Horizontal and vertical movement of yellowtails Seriola quinqueradiata during summer to early winter recorded by archival tags in the northeastern Japan Sea

Yellowtails Seriola quinqueradiata are an important fishery resource around Japan. Here we investigated the movement ecology and habitat utilization of this migratory fish. Archival tags were implanted in 26 adult yellowtails (61-90 cm in fork length) to examine their seasonal movement patterns and vertical distribution. Yellowtails were captured and released around Noto Peninsula in the Japan Sea on 27 May 2004. Eight individuals were recaptured more than 2 mo later, and we analyzed their daily position and vertical movement with ambient water temperature recorded in 60 or 120 s intervals. Most yellowtail individuals moved from the central coast of Japan to the north (from the west of Tsugaru Strait to the west of Hokkaido) in June. Individuals resided in the northern part of the Japan Sea from summer to mid-fall (late July to late October). Seasonal thermoclines developed during this northward movement and subsequent period of residency, with individuals primarily occupying the surface mixed layer during the daytime and at night; however, individuals made frequent short dives through the thermocline, especially during the daytime. These phenomena may be related to foraging based on the distribution of their prey. In late October, yellowtails started a rapid southward movement, primarily remaining in vertical thermal mixing coastal areas, and not entering the coldwater masses that formed offshore. This southward movement pattern might indicate that yellowtails avoid cold offshore water temperatures.