Association of yellowfin tuna (Thunnus albacares) with tracking vessels during ultrasonic telemetry experiments

Three yellowfin tuna (Thunnus albacares) carrying ultrasonic depth; sensiti ve transmitters developed a strong association with the tracking vessel, fo llowing it at speeds up to 5 knots (2.6 m/s). Two fish associated with the tracking vessel during daytime, and the other fish during day and night per iods. Swimming behavior appeared to depend on the speed of the vessel. The tuna remained within a few meters of the surface when the vessel was travel ing at high speeds hut moved deeper when the vessel drifted. The behavior o f these fish is compared to those of other yellowfin tuna tracked in other situations (associated with fish-aggregating devices or unassociated with d evices. The reasons for these associations are not known but some hypothese s are advanced.