桝網にはいる魚は嚢の位置・網の種類をどのように選擇するか-I : カイズ・クロダイ

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“Masu-ami” is a common type of trap nets for use in shallow wate: fisheries in Japan. The net is constructed with three main parts, a lead net, fence and bags, as shown in Fig. 1. In general practice three or more bags are placed at different position of the fence. Fishermen haul the bags once or twice a day to capture the fish which have entered in to them. The purpose of the present study is to examine fishing efficiency of the bags which may vary depending upon their positions in the net and thread materials used for the bags. A factor as to whether or not the bags have been dressed with a dye may also have different effect upon the catch. For this reason series of experiments were carried out at two fishing grounds in Ka-nagawa Prefecture during the periods of May to December 1951, and March to November 1952, using from three to five bags per set for a test as shown in Figs. 3-5. Each of the bags was made of different materials of thread such as nylon, vinylon andcotton which were either dyed or not dyed. From the results indicated in Tables 1-4 and Figs. 6-9, we may assert the following: 1. If all the bags of a net were made of the same kind of a thread material and a dressing dye, the catching ratio of each bag is nearly constant in accordance with their respective position in the net throught a period of the test. The catching ratio by position may be summarized as follows: i) The net at Ottomo, May 17 to December 27, 1951 Position of Bags I II III IV Catching Ratio (S%) 11 39 39 11 ii) The net at Natsushima, June 9 to November 25, 1951 Position of Bags I II III Catching Ratio (S%) 14 31 55 iii) The net at Natsushima, March 9 to November 11, 1952 Position of Bags I II IV V Catching Ratio (S%) 18 32 32 18 S%: Strength of selective action of the fish for a bag position calculated by dividingthe catch of a bag at a position by the total catch of the net. No bag used at the position III. 2. When the bags, each made of a different material and dressing, were used together in the same net, a nylon bag dyed in blue was found more efficient than any other bags. Both the bags of non-dyed nylon and of the one dyed with cutch followed the blue nylon bag in their efficiency. The bags made of either vinylon or cotton had good catch, too. However, when dyed with cutch, they were-not so effective as the ones used without being dyed. The cotton bag dressed with coal tar had the poorest catch among them. This conlusion has been drawn on the basis of the following calculation and comparision. Let S represent the strength of selective action of the fish for a position of a bag, and E the strength of selective action of the fish for a kind (thread material and dressing) of a bag. Then the strength of a bag at a position prepared in a certain kind may be expressed by SE. As the value of S corresponding to a bag at a position has been determined as above, the value of SE will be obtained from experiments (Figs. 8-9). Take the test 5 in Fig. 8 for example. SIEV=14.3 SVEV=8.6 SI=SV=18 4; 18EV+18EV-14.3+8.6 4; EV=0.64 SIIEA=28.6 SIVEA=48.5 SII=SIV=32 4; 32EA+32EA=28.6+48.5 4; EA=1.24 Accordingly EV:EA=0.64:1.24 ?? 1:2 Here SI to SV denote the strength of selective action of a bag when placed at the positions I to ∇ ; and EV, EA the selective strength of a bag made of vinylon or nylon respectively. Table 6 and Fig.
公益社団法人日本水産学会の論文

著者

宮本秀明
東海区水産研究所

桝網にはいる魚は嚢の位置・網の種類をどのように選擇するか-I : カイズ・クロダイ

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