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.
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.
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.
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.
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.
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.