In order to observe of fish behavior to the set net, a radio transmission system for underwater video image was constructed and tested. This system consists of a transmitting station on the sea and a receiving station on the land. The transmitting station is composed of an underwater video camera, a video transmitter, a transmitting antenna, lead-acid batteries, a cellular phone and a sound sensor for remote control of power supply. The underwater video image is transmitted to the receiving station with microwave of 1.2 GHz. The receiving station is composed of a receiving antenna, a video receiver, a monitor and a VCR. The maximum transmission distance of the system was measured with about 7 km on the sea. The test run of the radio transmission system for underwater video image was conducted on the set net fishing ground in Tateyama Bay, Chiba Prefecture. The underwater video camera was installed in front of a funnel net to observe the fish behavior to the final trap of the set net. The transmitting station was moored near the final trap and the receiving station was set up in the Banda Marine Laboratory of Tokyo University of Fisheries where is 1.5 km away from the set net. The test run lasted for 23 days in November, 2002. A total of 60 hours of the underwater video image were recorded and the fish behavior of 18 species were observed clearly during the test run. The inshore fish such as rudderfish Kyphosus vaigiensis, filefish Stephanolepis cirrhifer and blackfish Girella punctata frequently swam in and out the final trap through the funnel net. In contrast, yellowtail Seriola quinqueradiata did not escape from the final trap except for only one fish. The radio transmission system for underwater video image is useful equipment for the rationalization of set net fishery.

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北海道日本海南西部沿岸ではホソメコンブやフシスジモクの分布が極浅所に限られ,海底は無節サンゴモが覆い,その上にはキタムラサキウニが優占している。そして藻場造成のためにはキタムラサキウニの食圧制御が必要である。小樽地先のサンゴモ平原上のキタムラサキウニを除去し,ホソメコンブ群落を造成した。しかしホソメコンブの現存量には,冬季の水温や平均底面流速が大きく影響した。水温と栄養塩には関係があるため,泊地先における冬季の硝酸塩濃度の平均と範囲を解析した。そして平均的な濃度の範囲におけるホソメコンブ配偶体の細胞数増加速度と硝酸塩濃度の関係を,室内実験で求めた。細胞数の増大は4.0μM以上で見られ,細胞数増加速度は濃度と共に上昇した。寿都地先におけるフシスジモクの繁殖時期を明らかにし,繁殖時期前にキタムラサキウニの漁獲を行ったところ。フシスジモクの現存量は急増した。漁獲時期の管理によるフシスジモク群落の長期的な維持を実証した。

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キハダの鉛直方向の分布について,水温に成熟を加えた要因が相互に関連して影響を及ぼす可能性が高いにもかかわらず,従来の研究では水温を主な要因として捉えるだけの検討にとどまっていた。本研究では要因としてキハダが分布する水温と成熟との関係に着目して,成熟個体が多獲される可能性の高い海域(ソロモン諸島北東海域)および時期を選び,延縄操業と海洋観測を実施することにより以下を解明した。鉛直方向からみたキハダの分布深度およびその位置における水温の範囲は,それぞれ「80-150mおよび25-29℃」であり,既往の研究成果と比べて,浅く,かつ高水温の環境であった。この原因として,本研究で釣獲されたキハダは,既往の研究成果よりも,「成熱度が高く,浅・高水温の環境で産卵する個体」であったことが強く影響を与えたものと推察した。

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In this paper, we discuss the optimization of the high-pressure-water washing system used in the recycling process for polystyrene-paper(PSP) trays used for wrapping fishes, which is expected to reduce the cost of recycling and environmental load. The washing time and energy required to clean a test tray were measured under various water pressures and flow rates. Two criteria for optimization in terms of energy saving and cost saving were developed on the basis of the measurement results, the respective optimum washing conditions were then calculated. Moreover, we proposed a method of searching for the optimum condition that gives the lowest cost under a given allowable energy consumption.

