Covered-codend fishing experiments were conducted with using square mesh top window of four different types attached at the anterior half of the codend. Top window of three lengths: 4m, 3.5m, and 3m lengths with square mesh of 90mm nominal mesh size (81mm mesh opening) were tested, compared with 4m-length square mesh panel of 80mm nominal mesh size (72mm mesh opening). Individual haul selection curves and the mean selection curve of each codend type were estimated for blackthroat seaperch Doederleimia berycoides and for white-spotted conger Conger myriaster by maximum likelihood method with SELECT process considering sampling fraction. There was large variation in individual haul selection curve, and no effect of total catch size in codend on the selectivity parameters (50% retention length and selection range) was found. Differences in mean selection curve were found between window-lengths by the AIC model selection. The 50% retention lengths of 4m-, 3.5m- and 3m-window length were 14.1cm, 14.6, and 13.6cm in total length for blackthroat seaperch, and 28.1cm, 29.5cm, and 24.5cm in pre-anal length for white-spotted conger, respectively. Effect of window length on size selectivity of the codend was remarkable for white spotted conger, rather than for balckthroat seaperch. To reduce the bycatch of small-sized blackthroat seaperch while retaining marketable white-spotted conger as much as possible, square mesh top window of 3m length is preferable.
It is common knowledge that the receiving distance of ultrasound in water varies in inverse proportion to the transmitting frequency. However, empirical data has been obtained mostly from experiments in water tanks and this relation has not been sufficiently tested in ultrasonic biotelemetry under field conditions or moving objects. In this study we investigated the effect of transmitting frequencies of 51, 63, and 78kHz on receiving distance under field conditions when the transmitter and receiver were either drifting, approaching or getting farther in relation to each other. The results show that receiving distance estimated in the field is shorter than that in water tanks and that unlike in the latter it is virtually constant with moving objects regardless of the transmitting frequency.
The growth of abalone, Haliotis discus hannai, cultured in a multi-tiered, continuous-flow system (MTCFS), was examined to determine the effects of density and tank position in a MTCFS, from mid June 2007 to the end of March 2008, at the abalone culture facility in Fukushima-chou, southern Hokkaido, Japan. Mean shell length and body weight of abalone at the start were 34mm and 5.3g. After 290 days, they grew to 56.7mm, 53.7mm, and 53.0mm in shell length and, 25.3g, 22.3g, and 20.6g in body weight for the high and low density groups in a MTCFS, and for the cage cultured group, respectively. Density in the cage cultured group was kept at the same density as the high density MTCFS group. Mean shell length and body weight increased most in the low density MTCFS group. At the same density, the weight of abalone cultured in the MTCFS was significantly higher than in the cage cultured group, but the shell length did not significantly differ between the high density group and the cage cultured group. The size of the abalone, 119days into experiment, differed depending on the tank's position in the tiered system. Shell length and body weight were bigger in the upper tanks and smaller in the lower tanks. As more food leavings and feces remained in the lower tanks, water quality was suggested to be the most important factor affecting the growth of abalone in relation to the position of a tank in the multi-tiered continuous-flow system.
Two problems of the reduction of the fuel consumption using spreadsheet software are taken up for the energy saving of coast fishing vessels. The first problem is the optimization of the principal dimensions of a fishing vessel for every Froude number, using the nonlinear programming system of spreadsheet software, the estimation charts of the effective horsepower for small FRP boats and their regression equations. The optimized hull forms have the narrower beam and the deeper draft at low speed, but have the wider beam and the shallower draft at high speed. In the results of the optimized calculation, the effective horsepower reduced about 10%. The second problem is optimization of the round trip speed of a coastal fishing vessel. The product at the effective horsepower and the sailing time is made the index of the fuel consumption. The combination of the best round trip sailing speeds is obtained for sailing time. Pareto charts show the minimum fuel consumption for sailing time.
Fishery works by fisherman are essential for fishery and making improvements of working environments for fishery work in the fishing boat would be more and more important in relation to the sustainable fishery production. These working environments are characterized by ship oscillating motion, limitary space for work and rest. In addition to these items, hours of work have significant impact on the characteristics of fishery work. In this report, the characteristics of working environments in the fishing boat are made a summary through research results and criterion value to provide a source of perspective on improving the working environments for fishery work.
Acoustics is the most effective tool of underwater remote sensing, and so fish finder using ultrasonic has been used from the 1950's. Many new digital acoustic instruments have been developed for these 20 years by advanced technologies of digital signal processing, PC, and mass storages. A quantitative echosounder to estimate the size and amount of fish is one of the equipment most evolved in the past 20 years. The recent system can measure not only large adult fish but also, larvae, micro nekton, and zooplankton with high resolution. As echo from an animal is changed on various conditions, such as size, species, action, maturity, etc., in order to estimate these details from echo signals inversely, it competes for the development of multi-beam quantitative echosounder and analysis technology using multi-frequency or broadband sound.
Fishing boat is wide variety of use, size and locality. And environment surrounding fishing vessel is vastly-complicated. After classifying studies of such as fishing vessel in Fisheries Engineering, these were classified into two general groups: safety and energy saving. The study of safety was classified as either solving a problem with mechanically-processed method or basic study for safety. The Study of energy saving was classified as either introduction of new technology or improved operating procedure of existing equipments. However, these studies did not contribute much to the breakthrough in fishing boat fishery remained relatively stagnant. On the other hand, inexpensive way such as improved operating procedure of existing equipments begin to be required as fishery household economy faltered. As more young are moving away from the fishing boat fisheries, Japanese fisheries need a construction of attractive fishing boat which satisfies safety, workability, habitability and economic efficiency.
In the past two decades technologies innovations have increased performance of underwater fishery ultrasound equipments and also have created new functions such as fish size measurement, school abundance measurement, fish classification and bottom classification. Furthermore quantitative scanning sonar system enabling abundance estimation of fish schools by using quantitative echo data has been developed.