Meeting Abstract
Early models treated shark pectoral fins as semi-rigid foils, functioning to generate lift and adjust the shark’s vertical position in the water column. However, DPIV analysis demonstrated that for at least two species negligible lift is generated during swimming, suggesting that pectoral fins may serve another function. In bonnethead and thresher sharks, pectoral fins have been observed to play a role in turning and braking, respectively. Here we propose that Pacific spiny dogfish, Squalus suckleyi, use their pectoral fins when executing turns by rotating with three degrees of freedom about the articulation between the pectoral girdle and the base of the fin. We used Video Reconstruction of Moving Morphology (VROMM) to track rigid body points in 3D and quantify the movement of the pectoral fin in relation to the body. Volitional swimming data were paired with post-mortem electrical stimulation of pectoral girdle muscles to infer how specific kinematic outcomes are produced. We found that during volitional turning, the pectoral fin on the inside of the turn is depressed, protracted, and supinated. Similar depression and supination of the pectoral fin occurred with electrical stimulation of the ventral pterygoideus muscle, and stimulation of the cranial pterygoideus was solely responsible for protraction. We infer that the cranial and ventral pterygoideus muscles produce these pectoral fin movements. This study is the first to use underwater cameras in a large volume tank for VROMM. We propose that with more testing, these or similar cameras may be used in natural environments for VROMM analyses.
