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1.
完善农户农村土地承包经营权的退出机制   总被引:2,自引:0,他引:2  
农户农村土地承包经营权主动退出被忽视是当前土地利用存在问题的重要原因,建立健全农村土地承包经营权退出机制是当前农村土地制度深化改革的重要方面。完善农户农村土地承包经营权退出机制,需要保证农民的自由选择权,重点建立农户农村土地经营权退出的程序、冷静期、引力机制、联动支持政策体系及充分补偿等机制。  相似文献
2.
Oil and natural gas (ONG) development can affect aquatic ecosystems through water contamination, water withdrawals and disturbance of soil and vegetation (surface disturbance) from infrastructure development. Research on how these potential sources of watershed and aquatic ecosystem impairment can affect fish assemblages is limited. Fish–habitat relationships were evaluated across stream sites experiencing differing levels of ONG development. Colorado River cutthroat trout, Oncorhynchus clarkii pleuriticus (Cope), and mottled sculpin, Cottus bairdii Girard, presence and abundance were associated with habitat conditions predominantly found in the less disturbed streams, such as higher proportion of shrub cover, greater stream depths and gravel substrate. Mountain sucker, Catostomus platyrhynchus (Cope), appeared to be a habitat generalist and was able to persist in a wide range of conditions, including degraded sites. Natural resource managers can use habitat preferences of these fish species to establish the development plans that mitigate negative effects of ONG development by protecting the aquatic habitats they rely upon.  相似文献
3.
Migratory fishes can be threatened by conditions encountered along dispersal pathways that impede access to feeding or breeding grounds. In this study, we tested the hypothesis that amphidromous fishes are equally or more sensitive to conditions along dispersal pathways than conditions in primary residential habitats. We did so by conducting distribution‐wide population surveys of all five amphidromous gobies native to the Hawaiian Islands to assess responses to in‐stream habitat, invasive species and watershed land use. We used Redundancy Analyses to assess whether goby densities varied according to local, downstream or upstream conditions. We found that population densities of the two non‐climbing species (Eleotris sandwicensis, Stenogobius hawaiiensis) varied according to local land use and local habitat conditions. Greater densities of E. sandwicensis also were found in watersheds with greater forest cover upstream of survey sites. Lower densities of two species that migrate farther inland (Awaous stamineus, Sicyopterus stimpsoni) were observed in watersheds with greater anthropogenic land use downstream or at the stream mouth. Population densities of E. sandwicensis and both Sicydiine species (Lentipes concolor, S. stimpsoni) also were lower when non‐native Poeciliids were locally present or present downstream in the watershed. These findings suggest that densities of native Hawaiian amphidromous fishes are equally or more sensitive to conditions along migratory pathways relative to conditions in primary residential habitats. Thus, alleviating pressures by removing invasive species and restoring habitat along dispersal pathways could be effective approaches to increasing densities of amphidromous species, especially those that migrate farther inland to higher elevations.  相似文献
4.
Understanding variability in the composition of aquatic assemblages requires a multiscale perspective, since processes operating at different spatial scales (from regional to local) drive the community assembly. Here, the relative importance of environmental variables on fish species composition in streams of the Brazilian savanna (Cerrado) is assessed and quantified at local and landscape scales. The importance of both local and landscape environmental variables in structuring fish assemblages was supported. Local variables explained a substantially higher amount of variance of fish assemblages than landscape variables. However, the shared explanation indicate that landscape variables had a complementary effect. The streams sampled were mostly headwaters at similar altitudes and with similar watershed sizes, so the sensitivity of the fish assemblages, even to small landscape gradients, is highlighted. Maintaining these important instream habitat characteristics close to natural conditions seems to be essential for conserving stream fish species, and for this, the landscape context should be taken into account. Considering the near‐pristine condition of the streams studied, these findings can be used as a reference for further studies addressing the effects of human modifications on stream fish biodiversity of the Cerrado.  相似文献
5.
