P3.137 Friday, Jan. 6 Batoid out of hell: Hydrodynamic geometry of rays related to swimming mode FONTANELLA, J.E.*; FISH, F.E.; BARCHI, E.I.; CAMPBELL-MALONE, R.; NICHOLS, R.H.; BENESKI, J.T.; West Chester Univ., PA; West Chester Univ., PA; West Chester Univ., PA; Johns Hopkins Univ., Baltimore, MD; Univ. of Rhode Island, Kingston; West Chester Univ., PA firstname.lastname@example.org
Batoid fishes possess depressed bodies and greatly expanded pectoral fins to form a broad planform. The pectoral fins are used for thrust generation by undulation or oscillation. Undulatory locomotion is performed by benthic species, whereas more derived, pelagic rays use the oscillatory mode. To examine morphological differences between the two locomotor extremes, planform geometry was measured from digital images on 106 batoids. A clear distinction between oscillators and undulators was observed with respect to pectoral fin shape and aspect ratio (AR=pectoral fin span2/fin area). Oscillatory rays had fin shapes that were elongate and wing-like and an AR >2.7. Undulatory rays had fins that were round or rhomboidal in shape with AR <2.7. The three-dimensional geometry was obtained from CT scans. Measurements along the semispan of each pectoral fin showed that undulatory rays had thinner fins relative to both chord length and position of maximum thickness compared to oscillatory rays. The thickness of the fins decreased steadily for undulatory rays, whereas thickness relative to chord remained essentially steady for oscillatory rays. Because of the flattened venter of undulatory rays, the pectoral fins showed cambering along the entire span. Oscillatory rays had fins with a symmetrical profile, but showed cambering in the central body. Analysis of the two- and three-dimensional geometry of batoids indicates that the morphology of these fishes is associated with habitat and phylogeny. These differences in fin shape may determine levels of swimming performance within Batoidea.