The role of the pectoral fins in body trim of sharks

In a large aquarium the leopard shark Triakis semifasciata, sand tiger shark Odontaspia taurus sandbar shark Carcharhinus plumbeus, and spiny dogfish Squalus acanthias cruised steadily at 0.1-0.7 body lengths s(-1). Relative to the trajectory of the shark, the pectoral fins were maintained at a positive angle of attack regardless of vertical direction. for level swimming the mean angle of attack for the pectoral fin was 11 +/- 1.7 degrees, 10.1 +/- 1.3 degrees, 9.3 +/- 1.3 degrees, and 15.0 +/- 0.0 degrees for T. semifasciata, C. plumbeus, O. taurus, and S. acanthias, respectively. The long axis of the body was canted at an angle of attack for T. semifasciata and S. acanthias, but trim was maintained during level swimming for C. plumbeus and O, taurus. Hydrodynamic analysis of the body and fin design of T. semifasciata indicated that the pectoral fins could develop sufficient; pitching moment to maintain depth and keep the body in trim. Demonstration of positive angles of attack support the hypothesis that lift is generated in the anterior body to counterbalance the lift produced by the heterocercal tail. (C) 2000 The Fisheries Society of the British Isles.