The propulsive swimming modes of river otters (Lutra canadensis) were examined relative to behavior. Six river otters were filmed in zoo enclosures that provided surface or submerged views. The repertoire of swimming modes observed for otters included quadrupedal paddling, forelimb paddling, alternate hind-limb paddling, simultaneous hind-limb paddling, and body and tail dorsoventral undulation. Paddling modes accounted for 88% of surface swimming observations and for 86% of observations involving submerged maneuvers. Dorsoventral undulation predominated during rectilinear submerged swimming. Transition from paddling to undulatory propulsion was accomplished by use of simultaneous hind-limb paddling in concert with dorsoventral body and tail flexion. These motions produced a posteriorly directed traveling wave in the tail with an average velocity 1.62 times the swimming velocity. The higher velocity in the tail could produce hydrodynamic thrust during all phases of the paddling cycle.
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F. E. Fish (1994) studied this question.
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