| Summary: | The tuna long line fishery is now actively operated not only in the Pacific and Indian Ocean but in the Atlantic Ocean. However, it has been observed that recently there is a tendency of the decrease of hookedrate and the shortening of a fishing season, in the Atlantic fishing areas which are rather new in comparison with those of the Pacific and Indian Ocean, especially in the equatorial waters which have been considered the best fishing areas. Recently, many fishing boats have operated tuna long line in the Atlantic of middle latitude, 30°to 40°N or S. This fishing ground is inferior to that of equatorial waters due to the unfavorable sea condition, and accordingly the operating condition here is inferior to that of equatorial waters. The author had employed long lining on board the "Sumiyoshi-Maru, No. 11" in the Atlantic from February 1964 to December 1965. The south-eastern area off Brazil was selected as the experimental fishing ground in accordance with the view point as mentioned above, and the interrelation between the lunar age and hooked-rate was analysed statistically by arranging the fishing log-book, as follow. 1) It is admitted that the hooked-rate of marlin has a cycle of 15 days in accordance of the lunar age and that the hooked-rate is very poor at the time of the new and full moon, and it is best at the time of the first and last quarter of moon. 2) The hooked-rate of tuna has a cycle of 30 days in accordance with the lunar age and showed a comparatively high rate at the time of the new moon and the worst rate at the time of the full moon. 3) It is assumed from the periodgram of hooked-rate that, the factor of tide being compared with that of the underwater light intensity caused by the chang in lunar age, tuna has a high response to the underwater light intensity of the moon in accordance of the lunar age, while marlin showed high response against the tidal factor. 筆者の乗船した第11住吉丸の操業を通じて見た月令と釣獲率との関係に就いては,次のような傾向が認められた. 1) カジキ類については,月令に対して15日周期の変動が認められ,朔,望の時期に釣獲率は悪く,上弦,下弦の時期に最も良好である. 2) ...
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