Land use,associated eel production,and abundance of fish and crayfish in streams in Waikato,New Zealand     

Brendan J. Hicks  Helen M. C. McCaughan 《新西兰海洋与淡水研究杂志》2013,47(5):635-650

Abstract

The density and biomass of fish and crayfish, and the production of eels, was compared among streams in native forest, exotic forest, and pasture. Populations were estimated by multiple‐pass electroshocking at 11 sites in hill‐country streams in the Waikato region, North Island. Three sites were in native forest, four in exotic forest, and four in pasture. Length of stream sampled at each site was 46–94 m (41–246 m² in area), and catchment areas up stream of the sites ranged from 0.44 to 2.01 km².

A total of 487 fish were caught. The species were longfinned and shortfinned eels, banded kokopu, Cran's and redfinned bullies, and common smelt. Eels were the most abundant fish in all three land‐use types, and shortfinned eels were more abundant at pastoral sites (mean density 1.11 fish m^?2) than longfinned eels (mean density 0.129 fish m^?2). Banded kokopu were present only at forested sites. Mean fish densities were greater at pastoral sites (1.55 fish m^?2) than under either native forest (0.130 fish m^?2) or exotic forest (0.229 fish m^?2). Mean fish biomass was also greater at pastoral sites (89.7 g m^?2) than under native forest (12.8 g m^?2) or exotic forest (19.3 g m^?2). Longfinned eels made a greater contribution to the fish biomass at all sites than did shortfinned eels. Densities of crayfish were high (0.46–5.40 crayfish m^?2), but were not significantly different between land‐use types. Crayfish biomass ranged from 1.79 to 11.2 g m^?2. Total eel production was greater at pastoral sites (mean 17.9 g m^?2 year¹) than at forest sites (mean 2.39 gm^?2 year^?1).  相似文献   

Description of the larval development of Galaxies maculatus in landlocked lentic and lotic systems in Western Australia     

Andrew Chapman  David L. Morgan  Howard S. Gill 《新西兰海洋与淡水研究杂志》2013,47(2):563-569

The larvae and larval development of Galaxias maculatus are described from a freshwater lake and a saline river in southwestern Western Australia. The size at hatching (7.0 mm total length) was similar to that recorded elsewhere for G. maculatus and the sequence of fin development (i.e., caudal, dorsal, anal, pectoral, and pelvic fins) was identical to that recorded for galaxiids generally. There were relative increases in the proportions of head length and body depth with larval growth and a decrease in proportion of pre‐anal length. Larvae from river habitats were smaller throughout larval stages of development than those from the lake. Fins of riverine fish began and completed development at a smaller size of fish than the lacustrine population, presumably as a response to the need for great motility at a smaller fish size in lotic environments.  相似文献   

探地雷达探测中对媒质相对介电常数的测定   总被引：3，自引：1，他引：2  

邓小燕  王通 《物探与化探》2009,33(1):43-45

分别就探地雷达探测中的收发一体式天线、收发分离式天线在实际工作中对媒质相对介电常数的几种主要测定方法：已知目标深度法、点源反射体法、共中心点（CMP）法及层状反射体法,从理论到实例一一做了详细的论述。实践证明,这些方法能够满足生产要求。  相似文献   

Multiple group principal component analysis     

Richard A. Reyment 《Mathematical Geology》1997,29(1):1-16

Common Principal Component Analysis is a generalization of standard principal components to several groups under the rigid mathematical assumption of equality of all latent vectors across groups (i.e., principal component directions), whereas the latent roots are allowed to vary between groups (differing inflations of dispersion ellipsoids). In practice, data that fulfill these strict requirements are relatively rare. Examples from palaeontology are used to illustrate the principles. Compositional data can be made to fit the Common Principal Component (CPC) model by the appropriate logratio covariance matrix.  相似文献   

边坡岩体结构的三维失稳形式及稳定性分析研究   总被引：2，自引：0，他引：2  

张菊明  王思敬 《工程地质学报》1997,5(3):242-250

由两组结构面控制的四面体块体是岩体中最基本的结构体, 其稳定性取决于块体所受荷载及结构面上的摩阻力。正确判定边界面上摩阻力分布是评价块体稳定性的关键。本文提出的块体稳定性分析适用于岩体所受荷载为三维非共点力系。在不同外力作用下块体可产生平动、转动、翘扭及倾倒等各种三维失稳组合形式, 从而得到更为合理的块体稳定性评价。  相似文献   

