West Chester University, West Chester, PA 19383, USA.
SLEWTHS, Animal Training & Research International, Moss Landing, CA 95039, USA.
J Exp Biol. 2021 Oct 15;224(20). doi: 10.1242/jeb.243020. Epub 2021 Oct 25.
California sea lions (Zalophus californianus) are a highly maneuverable species of marine mammal. During uninterrupted, rectilinear swimming, sea lions oscillate their foreflippers to propel themselves forward without aid from the collapsed hindflippers, which are passively trailed. During maneuvers such as turning and leaping (porpoising), the hindflippers are spread into a delta-wing configuration. There is little information defining the role of otarrid hindflippers as aquatic control surfaces. To examine Z. californianus hindflippers during maneuvering, trained sea lions were video recorded underwater through viewing windows performing porpoising behaviors and banking turns. Porpoising by a trained sea lion was compared with sea lions executing the maneuver in the wild. Anatomical points of reference (ankle and hindflipper tip) were digitized from videos to analyze various performance metrics and define the use of the hindflippers. During a porpoising bout, the hindflippers were considered to generate lift when surfacing with a mean angle of attack of 14.6±6.3 deg. However, while performing banked 180 deg turns, the mean angle of attack of the hindflippers was 28.3±7.3 deg, and greater by another 8-12 deg for the maximum 20% of cases. The delta-wing morphology of the hindflippers may be advantageous at high angles of attack to prevent stalling during high-performance maneuvers. Lift generated by the delta-shaped hindflippers, in concert with their position far from the center of gravity, would make these appendages effective aquatic control surfaces for executing rapid turning maneuvers.
加利福尼亚海狮（Zalophus californianus）是一种高度机动的海洋哺乳动物。在不间断的直线游泳中，海狮会摆动前鳍来推动自己前进，而不需要后鳍的帮助，后鳍是被动拖曳的。在转弯和跳跃（海豚式跳跃）等动作中，后鳍会展开成三角翼形状。关于 otarrid 后鳍作为水动力控制面的作用，信息很少。为了在运动中检查加利福尼亚海狮的后鳍，训练有素的海狮通过水下观察窗进行海豚式跳跃行为和倾斜转弯表演，被水下视频记录下来。比较了一只受过训练的海狮的海豚式跳跃和在野外执行该动作的海狮。从视频中对解剖参考点（脚踝和后鳍尖端）进行数字化，以分析各种性能指标并定义后鳍的使用。在海豚式跳跃期间，当后鳍以平均攻角 14.6±6.3 度浮出水面时，被认为会产生升力。然而，在执行倾斜 180 度转弯时，后鳍的平均攻角为 28.3±7.3 度，在最大 20%的情况下，攻角还要再增加 8-12 度。后鳍的三角翼形态在高攻角下可能具有优势，以防止在高性能机动中失速。由三角形后鳍产生的升力，加上它们远离重心的位置，使这些附肢成为执行快速转弯机动的有效水动力控制面。
