A new method to compute the hydrodynamic force acting on a moving body with velocity w in unsteady flow with velocity u has been studied. Firstly, the hydrodynamic force acting on a moving body with velocity u in a flow with the same velocity u has been formulated. Secondly, the hydrodynamic force acting on a moving body with velocity w-u in a static flow field has been formulated. Thirdly, based on linear superposition principle, these two hydrodynamic forces are superposed and combined with gravitational force and buoyancy, and the equation of motion of a moving body in gravitational and viscous unsteady flow field has been formulated as a differential equation. Solving the differential equation under regularly reciprocating current condition by difference scheme, supposing that the sinking body is sphere, the following facts have been revealed; (1) Regularly and vertically reciprocating fluid movement reduces the terminal speed of a free sinking body. (2) Suppose plankton regularly and reciprocally moves up and down by itself, its movement reduces the terminal sinking speed substantially. These results have never been derived from neither conventional Stokes' law approach nor Newton's law approach.

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本研究ではクロマグロの鉛直運動パターン解析に必要なデータを,東シナ海にてクロマグロ7個体の遊泳深度を一秒間隔で収集した。クロマグロの水平方向の回遊に着目した研究は多く存在するが,本研究では膨大な鉛直方向のstep-lengthに関するデータ解析を行った。自然界に存在する多くの生態的な行動特性は餌との遭遇確率を最適化するためにレヴィウォークに従うランダムウォークとなることが多くの研究で示されている。しかしながら我々の分析結果は,step-lengthが指数関数的減衰で分布し,運動パターンはランダムウォークに近い事を示した。

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An acoustic telemetry by a manual tracking receiver was used to observe the behavior of 4 adults of Nigorobuna Carassius auratus grandoculis, in the south basin of Lake Biwa, Japan from 7 May through 4 June, 2008. The fish were implanted with acoustic transmitters and were released. Positions of the individuals during daytime were recorded for 7, 8, 3 and 2 days, respectively. Ambient water temperatures of individuals were recorded during tracking simultaneously. In addition, water temperatures in 9 sites of the south basin were continuously recorded at an interval of 30 minute by data loggers and contours of the lakebed of tracking area were recorded by an echo sounder. Maps of geographical environments including temperature and depth were made by GIS software and compared to the fish positions. The fish moved according to the horizontal graduation of water temperature. The ambient water temperatures of fish distributed in narrower range rather than the water temperatures recorded by data loggers in the south basin. These results suggest that Nigorobuna prefer certain temperature range (18-20℃) and move to the preferred temperature area during the spawning season.

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This paper considers why fish would gather in fish aggregating devices from the viewpoint of hydraulics. The data such as the feature seen from the environment of the area of the sea where the fish aggregating devices is set up, the range of fish which gather in the floating artificial reef, and the observation record of the movement of the fish aggregating device set up was collected. The interesting fact is that fish gather in the upstream side of the artificial reef. Also the size of the wake volume which develops by the floating artificial reef was simulated using the author's model on the wake. The result can not explain about fish which gather in the upstream side but fish gather in the wake. Therefore, seen from the point of the view of the occurrence of the mountain wave, the effect on mixing of the water mass by the occurrence of the mountain wave was guessed in the area of the sea where the artificial reef is set up. And it was supposed that it contributes the selection of the area of the sea where the fish aggregating device is set up and the effect of the gathering.

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In order to investigate aggregating effect of an artificial fish reef, it is necessary to take into consideration two sides of influence by the economic effect and fishes resource environment by the increase in a fish catch. Since FAD is installed for the purpose of collecting the fishes of a large size and a medium size and fishing efficiently in the offing where individual density is low, evaluation of only the economic effect for a useful fish stock may bring about the increase in fish catch pressure. In order to evaluate the aggregating effect of a fish reef, it is necessary combining some examination methods to investigate the whole resource environment of a fishery. Especially the method of combining optical observations and a split beam echo sounder investigation is effective in order to evaluate fish resource environment comprehensively. The payaw investigation in the Philippines and the artificial fish reef investigation in the Kagoshima bay were conducted combining split beam echo sounder and optical observations. The results of these investigations are described by this paper. For sustainable fish resource use, it is important to decide a suitable fishing method and period using the investigation results.

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Movement and behavior of bigeye Thunnus obesus, yellowfin Thunnus albacares and skipjack tuna Katsuwonus pelamis were investigated based on conventional and archival tagging. The fish were mostly released around anchored FADs in the Nansei Islands area. Many of the recaptures were obtained within 200 days after release. The fish were mainly recaptured in the Nansei Island area and in the area between around Kyusyu and off Tohoku as well as in the south of Japan such as around Philippines especially as for yellowfin tuna. Between Kyusyu and central Honsyu, bigeye and yellowfin tuna were mainly recaptured in the offshore and nearshore area, respectively. The distance between release and recapture locations increased with time, although difference between individuals was observed. Based on the data recorded by archival tags, diurnal movements with deeper layer during daytime were observed both for bigeye and yellowfin tunas. Daytime swimming depth of bigeye tuna varied and was sometimes shallow (around 100m or shallower) suggesting association with FADs or other objects based on past study, although clear difference of daytime depth was not observed for yellowfin tuna. Synchronicity of vertical behavior was observed for bigeye tuna individuals which were released on the same day at the same FAD.

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We introduced the system on two round haul net fishing boats of Miyazaki Prefecture in Japan, which transmit the datum of surface water temperature and currents at 3 layers observed by fishing boat to Miyazaki Prefectural Fisheries Research Institute in real time. We have monitored the oceanic conditions in Hyuga-Nada with this system since August, 2010. We studied on the characteristics of current data measured by round haul net fishing boat, and its availability in terms of oceanic condition monitoring. The oceanographic data from round haul net fishing boats were measured mainly in the inshore areas of Kuroshio axis along isobaths from 50m to 300m in north-central Hyuga-Nada, after sunset. In addition, it depended on the prohibition of fishing period and zone, the change of fishing ground. The current data by fishing boats were almost valid except the fishing boat speed during low-speed operation and that during high-speed movement. The temperature and current data from round haul net fishing boats could detect a part of Kuroshio warm water intrusion into the northern coast of Hyuga-nada that was difficult to observe by regular observations. It is possible that the oceanographic data from fishing boats give an effective monitoring result after removing tidal current components and that after many deployment procedures of this system.

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For a coastal fishing vessel sailing in semi-planing state, her trim has a large effect on speed and fuel consumption. By keeping the proper trim, coastal fishing vessels can sail higher speed and can save the fuel consumption. In this report, the author shows the optimum ballast loading method to obtain the proper initial trim using the optimization function of spreadsheet software combined with an existing effective horse power estimation formula.

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