Meeting Abstract
Tunas are considered to be energetic swimmers that are capable of exceptional migrations across ocean basins. Their aquatic performance is due to the thunniform, lift-based propulsion, stiff fusiform body shape, and large muscle mass. Rigid bodies present a limitation to the turning performance of aquatic organisms. To examine turning capabilities in a captive setting, Pacific bluefin tuna (Thunnus orientalis) were video recorded from a dorsal view as the tuna routinely swam around a large tank or when being fed. Three different types of turning behaviors were observed. Tuna would glide through the turn using the caudal fin as a rudder. Tuna would continually power through the turn using symmetrical strokes of the caudal fin. Lastly, the tuna used a ratchet turn where the global turn was accomplished by a sequence of rapid, short turns by asymmetrical strokes of the tail. Each short turn rotated the tuna about its center of mass changing the trajectory of the rigid-bodied tuna to collectively turn the fish. The angular velocity of the ratcheting action was over 2.7 times that of the global turn. This previously undescribed maneuver provides a mechanism to turn rigid-bodied aquatic organisms and underwater vehicles.
