Sizes of adult bluefin tuna Thunnus orientalis in different areas of the western Pacific Ocean

ABSTRACT:   The length frequencies of adult Pacific bluefin tuna Thunnus orientalis caught near Japan, near Taiwan, in the tropical western Pacific Ocean, and in the South Pacific Ocean, were compared. The largest catches consisted of medium-sized adults (160–209 cm fork length) taken near Japan and large adults (≥210 cm) taken near Taiwan. Small adults (120–159 cm) were occasionally caught in the Sea of Japan. Small numbers of medium-sized and large adults were caught in the tropical western Pacific and the South Pacific. The length frequencies of the fish greater than 160 cm in length caught in different areas around Japan were similar to each other. As adult bluefin tuna grow older they spawn earlier, and their distribution, movements, and spawning areas change.