To improve the positioning accuracy of LORN-C Northwest Pacific Chain (8930 chain), the differential correction method was proposed in this paper and tried at Tateyama Bay in 1997. The reference station which measures the correction value of LOP (Line of Position), was set at the land fixed point being not far from observation sea area. The large local LOP errors l.56μs in Y station (Hokkaido) and 2.48/`S in Z station (Korea) were observed. It is thought that these errors were caused by the change of SF (Secondary Factor) with long land propagation of ground wave. By using the differential correction, the LOP errors were decreased to 14.7% in Y station and 26.9% in Z station. From this result, the efficiency of differential method was verificated.

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Transport of blown sole (Pleuronectes herzensteini) eggs and larvae from the spawning ground near Sado Strait, Sea of Japan is simulated using a numerical model to evaluate the effect of daily wind variation on the larval retention rate, which indicates the percentage of eggs and larvae retained in the shelf area shallower than 100m. Observed winds in March (main spawning period) of three years (1983, 1984 and 1996) and a current profile observed by ADCP at the entrance of Sado Strait are used as driving forces. The vertical movement of eggs and larvae estimated from field observations is also considered in the model. One hundred eggs are produced every 5 days and tracked for the planktonic period (30 days) using a drifter advection/dispersion model based on the water circulation calculated by a three-dimensional hydrodynamical model. In 4 cases out of 21, the retention rates are over 30%. They have a similar wind condition that weak wind continues for several days after spawning. Therefore short-term wind fluctuation could have a great effect on the retention rate. From the simulation results under the modeled wind condition, it is revealed that the strong wind blow during 9- 14 days after spawning increases the retention rate, while that during the other days decreases it.

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1997年6月,インド洋東部において行った10回のマグロ延縄操業の際に,投揚縄に要した時間及び各乗組員の歩行数(1時間当たりに換算)を記録し,それらと漁具構成に関する要因及び海況・風速との関係を調べ,次の結果が得られた: 1.作業時間の長さは漁具構成によって決まる。 2.揚縄時間の長さは幹縄の長さによって決まるが,深くに設置した縄を揚げるときには長く,右舷から風を受けたときには短くなる。 3.投縄及び揚縄作業に従事した乗組員の半数の歩行速度に関して,有意とみなせるか重柏関係数0.5以上の回帰式が1つか2つの説明変数を用いることによって得られる。 4.揚縄中の歩行速度を表示する有意とみなせる式の説明変数には海況・風速に関する説明変数が含まれる。 5.これらの式が示す傾向は我々の経験と一致する6.さらに明確な結果を得るためには,今後操業回数が多く,説明変数相互間の相関がみられにくい資料を用い分析しなければならない。

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Theoretical fomulas of narrowing the breadth of the river mouth (i.e. side gate) in the finite depth estuary were figuredout. The enlargement effect of the entrainment rate by the side gate was also investigated. The results indicated that potential of the entrainment rate was related to the four parameters, i.e. the densimetric Froude number at the outlet of river water, the depth of river mouth relatives to bay, the relative opening rate of the gate and the supply of sea water at the bay mouth. Moreover, the decrease of the relative opening rate of the gate influenced to the increasing of l) the outlet densimetric Froude number of river water, 2) the relative breadth of the river mouth, and 3) the potential of the entrainment rate.

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1, 000GT型練習船が1997年11月～12月に三陸沖及び四国沖で行った中層トロール中に集めた作業時問の長さと歩行活動に関する記録から求めた重回帰式に,乗組員の活動の変化を通じてそれらに影響を及ぼすと考えられる要因が説明変数として取り入れられるかどうかを検討し,次の結果が得られた: 1.投網時間の長さは主に網口の開きを確認するための時間の長さ,揚網時間の長さは主にワープの長さによって決まる。しかし,これらの時間の長さには乗組員の活動を通じた影響がみられた。 2.各乗組員の歩行活動を表示する重回帰式の説明変数には,船や網を通じてでなく乗組員を通じて影響を及ぼすと考えられる変数が含まれる。 3.各乗組員の歩行活動を表示する重回帰式の説明変数には作業分担と関係が見られる。

