Meeting Abstract

50.1  Saturday, Jan. 5  3D Kinematics of the Dorsal Fins in Spiny Dogfish during Steady Swimming MAIA, A.*; WILGA, C.D.; Univ. of Rhode Island, Kingston; Univ. of Rhode Island, Kingston amaia@mail.uri.edu

The dorsal fin in actinopterygians has been shown to function as a stabilizer in some species and as a propulsive element that augments the thrust from the caudal fin in other species. Although sharks exhibit diversity in size and anteroposterior position of the dorsal fins, little is known about the ability to control fin movements and thus alter the force balance during steady swimming. Predicted phase lag of the dorsal to the caudal fin, based on relative position of the dorsal to the caudal, has been used to demonstrate independent dorsal fin movement in bony fishes. In order to investigate this in a shark, high speed video was used to record movements of the dorsal and caudal fins of four spiny dogfish, Squalus acanthias, swimming at 0.5 BL s^-1 and 0.75 BL s^-1 in a flow tank. Two cameras, capturing dorsal and lateral views, recorded images at 125 f s^-1, enabling 3D visualization. Points on the dorsal and caudal fins were tracked during five tail beats for each individual. The data was plotted and analyzed for 3D displacement and temporal variables. Average tail beat frequency was 0.88 s^-1 at 0.5 BL s^-1 and 1.20 s^-1 at 0.75 BL s^-1, although caudal fin amplitude remained constant. Speed influences lateral excursion of the dorsal fins relative to the caudal fin, with larger magnitudes occurring at the lower speed. The first dorsal fin beats at a different phase lag relative to the caudal than predicted by its position on the body. Thus, like some bony fishes, it appears that spiny dogfish are controlling movements of the first dorsal fin during steady swimming. Further investigation using electromyography and fluid dynamics will clarify whether the dorsal fins have a stabilizer function or augment thrust from the caudal fin.