2015–16 ENSO contributed reduction in oil sardines along the Kerala coast,south‐west India

Fishery along the west coast of India largely depends on pelagic fish such as oil sardines, which are dominant during the south‐west monsoon. However, the response of sardine population to the warming caused by the climatic events such as El Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) is poorly studied. Here, we hypothesize that the ENSO‐related changes in biogeochemistry can adversely affect the oil sardines. We have used biogeochemical data collected along the Kerala coast during September 2015 (ENSO year) and September 2017 (a normal year) supported by catch per unit effort (CPUE) and fishery landing data to show the ENSO‐related bio‐physical dynamics and its impact on the oil sardine population along the south‐west coast of India. During the 2015 ENSO year, upwelling velocity decreased minimizing cooling of surface waters and resulted with an increase in sea surface temperature (SST) (~1.8°C). Consequent decrease in nutrient levels favoured nano‐phytoplankton and pico‐phytoplankton. On the other hand, during September 2017 when the ENSO effect was nullified, the decreased SST and availability of nutrients in the euphotic zone resulted in the dominance of micro‐phytoplankton. The hydrographic conditions (reduction in upwelling intensity), and reduction in micro‐phytoplankton abundance and zooplankton density in turn perhaps affected the fishery potential of the region. Oil sardines population (along the west coast) collapsed from 1.55 lakh tones (2014) to 0.46 lakh tones during 2015–2016 ENSO event, while in 2017 the conditions become favorable and their population was back to normal (1.27 lakh tones). Our results are in close agreement with our hypothesis and suggest that ENSO events could reduce phytoplankton productivity and disrupt the food chain, which in turn can affect the oil sardine population along the west coast of India.     

Spatiotemporal distribution of fish eggs and larvae in the Huanghe(Yellow) River estuary,China in 2005–2016

Decreasing fish resources in estuaries is a subject of anthropogenic activities. Studies of the spatiotemporal distribution of fish eggs and larvae can help identify the status and processes underlying recruitment in a fishery. As the fifth largest river estuary in the world, the Huanghe (Yellow) River estuary (HRE) is a typical estuary that has been seriously aff ected by human activities. Annual surveys on ichthyoplankton and environmental factors were conducted in the months of May of 2005 and 2009-2016 in the HRE to investigate the spatiotemporal distribution of fish eggs and larvae and the associated infl uencing factors. A total of 23 and 20 species of eggs and larvae, respectively, were collected. The dominant orders were Perciformes (51.2%) and Clupeiformes (25.6%). The average number of fish species eggs and larvae were 6.0 and 4.1 in average abundance of 0.91 and 0.13 ind./m^3 , respectively. The dominant species were mainly low-commercial-value small-sized fishes, such as Clupanodon punctatus , Harengula zunasi, and Acanthogobius, whereas certain traditional commercial fishes, such as Trichiurus lepturus , and Clupea pallasii, were not seen. Analysis of the fish egg and larval community revealed four temporal assemblages and two spatial assemblages. Salinity was the main factor on the spatial distribution of ichthyoplankton communities, the species number and Shannon-Weiner diversity index (H′) of the fish egg and larval community near the river mouth with lower salinity were signifi cantly lower than the community far away from the river mouth with higher salinity. In addition, increases of water temperature promoted the number and abundance of fish species eggs, and the areas of abundant prey tended to have a more diversified and abundant of ichthyoplankton species. In overall, overfishing, dam construction, and other human activities were the main drivers that led to the substantial decline in fishery resources in the HRE.     

Distributions of Water Masses and Currents in Tachibana Bay, West of Ari-ake Sound, Kyushu, Japan

We have investigated the water mass distribution and circulation in Tachibana Bay, which is located in the junction area between Ari-ake Sound and Amakusa-Nada in western Kyushu, Japan. This was done to clarify the mechanism by which ghost shrimp larvae, originating from a sandflat of Amakusa-Shimoshima Island, are transported. Temperature and salinity data repeatedly obtained over the area of Tachibana Bay show that relatively low salinity water lies over northern part of the bay, while high salinity water lies over southern part of the bay. The location of the low salinity water margin tends to depend on the amount of rainfall several days before the observation. A large amount of rainfall makes a clear boundary between low and high salinity waters. Current velocity data indicate an eastward mean flow just north of Tomioka, northern tip of Amakusa-Shimoshima Island, and a clockwise mean flow approaching the Tomioka Bay sandflat, which should be suitable for the on-shore transport of the ghost shrimp postlarvae. Current measurements with shipboard ADCP just west of Hayasaki Strait, at the entrance of Ari-ake Sound, show that a westward tidal residual current tends to incline to the north, with evidence of a density current in the northern part of the western Hayasaki Strait.     

