Pinnipedia, an order of semi-aquatic marine mammals, adapted a body design that allows for efficient aquatic locomotion but limited terrestrial locomotion. Otariids, like the California sea lion (Zalophus californianus), have enlarged forelimbs and can bring their hindlimbs under the body to locomote quadrupedally on land. Phocids (true seals) have reduced forelimbs and are unable to bring their hindlimbs beneath them during terrestrial locomotion. Due to these differences, phocids are expected have greater energetic costs when moving on land compared to otariids. The mechanical costs of transport and power outputs of terrestrial locomotion were first obtained from one male and two female adult California sea lions through video recording locomotion sequences across a level runway. The center of mass, along with six other anatomical points, were digitized to obtain variables such as velocity (V), amplitude of heave (A), and the frequency (f) of oscillations during the locomotion cycle. These variables represent the principal parameters of a biomechanical model that computes the power output of individuals. The three California sea lions in this study averaged a power output of 112.04 watts and a Cost of Transport of 0.63 J kg−1 m−1. This footage was compared against video footage previously recorded of three phocid species (harbor seal, gray seal, and northern elephant seal). Power output and mechanical Cost of Transport were compared between all four pinniped species following the animals’ center of mass. The quadrupedal gait of sea lions showed lower vertical displacements of the center of mass, and higher velocities compared to the terrestrial gait of phocids. Northern elephant seals, gray seal, and the harbor seal showed significantly higher Costs of Transport and power outputs from the sea lions. California sea lions locomote with lower energetic costs, and thus higher efficiency compared to phocids, proving that they are a mechanically intermediate species on land between terrestrial mammals and phocids. This study provides novel information on the mechanical energy exerted by pinnipeds, particularly California sea lions, to then be used in future research to better understand the limitations of these aquatic mammals.
Biomechanical Energetics of Terrestrial Locomotion in California Sea Lions (Zalophus californianus)
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Sarah J. Kerr, Frank E. Fish, Anthony J. Nicastro, Jennifer A. Zeligs, Stephanie Skrovan, Megan C. Leftwich; Biomechanical Energetics of Terrestrial Locomotion in California Sea Lions (Zalophus californianus). J Exp Biol 2022; jeb.244163. doi: https://doi.org/10.1242/jeb.244163
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