Faster is not always better: Turning performance trade-offs in the inshore squids Doryteuthis pealeii and Illex illecebrosus

Abstract

Jet-propelled swimmers move differently than fin and flipper-based locomotors, relying heavily on directed, pulsed flows to effect maneuvers and turns. Despite a unique propulsive system involving both fins and a jet, little is currently known about the turning performance of most squids. In this study, the maneuverability of two morphologically and ecologically different squids, the shortfin squid, Illex illecebrosus, and longfin squid, Doryteuthis pealeii, was studied using kinematic tracking approaches. We recorded 128 spontaneous turns using a multi-camera system, tracked several landmarks on the squids, and calculated a range of kinematic parameters, including angular velocity and length-specific turning radius along the yaw axis for all turns. Illex illecebrosus completed faster but broader turns than D. pealeii. Doryteuthis pealeii relied more heavily on its fins for turning, with higher fin flap frequencies and amplitudes than I. illecebrosus. Both species were able to complete tighter turns when oriented arms-first versus tail-first, and I. illecebrosus curled its arms more in the arms-first mode, which likely increased angular velocity through a reduction in moment of inertia. The results of this study indicate that the jet, fins, and arms of squids all play important roles in turning performance, and there is a trade-off in squids between maximizing angular velocity and minimizing turning radius. SummaryA kinematic analysis of maneuverability and agility of two inshore squid species: Doryteuthis pealeii and Illex illecebrosus.