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  1. Several eel species have undergone extensive declines at both local and global level. The aim of this study was to identify the reasons for the collapse of the European eel (Anguilla anguilla) stock in an important area for biodiversity conservation (Comacchio Lagoon, Italy), in order to support the development of eel conservation plans.
  2. The records of silver eel catches from Comacchio describe the total migratory population and cover the period 1781–2013. The data are accompanied by information related to habitat loss and other local factors. The role of local factors on the decline of the local stock was investigated, while additional information from the literature was also used to discuss the effects of global factors (including glass eel harvest for aquaculture, climate–oceanographic changes, habitat loss, pollution and parasitism) on the three eel species A. anguilla, Anguilla japonica and Anguilla rostrata.
  3. The records from Comacchio provided significant information about the effects of local factors on the local eel populations in the past. However, the current population collapse, which started in the 1970s, could not be explained by local factors.
  4. The literature on global factors suggests that the three eel species are under combined threat from various factors. The correlations between European aquaculture production data compared with the Comacchio yields and published data from other European eel and glass eel fisheries were found to be highly significant. Aquaculture, which depends entirely on wild‐caught glass eels, seems to play a key role in the decline of natural stocks.
  5. Conservative estimates using FAO data showed that the current numbers of glass eels needed to support aquaculture production in Europe and Asia exceeds 2 × 109 specimens. This requirement, largely supplied by A. anguilla glass eels, can explain the decline of eel populations since the glass eel trade has been expanded at an international level.
Copyright © 2016 John Wiley & Sons, Ltd.  相似文献
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  1. The population status of the coastal bottlenose dolphin (Tursiops truncatus) inhabiting the inner estuary of the Gulf of Guayaquil, Ecuador (3°S, 81°W) was assessed. Evaluated aspects included social organization, abundance and spatial distribution.
  2. Surveys focused on the western part of the estuary (Posorja and Estero Salado) but other areas in the central and eastern inner estuary were also surveyed.
  3. Effort included 68 trips, 5001 km of survey and 288.8 h at sea. Between 735 and 793 dolphins in 92 groups were recorded during the study.
  4. Dolphins are not evenly distributed but concentrated their activities in the mouths of large channels.
  5. A cluster analyses indicated that dolphins organize in partially discrete subunits referred to as communities.
  6. Abundance estimations were obtained using mark–recapture modelling for two communities: Posorja and Estero Salado (43 dolphins, 95% CI 37–49 and 65 dolphins, 95% CI 52–82 respectively).
  7. Four demographic parameters: average size of communities, average group size, average encounter rate and average density were compared with information obtained during the 1990s. In all cases the current values were between 39 and 54% lower; in the last three cases the difference was statistically significant.
  8. Possible causes of this apparent decline include bycatch, ship strikes, pollution and habitat degradation; however, none of these have been assessed in depth. Most probably, different stressors are affecting dolphin communities to different extents.
  9. A comprehensive assessment of the whole population inside the gulf is needed. Identifying major threats is a priority to define concrete actions to prevent further population decline.
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