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Zostera marina L. form dense populations on shallow sandy and muddy bottoms in inner bay areas, and play important roles from ecological and fisheries points of view. In this study, photosynthesis characteristics of Z. marina were examined under several light intensity and the water temperature conditions, and the daily net production was estimated. Samples were collected from Miya in Mikawa Bay, Aichi Prefecture, Japan. Photosynthesis and dark respiration rates were measured under various light intensity and in situ temperature condition using a product meter and oxygen electrode system. Z. marina showed high light-saturated net photosynthetic rates(1.5〜7.6mgO_2 gd.w.^<-1> h^<-1>). Dark respiratory rate of Z. marina was between 0.4 and S.SmgO_2 gd.w.^<-1> h^<-1>, I_k values and compensation points ranged from 88 to 129μmol m^<-2> s^<-1> and from 13 to 111 μmol m^<-2> s^<-1>, respectively. Daily net production of Z. marina was estimated from the model equation of photosynthesis-light curve and the data on light intensity sampled in Zostera bed. High dark respiratory rate and low light intensity in the population lead to low net production, and result in withering and loss during the early summer season.

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Various techniques, for example, swinging chains, jet of compression air, and underwater bulldozer etc., were introduced to remove needless seaweeds as a countermeasure of barren grand. These removal effects, however, were not yet reported so much. Then, improving the occasion when fishermen's cooperative association removed needless seaweeds using underwater backhoe in waste Laminariajaponica beds off the Ohma-cho, Aomori prefecture, we made investigations into effects of seaweeds removal from December 1999 to June 2003. As a result, the good insertions and growths of Laminaria japonica were observed in every surveyed areas after removing seaweeds. But, with the lapse of time needless seaweeds began inserting again and their intermixture rates were about 17.0% in wet weight in the removal ranges from 30 to 42 months. It is suggested that the durations of removal effects are estimated to be approximately 3 years.

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The spatial distribution of genotypes in Zostera marina L. community in Ise Bay using six microsatellite markers was examined. Allele sizes of six microsatellite markers were the same between rhizome connected shoots in Kosugaya community, but different at the other shoots. This result shows that these microsatellite markers can discriminate individuals and be useful of studying community structure in Z. marina. This fact suggests that most of the reproduction in Kosugaya community was maintained by cross-fertilization and seeds transferred from some other community. And also the distribution of vegetative reproduction was found to be within the limits of about 0.5m. These reproduction structure showed in Kosugaya community seem to be caused by geographical features of the seabed.

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During the period from 1987 to 1994, the harvests of Japanese short-necked clam, Ruditapes philippinarum, were kept between 98 to 160 tons each year on the estuary of the Banjyo River in Saiki Bay. However the harvests sharply decreased to 14 tons in 1995. We, therefore, examined the sexual maturity, recruitment, growth of the clam and environmental factors in the ground from 2001 to 2004 to find out the clam population factors. In environmental factors, water temperature ranged 12.1-30.0℃ on the bottom of the water, 9.7-28.2℃ on the tidal flats, and salinity ranged 6.8-10.6psu on the tidal flats at low water. At various ground levels, emergence of tidal flats was about 3-7 hours during spring tides and river discharge in normal year was lower, below 20m^3/sec. The population maturity rate increased from the middle April to the middle November and reaches its peak from September to October. Therefore, the main spawning season for the clams seems to be in autumn. After settlement, the juvenile clams with 5-8 mm in the average shell length appeared from July to September in the ground. The origin of this recruitement was estimated in the previous autumn fisheries population. The length frequency analysis shows that the clams grow up to 9-10mm in shell length for age of 1 year, and 18-20mm in shell length for age of 2 years. This growth rate is lower than those in the Ariake Sea, Maizuru Bay and Tokyo Bay. We suggest that the lower growth rate of the clam results from low salinity, long emergence hours and low river discharge.

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To understand the establishment process of Sargassum horneri stands, seasonal colonization and coverage of seaweeds on experimental substrata set in a S. horneri community were researched for about three years. The substrata(concrete plates : 50 × 50 × 5cm) were designed to have a similar height with that of natural substrata of S. horneri and set every two months from June 1998 to April 1999. During the experiment, total 42 seaweed species appeared on the substrata and six species among those became dominant(>25% coverage on any of the substrata). Ulva pertusa, Laurencia sp., Padina arborescens, Sargassum fusiforme and S. thunbergii became dominant mainly in the first year on different substrata set in different seasons, but their dominance was seasonal and temporary. In the second year, a number of young S. horneri plants succeeded to colonize and became the only dominant species forming mono-specific stands on all the substrata. Mass colonization and dominance of S. horneri also occurred in the third year. In this report, specific conditions of the habitat leading to the sustainable dominance of S. horneri were discussed, especially referring to the characteristics of the substrata.

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