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潮流が岬や半島にあたる場合,岬先端部で剥離渦が生じる。この剥離渦は岬に沿って発達する境界層内で渦度を発達させたもので,剥離後スピンダウンし湧昇流を発生させる。本研究はこの剥離渦の発生周期と強さについて水理実験によって検討した。発生周期のストローハル数は一定値となりレイノルズ数によらないことを実験と現地データから明らかとなった。剥離状態の可視化から渦を形づくる過程が明らかとなり,剥離渦の強さは剥離点における渦度で求められ,岬長,外縁流速およびストローハル数で表される。さらに,岬に沿って発達する境界層厚さは岬長に比例することが導かれ,実験結果とよく一致した。

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Since prehistoric time, fishing gears have been used to catch fishes directly and auxiliary gears like shelters have been also used to gather fishes around them. In addition, there are some fishing gears like setnets or traps, which work as aggregating devices. The artificial stone bed located in the coast of Kochi prefecture, which is supposed to be built in the middle of 17th century, is a device to gather fishes and to catch them easily. The artificial stone bed located in the coast of Aomori prefecture, which is supposed to be built in the middle of 18th century is for the increase of tangle. They have been developed in different districts and their objects, i.e., fishes or tangle, are different from each other. But their purposes, i.e., making use of the function to gather objective creatures, are the same with each other. To develop these kind of techniques, it is important that ecological knowledge of objective creatures, especially their ethological knowledge against things Iocated in the water. In close cooperation with the resources management and environmental conservation projects, these techniques will keep or increase marine resources and lead to stable fishery.

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The purpose of this report was to investigate the effect of artificial reef for catch topshell, Batillus cornutus. The investigation was carried out from 1993 to 1996 for the block with vertical and horizontal (upper and under) grooves which were put into Nomuro fishing ground in the western part of Wakasa Bay in 1991. The density of topshells on the blocks with grooves were 2.7-11.8/m2 that were about 4-16 times higher that of the circumferance ground. The shell height of topshells on the blocks were 19. 3-90. 2mm, and the percentage of catchable size (individuals more than 50mm in shell height) of those shells were 72-80%. The number of topshells in the vertical grooves were more than in the horizontal grooves in day time because the number of topshells in the under horizontal grooves were less than in the vertical and upper horizontal grooves especially. Gelidium elegans was the most dominant algal species on the block, the relationship between the cover of Gelidium elegans and the number of topshell distributed on the block with grooves were positive. Few topshells distributed on the same blocks for long period and most of shells leave from blocks, however, the number of distributed she11s on the block was recovered within comparatively short period. It is concluded from these facts that the block with grooves is the effective artificial reef to catch topshell in the shallower coastal area.

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Research and development work on an observational technique for diagnosis and evaluation of coral reef activity is currently underway at JAMSTEC. An underwater microscope has been developed for in situ observation of corals. This paper describes the design specifications, construction, operational tests, and tests results for the underwater microscope. During the tests with the underwater microscope, it was possible to conduct observations of corallites, septas and the tentacles of a polyp. Moreover, by connecting a time-lapse video cassette-recorder, it was also possible to monitor the growth process for algae. It was found that the video cable must be extended for further improvement of operability. However, this would require significant improvements because of resulting sigrlal attenuation and phase delay.

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本研究は位置補正方式DGPSの測位精度について検討したものである。このシステムを評価するための実験をインドネシアのプラブハンラトゥにおいて実施した。実験の条件は,受信機を陸上に設置した場合および研究船の操縦性能試験時の海上航走時とした。陸上ならびに海上実験において,緯度と経度の補正値は陸上に設定した基準局で求めた。この方式による補正を行ったDGPSの測位精度は,補正を行わなかった場合に比較して非常に良い精度を有する事が確かめられ,陸上における位置誤差は標準偏差で2.0mであった。また,海上航走時においてもこの方式が非常に有用であることが確かめられた。

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The dynamic equations of a cylindrical two pojnt mooring buoy were induced on the fo1lowing assumptions ; 1) The cylindrical buoy set up horizontally, fully immersed in water. 2) Weight in water of the mooring lines and acting forces were ignore. 3) The motion of the buoy was two dimensional movement such as surging, heaving and pitching. Numerical calculations were done by the dynamic equations of which were modified as the linear approximately. The motion of buoy can be displayed by computer program.

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