Water circulation induced by mechanical aerators in a rectangular vessel for shrimp aquaculture

A water streamer was designed for the purpose of enhancing cost-efficient circulation between the water surface and bottom of shrimp aquaculture ponds. We took direct measurements of the water current field induced by the designed aerator in a large rectangular reservoir of dimensions (L)50 × (W)19 × (D)1.3 m³ and compared the results with those of a standard Taiwanese paddle-wheel aerator. Vertical circulation between the surface and the bottom induced by the paddle wheel aerator was less than that by the designed aerator. Furthermore, the paddle-wheel aerator consumed more electric power than the designed aerator. The structures of water current induced by the two aerators are elucidated, and the advantages and disadvantages of the aerators are discussed.Auxiliary employment of the designed aerators may contribute to delivery of high DO water throughout the pond, which is more efficient than a paddle wheel aerator.     

日本对虾内陆养殖的实验室模拟研究

我们将日本对虾进行实验室桶养作模拟内陆养殖试验。发现日本对虾可以顺利地养殖到体长５－７厘变,然后短人存活率急剧降低,这一现象与我们海边虾塘养殖所得到的结果极为一致,我们称之为“５－７”现象。     

Axial variations in anatomical properties and basic density of Eucalypt urograndis hybrid (Eucalyptus grandis 3 E. urophylla) clones

We studied two clones of Eucalypt urograndis hybrid (Eucalyptus grandis 9 E. urophylla), GR283 and GR330, grown in Tumkur district of Karnataka (India), and felled 5–6 years old three trees of each clo...     

基于轮廓重建的渔船雷达MAP-MRF快速反演研究

渔船雷达是渔船导航系统的重要组成部分,在海上复杂气象条件下,具有不受能见度影响进行全天候观测的优势。从雷达信号向可判读图像信号的反演过程中,对雷达照射夹角间的缺失数据进行重建是反演过程中计算和时间花费最大的部分。依据渔船反演过程中的特性,将统计力学模型引入到雷达图层轮廓的重建计算当中,应用最大后验概率马尔可夫随机场框架实现了渔船雷达的快速雷达图像反演过程。文章成果对于减少反演时间,提高雷达刷新率,及时准确地发现海上强对流灾害目标具有重要的意义和实用价值。     

Elemental analysis of otoliths of Japanese anchovy: trial to discriminate between Seto Inland Sea and Pacific stock

The ability to discriminate local stocks of Japanese anchovy Engraulis japonicus was assessed based on data from four elements (K, Na, P, and Sr) using an electron probe micro analyzer (EPMA) and data from three elements (Ba, Mn, and Sr) using inductively coupled plasma mass spectrometry (ICP-MS) from the otoliths of 40 anchovy (23.6–47.0 mm body length). Anchovy were caught at three sites (Aki-nada, Hiuchi-nada, and Osaka Bay) in the Seto Inland Sea, and one site (Kuroshio extension) in the Pacific Ocean in 2002. In order to discriminate different spawning grounds, EPMA data from the core portion (from core to 30 μm in the core-posterior axis) were used. Results showed that it was difficult to discriminate between the Seto Inland Sea and the Pacific anchovy by EPMA data. Conversely, it was possible to discriminate between the Seto Inland Sea and the Pacific anchovy by ICP-MS data from bulk otoliths. Our results showed that Mn contents of otoliths using ICP-MS discriminate between spawning grounds most, and Ba and Sr discriminate less. The difference in elemental compositions in anchovy otoliths between the Seto Inland Sea and the Pacific Ocean might be reflected by cumulative experienced elemental composition of ambient sea water during life history between the Seto Inland Sea and the Pacific anchovy.     

Interannual variability of the ecosystem of the Kii Channel, the Inland Sea of Japan, as influenced by bottom intrusion of cold and nutrient-rich water from the Pacific Ocean, and a recent trend of warming and oligotrophication

Interannual variability of the ecosystem of the Kii Channel, productive shelf water on the Pacific side of south‐western Japan, was analysed based on physicochemical environmental variables and abundance of major zooplankton taxa collected monthly for 12 yr from 1987 to 1999. The Kii Channel experienced both short‐term (i.e. 3–4 yr) cyclical changes and a long‐term (i.e. decadal) environmental trend. The short‐term variability was primarily associated with year‐to‐year differences in intrusion of subsurface, cold nutrient‐rich water along the bottom of the Kii Channel from the Pacific Ocean. When this bottom intrusion was intense, the Kii Channel experienced a cold, new production‐dominated ecosystem. The bottom intrusion, however, has become less intense in recent years, because of the closer proximity of the Kuroshio flow axis to the Kii Channel. Hence, there was a consistent trend towards warming and a regenerated production‐dominated ecosystem. In accordance with such environmental changes, the zooplankton community shifted towards more oceanic conditions; major herbivorous calanoids (i.e. Calanus sinicus, Paracalanus parvus (s.l.), Clausocalanus spp. and Acartia omorii) decreased, while carnivores (i.e. hydromedusae and Sagitta spp.) increased. The amount of total fish catch also decreased, while the catch of subtropical species increased. These findings lead us to conclude that the bottom intrusion from the Pacific Ocean plays a key role in determining the biological production in the Kii Channel.     

