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 hindfiippers, which are passively trailed. During maneuvers such as turning and leaping (porpoising), the hindfiippers are spread into a delta-wing configuration. There is little information defining the role of otarrid hindfiippers as aquatic control surfaces. To examine Z. califomianus 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 hindfiippers. 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.
Journal of Experimental Biology
Company Biologists LTD
Leahy, A. M., Fish, F. E., Kerr, S. J., Zeligs, J. A., Skrovan, S., Cardenas, K. L., & Leftwich, M. C. (2021). The role of California sea lion (Zalophus californianus) hindflippers as aquatic control surfaces for maneuverability. Journal of Experimental Biology, 224(20), 1-11. http://dx.doi.org/10.1242/jeb.243020