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.

抄録全体を表示

米国式カツオ・マグロまき網操業においては,魚群行動を予測し,短時間で魚群を包囲しなければならず,また,まき網の長さ(鶴洋丸では1350m)も決まっているため,自船の速力と舵角に対応する旋回圏の大きさや,旋回所要時間を把握しておく必要がある。著者らは,米国式カツオ・マグロまき網操業装備を擬し,単船操業ができる長崎大学水産学部漁業練習船鶴洋丸の旋回圏の測定を GPSを用いて行った。その結果, 3種類の各速力,各舵角での左右旋回時の旋回圏の大きさを測定できた。鶴洋丸においては,速力と舵角によって旋回所要時間に差はあるものの,舵角15度以上であれば,ほぼ網の長さに対応する直径の範囲内で旋回することが可能であった。

抄録全体を表示

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.

抄録全体を表示

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.

抄録全体を表示

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.

抄録全体を表示

1994-95年に2,000GT型の漁業練習船が行ったニュージランド・ハワイ航海において,甲板部乗組員6名の歩行活動を記録し,それに及ぼす兢海日数と海面状態に関する諸要因の影響を航行海域ごとに分けて調べ,次の結果が得られた: (1)有意とみなせる重回帰式は30例(人×海域)中16例に関して得られ,それらの分布は海域と乗組員によって異なる。 (2)有意とみなせない式を含め,各乗組員の歩行活動に関する最良重回帰式に取り入れられた説明変数は,乗組員によって異なり,同じ乗組員の歩行活動に関する式でも海域によって異なる。 (3)海面状態の荒さを表す変数と相関を示すために他の変数が代わりに取り入れられたとみなしても,海面状態が荒くなるに従って歩行活動が低下する傾向は1/3の例にしか認められなかった。

抄録全体を表示

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.

抄録全体を表示

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.

抄録全体を表示

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.

抄録全体を表示