Turning performance of batoids: Limitations of a rigid body

The ability to maneuver is an important aspect of the locomotor performance of fishes, but can be constrained by the inflexibility of the body, such as in batoid rays. Turning radius (maneuverability) and turning rate (agility) were measured from overhead video recordings of rays in a large pool during unrestricted swimming. The rays that were observed swam by oscillatory movements of the pectoral fins (Aetobatus narinari. Myliobatis freminvillii and Rhinoptera bonasus) or by undulations of the fins (Dasyatis americana and Dasyatis centroura). Oscillatory rays maneuvered by either powered or unpowered gliding turns, whereas undulatory rays turned using asymmetrical undulations of both pectoral fins. Underwater observations showed that both rays used banking while turning, where bank angle ranged from 15-70 degrees. No differences were found between mean turning parameters between the two locomotor types. Minimum turn radius and maximum turning rate based on the extreme 20% of measurements were respectively smaller and larger for oscillatory rays (0.7 m; 44.4 degrees s(-1)) compared to undulatory rays (1.0 m; 30.4 degrees s(-1)). Compared to other aquatic animals, the turning performance of rays is lower than flexible bodied animals, but similar to other animals with rigid bodies. (C) 2011 Elsevier B.V. All rights reserved.