Water absorbing and desorbing properties of nylon monofilaments used for tuna long line fishing were investigated. Water absorbing experiments were conducted in distilled water at constant water temperatures, 10 ℃, 20 ℃ and 30 ℃. And, Water desorbing experiments were conducted at constant relative humidities, 20%, 60% and 85% at an air temperature 20 ℃. For water absorbing process, the amount of absorbed water (Qs (mg/cm2)) was represented as the function of time (t) elapsed, ln (Qs)=ln a十b ln(t), Where, a and b are constants. The amount of absorbed water (Qs) and the rate of absorption (Ra (mg/cm2. h)) depended largely on the Water temperature. For desorbing process, the following equation between the amount of water desorption (Qr (mg/cm2)) and time (t) was obtained ; Qr=a'+ b' ln (t), Where, a'and b'are constants. The rate of water desorption (Rr (mg/cm2.h)) was largely affected by relative humidity. The time (td) required for drying the nylon monofilaments can be estimated from the desorption equation, (6) when Qr= 0. The drying time (td(day)) estimated ranged 0.6-1.6 at relative humidity 20%, 2.9-9.1 at relative humidity 60% and ∞ at relative humidity 85%, respectively.

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A series of field tests was conducted by using a 12GT fishing boat with a 4 cycle marine diesel engine of 265kW/2,200rpm, for the purpose of finding out the cleaning effects in respect of fuel consumption and NOx As the results, it was revealed that (1) fuel consumption [kg/h] as well as NOx emission [kg/h] was reduced remarkably by cleaning propeller, rudder and bottom of hu11, especially the first one, which occupied as much as about 30 to 40% of the cleaning effect and (2) that the foul of boat before cleaning prevented her from sailing more than l0 knots, i.e, she could not sail in the range of speed of low NOx emission.

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This study was carried out in 1994 as a chain program for putting the tidal dam to practical use. The experimental dam was made by reconstructing a nursery facility for prawns in possession of Hukaura Fisheries Cooperative Association near the mouth of Uranouchi bay. The dissolved oxygen improvement effect of buoyant jet was examined as a factor of environment reformation by tidal dam. To identify the species of fish and shellfish living in the reservoir, they were caught at the reservoir gate when the tidal dam was demolished. The problems of the practical tidal dam was discussed. The tidal dam has several advantages. First it uses the tidal energy-an extremely stabilized natural energy. Second, it contributes to the environment improvement of bay area. Besides, it can do much for developing the sightseeing and leisure facilities.

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Fisheries produce large amounts of food, but consume enormous amounts of oil resources. Recently the total quantity of fuel used for fishing has reached about four miｌｌion tons a year in Japan, equivalent to half of the quantity of fish caught from the sea. It is important to reduce fuel consumption in order to prevent the waste of fossil resources. In this paper, the input and retum energies per one fishing unit were estimated from total fuel for fishing boats and the catch per year, respectively. The term 'the production efficiency of energy' can be defined as rate of retum energy to input energy. Using this rate, the efficiency of fishing methods was discussed.

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A towing live fish preserve is used for carrying the fish that are caught to a port of landing while the fish are alive. Research into the live fish preserve is needed because the demand for live fish is increasing. This research concems preserve used for carrying sardine at Nobase in Yamaguchi prefecture. The user requested the improvement of the flow in the preserve. We performed experiments using a one-tenth model of an actual preserve as the basic preserve in a circulating water tank. First, We cleared the flow in the basic preserve by the tuft grid method. Then, we measured the drag force. Secondly, we improved the preserve by making many holes on the bow-shaped cover in front of the preserve. The area ratios of the holes to the cover were 2. 2%, 7. 5%, and 15. 9%. We repeated the same experiments using these improved preserves. By the tuft grid method, a large vortex was confimed in the basic preserve. The vortex changed only slightly to the area ratios of 2. 2% or 7. 5%. But at the area ratio of 15. 9%, the vortex disappeared and the flow in the preserve became moderate and unifom asawhole.

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A survey, Via beam trawl, of the abundance, composition (plastics, metal, glass, fishing gear and others), and distribution of litter was conducted on the sea-bed of an area in the central portion of Tokyo Bay. From 5 years of surveys during 1989-1994, it was found that plastic items constitute the major part of the litter, accounted for approximately 60-80% of the total. In the survey over 5 years, the mean litter values in numbers and weight were several (2-6 pieces/ha) and 50-300 g/ha, respectively. There was not a significant variation in the amounts and composition of the:litter. This amount of litter accumulated on the sea-bed was not so large (several pieces per hectare), but they were widely distributed over the whole range of Tokyo Bay. Litter collected from the sea-bed consisted of both very soiled, old items which appear to have been submerged for a long period of time as well as about half of the items being new, Without much fouling and appear to have been only recently disposed of.

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Pelagic eggs and larvae of brown sole (Pleuronectes herzensteini) are transported from the spawning grounds near the Sado Strait in Japan Sea to the nurseries in the downstream of coastal currents. The success or failure of the transport could determine the year-class strength of the brown sole population in and around the Sado Strait. Since strong north-northwest winds prevail during the main spawmng period, wind-induced currents would contribute to offshore/inshore drift of the eggs and larvae. In order to expIore the wind effects on the transport process, numerical simulation was made usmg a three dimensional current model with a horizontal grid size of 2.5km and vertical resolution of 3 layers (upper : 0-20m, middle : 20-60m, lower : 60-bottom). It should be noted that, by adding the strong wind drift induced by northwest, west and north winds to the basic flow pattem in and around the Sado Strait, the percentage of eggs and larvae retained in shelf areas shallower than l00 m appreciably reduced, compared to that for the case of no wind. However, corresponding to the reduction by half in the inflow velocities below the middle layer at the open boundary of the model, the percentage of eggs and larvae retained rapidly increased under the west wind, while it further decreased under the north wind. This suggests that, in addition to the wind conditions, the inflow into the Sado Strait could affect the retention of brown sole eggs and larvae in the coastal nurseries.

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In order to clarify the physhical characteristics of jig for oval squid Sepioteuthis lessoniana, the authors investigated local varieties and the necessary qualities of fishing jigs for oval squid. About 280 jigs were sampled in 12 areas of Shikoku, Kyushu, Amami Islands, and Menado of Indonesia. Various dimensions of jigs were measured and the physical characteristics of the jigs were examined. The jigs were divided into two categories for quaptitative analysis : fish jigs and prawn jigs. The fish type was found in the Amami area only, but the prawn type was found in all areas. Two categrioes of jig had a common characteristic : the specific gravity was concentrated into l.0, and the location of gravity center from the probosics was about 40% of the total length of the jig. Based on the results, we may assumed that these were the basic characteristics of the jigs forl oval squid.

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