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Sustainable fisheries management requires assessment of exploited populations and communities. Traditional fisheries stock assessment methods need species‐specific input data, which for skates have only recently become available in Europe. To overcome this limitation, a Bayesian multispecies biomass production model was developed. In addition to aggregated landings, input data are short time series with species‐specific information (landings and biomass indices). Applying the approach to four main skate species and a group of two skate species, all managed together in the Bay of Biscay (Northeast Atlantic), long‐term changes in the skate assemblage composition were identified. Since the 1990s, Leucoraja naevus became increasingly dominant, while the contributions of the other three species (Raja brachyura, Raja clavata and Raja montagui) declined. The abundance of the grouped Leucoraja fullonica and L. circularis has also strongly decreased, suggesting long‐term overexploitation. All species except this species group are expected to increase over the next decade under current harvest rates. Currently, the species considered here are managed under a single fishing quota making it unlikely that the group of the two most depleted species will recover soon. The multispecies modelling approach bears promise for other harvested assemblages for which only grouped harvest information is available for certain periods.  相似文献
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  • 1. The effect of a newly introduced population of signal crayfish (Pacifastacus leniusculus) on a riverine invertebrate community in the River Clyde, Scotland, is examined. Five hypotheses related to crayfish impact on the invertebrate community are tested by comparing sites containing signal crayfish with similar sites in the same river which have not yet been colonized.
  • 2. The hypothesis that crayfish significantly reduce the total numbers of invertebrates in the community was supported by this study, with invertebrate density in areas containing signal crayfish around 60% of that with no observed crayfish.
  • 3. The hypothesis that crayfish presence affects some groups more than others was also supported. Plecoptera, Chironomidae, Diptera and Hirudinea, in particular, showed evidence of reduced species numbers in areas containing crayfish, and Plecoptera, Hirudinea, Tricladida and Hydracarina showed evidence of reduced densities. Community diversity and richness was also lower at sites containing crayfish.
  • 4. Neither the hypothesis that overall invertebrate biomass would be lower at sites with crayfish present nor the hypothesis that individual invertebrate size would be lower at sites with crayfish was supported.
  • 5. Overall the study indicates that introduced signal crayfish can significantly and fundamentally modify fluvial macroinvertebrate community structure.
Copyright © 2006 John Wiley & Sons, Ltd.  相似文献
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太湖流域城市湖泊富营养化问题严重,研究不同营养水平城市湖泊底栖动物群落的差异及成因,可为丰富底栖动物生态学研究和城市湖泊生态系统恢复提供参考。本研究于2018年12月、2019年3月、6月、9月在太湖流域15个城市湖泊开展了四个季度的调查,结果显示,重度、中度、轻度富营养和中营养水体分别占10.03%、36.89%、42.07%和11.00%。随水体营养下降,透明度显著上升,浊度、总磷和叶绿素a浓度显著下降,大型底栖动物总生物量、蚌类密度和生物量上升,寡毛类密度和生物量下降。在重度富营养水体中,底栖动物总生物量显著小于其他类型水体(P<0.01);在轻度富营养和中营养水体中,蚌类密度和生物量显著大于重度和中度富营养水体(P<0.01),寡毛类密度则显著小于重度和中度富营养水体(P<0.01)。Shannon-Wiener、Simpson和Pielou指数随水体营养水平下降,先上升再下降,在轻度富营养水体中最高。结构方程模型分析发现,在轻度富营养和中营养湖泊中,水温、总磷和叶绿素a浓度是影响底栖动物群落的关键环境因子。总磷浓度升高会显著促进软体动物增长(P<0.01),对螺、蚌的路径系数分别高达0.414和0.440。总磷浓度与水温上升都能显著促进多毛类种群增长(P<0.01),抑制水生昆虫种群(P<0.01),路径系数分别为0.376和-0.423。本研究认为,城市湖泊水体中总磷和叶绿素a浓度对大型底栖动物群落结构有重要影响,对磷和藻类的控制,对城市湖泊底栖动物群落恢复和水生态系统修复有重要参考价值。  相似文献
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