南西諸島海域における浮魚礁とカツオ・マグロ類の移動

概要

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Movement and behavior of bigeye Thunnus obesus, yellowfin Thunnus albacares and skipjack tuna Katsuwonus pelamis were investigated based on conventional and archival tagging. The fish were mostly released around anchored FADs in the Nansei Islands area. Many of the recaptures were obtained within 200 days after release. The fish were mainly recaptured in the Nansei Island area and in the area between around Kyusyu and off Tohoku as well as in the south of Japan such as around Philippines especially as for yellowfin tuna. Between Kyusyu and central Honsyu, bigeye and yellowfin tuna were mainly recaptured in the offshore and nearshore area, respectively. The distance between release and recapture locations increased with time, although difference between individuals was observed. Based on the data recorded by archival tags, diurnal movements with deeper layer during daytime were observed both for bigeye and yellowfin tunas. Daytime swimming depth of bigeye tuna varied and was sometimes shallow (around 100m or shallower) suggesting association with FADs or other objects based on past study, although clear difference of daytime depth was not observed for yellowfin tuna. Synchronicity of vertical behavior was observed for bigeye tuna individuals which were released on the same day at the same FAD.
2013-07-15