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Keywords:

  • Steller sea lion;
  • Eumetopias jubatus;
  • kinematics;
  • turning;
  • speed;
  • acceleration;
  • forces

Abstract

Steller sea lions are highly maneuverable marine mammals (expressed as minimum turning radius). Video recordings of turns (n= 195) are analyzed from kinematic measurements for three captive animals. Speed-time plots of 180° turns have a typical “V-shape.” The sea lions decelerated during the first half of the turn, reached a minimum speed in the middle of the curved trajectory and reaccelerated by adduction of the pectoral flippers. The initial deceleration was greater than that for passive gliding due to pectoral flipper braking and/or change in body contour from a stiff, straight streamlined form. Centripetal force and thrust were determined from the body acceleration. Most thrust was produced during the power phase of the pectoral flipper stroke cycle. Contrary to previous findings on otariids, little or no thrust was generated during initial abduction of the pectoral flippers and during the final drag-based paddling phase of the stroke cycle. Peak thrust force at the center of gravity occurs halfway through the power phase and the centripetal force is maximal at the beginning of the power stroke. Performance is modulated by changes in the duration and intensity of movements without changing their sequence. Turning radius, maximum velocity, maximum acceleration and turning duration were 0.3 body lengths, 3.5 m/s, 5 m/s2, and 1.6 s, respectively. The relative maneuverability based on velocity and length specific minimum turning radius is comparable to other otariids, superior to cetaceans but inferior to many fish.