The detailed topographical changes of the inshore area caused by the sea waves have yet to be elucidated. One of the reasons is the difficulty of inspection of shallow areas by usual vessel due to danger of the stand or overturn. However, the demand to catch correctly the inshore topography is of great importance for the coastline preservation. Recently, the miniaturization of the measurement devices made a rapid progress due to technological innovations. This has stimulated the intensive use of the Real Time Kinematic GPS (RTK-GPS) technology featuring an extremely high accuracy about the vertical axis for maritime measurements. The accuracy characteristics of the RTK-GPS allow the detection of the vessel heaving. In this paper, a system for safety sounding is proposed, and the testing results are discussed. The system equipment includes the RTK-GPS, echo sounder, motion sensor, magnetic compass, indicator and cellular phone, which are mounted in personal water craft. An original short-range echo sounder was newly designed to meet the demands of limited working space. The transducer of the echo sounder was fixed to the inside of the bottom to prevent possible damages in the case of stand. It has been found experimentally that the proposed sounding system with use of personal water craft is accurate to better than 0.1m.

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In Mikawa Bay, central Japan, where hypoxia is observed annually, water temperature and oxygen concentrations near the bottom were measured continuously for about two months during the summers of 1997 and 1998 Samples of macrobenthos were also collected at weekly intervals. In order to analyze the factors causing temporal variation in the macrobenthic community, a new index called the "cumulative relative sensitivity index of mortality by hypoxia" ("czox") was proposed by the authors. The czox index is calculated from water temperature and oxygen concentration data. This study examined the relationship between the czox index and the biomass of dominant species, water purification and biodiversity of the macrobenthos. Relationships between czox and these parameters were examined using regression analyses, etc. These analyses represented well previous knowledge about relationships between the environment and macrobenthic community. This suggests that it is possible to predict changes in the macrobenthic community structure and function when oxygen concentrations change with human activities such as environmental habitat restoration.

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小型漁船の横揺れ応答は船型の特徴から波等の外力に対し一般に強い非線形性を示す。操業状態では,船体規模に比べ大きな漁具を使用し,船体を漁業施設に係留する等それぞれ漁業形態により操業過程で複雑な外力が作用する。これら外力の船体横揺れ応答への影響は極めて大きい。さらに,漁獲物の揚収により載貨状態が短時間で大きく変化する。荒天下操業時に発生する大振幅横揺れ等から危険を回避するためには,操業状態に即した小型漁船の横揺れ応答系を適切に推定する必要があるが,物理モデルでは困難なことから柔軟な学習能力を有するニューラルネットワークモデルの適応を試みた。本報では北海道内浦湾のホタテ貝養殖漁船を対象に,リカレント型ニューラルネットワークを用い実船実験に基づく横揺れ運動の予測モデルの構築を行った。その結果,養殖施設への上下方向の係留張力と,左右・上下方向の加速度を人力とした簡単なモデル構造で十分な精度の横揺れ運動の予測が可能となった。

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Yearly changes of concentration of nitrate and phosphate in Tomari, Hokkaido, Japan, from 1986 to 2001, were analyzed. Mean concentration of nitrate at 0m depth was 2.2±1.6SD (range, 0.3-6.1) μM. Gametophytes of Laminaria religiosa were cultured for 29 days in different nitrate concentrations (+0.0, +1.0, +2.0, +3.0, +4.0, +5.0, +6.0μM) in order to examine the effects of nitrate on the growth of gamethophytes in batch culture. Cell number of the gamethophytes increased at concentrations of more than +4.0μM nitrate. To observe the effects of deep seawater on growth of gamethophytes of L. religiosa, the gamethophytes were cultured in deep seawater at Otaru, Hokkaido, Japan, (concentration of nitrate, 15.8 μM) and in surface seawater at Yoichi. Hokkaido, (mean concentration of nitrate, 4.4μM) under laboratory conditions. After 29 days from start of batch culture, cell number in the deep seawater was 2.6 times of the cell number in surface seawater.

