| Remarks |
Temperature and thermocline depth seem to be the main environmental factors governing the vertical and horizontal distribution of this species (Ref. 168). Bigeye tuna are more tolerant of lower temperatures and lower dissolved oxygen concentration than are other tunas and tend to occupy deeper waters (Ref. 30326). For example, during the day, adult bigeye tuna inhabit the thermocline zone at about 150-250 m in tropical waters where temperatures descend to almost 10°C, provided dissolved oxygen concentration is more than 1 mg per l (Ref. 28952, 30327). The tuna make occassional short ascents to 100 m or shallower (Ref. 6390).
Young bigeye tuna have not been reported outside tropical waters (Ref. 30326). In Australia, bigeye tuna smaller than 20 kg may form surface-dwelling schools of similar sized fish with other species such as yellowfin tuna and skipjack tuna (Katsuwonus pelamis). Schools of only bigeye tuna are less common (Ref. 30328). In tropical waters, young bigeye tuna are often caught 50-100 m below floating objects such as logs and fish aggregating devices (Ref. 30326). Adults tend to be solitary (Ref. 6390). Behavioural studies in Hawaiian waters using ultrasonic tags (Ref. 30329) found that the distribution of adult bigeye tuna was closely correlated with the 15°C isotherm during the day (Ref. 6390). Like yellowfin tuna, bigeye tuna move into the warmer surface waters (within 50 m of the surface) at night. Feed during the day and at night. In Hawaii, more abundant in late fall through late spring. |