Plate-type heat-exchangers are increasingly used in the cooling systems of vessels. Those systems have numerous merits, whiie the disadvantage is decreased performance associated with the formation slime on the cooling surface of the heat-exchanger. A new cleaning system for plate-type heat-exchanger mixing particie of natural material in cooling water has been developed in order to solve the problem. Grains of walnut and zeolite, shell powder of scallop were used for the particle on the experiment. Evaluations of the slime removal efficiency were shown to be affected by kinds of the particle, injection quantity of the particle, flow of cooling water and washing time.

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The movement of the trolling depressor is important for catching the target species. The purpose of this study is to clarify the dynamics of the trolling depressor by using the data-logger. A fiume tank experiment was conducted to measure the tension of the line and the attitude and the angular velocities of the trolling depressor. The length of the main line was 2.5m. The flow speed was 1.10m/s. In this experiment, a two times larger model of the trolling depressor was used to install the underwater motion measuring unit. The acceleration, the attitude and angular velocities of the trolling depressor were measured by using this unit at the intervals of 0.01 seconds. As a result of the experiment, it was possible to clarify the change of pitching angle, rolling angle, yawing angle of the trolling depressor, and each periods were 0.7, 1.4, 1.4 seconds.

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Recently, thinned trees are used in artificiai reefs in Japan but their effect on fish aggregation, increase of periphyton and their usefulness have not been studied. We researched utilization of the thinned tree reefs by a fieldwork and questionnaire survey. Ten thinned tree reefs and the normal reefs those are not using any tree, were placed on the frontage of Shimonoseki city in the depth of 12m and 34m November, 2002. The change of a shape of thinned trees, fish aggregation and the increase effect of periphyton were observed in 7-9 times a year for 3 years. The utilization of the artificial reefs with thinned trees were examined by questionnaire survey for 39 fishery bureaus of the metropolises and prefectures and for 39 companies producing artificial reefs in 2005. As a result, artificial reefs with thinned trees contributed to early increase of periphyton including marine borers, and superiority was recognized in fish aggregation compared with artificial reefs that do not install thinned trees. In addition, some useful knowledge are also reported for the utilization and the durability of thinned tree reefs.

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A Micro Bubble Jetter (MBJ) was used in field experiments on improving bottom sediment quality in order to determine whether this new technology can prevent the mass mortality of shellfish during the summer season due to deteriorating sediment quality in the ark shell fishing ground in inner Ariake Bay. The MBJ is mounted on a small fishing boat and is used to draw up surface water and inject it with microbubles and to improve bottom sediment quality by directly squirting microbubbles into surface mud using a towed nozzle unit. Improvements in bottom sediment quality were measured by investigating surface sediment quality before and after the towed device (including oxidation-reduction potential [Eh] and acid volatile sulfides [AVS-S]), benthic organisms (wet weight, number of species, and numbers of individuals), and ark shell mortality rates. Using this method, there was an increase of 100〜200mV in Eh and a reduction of 0.1〜O.2mg/g DW in AVS-S in the region where the MBJ was towed compared with the control region. Moreover, a reduction in organic C, total-N, and total-P concentrations was observed in the region where the MBJ was towed. Finally, in comparison with the control region, there was a significant decrease in the ark shell mortality rate in the region where the MBJ was towed that was commensurate with amount of MBJ towing performed. Therefore, this study demonstrates that this method is useful in improving bottom sediment quality in inner Ariake Bay.

