Functional morphology of the pectoral fins in bamboo sharks, Chiloscylliumplagiosum: Benthic vs. pelagic station-holding

Bamboo sharks (Chiloscyllium plagiosum) are primarily benthic and use their relatively flexible pectoral and pelvic fins to rest on and move about the substrate. We examined the morphology of the pectoral fins and investigate d their locomotory function to determine if pectoral fin function during bo th benthic station-holding and pelagic swimming differs from fin function d escribed previously in leopard sharks, Triakis semifasciata. We used three- dimensional kinematics and digital particle image velocimetry (DPIV) to qua ntify pectoral fin function in five white-spotted bamboo sharks, C. plagios um, during four behaviors: holding station on the substrate, steady horizon tal swimming, and rising and sinking during swimming. During benthic statio n-holding in current flow, bamboo sharks decrease body angle and adjust pec toral fin angle to shed a clockwise fluid vortex. This vortex generates neg ative lift more than eight times that produced during open water vertical m aneuvering and also results in an upstream flow that pushes against the pos terior surface of the pectoral fin to oppose drag. In contrast, there is no evidence of significant lift force in the wake of the pectoral fin during steady horizontal swimming. The pectoral fin is held concave downward and a t a negative dihedral angle during steady horizontal swimming, promoting ma neuverability rather than stability, although this negative dihedral angle is much less than that observed previously in sturgeon and leopard sharks. During sinking, the pectoral fins are held concave upward and shed a clockw ise vortex with a negative lift force, while in rising the pectoral fin is held concave downward and sheds a counterclockwise vortex with a positive l ift force. Bamboo sharks appear to sacrifice maneuverability for stability when locomoting in the water column and use their relatively flexible fins to generate strong negative lift forces when holding position on the substr ate and to enhance stability when swimming in the water column. J. Morphol. 249:195-209, 2001. (C) 2001 Wiley-Liss, Inc.