Meeting Abstract
California sea lions (Zalophus californianus) are a highly maneuverable species of marine mammal. They possess four control surfaces in the form of paired foreflippers and hindflippers. Unlike the foreflippers, whose wing-like morphology is fixed, the hindflippers are adjustable in which the digits of the hindflipper can be collapsed (adducted) with a low drag profile or spread (abducted) with a shape similar to a delta wing. During uninterrupted, rectilinear swimming, sea lions oscillate their foreflippers to propel themselves forward without aid from the collapsed hindflippers, which are passively trailed. Sea lions utilize the spread hindflippers during maneuvers, including turning and leaping (porpoising) behaviors. Little has been done to define the role of the hindflippers as a control surface when maneuvering. To examine hindflippers during maneuvering, trained sea lions were video recorded underwater through viewing windows performing porpoising behavior and banking turns. Anatomical points of reference (nose, ankle, and hindflipper tip) were digitized from videos to measure velocity and angle of attack. During porpoising bouts, the average hindflipper angle of attack through the submerged lift-producing phase was 14.6 deg. However, while performing small-radius banking turns, the angle of attack of the hindflippers was much higher, ranging from 25.6 to 35.3 deg. The high angle of attack measured when turning supports the assertion that the hindflippers act as a delta wings to help provide a centripetal force from hydrodynamic lift without stalling to achieve high-performance maneuvers.