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琵琶湖のエリ漁には,漁場に吹く風が漁獲量に影響を与えるという伝承事項が古来から存在する。この伝承事項の発生は,湖面に強い風が吹いた時に湖水の水温が変化し,漁場へのコイの来遊に影響を与えるためと考え,2003年6月〜9月に,琵琶湖南湖のエリ周辺で水温,風系,コイの行動を測定した。本エリで漁獲されたコイ4尾の腹腔内に超音波発信機を装着し,受信機を設置したエリ周辺で放流した。その結果,最大で95日間にわたって供試魚の出現を測定することが出来た。記録計によってエリ周辺の水温2層(2.5m, 4.5m)を15分間隔で測定した。供試魚は水温が25℃以下の間はエリ周辺に出現したが,25℃を超える水温上昇に伴いエリ周辺を離れた。その後,南西あるいは北東の強い風が吹き,急激に水温が25℃前後に低下したあとに供試魚は再び出現した。本研究の結果では夏季におけるコイの行動と急激な水温低下現象との間に一定の関連性が認められた。

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Marine afforestation of Ecklonia cava by using a net cage for protection from grazing was examined in the Hainan Isoyake area of Shizuoka Prefecture. Algal reef blocks made of concrete were placed on the bottom of a rocky reef at 12 meters deep in October 1997,onto which hundreds of E. cava plants grown in a water tank were transplanted. The E. cava plants were covered with a net cage for protection from grazing by herbivorous fishes, and the net cage could be removed in the winter, when grazing pressure by the herbivorous fish Siganus fuscescens, decreased. E. cava plants consisting of multiple-year classes survived on the algal reef blocks with a net cage in the summer of 2000, and many young plants spread over the natural rocky reefs around the algal reef blocks. The E. cava that spread around the algal reef blocks were grazed by S.fuscescens in the autumn and disappeared. However, E. cava spread again in the spring of the following year and grew in the summer.

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The sea urchin Strongylocentrotus nudus is commercially important but their intensive grazing often leads to the formation of extensive, unproductive barrens along the coast of northern Japan. A simple device that could defend urchin invasion and allow kelp to grow by utilizing waves was developed after repeated field experiments with test devices. The final device for practical use had a swing bed that consisted of a horizontal shaft with frames for kelp settlement and growth on both sides and a plate on the underside. The swing bed was supported with two columns and was swayed by hydrodynamic force on the plate bearing wave-induced oscillatory flows. Invasion by urchins into the bed was prevented primarily in moving from the column to the constantly moving surface of the shaft. To enhance the relative movement of the swing element to the immobile supports, disks were attached to the shaft and to the columns with interstices. The device that was placed in S. nudus-dominated barrens protected from ocean waves successfully prevented urchin invasion into the swing bed leading to the formation of a canopy by the perennial kelp Eisenia bicyclis.

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伊勢湾東部沿岸のサガラメ藻場が残存している内海地先と消失した豊浜地先において,アイゴの季節的な分布を比較するために,2004年に小型定置網のアイゴの漁獲を調査した。豊浜地先は内海地先に比べてアイゴ未成魚の個体数が多く,成魚の滞留期間が長かった。また,伊勢湾東部沿岸及び三河湾沿岸のアイゴの季節的な分布を推察するための,小型定置網漁業を営む漁業者に対する2004年のアイゴの漁獲の聞き取り調査から,成魚,未成魚ともに三河湾が分布の中心であることが示された。豊浜地先は内海地先に比べてアイゴの分布の中心である三河湾に近く,アイゴの摂食圧を大きく受けると考えられた。伊勢湾東部沿岸においてサガラメ藻場を再生するためには,移植した種苗を9月から12月にかけてアイゴの摂食から防御することを提案した。

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In recent years, the heavy infestation of giant jellyfish (Nemopilema nomurai) has been affecting coastal fishery in Japan. The authors analyzed, as a case study, working process in set-net operation in the Hachinohe coast in northeast Japan. By evaluating work posture during the operation using a "pain index", they quantitatively showed the load of fishing workers when giant jellyfish entered the net. Fishing workers scoop a large amount of jellyfish, which cannot be commercialized, after hoisting the net, and then collect useful fish species such as salmons. In the case reported here, fishing workers used to spend 61 min for scooping giantjellyfish, while spending 54 min for hoisting the net, 14 min for collecting fish and 20 min for releasing the net. During the scooping operation, overburdened work posture was repeatedly forced.

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