Report of the ongoing tagging project on tropical tunas in the southern part of Japan

Summary Tropical tuna tagging project in the southern part of Japan has been conducted by Fisheries Agency of Japan since 2000. By the end of 2006, 2,083 bigeye and 9,155 yellowfin tunas, mainly small fish, were tagged and released around Nansei Islands of Japan (24-29°N, 123-130°E), and 223 bigeye (recapture rate is 10.7%) and 732 yellowfin (8.0%) were recaptured. Many fish were recov- ered within a short time and distance, but some fish made a long distance movement (more than 1000nm). The range of the movement is mostly limited to the vicinity of Japan and most movements are usually northeastward. Yellowfin indicated slightly larger movement than bigeye during the first 300 days. Archival tagging was also conducted. Of 105 bigeye and 80 yellowfin attached with ar- chival tag, 19 bigeye and 5 yellowfin were recaptured. Data could be successfully downloaded from 16 bigeye and 5 yellowfin. Archival tag data indicated that swimming depth of bigeye and yellowfin tunas changed depending on the time of the day; it usually dived deeper during the daytime and stayed in the shallower depth during the night.