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21.
刺网选择性对鱼类表型性状的选择作用研究 总被引：2，自引：0，他引：2
本研究从刺网选择性对鱼类表型性状的影响入手,应用数值模拟方法,模拟了一个具有一定体长特征的鱼类种群,利用具有多项选择参数(曲线标准差σ,最适体长l0,选择性因素R0)的刺网曲线对其进行长期捕捞作用,并在去除捕捞的情况下探讨这种影响的稳定性。结果表明,刺网捕捞作业长期作用于鱼类种群,会对种群体长组成产生深远的影响,开发率(E)越大,效果越明显。当刺网最适捕捞体长与初始种群优势体长重合时(l0=15),造成种群体长分布峰值的分化;如果l0>15,则导致种群体长组成向小型化方向偏移;反之则会造成种群体长组成向大型化方向偏移;而且这种影响可能伴随遗传因素,具有不可逆性。 相似文献
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The estimation of gear selectivity is a critical issue in fishery stock assessment and management. Several methods have been
developed for estimating gillnet selectivity, but they all have their limitations, such as inappropriate objective function
in data fitting, lack of unique estimates due to the difficulty in finding global minima in minimization, biased estimates
due to outliers, and estimations of selectivity being influenced by the predetermined selectivity functions. In this study,
we develop a new algorithm that can overcome the above-mentioned problems in estimating the gillnet selectivity. The proposed
algorithms include minimizing the sum of squared vertical distances between two adjacent points and minimizing the weighted
sum of squared vertical distances between two adjacent points in the presence of outliers. According to the estimated gillnet
selectivity curve, the selectivity function can also be determined. This study suggests that the proposed algorithm is not
sensitive to outliers in selectivity data and improves on the previous methods in estimating gillnet selectivity and relative
population density of fish when a gillnet is used as a sampling tool. We suggest the proposed approach be used in estimating
gillnet selectivity. 相似文献
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印度洋金枪鱼渔业现状 总被引：6，自引：0，他引：6
报道了印度洋海域金枪鱼渔业近十年的生产概况，结果显示，印度洋金枪鱼渔业从业国家和地区已达40个，从业国家(地区)中以欧共体、印度尼西亚、印度、伊朗、斯里兰卡、中国台湾、马尔代夫等所占份额较高，以2000年计占当年印度洋金枪鱼渔业总产量的68．17％。产量140万吨，以金枪鱼类所占份额最高．主要金枪鱼渔获种类依次为鲣、黄鳍金枪鱼和大眼金枪鱼，主要渔业方式为金枪鱼围网、刺网及延绳钓。中国在印度洋海域金枪鱼渔业中年占份额较小，捕捞产量从1995年的444吨逐渐上升到2000年的6408吨。 相似文献
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根据目前我国深海抗风浪网箱电力设备的配置情况 ,通过对 LA361 K51 S型太阳能电池性能的测试 ,确定了太阳电池的电流、电压、太阳强度及气温等随时间变化的规律以及天气变化情况对太阳电池的功率、转化效率的影响。在计算深海抗风浪网箱日用电量的基础上 ,对所需太阳电池的功率、蓄电池的容量进行了计算 ,并依此确定了深海抗风浪网箱配置太阳电池和蓄电池的规格及型号 相似文献
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对黄、渤海鱼类等级多样性的推算 总被引：16，自引：2，他引：16
为给不同取样地点或时期鱼类群落多样性的比较提供基础资料，根据20世纪80年代以来的黄、渤海底拖网调查，并综合迄今为止的鱼类分类学研究，系统地更新了黄、渤海鱼类组成名录，并计算了其等级多样性特征。结果表明，黄、渤海有鱼类379种，隶属于264属，129科，36目，3纲。其中软骨鱼类12目，24科，50种；硬骨鱼类23目，104科，328种。根据黄、渤海鱼类总名录，计算了其等级多样性指数(△^ )和分类差异变异指数(A^ )的理论平均值及95％置信漏斗曲线，其中等级多样性指数(△^ )的理论平均值为77．7。 相似文献
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附着基粗糙度及表面沉积物对6种海藻孢子附着和幼苗数量的影响 总被引：1，自引：0，他引：1
本项研究试验了人工放散的蜈蚣藻(Grateloupia asiatica)与多管藻(Polysi phonia urceolata)孢子及其幼苗在不同粗糙度的附着基上的附着数量、三叉仙菜(Ceramium kondoi)、假根羽藻(Bryopsis corticulans)、酸藻(Desmarestia viridis)和尾孢藻(Urospora penicilli formis)在海水中自然附着幼苗在不同粗糙度的附着基上的附着数量;还试验了不同粗糙度附着基上不同类型的沉积物对自然附着酸藻和尾孢藻的幼苗数量的影响。试验方法是以市售塑料扎带模拟表面粗糙度不同的人工藻礁,使人工刺激后释放的海藻孢子附着在其表面后,吊挂于海中使孢子萌发;空白附着基吊挂于海水中使海藻繁殖体(孢子、合子或受精卵)附着并萌发生长。以普通海泥、高温灭活海泥、底栖硅藻3种不同沉积物覆盖于人工附着基表面,统计各种沉积物在各种粗糙度的附着基上海藻幼苗数量。结果表明,对于无鞭毛的繁殖细胞(蜈蚣藻、多管藻和三叉仙菜的孢子,假根羽藻的合子、酸藻的受精卵)萌发成的幼苗数量受附着基粗糙度影响显著;在一定范围内,两者呈正相关。而萌发自游动孢子的尾孢藻,附着基的粗糙度影响不显著。3种沉积物中,高温灭活的海泥更有利于尾孢藻和酸藻的附着。 相似文献
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Flume experiments and numerical simulation were conducted to characterize the hydrodynamics of a trapezoid artificial reef. Measurements in particle image velocimetry were conducted to observe the formation of upwelling and vortices; and forces for the reef model were measured by load cell. The results of flume experiments agree well with the numerical data. In addition, the flow structure around a reef combining trapezoidal and cubic blocks was simulated numerically under two deployment schemes, showing a more complicated flow structure than that of a stand-alone reef. Relationship between drag coefficient and Reynolds number suggest that the degree of turbulence can be assessed from the value of drag coefficient downstream from the reef. The role of the reef in water flow is to reduce flow velocity and generate turbulence. 相似文献
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The present study theoretically as well as experimentally investigates the interaction between waves and an array of porous circular cylinders with or without an inner porous plate based on the linear wave theory.To design more effective floating breakwaters,the transmission rate of waves propagating through the array is evaluated.Each cylinder in the array is partly made of porous materials.Specifically,it possesses a porous sidewall and an impermeable bottom.In addition,an inner porous plate is horizontally fixed inside the cylinders.It dissipates the wave more effectively and eliminates the sloshing phenomenon.The approach suggested by Kagemoto and Yue(1986) is adopted to solve the multiple-scatter problem,while a hierarchical interaction theory is adopted to deal with hydrodynamic interactions among a great number of bodies,which efficiently saves computation time.Meanwhile,a series of model tests with an array of porous cylinders is performed in a wave basin to validate the theoretical work and the calculated results.The draft of the cylinders,the location of the inner porous plate,and the spacing between adjacent cylinders are also adjusted to investigate their effects on wave dissipation. 相似文献