Meeting Abstract
Batoid fishes are unique among elasmobranchs in having dorso-ventrally flattened bodies with largely expanded pectoral fins that form a disc. Benthic batoids lift from the substrate and swim in the water column by undulation of their pectoral fins — where the thrust is generated by propulsive waves of bending along the pectoral fin, from anterior to posterior. This unique locomotory mode has long been of scientific interest, with many attempts in recreating the kinematics for underwater bio-inspired robots, based on the assumption that undulatory movement is in fact efficient. To understand the kinematics and energetics of batoid locomotion we present three integrated experiments on pectoral fin locomotion in the little skate Leucoraja erinacea: a three-dimensional kinematic study accompanied by a descriptive analysis of fluid dynamics using digital particle image velocimetry at two speeds (1 and 2 BL/s), and a quantification of the energetic costs of locomotion at three speeds (0.75, 1, 1.25 BL/s) using a swim tunnel respirometer. We analyzed nine points on the left pectoral fin of three skates to compare kinematics variables, including amplitude, frequency, wave speed, and body angle, at two speeds. The shape of the pectoral fin is considerably different during upstroke and downstroke. During the downstroke, there is a sharp transition point in the middle of the fin margin as the wave propagates posteriorly. The bioenergetic study on five skates demonstrates a decline in oxygen consumption rates across the speeds tested, and the lowest swimming metabolic rates measured in any elasmobranch. However, the cost of transport calculated from oxygen consumption data reveals that little skates are rather inefficient swimmers when compared to other elasmobranchs and teleosts.
