Meeting Abstract
Scombrid fishes are known to attain exceptional swimming speeds due to their thunniform, lift-based propulsion, large muscle mass, and a rigid fusiform body shape. A rigid body should restrict maneuverability in regard to turn radius and turn rate for aquatic organisms. To test if turning maneuvers by the rigid-bodied Bluefin tuna (Thunnus orientalis) are constrained, captive animals were video recorded from above as the animals routinely swam around a large circular tank or during feeding bouts. The turning performance was observed and classified into three different types of turns: 1) Glide turn, where the tuna uses the caudal fin as a rudder to passively move through the turn, 2) Powered turn, where the animal uses continuous symmetrical strokes of the caudal fin to propel itself through the turn, and 3) Ratchet turn, where the overall global turn is completed by a series of small local turns by asymmetrical stokes of the caudal fin. Individual points of the rostrum, peduncle, and tip of the caudal fin were tracked and analyzed using Tracker software. Frame-by-frame analysis showed that the glide turn had the fastest turn rate at all three points tracked, with a maximum of 224.1 deg/sec. During the ratchet turn, the rostrum exhibited a minimum global turn radius of 0.43 m. However, the local turn radii were only 18.6% of the global ratchet turn. The minimum turn radii ranged from 0.38 m to 1.62 m as a proportion of body length. Compared to the performance of other swimmers, Bluefin tuna are not constrained in turning performance due to the rigid body because of flexibility of the tail and specialized turning behaviors.