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前の3報に続いて,海中に設置した電極に微弱電流を流すことにより,海洋生物の付着を防止する試みを行った。水産大学校桟橋下と近くの海面に測定板を沈め,測定板への生物付着状況を調べた。2000年5月30日から10月2日までの4ケ月間(第1期)と,同年10月11日から翌年1月12日までの3ケ月間(第2期)に分けて実験を行った。電極には白金メッキされたチタン細線を使用した。あらかじめ,電極間隔および電極長と電流との関係を調べ,電極間隔50cm・電極長3mmの粂件のもとで,8V・数十mAの電流を常時印加した。海中に設置された電極に流れる電流は,電極間隔にはほとんど依存せず,電極長に大きく依存することが確認できた。8V・数十mAの電流を常時印加することにより,第1期と第2期を通じて,付着性の動物,特にフジツボに対しての周年の付着防止効果が確認された。ただ,第2期では,海藻類に対しての付着防止効果は認められなかった。しかし,海藻以外の付着生物(特に動物)は明らかに対照区に多く,8V・数十mAの電流による付着防止効果が認められた。

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漁業において,漁具は魚を捕獲するために欠かせない道具であり,その種類,構造,規模は千差万別である。漁業の全盛期では漁獲性能の向上を目指した漁具の研究が中心的に行われてきたが,近年では混獲防止・分離漁獲型漁具など資源保護型漁具の開発研究が進められている。こうした漁具の設計・開発には,漁具の性能を把握することが何よりも重要である。ここでは,曳網漁具を中心に漁具の設計・開発のために不可欠な網地や拡網板などの流体力学的特性,操業時における網の形状や流れから受ける抵抗,さらに漁具を開発する際に行われる模型実験における相似則,中層トロールの網位置制御などについて,理論と実験の両面から捉えて行ってきた研究について述べる。

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In order to estimate fishing net configuration and load numerically and visualize them dynamically in 3-D images using a PC, we have developed "NaLA", which is a system for determining net shape configuration and load. The numerical simulation system can provide useful information to fishermen, fishing gear manufactures and researcher for evaluating fish stocks, since, in general, it is not easy to fully understand shapes of fishing nets underwater and the influence of the dynamic behavior of a fishing net gear on capture processes. In this report, numerical simulation methods about fishing net configuration, which have been developed by other research institutes, are reviewed, the outline of NaLA and examples of computational results by NaLA are introduced and we consider the role and potentiality for the numerical simulation technique to estimate fishing net configuration and load.

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Offshore trawls in Hokkaido have been operated with a pattern of production on a large scale since the end of World War n. However, due to the 200 mile exclusive economic zone set by Russia (Old U.S.S.R) in 1976, and the serious deterioration of the domestic economic situation in 1990's, it has became more difficult for the fishermen and fishing firms to continue the pattern of production on a large scale. The purpose of this paper is to devise a new style of management strategy of offshore trawls in Hokkaido. In this study, I interviewed the fishermen and also individuals from relevant organizations. Further more, I examined several sources of statistical data concerning fisheries production. In conclusion, necessary conditions for a new management strategy of offshore trawls in Hokkaido are to curtail the labor cost that accounts for the greater part of the fishing cost, and to improve the financial structure. I propose two schemes that meet these two conditions as follows: (1) to change from onboard to on-a-wharf fish sorting work that needs a large crew; (2) to start joint management or just joint contorol of production facilities. When these schemes are implemented, it is desirable that as many firms as possible should join the project.

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In this paper the authors describe recent tendencies and causal factors of fishing vessel sea casualties. Then, we introduce recent developments in capsizing prevention technology, including capsizing mechanism study based on model experiments and onboard stability device. From view point of establishing safety securing system for existing fishing vessels, the possibility of real-time forecasting of encountering waves and development of decision support tools for safe and effective operation are discussed.

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