For reducing CO_2 emissions and fuel cost reduction, energy-saving modification is necessary even for existing fishing vessels. For this purpose, a fishing vessel with high Froude number, the reduction of wave-making resistance is important. In this study, the author discuss about the constraints in the case of applying the minimum wave-making resistance theory to an existing hull form. In this paper, the author reports on the calculation results, if the Cp curve of an existing hull form were fixed at several points. By the number of constraint is sometimes rippling Cp curve has been computed, it should be noted that the position and number of constraint was found. In addition, if the restraint is too small Cp value yielded a partial Cp curve becomes negative near the bow.
Previously, Shiotani et al. (2005) investigated the flow field in a rearing tank as a single-phase flow and carried out two dimensional calculations by finite difference method. However, the result did not always agree with flow visualization results. The most likely causes were the assumption of single-phase flow and the boundary condition, in which tank center-line velocity was set equal to that on the free surface. Therefore, we focused on improving the precision of the calculation. In this study, we considered the flow field as a two-phase flow and re-examined boundary conditions to more closely match the actual flow. The calculation was also performed using finer grid resolution than the former study. We found that the vertical vortex pattern in a tank changed from a single-pair vortex system to two-pair vortex system as aspect ratio AR (the ratio of water depth to tank radius) varied between 1.0 and 2.0, consistent with previously reported results. Moreover, clear corner vortices were found in both the region between the free surface and upper side wall, and between the bottom and lower side wall. With increasing AR, the vorticity increased at the upper region, and it was larger than that of the lower region. Furthermore, at constant aeration rate in the same tank, the maximum vertical velocity on the center-line at the tank increased with increasing AR. Our results indicate that both H and AR of the rearing tank should be considered for optimizing flow field in larviculture.
In this study, we developed a measurement method for the total length of white spotted conger eel Conger myriaster, caught with conger eel tubes, by using video images. In case of conger eel, the total length fails to measure the length of the line which was connected the snout and the end of the caudal fin, because conger eel swims meandering. To solve this problem, we made some points of division between the snout and the end of the caudal fin, and measured the length of the line connecting each point. The relation between the number of points and measurement accuracy was examined and this method was developed to a practical level with over eight points and a correction factor. This method was applied to an actual fishing operation, and 97% of total catch was measured without handling conger eel directly. Additionally, it could arrange a total length distribution every location by adjusting fishing location.
We conducted a research on behavioral patterns of different fish species in artificial reefs by attaching ultrasonic wave transmitters to jack mackerel Trachurus japonicas (total length ; 290-360mm) and red sea bream Pagrus major (total length : 228-249mm), which are migratory fish species, and scorpion fish Sebastiscus marmoratus (total length : 191-203mm) and rockfish Sebastes sp. (total length : 197-225mm), which are resident fish species. The behavioral research on fish species using ultrasonic biotelemetry technology enabled us to quantitatively identify gathering areas and residence periods of fish species in artificial reefs. Such data will help (i) scientifically evaluate effectiveness of development of fishing and breeding grounds utilizing artificial reefs and (ii) effectively set the size of efficient artificial reefs and formulate appropriate arrangement plans. It should be noted, however, that artificial reefs are used by diverse fish species, and that many artificial reefs are used primarily by young and immature fishes. Thus, to ensure behavior measurement of these fishes, it will be necessary to further reduce weight and size of ultrasonic wave transmitters and solve other problems including the limited recording time due to the battery capacity.
The FADs (Fish aggregating devices) are floating structures on the surface or under the surface which gather migrating fish. It is constructed 3 main part that floating devices, mooring rope and anchor part. The FAD concept was based on indigenous structures such as drifting wood, bamboo and seaweed that tend to aggregate migrating fish in natural condition. In this report, it is introduces about the FAD concepts, histories, design methods, using situations, kinds, specifications, installation and removing methods and some issues in Japan.
The first Fish Aggregating Devices that made fishermen enable to catch tunas efficiently with less time and fuel, were developed in 1982 by fishermen in Irabu, Okinawa. Fishery on FADs spread rapidly since the fishermen needed new catch resource that had decreased in coral reefs in early '80s. FADs built and set in the ocean by fishermen drift away in short term, so Okinawa Prefectural Government has introduced FADs with high durability in public works. There are about 200 FADs set by prefecture and fishermen's associations around Okinawa islands. This issue introduces how FADs are managed and used for tuna fishing in Okinawa.
Several hundred of FADs (Fish Aggregating Devices) were set offshore of Kagoshima prefecture. FADs (Fish Aggregating Devices) are very important and useful device especially for catching tuna and skipjack with poles and lines, trolling and vertical line. About 1200 tons of tuna and skipjack were caught by three types of fishing gear mentioned above in Amami area. Tuna and skipjack fishery in this area much depend on FADs (Fish Aggregating Devices). On the other hand FADs (Fish Aggregating Devices) has many problems. Those are accident of rost out that happened less than 10 years of planning period, fisheries adjustment for an illegal fishery by non-registration fishing vessels and the difficulty of estimating of fish aggregating effect of it.
Miyazaki prefecture government has been setting up five Surface FADs (Surface Fish Aggregating Devices) and 12 Sub-surface FADs (Sub-surface Fish Aggregating Devices) at the areas around Miyazaki prefecture offing and around Okinawa prefecture west offing since 1995. The Surface FADs and Sub-surface FADs have made it possible to catch tunas and skipjack tuna and dolphin with poles and lines fishing method and trolling and dolphin round haul fishery. These devises have Oceanographic Observation system and the information that takes has made fisherman deciding easier to go or not. And they have contributed to fishermen's safety operations. Recently Miyazaki prefecture government has developed new method of analyzing the effect of artificial fishing reef by using GPS-data logger. The result of track analysis shows that the these FADs are more important for fishermen in Miyazaki prefecture.
In Kochi Prefecture, surface type fish aggregating device for Katsuwonus pelamis and genus Thunnus is installed from December, 1984. In the Kochi ocean space, 15 sets of surface type fish aggregating device are fixed now. Among these, the apparatus which collects the situations of an oceanic condition is attached to three sets. Fishery operators utilize the information acquired from them, and judge whether it can sail out to fish. There are two kinds of surface type fish aggregating device, discus type and an ellipse type. Discus type is installed in the ocean space where oceanic conditions are severe. The Kochi prefecture fisheries experimental station investigates the effect on a fish catch every year. As a result, it turned out that the about 48 million yen effect per set is in one year. Proper arrangement is due to be considered in order to heighten an effect more from now on.