鈎にかゝつた魚の引きの強さに就て
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概要
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Although it is a commonest phenomenon that a fish rushes violently when caught by a fish-hook, there does not seem to be any exact study on the strength with which such fish pulls the fishing tackle. This paper reports an experiment in which an attempt was made to measure that strength. Fig. 1 shows the apparatus used for this measurement. When a fish catches a hook (H) and pulls the fishing tackle downward, the spring (S) is stretched and the stress is recorded by the kymograph (K). The force with which a fish pulls the tackle downward, and the amount of work done thereby by the fish, are given respectively by (F)=c•y+r•g=ky/n+r•g and (W)={k(y/n)2+r•g•y}/2 where y is the displacement upward of the free end of the writing lever, and n, the magnification of the kymograph. c and r are the constants proper to each spring, and they can be determined from the damped oscillation brought about by hanging a known weight on the hook (Fig. 2A). The friction between the recording paper and the pen has been found to be negligible. The measurment was carried out at the Shinmaiko Aquarium, Aichi Pref., using several species of fish reared there as the material for this study. Kymographic records obtained by this method (Fig. 2 B, and 3 A-C) are characterized by the major peaks o ?? curring at intervals and the minor peaks that follow each major peak. Since the major peak, y, represents the maximum instantaneous force exerted by the fish, (F), and a major peak and the subsequent minor peaks are taken into account in computing (∑W), the feature of the pull can be expressed in the terms of (F), (∑W), and the time intervals of each major peak. While both (F) and (∑W) are necessary to express the strength of the pull, only (F) has been studied in some details. In the rockfish, Sebastiscus marmoratus, the maximum of (F), (Fmax), increases nearly proportionally with the body weight (Fig. 4). Assuming this relation holds also in other spec-ies, (Fmax) per 100gr of body weight is adopted as the basis on which the forces of the instan-taneous pull in different species are compared (Table. 1).
- 公益社団法人 日本水産学会の論文