Sea-ranching of brown trout, Salmo trutta L.

Abstract  In total, 8211 1-year-old and 14839 2-year-old hatchery-reared brown trout, Salmo trutta L., from 11 stocks were released at the mouth of the River Imsa, southwestern Norway. The recapture rates and total estimated yield were higher for 2- than 1-year-old trout, although recapture rates varied between years of release and stocks. The recapture rate increased with mean individual weight at time of release. Total estimated yield from the individual groups of 1+ trout ranged from 2 to 20 kg per 1000 trout released and for 2+ trout between 11 and 250 kg per 1000 fish released. In all cases, yields were lower than the economic break-even yield. Most fish were recaptured the year of release (89.2% of 2+ and 76.2% of 1+ trout). Almost 31% of the recaptures were caught at sea and 69% in fresh water; 95.8% of the latter were taken in the River Imsa trap.     

基于高精度声学图像的海洋牧场海床类型识别

人工鱼礁作为海洋牧场建设的基础生态工程,在海洋生态环境修复和渔业资源增殖方面起着重要作用。随着人工鱼礁的大量投放,海洋牧场海床逐步转变为高度异质性的底栖生境,底栖生态变化会直接影响到底栖及底层生物的栖息与繁衍。针对传统调查方法在海洋牧场中的局限性,聚焦天津海洋牧场,基于侧扫声纳后散射数据和多波束测深数据,从侧扫图像亮度、图像纹理及地形起伏度等3个维度,探索了天津海洋牧场海床类型识别、分类和面积量化的新方法。研究表明,天津海洋牧场共发现人工鱼礁、牡蛎类、淤泥类、蛤仔泥混类、牡蛎泥混类及碎贝泥混类等6种海床类型,基于声学图像特征的海床类型识别方法准确率达90%,可满足海洋牧场底栖生态研究的需求;通过对比分析,天津海洋牧场本底淤泥类海床消退为58.19%,贝类海床增至7.96%,贝类资源增殖效果明显;人工鱼礁周边新生牡蛎礁0.246 km2,并伴有0.303 km2的牡蛎泥混海床待发育为牡蛎礁,海洋牧场建设对牡蛎礁具有重要的修复作用。本研究探索了适宜于海洋牧场的海床声学分类方法,探讨了声学技术对传统底栖调查方法的补充与完善作用,明确了海床类型与声学图像特征的紧密联系,验证了海洋牧场对牡蛎礁的修复作用,成果可有效应用于近岸海域生境修复、贝类资源量精准评估及牡蛎礁演化机理等领域的研究。     

Land degradation and the decline of ranching in the Sierra Nevada foothills,California

Land use is a critical determinant of land degradation. In this article, I examine how changes in land use from 1957 to 1997 in El Dorado County, located in the Central Sierra Nevada of California, have resulted in the degradation of hardwood rangelands. To do so, I analyze the environmental discourse of land use and land degradation, and examine changes in land use, property rights, and laws and regulations governing land use from 1957 to 1997. I argue that understanding the political ecology of land use is essential to understanding why hardwood rangelands have been degraded while upland coniferous forest has been largely protected. This has implications for conservation of the Sierra Nevada Ecosystem, which is currently the focus of increased scholarly as well as political attention. Copyright © 1999 John Wiley & Sons, Ltd.     

What accounts for the divergence between ranchers' WTA and WTP for public forage?

Results from a 2002 survey of Nevada ranchers that asked about willingness to pay for public forage and willingness to accept compensation to part with grazing rights provide empirical support for the contention of large divergence between WTA and WTP. WTA and WTP are estimated simultaneously, thereby enabling the identification of ranch characteristics that could explain the discrepancy in valuations. We find that some of the discrepancy might be explained by the size of a ranch's herd and the amount of public forage the ranch can access. We find little evidence that the ranching lifestyle accounts for the difference between WTP and WTA for public forage, as asserted by some ranch economists. It would appear that the discrepancy between WTA and WTP can be attributed primarily to an endowment effect.     

High marine survival rates of sea‐ranched Atlantic salmon smolts (Salmo salar) that had previously matured as male parr

Abstract The growth and recapture rates of Atlantic salmon, Salmo salar L., smolts that had previously matured as parr were compared with those of immature siblings in a sea‐ranching experiment in western Norway. The smolts were the offspring of three river populations. They were individually tagged, transferred to cages in a small bay where estuarine salinity gradients had been established and released on four dates from mid‐May to early June after either 3 or 7 days of acclimatisation. The previously mature male parr (PMMP) were smaller than their siblings before release, but performed much better during their time in the sea. As grilse, they reached sizes comparable with the formerly immature fish, and their recapture rate was more than four times higher (8.6 vs 2.1%). This difference decreased somewhat during the following years because 0.85% of the immature fish and only 0.1% of PMMP were recaptured as multi‐sea‐winter salmon. The highly successful marine performance of the PMMP demonstrated that this life history strategy may be more flexible than previously believed.     

