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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The time length of extending and retrieving work of 10 strings of tuna longline settled June, 1997 in the eastem part of the Indian Ocean by a stem ramp trawler type l,000 G.T. fishery training vessel and the walking pace of crew members during these works were recorded. Their relation to the gear construction and the surface conditions was examined, and the following results were obtained : 1) The length of working time depended on the gear construction. 2) It took a longer time to retrieve a deep-lying string, While it required a shorter time when the string was retrieved by the vessel facing a wind from starboard. 3) Equations, which could be regarded to be significant at 0.05 level or yielding the multiple correlation coefficient higher than 0.5 using 1 or 2 explanation variables, could be obtained for the walking pace of more than a half of the members concemed. 4) The significant equations for walking pace during retrieving work adopted the variables of surface conditions as the explanation ones. 5) Suggested influence of the surface conditions from the present results coincided with our experience on board. 6) To reach a clear conclusion, further studies were found to be needed, using the records for more strings, in which the probable explanation variables less frequently showed correlation to one another.

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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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The present report deals with the relation between working conditions and the length of time for shooting and hauling a midwater trawl or the walking activity of the respective crew members during this work, using the records collected from a l,000 G. T. fishery training vessel in Nov. and Dec. of 1997 in the waters off the east coast of Japan. Whether or not the time length and the walking activity were affected by the variables which may affect them through the physical or psychological conditions of the crew members, was examined by estimating multipule linear regression equations. The obtained equations indicated that 1) The time length for shooting the trawl depended on the probable length of the time for confirmation of the net mouth being safely opened and that for hauling depended on the length of the warps. These time lengths could not be free from the influence of the working conditions, through the activity of the crew members invoIved. 2) The equations for the walking activity of the respective members during this work included some variables the probable influence of which was through the conditions of the crew members. 3) The estimated equations suggested that the actually adopted explanation variables had a relation to the allotted charge on board.

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Separation vortices are generated at the tip of a cape exposed to a tidal current perpendicular to the major axis of the cape. The boundary layer thickness increases with increasing distance along the cape. Vortices are generated when the flow separates at the tip of the cape. An upwelling is generated due to the spin down of this separated vortex. This study examines the generation period and the strength (circulation) of the separated vortex by means of hydraulic experiments. The experimental results show that the Strouhal number is constant and does not depend on the Reynolds number when the flow condition is higher than a Reynolds of 300. The formation process of separated vortices is visible by these experiments. The strength of the separated vortex is related to the vorticity at the separation point. This vorticity is govemed by the headland length, the current velocity and the Strouhal number. A theorem is proposed to describe the boundary layer development along a cape in which the boundary layer thickness increase along the cape is proportional to the headland length. This theorem shows good agreement with the experimental data.

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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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The positioning accuracy of differential GPS by latitude-and-longitude correction is reported in this paper. Evaluation of this system was conducted in Perabuhan Ratu, in Indonesia. Experiment conditions included fixed conditions on land and moving conditions at sea during a maneuvering trial of a research vessel. The correction value for latitude and longitude in both cases was measured at a DGPS reference station established in a fixed point on land. The positioning accuracy of this system during the experimental period was very high when compared to that uncorrected GPS position. The positioning error determined on land was about 2.0m in terms of standard deviation. And it was confirmed that this system is also useful in moving conditions.

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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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