The tiered aquatic life unit (TALU) model allows quick and efficient bioassessment with goals that are based on practical, systematic sampling of commonly measured stream variables. A six‐tier hybrid TALU model was developed as a proof of concept study for streams in six level IV ecoregions in the north‐central Gulf of Mexico coastal plain. The model used in‐stream habitat variables, land use, surveys of the unionid mussels, number of intolerant fish species and fish diversity in streams varying from 2nd through 6th order. The model classification identified sites considered a priori either as impaired or best available and minimised Type I (mistakenly concluding impairment) and Type II (failing to detect impairment) errors. The model also detected transitional sites, thereby illustrating incremental degradation or recovery, in contrast to previous monitoring tools focused on pass/fail approaches. Because the model classifies transitional sites and is easily modified to fit other ecoregions, it offers a useful foundation for resource managers to monitor the health of coastal plain rivers.  相似文献
6.
  1. Modification and loss of natural habitats caused by human activities are among the main drivers of biodiversity decline worldwide. To evaluate how land‐use changes affect species diversity at different spatial scales, amphibians represent an excellent group given that their complex life cycle requires both aquatic and terrestrial habitats.
  2. In this study, the influence of wetland characteristics and surrounding landscape features on richness and functional diversity of anurans was investigated in 26 natural wetlands in a human‐modified landscape within the Southern Andean Yungas.
  3. The analysis was performed at two spatial scales: wetland scale (the breeding pond structure) and the surrounding landscape scale. The classification of the landscape was limited to land uses modified by human activities within concentric circular buffers (radius = 0.1, 0.2, 0.5, and 1 km) centred on each breeding pond.
  4. Generalized linear models were applied to investigate the relationship between environmental variables measured at different scales and anuran species richness and functional diversity, respectively.
  5. Pond area best explained the observed variation in both diversity measures, which is consistent with other studies on anuran diversity in disturbed landscapes. In contrast to regression models including landscape scale variables only, integrated models (which included variables on both scales) highly improved model fit.
  6. Conservation strategies for anuran species diversity in these altered Andean Yungas forests should include efforts to maintain or restore aquatic habitats (e.g. breeding ponds) placed within suitable landscapes.
  7. Successful long‐term management will require an understanding of relationships between habitat characteristics at different spatial scales to identify variables that relate to species diversity in such heterogeneous habitats.
  相似文献
7.
  1. Only 800 years ago, New Zealand became the last major land mass to be settled by humans, leading to environmental degradation and precipitating a decline in indigenous fauna. Such ecological downgrading can alter ecosystem processes and drive down the capacity for remnant ecosystems to withstand the anthropogenic pressures of today.
  2. In New Zealand, these impacts are chronicled in a concise and remarkably complete archaeological record and are distinguishable from natural changes due to changing climate.
  3. Estuaries are subject to strong environmental gradients that drive productivity and contain critical habitats for key life‐history phases for marine and terrestrial species. Linking land to sea, they host abundant, accessible human resources and are sensitive to anthropogenic environmental modification.
  4. Austrovenus stutchburyi is a common filter feeding bivalve in New Zealand estuaries. An important food source for Māori, their shells are abundant in middens. Growth rates of A. stutchburyi are affected by multiple environmental factors, including temperature, salinity, nutrients, and sediment, and are recorded through time as easily measurable annual shell bands. Measuring spatial and temporal variation in growth rate of A. stutchburyi can be used to identify the timing of changes in estuarine conditions.
  5. Growth bands were measured in archaeological and modern (AD 1300–present) A. stutchburyi shells from six sites around New Zealand with varying occupational histories. There were no increases in growth rate, and rates declined measurably over time at three sites (up to a 50% reduction in growth per year). This decline was greater at estuaries that had experienced greater catchment modification, indicating that sediment loading due to land clearance was a likely driver of this change.
  6. New Zealand's coastline and marine resources are often perceived as wild and pristine. We propose that fundamental changes have occurred in the functioning of coastal marine ecosystems, which constrain its future.
  相似文献
8.
  1. Water insecurity is a defining feature of the Anthropocene, with degraded water quality and unreliable flows putting the well‐being of upstream and downstream communities, both human and aquatic, at risk. Within this context, the protection of drinking water at its source – ‘source water protection’ – is growing as a complementary water security solution to conventional built infrastructure, particularly but not only to address non‐point source pollution.