Problems of Artisanal Marine Fishermen in Ghana: The Way Ahead   总被引：1，自引：0，他引：1  

John Victor Mensah  & Barima Kwabina Antwi 《Singapore journal of tropical geography》2002,23(2):217-235

Marine fishing is an important traditional economic activity of the coastal communities in Ghana and contributes over 80 per cent of the total fish catch. The traditional sector accounts for over 75 per cent of the marine catch. The small-scale artisanal marine fishing communities, which contribute less than 30 per cent of the traditional sector landings, are generally characterised by low levels of production and, hence, low incomes, poor living conditions and chronic indebtedness. Based on field data on artisanal fishing communities in the Ahanta West and Gomoa districts, this paper summarises the chronic problems of artisanal fishermen that perpetuate their precarious existence in the coastal environment. Overcoming the problems of these increasingly marginalised and migrant communities calls for the provision of supplementary employment opportunities, improved social services and the formation of solidarity groups to enhance access to micro credit. These would require technical and management training as well as support services from government and non-governmental organisations (NGOs).  相似文献   

Producers'' organizations and devolved fisheries management in the United Kingdom: Collective and individual quota systems     

Aaron C Hatcher  Research Fellow 《Marine Policy》1997,21(6):519-533

In the United Kingdom responsibility for the management of national catch quotas has since 1984 been extensively devolved to producers' organizations, Institutions created by the European Community in order to implement the common organization of the Community market for fish. The paper describes the development of the UK quota management system and the approaches adopted by different producers' organizations to the internal management of their quota allocations. Because of changes in the UK fishing vessel licensing rules as well as developments in the quota allocation system, there is an emerging market in quotas at both individual and collective levels. The implications of these developments are discussed, including the possible evolution, largely through industry-led innovation, of some sort of individual transferable quota (ITQ) system for the UK.  相似文献   

The influence of tilt angle on the acoustic target strength of the Japanese common squid (Todarodes pacificus)     

Kang  Donhyug; Mukai  Tohru; Iida  Kohji; Hwang  Doojin; Myoung  Jung-Goo 《ICES Journal of Marine Science》2005,62(4):779-789

  相似文献   

扎龙湿地火烧严重度分析及火灾对丹顶鹤生境的影响   总被引：3，自引：0，他引：3  

孔博  张树清  张柏  那晓东  李晓峰  卢晓宁 《湿地科学》2007,5(4):348-355

利用ETM 遥感影像资料,分析了扎龙湿地火烧严重度及火灾对扎龙湿地丹顶鹤(Grus japonensis)生境的影响。采用火灾前、后的ETM 影像数据,计算差异性归一化燃烧率(dNBR)和制作扎龙火烧严重度分布图,用综合燃烧指数(CBI)分析植被死亡率对生境变化的影响程度,并分析两者的相关关系;利用两种燃烧指数与对应的高程、植被类型、坡度、功能分区和丹顶鹤巢位等因子叠加分析作为火烧区的评价指标;再根据火烧严重度分类图定量化分析火灾对丹顶鹤生境和巢址变化的影响。结果表明,CBI与dNBR之间有非线性关系(n=59,R2=0.8724);判定高程在148.3~154.6m和坡度在0°~0.185°之间,且分布有大量芦苇(Phragmites australis)沼泽的核心区低洼地易发生火灾;在火烧强度较高的情况下,迫使丹顶鹤选择次适宜的栖息环境,降低了丹顶鹤对隐蔽条件和食物资源的标准,导致丹顶鹤重新选择巢址的位置,其种群数量迅速减少。研究结果对扎龙湿地动物资源可持续发展具有一定的指导意义。  相似文献   

3D定向钻孔雷达系统及应用     

王正成  侯胜利 《物探与化探》2007,31(1):86-89

3D 定向钻孔雷达系统能够对钻孔四周进行高精度三维成像,在单个钻孔中即可完成目标体距离、方位的探测,相对2D钻孔雷达具有探测精度高、速度快、深度大的优点.笔者对3D 定向钻孔雷达系统的工作和成像原理、技术规格进行了详细说明,并结合现场数据说明了其实际应用效果.  相似文献