南海区桁杆虾拖网40 mm方目分离网片选择性的初步研究

为了研究桁杆虾拖网40 mm方目分离网片对渔获物的分隔效果和选择性,作者采用"套网法"于2015年8月在南海北部近海渔场进行了试验。计算分离网片对主要渔获物的尾数分隔率和质量分隔率,使用Logistic曲线作为选择性模型,运用极大似然估算法估算选择性参数。结果表明:虾拖网的目标种类为刀额新对虾(Metapenaeus ensis)和周氏新对虾(Metapenaeus joyneri),优势副渔获为丽叶鲹(Caranx(Atule)kalla);刀额新对虾和周氏新对虾的尾数分隔率和质量分隔率均大于90%;尾数分隔率和质量分隔率均大于80%的种类有:杂食豆齿鳗(Pisoodonophis boro)、黄斑蓝子鱼(Siganus oramin)、高体若鲹(Carangoides equula)和卵鳎(Solea ovata Richardson);丽叶鲹和脊突猛虾姑(Harpiosquilla raphidea)的尾数分隔率和质量分隔率均大于60%;周氏新对虾、脊突猛虾姑、丽叶鲹和黄斑蓝子鱼对分离网片的接触率分别为0.51、0.69、0.41和0.39,其50%选择体长(L50)分别为57.96±2.07、69.62±2.13、68.19±0.49和73.12 mm±1.26 mm。研究结果可为提高南海桁杆虾拖网的选择性积累数据,为缓解其对渔业资源补充群体的不良影响提供参考。     

海洋渔业GIS中温度水平梯度计算的误差分析和新算法研究

在海洋渔业GIS应用中,用现有GIS直接计算渔区温度水平梯度时,由实际距离问题引起的相对误差达26％、绝对误差达0.124℃／10km,同时还存在渔区格网不规则问题和渔区格点值问题。本文提出了基于SST等值线计算渔区温度水平梯度一种新的GIS算法。该算法的结果优于用ArcGISTIN计算的结果,并可用于计算盐度、叶绿素等其它海洋要素的水平梯度。     

中国对虾人工诱导雌核发育的研究Ⅰ──四步诱导法

１９９０～１９９３年于青岛采用研究鱼类人工诱导雌核发育相类似的方法 ──紫外线照射精子、受精、温度或细胞松胞素Ｂ处理卵子方法，对中国对虾进行 人工雌核发育的研究。实验结果，有三批材料获得较好的效果：二批培育到蚤状幼 体，另一批培育到３～３．５ｃｍ幼虾。经受精细胞学观察，被照射的精子经受精，其核 有的不能原核化，有的虽能原核化，且能向中央迁移，但都不能与卵原核结合。实验 表明，这三批育出的个体是雌核发育的个体。     

藻虾混养的研究 Ⅰ、江蓠与新对虾、青蟹在鱼塘中混养的试验

文中详述细基江篱繁枝变型与刀额新对虾、中型新对虾、锯缘青蟹在鱼塘中混养的试验。试验结果表明，藻虾混养构成海洋动植物互为有利的生态系，充分利用养殖水域，达到坛产坛收的目的。细基江蓠繁枝变型是鱼塘养殖的优良品种，从试验结果可推断出其生长的最适温度和盐度分别为17～30℃、17～29‰，它的最适生长水层是：1～4月为20～50厘米，5～6月50～80厘米、7～8月70～80厘米、9月35～70厘米、10～12月20～70厘米。文内还讨论藻虾混养的生态环境和共生关系、江篱的生长规律与藻种移植等问题。