  2. An assessment of the likely source catchments of 4000 cities, supplying water to as many as 1.7 billion city dwellers, found that 85% of the total area of the catchments overlaps with freshwater ecoregions of high biodiversity value. Source water protection could contribute to conserving important freshwater biodiversity elements in these catchments, through activities such as land protection, restoration, and agricultural and ranching best‐management practices.
  3. Empirical evidence supporting the benefits of these types of activities to freshwater species and ecosystems is sparse, especially when considered at the scales required to achieve meaningful conservation objectives. This article explores the potential of source water protection to deliver freshwater conservation benefits, and solutions are proposed to address the challenges related to evidence gaps, trade‐offs, and financing.
  4. The broader opportunity for leveraging water security investments for biodiversity conservation, and the overall efficiencies that may accrue from optimizing for multiple benefits simultaneously, are discussed in the context of global frameworks such as the Sustainable Development Goals.
  相似文献
9.
  1. Local extirpation events are often poorly documented and the causes are not well understood. A case in point is the bridle shiner (Notropis bifrenatus), a cyprinid that is declining and carries various conservation listings over most of its range.
  2. Recent research suggested that the apparent decline of the bridle shiner in the state of Connecticut may be in part an artefact of changes in survey methods: seining has been replaced by electrofishing, which is less efficient in bridle shiner habitat. The present study included a re‐evaluation of the distribution of the species in light of this recent finding.
  3. Historical sites in Connecticut were seined, and it was found that nine populations once thought to be extirpated were in fact extant. Nonetheless, bridle shiner occurrences have declined by 60% over 50 years. Potential correlates of extirpation, such as landscape and habitat fragmentation metrics, were identified using geospatial tools. Through an information‐theoretic approach, models were constructed to investigate the relative contribution of land use and habitat fragmentation to the extirpation of the bridle shiner.
  4. Land use had greater support as a correlate of the decline, and the current bridle shiner distribution in Connecticut could be explained by areas of high forest cover and low impervious cover. It is hypothesized that the adverse impacts of land use on the bridle shiner are attributable to its ecological specialization on submerged vegetation, notwithstanding its otherwise broad physiochemical tolerance.
  5. These results provide needed context on the decline of this species and provide potential avenues for conservation actions. This research emphasizes the impacts that land alterations can have on freshwater species and the importance of accurately characterizing extirpation events.
  相似文献
10.
  1. The Burdekin River floodplain wetlands are internationally important and act as a sink for sediments and nutrients that would otherwise enter the World Heritage‐listed Great Barrier Reef lagoon.
  2. The Burdekin River has the highest natural discharge of any Great Barrier Reef catchment and contributes the greatest mass of sediment to the reef. The river and its catchment have been substantially modified by land clearance, river regulation introduced in the 1960s, the construction of the Burdekin Falls Dam in 1987 and invasive aquatic plants.
  3. We hypothesised that the natural variability of Burdekin River discharge would render its wetland ecosystems resistant to human‐induced pressures.
  4. Diatoms were analysed from the sediments of two lower Burdekin River floodplain wetlands with contrasting regulation histories. Labatt Lagoon has a long history of flow alteration, whereas Swan's Lagoon has experienced limited regulation.
  5. Both wetlands experienced dramatic increases in sedimentation as a result of land clearance, yet the Swan's Lagoon diatom record indicates that the wetland's ecology remains within the range of natural variability. In contrast, Labatt Lagoon is markedly different from its pre‐settlement state. It is now permanent, having been ephemeral for more than 1000 years before European settlement. The conversion to artificial permanence facilitated aquatic plant invasion, resulting in more marked changes than widespread pastoralism.
  6. Modern diatom assemblages from 28 lower Burdekin River floodplain wetlands indicate that the contemporary flora of Swan's Lagoon is unusual. Most wetlands have similar assemblages to those in the Labatt Lagoon record in its present, altered state. It is possible, therefore, that the ecological shift registered in Labatt Lagoon is widespread.
  7. Diatom records highlight the striking impact that river regulation has had on the trajectory of the Burdekin floodplain wetlands. It is likely that wetland rehabilitation can be facilitated by the re‐introduction of a variable hydrological regime.
  相似文献
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