| Remarks |
Confined to the upper 250 m (Ref. 6390) of the water column in areas with marked oxyclines, since oxygen concentrations less than 2 ml/l encountered below the thermocline and strong thermocline gradients tend to exclude their presence in waters below the discontinuity layer. Feed during the day and at night (diurnal and nocturnal). In Hawaii, adults more common in late spring through early fall; juveniles common in fall and winter (Ref. 4887).
Yellowfin tuna smaller than 15 kg often form surface schools of similar sized fish (Ref. 6390). Schools may be mono-specific (ie, consist of only 1 species) or include other tunas, such as skipjack tuna Katsuwonus pelamis) (Ref. 6390). Dolphins often associate with surface feeding schools in the eastern Pacific Ocean, but a similar association is not found in the western Pacific (Ref. 6390).
Off southeastern Australia, adult yellowfin tuna tend to be more solitary (Ref. 6390). Fish larger than 15 kg inhabit the deeper waters above the thermocline and tend not to school in Australian waters (Ref. 6390).
A behavioural study in Hawaiian waters using ultrasonic tags (Ref. 30307) showed that during the day yellowin tuna inhabited waters just above the thermocline (50-90 m), with occasional short descents to depths as great as 250 m (Ref. 6390). At night, the tuna tended to stay within 50 m of the surface (Ref. 6390).
Large concentrations of larvae and eggs are reported from the western Pacific, including the Coral Sea, and from the Indian Ocean adjacebt to Australia's North West Shelf (Ref. 30274).
Tagged yellowfin tuna have been reported to move 1000 km or more over a 12-month period, but no directed migration has been demonstrated (Ref. 6390). Recoveries from a tagging study of yellowfin tuna on the Australian east coast between 27°S and 38°S suggested that most yellowfin tuna form local groups that moved no more than a few hundred miles over several years (Ref. 6390). This northward and southward movement of yellowfin tuna along the south-eastern Australian coast is probably associated with the seasonal movement of the warm East Australian Current (Ref. 30310). Also Ref. 10406. |