"鱼类全生活史"型海洋牧场构建理念与技术

海洋牧场是一种新型的海洋渔业生产方式,休闲垂钓型海洋牧场是其重要的组成部分。本文在系统梳理休闲垂钓型海洋牧场研究和产业发展现状的基础上,针对我国休闲垂钓型海洋牧场成鱼补充量不足的问题,以"产卵—仔稚鱼—幼鱼—成鱼"为保护链,提出构建"鱼类全生活史"型海洋牧场的理念和相关技术,可在同一海洋牧场区域内完成鱼类全部生活史,同时可以恢复鱼类资源、增加生物多样性,为休闲垂钓型海洋牧场建设的发展起到示范作用。"鱼类全生活史"型海洋牧场因休闲垂钓型海洋牧场的构建而提出,但其理念同样适用于其他生物种类比较集中、能够在海洋牧场区完成其全部生活史或大部分生活史的资源养护型、资源增殖型海洋牧场的构建。     

海洋牧场鱼类驯化装置设计与试验

当前海洋牧场鱼类驯化以人工操作为主,鱼类自动驯化是建设高效海洋牧场运行模式的重要技术措施。根据部分鱼类具有趋声性或趋光性习性,设计了能定时播放声音和开启灯光、同时配合饵料定时定量供应的鱼类驯化装置。通过无线水下视频监控和定位通讯,实现对驯化效果监控和远程控制。实际试验中,以黑鲷鱼苗为研究对象,经过30 d的驯化,在播放声音和开启灯光后,黑鲷幼苗集群效果明显。试验结果表明该驯化装置的驯化效果明显,声音、光线、饵料供应、能量供应系统等工作正常,达到了设计要求,为海洋牧场鱼类自动驯化提供了有效的装备支撑。     

基于EVA的鱼类音响驯化装置设计与实验

针对海洋牧场增殖放流过程中的驯化需求,为提高有效性、可靠性和操作方便性,设计基于EVA材料的鱼类音响驯化装置,并进行装置的应用实验。以EVA实心材料为浮体,设计集远程控制、音响驯化和鱼类行为监控于一体的鱼类驯化装置整体结构;根据驯化饵料的特点确定料箱底部的自然下料角度,采用螺旋控料装置实现饵料按需均匀投料,每分钟下料量113 g;系统总体平均日耗电量27.47 Wh,设计满足连续阴雨13 d正常工作的太阳能供能系统。经计算装置稳心高度0.37 m满足规范要求,横摇固有周期2.3 s避开了波浪主能量频率,表明装置有较好的随浪运动特性;以条石鲷(Oplegnathus fasciatus)为对象进行音响驯化实验,实验表明：经25次驯化,以驯化点直径1 m范围鱼群聚集率40%为标准,对照池聚集持续时间为28 s,简易驯化实验池聚集持续时间为115 s,集成式驯化实验池聚集持续时间为473 s;从鱼群聚集率变化角度,简易驯化实验池驯化12次后趋于平稳,约为49%,最终为58%,集成式驯化实验池驯化8次后趋于平稳,约为95%,最终达到了99%。所研发装置在网箱和开放海域进行了应用,良好的效果显示...     

凝石胶凝材料作为人工鱼礁材料的可行性研究Ⅱ——供试体附着生物种类与生物量

将用凝石胶凝材料制作的水灰比为0.60、0.55、0.49、0.44的4种凝石供试体和相同水灰比的4种水泥供试体同时投放到同一海域中进行150 d的生物附着对比试验,每隔30 d观察并测定1次供试体表面附着生物的种类和生物量.结果表明:1)投放第30天时,凝石供试体与水泥供试体均无生物附着;第60天、第90天、第120天时,两种供试体表面附着生物的种类相同,均为10种;第150天时,两种供试体表面附着生物的种类相同,均为13种,主要有孔石莼Ulva pertusa、刺参Apostichopus japonicus、虾夷马粪海胆Strongylocentrotus intermedius、矮拟帽贝Patelloida pygmaea等.2)投放第60天和第90天时,凝石供试体附着生物总量低于水泥供试体,但第90天时,凝石供试体附着生物量的增加速度明显快于水泥供试体;第120天时,凝石供试体附着生物总量已超过水泥供试体;第150天时,凝石供试体附着生物量平均值为344.85 g/cm2,水泥供试体附着生物量平均值为260.15 g/cm2,凝石组明显高于水泥组.3)投放第150天时,4种水灰比的凝石供试体附着生物量平均值分别为58.63、79.32、89.66、117.25 g/cm2,可见在试验范围内,凝石供试体表面附着生物量随着水灰比的降低即凝石胶凝材料含量的增加而增大.试验表明,凝石胶凝材料作为人工鱼礁的造礁材料在生物附着方面比水泥具有优越性,因而凝石胶凝材料作为人工鱼礁造礁材料具有实用性.