東部太平洋赤道海域におけるマグロ類・カジキ類の摂餌生態と釣獲傾向

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In order to estimate the feeding activity, the authors observed the degree of digestion of food in the stomach of tunas and marlins caught by the long line fishing method in the eastern equatorial Pacific. The difference in the fishing tendency of these tunas were also examined for estimating changes in the hooking tendency. The feeding of yellowfin tuna, bigeye tuna and striped marlin were more active during daytime than at night, and the bigeye showed more activity than the yellowfin after sunset. The feeding of striped marlin became inactive toward sunset and very little activity at night. The catch of yellowfin, bigeye, albacore and skipjack were more during the day than at night, but the hooked-rate of albacore was relatively high even at night. The hooking tendency of yellowfin and bigeye showed a diurnal change, with the fishing peak at 10:00 A. M. for yellowfin and at 11:00 A. M. for bigeye. The time that the yellowfin and bigeye are most hooked is considered between sunrise and fishing peak, after which the hooking rate decrease gradually. The hooked-rate of albacore slightly decreased at night but their hooking tend-ency in the daytime has no such charcteristics as seen in the case of yellowfin and bigeye.
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