Kinematics and Hydrodynamics of Cephalopod Turning Performance in Routine Swimming and Predatory Attacks

Steady rectilinear swimming has received considerable attention in aquatic animal locomotion studies. Unsteady swimming movements, however, represent a large portion of many aquatic animals’ locomotive repertoire and have not been examined extensively. This study incorporates kinematic analyses of routine turning performance of brief squid Lolliguncula brevis and dwarf cuttlefish Sepia bandensis (Chapter 2), 3D velocimetry techniques to examine hydrodynamic turning performance of L. brevis (Chapter 3) and kinematic analyses of turning performance of L. brevis during predatory attacks on shrimp and fish prey (Chapter 4). Both L. brevis and S. bandensis demonstrated high maneuverability, having the lowest measures of length-specific turning radii reported to date for any aquatic taxa. Lolliguncula brevis was more agile than S. bandensis, i.e., L. brevis exhibited higher angular velocities during turning. In L. brevis, jet flows were the principle driver of angular velocity. Asymmetric fin motions played a reduced role in turning, and arm wrapping increased turning performance to varying degrees depending on the species. Flow patterns and relative torque contributions from the fins and jet varied with the speed of oncoming flow and orientation of the squid. Four turning categories were identified: (1) short tail-first turns, (2) long tail-first turns, (3) vertically oriented turns and (4) arms-first turns. The jet generally contributed more to turning torque than the fins in short tail-first, long tail-first and vertical turns. However, the fins produced a wider repertoire of flows, including isolated vortex rings, linked vortices and regions of elongated tubular vorticity, and were more important than the jet for turning torque generation during arms-first turns. Both the jet and fins produced torque contributing to roll and pitch, but the relative importance of these flows differed by turning category, with jet roll/pitch stabilization being critical for short tail-first turns and fin roll/pitch stabilization being integral to arms-first and vertical turns. Squid attack sequences involved three phases: (1) approach, (2) strike and (3) recoil. Lolliguncula brevis employed different attack strategies for fish and shrimp and turning performance played a significant role during predatory encounters. The squid exhibited high agility during the approach for both prey types. However, positioning, maneuverability and synchronized fin motions were more important for attacks on shrimp than fish. For attacks on fish, squid favored maximizing linear attack speeds over high maneuverability. Squid controlled their translational velocity and tentacle extension velocity during the strike, and demonstrated considerable rotational control during the recoil phase despite prey escape attempts. This study represents the most comprehensive quantitative turning performance study of cephalopods to date and demonstrates that the unique body architecture of these taxa provides exceptional advantages for maneuvering in the marine environment