Behaviour of immature yellowtails (Seriola quinqueradiata) observed by electronic data-recording tags

The long-term behaviour of immature yellowtails, Seriola quinqueradiata, wa s studied using electronic data-recording tags in Sagami Bay, Japan, during the autumn and early winter. Temperature or depth data were continuously r ecorded for 5-69 days on six yellowtails. The temperature recorded from the 0-year-old yellowtails showed only small variations (< 0.5 degrees C day(- 1)) around the SST on the coast, indicating the 0-years stayed in the immed iate coastal area with little horizontal movement. The 1-year-old yellowtai l showed larger temperature variations that reached 3 degrees C day(-1), wh ich implies distinctly larger horizontal movements than the 0-year-olds. De pth records showed the 0-years stayed around 10 m while the 1-year yellowta il swam in deeper water (mainly 10-30 m) with large variations. The latter often dived to 40 m in the daytime, but shallower than the depth of the the rmocline. Both temperature and depth records showed apparent diurnal patter ns. Comparing the fish data with environmental conditions, it is suggested that 1-year yellowtails stay close to the coast during the night, move at d awn to feed in the daytime and return at dusk via a frontal zone. In additi on, wind stress could change yellowtails' behaviour.