) with distinct levels of fish‐pass effectiveness was investigated in the summers of 1998 and 1999 by comparing fish assemblage composition and structure at 36 sites, above and below SHPs.
  • 3. With regard to effectiveness, it was estimated that eight (44.4%) of the surveyed passage facilities were suitable for target species, whereas the remaining 10 (55.6%) were considered unsuitable. In neither case did the composition of fish assemblages upstream and downstream from SHPs differ significantly, while assemblage similarity was relatively high.
  • 4. Multivariate techniques identified cover, depth and coarse substrate as the main parameters structuring fish assemblages. It is suggested that these variables have created a rich, patchy, heterogeneous habitat, thereby providing satisfactory resources and favourable conditions required by fish and contributing to the maintenance of assemblages.
  • 5. Although populations of some species that occurred both upstream and downstream from SHPs have developed differences in their size structures, SHP‐induced fragmentation of fish populations may not necessarily result in genetic divergence among semi‐isolated populations.
Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

13.
Dibble ED, Pelicice FM. Influence of aquatic plant‐specific habitat on an assemblage of small neotropical floodplain fishes.
Ecology of Freshwater Fish 2010: 19: 381–389. © 2010 John Wiley & Sons A/S Abstract – This study investigated the effects of plant‐specific habitat on the distribution of young and small adult fishes in lagoons of the Upper Paraná River floodplain, Brazil. We compared fish catch per unit effort (CPUE) and species richness and used an indirect gradient analysis to investigate fish‐plant relationships within three aquatic macrophytes beds (Cabomba furcata, Eichhornia azurea, Nymphaea amazonum), and explored microhabitat influence (indexed by eight variables related to physical structure and water quality) on the structure of fish assemblages. Rarefaction analysis was used to compare fish species richness among the vegetated habitats. We captured a total of 1599 fish constituting 23 species, 7 families and 3 orders. Fish CPUE and species richness increased relative to microhabitat structure innate to the macrophytes; higher CPUE and richness were observed in C. furcata beds, a submerged aquatic macrophyte with finely dissected leaves. On the contrary, N. amazonum, a species that provides low microhabitat complexity, harbored fewer individual fish and number of species. Reproduction dynamics, hydrology and the amount of available plant‐generated habitat structure (surface effect) contributed to the disproportionally high number of individuals captured during the dry season. Our data suggest that the microhabitat physical structure (e.g., edge distance, stem density and patch size) provided by macrophyte beds in the lagoons of the Upper Paraná River may play a more important role than physicochemistry (e.g., oxygen, temperature and pH) at mediating distribution patterns of small‐sized fishes.  相似文献   

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