An investigation of avoidance by Antarctic krill of RRS James Clark Ross using the Autosub-2 autonomous underwater vehicle

The autonomous underwater vehicle (AUV) Autosub-2 was deployed on eight missions ahead of RRS James Clark Ross in the northern Weddell Sea and in the Bransfield Strait, Southern Ocean, to assess avoidance of the research vessel by Antarctic krill Euphausia superba. The AUV was equipped with the same type of scientific echosounder as the research vessel (Simrad EK500 operating at 38 and 120 kHz) and measured the density of krill along transect acoustically (g m⁻² wet mass) prior to the ship’s arrival. We hypothesised that if krill avoided the ship, perhaps in response to radiated noise, then the ship should detect less krill than the AUV which is known to have much lower noise levels than the ship. We were unable to detect any significant difference between the density of krill detected by the ship or the AUV, either at the transect level or at finer scales within transects. We conclude, therefore, that avoidance by krill of RRS James Clark Ross will not significantly bias acoustic estimates of krill abundance by this vessel.     

舟山渔场人工鱼礁投放海域生态环境前期评估

根据2002年6-7月在舟山渔场朱家尖外侧开展人工鱼礁投放海域本底调查所获的海洋生物和海洋水文环境资料及以往有关文献中对该海域的调查资料,对朱家尖外侧拟投人工鱼礁海域的海水理化因子和海洋生物种类组成、数量分布和群落结构特征作了较详细的分析研究,以评估该海域是否适于投放人工鱼礁.结果得知:该海域底质为粉砂质粘土,浮游生物种类和数量及底栖生物种类和数量较多,水深为14～19m,温、盐度季节变化明显、透明度较高、水色相对较清,水质绝大多数指标符合国家一、二类水质标准,海域适合沿岸岛礁性鱼类如石斑鱼、褐菖、鲈鱼等的栖息生长,历史上渔业资源丰富,也无工厂废水排放,不会对海洋生态环境产生重大污染,因此,可以为良好的投放人工礁之场所.     

长江口中华绒螯蟹(Eriocheirsinensis)蟹苗汛期预报的研究

报导了对长江口中华绒螯蟹 (河蟹 ,Eriocheirsinensis)蟹苗汛期预报的研究结果。蟹苗汛期决定于河蟹胚胎及溞状幼体发育的生物学因素、水温条件和潮汐?そ诘暮有芳性?2月底 3月初交配抱卵 ,5月初孵出溞状幼体。 1970～ 1981年的资料表明 ,从 3月 1日河蟹开始交配抱卵至大眼幼体 (蟹苗 )回归淡水 ,约需 12 77度日。按这一标准估算 ,在± 2d的变差下 ,12年中有 11年的发汛起始日在估算范围内 ,而若允许将变差时间提高到± 3d ,则 12年中的发汛起始日全部在预测范围内。长江口的大眼幼体要入江 ,必须借助潮汐的动力。而在潮汐半月周期的潮位曲线上 ,只有从起汛期至大汛期 (农历廿七到初三 ;十二到十八 ) ,潮位逐日上升 ,蟹苗才有可能从河口浅海进入江段。综合考虑度日和潮汐两个因素 ,即可预报蟹苗发汛的起始日     

智利外海渔场竹筴鱼资源分布特征

根据在智利 2 0 0海里专属经济区外海的渔场周年探捕调查 ,对智利竹鱼 (Trachurusmur phyi)单位努力量渔获量 (CPUE)的构成和季节变化及其资源分布特征进行了初步探讨。结果显示 ,竹鱼在智利外海分布广 ,30°～ 43°S ,78°～ 87°W海区均可形成拖网作业渔场。南半球冬季竹鱼密集分布区较偏南 (38°～43°S) ,8月密集分布区向北偏移至 35°～ 40°S,春季鱼群继续向北洄游至 30°～35°S ,并开始分散索饵 ,集群性较差 ,到翌年秋季再集群向南洄游 ,在 38°～ 43°S ,78°～ 85°W形成越冬场。CPUE以冬季最高 ,春、秋季次之 ,夏季最低。冬季以 6月份平均CPUE最高 ,达 1 5 .1 8t/h ,夏季以 3月份平均CPUE最低 ,仅 1 .1 2t/h。