The possibility of equalizing the length of the working hours of a tuna longliner was sought by examining the relation of working speed of the longliner to the adjustable and predictable factors observable in the records for 139 strings extended along a straight course, which were chosen from the records for 392 strings conducted by a research ship during 2 fiscal years. It was found that the time for retrieving work for the respective strings could be estimated for 74% of the strings, when a difference of 30 min was set as the permissible range. Namely, it is possible to adjust the length of the working hours by changing the length of a string according to the predicted speed from the number of sections, the distance covered by a section and the wind speed.

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In this study, we proposed a method, which promotes the entrainment of seawater by equipping the river mouth with the weir, and the effect was examined based on experimental and theoretical analysis. These results could be summarized as follows : (1) The energy, in which the river water entrains bay-seawater, consists of kinetic energy and potential energy of the river water following into the bay. The former is evaluated by densimetoric Froude number of the river water, and the latter is evaluated by the water-level difference of bay and river. (2) The effect of the water-level difference of bay and river on entraining the seawater in the bay is more effective as the kinetic energy of river water is smaller.

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For the accuracy of DGPS positions obtained in the service area of a certain DGPS station, the twice of standard deviation of position errors is approximately 4 - 5m and that is accurate enough for common navigation of ships. However, if more accurate positions are required, a set of RTK-GPS equipment or a set of high accurate DGPS equipment must be used. In this study, the validity of a simple and easy technique (hereinafter referred to as D-DGPS) to improve the DGPS positions was investigated using two DGPS receivers, which can receive the medium wave beacon transmitted from the DGPS stations, at two points. The results are summarized as follows : (1) The DGPS position error distribution was reduced to about one-half by the D-DGPS technique. (2) The correlation coefficients were approximately more than 0.8 between the two points. (3) When the difference of the reception delays of the pseudo range correction data is less than 10 seconds between the two points, the difference has no great influence on the accuracy of D-DGPS positions. (4) The allocation of the GPS satellites affects on the position accuracy by DGPS and by D-DGPS.

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In this study, we eｘamine a two-dimesional steady-state wind-induced flow in a closed-water area by use of a numerical simulation method with the k-εturbulence model. We consider the properties of flow induced by a discrete wind shear stress due to a film of algae that partially covers the water surface. We found that the distributions of mean velocity, turbulent kinetic energy, energy dissipation rate and kinematic eddy viscosity are remarkably affected by the discrete wind shear on the leeward end of the film.

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Berm breakwater is a rubble-mund structure, which is allowed to be reshaped by wave attack. The stones in the seaward sIope dislocate from the initial slope to the equilibrium profile. A simple analysis procedure is developed to obtain the formulas for designing the seaward slope s equilibrium profile of the bem breakwater under irregular wave attack. These fomulas include parameters such as the horizontal eroded berm, toe width, the vertical eroded bem, which are fomed after the seaward slope of structure become equilibrium, and the stability number. A new parameter of relative bem crest height is defined in the present study, because it slightly influences the relationships among some other parameters. The fomulas resulted in the present study may be applicable enough to be used in the field design of berm break-water.

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Phytopigment and organic substance in the sediment of Manila clam culture ground were investigated. Sediments were collected from the tidal flat of a Manila clam culture ground in Ariake Bay, Kumamoto Prefecture, Japan. It were detemined that contents of phytopigment (chlorophyll a and phaeo-pigments), organic substance, protein, crude fat and organic carbon in the sediment. Positive correlations were found between phytopigment and organic substances (r = 0.951), and protein (r = 0.946), and crude fat (r = 0.955) and organic carbon (r = 0.979) in the sediment. Fine particles of the sediment contained higher levels of phytopigment, protein and organic carbon. These results suggest that phytopigment quantity in the sediment may be good index for the food environment of the culture ground of Manila clam. Phytopigment contained digestive diverticula and glycogen included foot of Manila clam which were fed fine particles of sediment were also determined. Phytopigment contained digestive diverticula and glycogen of Manila clam increased with feeding fine particles of sediment. These results suggest that fine particles of sediment included phytopigment may be suitable food sources for the Manila clam.

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Floating artificial reef (FAR) was adopted as one of the business items of coastal fishing ground improvement and development project (CFGIDP) in 1994, in Japan. Therefor, the FAR should be designed based on design guidelines of CFGIDP. In this paper, the method, which calculates the mooring line tension by the division of the line, is shown. And mooring line tension of the floating fish reef constructed in Kochi prefecture (KUROBOKU No. 1) is calculated by the both two techniques and these results are compared.

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