Oxygen-deficient water mass on the bottom formed during period of stratification are broken down quickly by convection due to atmospheric temperature falling in abay. The quantitative study on convection has not been reported so far. Here we presented a one-dimensional model for quantifying convection due to surface cooling, and the results calculated by the model corresponded to both K. B. Katsaros's experimental values and ours pretty, such as the vertical distribution of temperature in the surface thermal boundary layer and the heat flux through surface, when the diffusion coeffcient for the model is given as half of that of water. Moreover by this model, the sinking value of the convection at surface layer can be estimated that which usually did not succeed in former methods, and the sinking flux of the convection due to the water temperature difference of 1-3° between surface and bottom, this time, is equal to the mass transfer coefficient due to the velocity of the wind of 3-5 m/s.

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We have to estimate an action of a schooI of fish and must surround a schooI of fish in a short time with American-type bonito-tuna purse sine operation. The net length of a purse seine of the Kakuyo-maru which belongs to the Faculty of Fisheries at Nagasaki University is decided. It is necessary to grasp it for size of the tuming circle that corresponds to a speed and a rudder angle, and for necessary time. By means of GPS, we measured a tuming circle of the fishery training ship Kakuyo-maru that has Americantype bonito-tuna purse seine operation equipment and can operate with a mono-ship. In result, we were able to measure the size of each tuming circle around a right and a left tuming at three kinds of speed and rudder angle. The necessary tuming times of the Kakuyo-maru differs by speed and rudder angle. However, if rudder angle is more than 15 degrees, the size of tuming circle of Kakuyo-maru was able to confirm that, inside the limit of a size of a circle that corresponds to a length of a purse seine net.

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In the present study we examined the effect of the bottom condition of fishing grounds on the cuttlefish basket trap. To evaluate which fishing grounds is superior for cuttlefish basket trap we calculated CPUE (kg/ trap/day) at two different fishing grounds (off Ariake Town fishing ground and off Fukae Town fishing ground) in Shimabara Sound in 1996. We carried out the sediment analysis of the bottom samples collected by SM-grab (0.05m2) in each fishing ground. The Mdφ; of off Ariake and off Fukae were -0.3 to 3.0 and 1.0 to 1.5 which were limited range against the whole Shimabara Sound (-5.4 to 5. 6). In addition off Fukae is narrower than off Ariake and the sediment type of off Fukae is medium sand suggesting that bait density of former fishing ground is higher than later fishing ground. In fact CPUE of off Fukae Town fishing ground (0.46) was 2-fold greater than that of off Ariake Town fishing ground (0.23). The significance of differences in CPUE between two fishing grounds was verified by taken together Mam-Whitney test ( p<0.05). These results suggest that the medium Sandy sea bottom is more preferable for capturing of golden cuttlefish by the cuttlefish basket trap.

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LOP (Line of Position) distortion of LORAN-C (Long Rang Navigation System-C) Northwest Pacific Chain (8930 chain) was investigated at Sagami Bay in 1996. The data of each LORAN-C station of W (Okinawa Gesasi), X (Minamitorisima), Y (Hokkaido Tokachibuto) and Z (Korea Pohang) were measured onboard a research ship under her cruising and at a fixed point in Tokyo. Though the LOPs shown in LORAN-C nautical chart are derived theoretically from assuming the ground wave. propagation along the sea surface, if land is contained in the paropagaiton path like coastal sea area, the delay of propagation time called secondary factor (SF) or additional SF (ASF) occurs due to the change of earth impedance and this leads to the LOP distortion. As the results of observation, the high repetition accuracy of 0.1μs of LOP was observed at the fixed point, and it was cleared that the large local distortion, which is caused by long land propagation and it attains to some hundred meters, are eXisting in Y and Z station’s LOP at Sagami Bay. In this paper, the influence of distortion for LORAN-C positioning accuracy is discussed and the proposal to improve the positioning accuracy is made.

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Accompanied with entry into force of United Nations Convention on the Law of the Sea, it is thought that the Exclusive Economic Zone (EEZ) will be set up in the East China Sea. In case of setting up the EEZ, the fishing boat of each country which operate fishery around a boundary line needs to determine exactly the operation position. Four States of Japan, Korea, China and Russia constructed Intemational Cooperative Chain of Loran C. So the coverage of the Loran C expanded all range of the Japanese nearby seas and the East China Sea. The authors measured a relative error of the Loran C on the basis of GPS at the East China Sea. Accuracy of measurement position with the Loran C 9930 chain was better than that of 8930 chain. We are able to expect the improvement of the Loran C position by setting up the correction figure of relative error with the Lorap C to the receiver.

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The pedometer readings for the 6 members of the deck section on board a 2,000 G.T. fishery training vessel were recorded twice・a day over 53 effective days during the New Zealand-Hawaii cruise in 1994-95. The influential factors in the walking activity of these members in the respective areas were sought by estimating the multiple linear regression equations on the presettable variables (number of days after departure and the AM-PM dummy variable) and the variables relating to the surface tonditions. The results obtained were summarized as follows : (1) Significant equations could be obtained for 16 cases (member x area) out of 30. Their distribution had no relation to the member and the area. (2) The actually adopted explanation variables in the equations differed according to the area even among the equations for the activity of the same members. (3) The decreasing trend with the increase in the variables showing the roughness of the surface conditions could be admitted for at most l/3 of the cases,)even when the variables showing significant correlation to the roughness variables were regarded to be adopted instead of them.

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In the contorol of active roll dampers such as a fin stabilizer, an active anti rolling tank and so on, it is very important to forecast on ship motions in irregular seas. In the many cases, the prediction model for ship motions in irregular seas is based on probabilistic considerations such as a typical conventional method with an auto-regression method. As an altemative to this conventional approach, a variety of techniques have been developed in recent years to deal with chaotic time series and to forecast complex time series generated by some deterministic mechanism. This paper describes the application of deterministic nonlinear short-term prediction by using reconstructed trajectories to time series data of angular velocity of ship roll motion and shows effectiveness of the method.

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Zostera, Seagrass beds, which are important components of shallow water ecosystems, have diminished due to land reclamation and water pollution in Japan. For this reasons, method to enhance Zostera beds is required for their restoration. In this paper, the distribution characteristics of Z.marina beds have been focused in relation to sheltering against disturbance to the sandy substrata by waveaction, off Kushiki, Naruto City, Tokushima Prefecture. Z.marina beds were rare and included annual plants in their population on the natural bottom in areas without shelter. Z.marina beds were abundant and perennial plants on the sheltered bottom by the breakwater inside of Kushiki fishing port. Heavy 10cm fluctuations in the level of the sandy bottom sediments caused by 2m (Hl/3) waves in winter were the limiting factor of formation of Z.marina beds in study sites.

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The artificial reef plays an important role in creating productive fishing ground and nursery. The aim of this study is to obtain basic understanding of the function of artificial reef which is closely related to the behavior pattem of fish. The first point of this study concems adequacy of the location of reef that has relation to the migration behavior of fish in coastal waters and to the reaction of fish to the reef. The second point related to the diel changes in aggregation of fish in the reef area in accordance with environmental water movement and underwater irradiance. The third point is that structural properties of the reef, such us a shape and a vacancy in the reef, has an effect on aggregation of commercial fish and cohabiting organisms including the young. In the last point, the current status of fishing activities in the reef area is described by vessel and gears used, fishing seasons and catches of target species. The reef area is used by various coastal fisheries with emphasis on fishes having high marketprice. Long-term artificial reef management is an important research subject to develop coastal fisheries and to sustain local fish stock in a favorable condition.

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