Troll Line Research Articles

曳縄漁具に対する魚の行動の水中観察

In order to understand the capture process of trolling gear, the fish response towards a trolling line was observed by a towed underwater video camera. Fishing tackle consisted of a main line, a depressor board, a leader line, and a lure. The underwater video camera was mounted on the depressor board to observe and record the sequence of responses towards the lure. Fish species that could be identified, were yellowtail Seriola quinqueradiata, frigate mackerel Auxis rochei, amberjack Seriola dumerili, and mackerel Scomber japonicus. Behaviour patterns were classified as follows: appearance into the camera view, approach to the lure, attack on the lure, touching the lure, being hooked, and captured. The total number of appearances in the camera view was 1361, in which the catch was only 18 due to the low attack response frequency to the approaches. A slight difference was also observed on the proportion of missed-hookings, which was attributed to the difference in struggling escape behaviour between yellowtail and frigate mackerel.

道糸張カから推定した曳縄漁具の動き

In order to solve problems of the characteristic movement of trolling gear, experiments were conducted in Kagoshima Bay in calm conditions by the research ship, Nanseimaru (83 G. R. T.). The tension of trolling line using two kinds of leader, i.e. nylon monofilament and sekiyama (ganged wire leader) for trolling depressor, were measured by a load cell which was fixed at the tip of a steel pipe, and were recorded on a data-recorder. These data were analyzed in the laboratory. Power spectra were estimated from these data. Dominant fre-quencies in these spectra were identified; one was a frequency of 0.2Hz ley with a propor-tional speed increase, while the other was a the frequency of 6.0Hz with a slight proportional speed decrease. The former occupied a major portion of the spectra, which suggested the movement of the whole trolling gear. The movement of the trolling gear suggested that two periodical components, i.e. about 5.0 seconds and about 1.7 seconds, were combined with different frequencies. Considering the information on the numerical filter process, the move-ment of the whole trolling gear was effected by differences in the material used in its leader.

Trolling depth controller

An automatic trolling depth controller is disclosed for a fishing boat employing a downrigger system. A sonar depth indicating unit with a sonar transducer continuously measures changing depth as the boat trolls. A depth control unit is connected thereto which automatically raises and lowers the trolling line via a reversible motor in response to depth indicating signals of the depth indicator unit so as to automatically maintain the end of the trolling line at a substantially constant given spacing from the bottom despite variations in lake depth as the fishing boat trolls.

曳繩釣漁業の研究-III

It is important in the design of trolling gear to measure the pulling force it will have on the fish (skipjack and frigate mackerel) when caught. The present experiments were carried out using the trolling gears off shionomisaki during the months of May 1969 and 1970. The results obtained are summarized as follows: 1) There was no relationship between the pulling force shown by the fish caught (frigate mackerel) and the length of the troll line in “Subiki”. 2) There was no relationship between the pulling force by fish caught (skipjack) and the trolling speed. 3) The following equation was delived: Tmax=3.31W+0.51 where Tmax is a regressive value of maximum tension and W is body weight of fish.

曳繩釣漁業の研究-II

It is important in the design of trolling gear to measure the pulling force it will have on the fish (skipjack and frigate mackerel) when caught. The present experiments were carried out using the trolling gears off shionomisaki during the months of May 1969 and 1970. The results obtained are summarized as follows: 1) There was no relationship between the pulling force shown by the fish caught (frigate mackerel) and the length of the troll line in “Subiki”. 2) There was no relationship between the pulling force by fish caught (skipjack) and the trolling speed. 3) The following equation was delived: Tmax=3.31W+0.51 where Tmax is a regressive value of maximum tension and W is body weight of fish.

ON THE LENGTH ANO WEIGHT OFTHUNNUS ATLANTICUS (LESSON) FROM NORTHEASTERN BRAZIL

During 1965- 1966 (October-January) fishing season of the Atlantic blackfin tuna, Thunnus atlanticus (Lesson), 611 specimens caught with trolling line thrown from sailing boats near the waters bordering Rio Grande do Norte and Paraiba States (Brazil), were measured and weighted at the fishing center of Baia Formosa (Rio Grande do Norte).

新海上衝突予防法第26条に関する考察(日本航海学会第11回講演会)

They appended specially the words "except trolling lines" which are not in the International original Law Art.26 to the New Japanese Law Art.26 of the Regulation for Preventing Collisions at Sea. Then the Japanese vessels fishing with trolling lines shall always keep out the way of the others, when they have risk of collision at sea, as the ordinal vessels observe generally the Art.19 in the Rules without any exception. But as the International original Law has none of such restricting words, we can construe the Art.26 by the Rule that the vessels fishing with trolling lines can take the stand to observe keeping their speeds and courses on, in Art.21, if necessary, nsing the lights in Art.9 (f). Then the seamen of the Japanese vessels engaged in the international navigation shall have contradictions to be obliged to observe the two different rules of the New Japanese Law and the International Law. There is no need to mention that they must firstly observe the International Law in the rules of preventing collisions between vessels at sea. After researching about the concerning rules. I came to this conclusion they should exclude the words "except trolling lines from the New Japanese Law Art.26, to express the same meaning with the International Law Art.26.