Running Mechanics of the New Zealand sea lion (Phocarctos hookeri): changes with speed and size

Abstract

The Otariidae New Zealand sea lion (Phocarctos hookeri) is an understudied terrestrial locomotor whose body morphology has been modified by the aquatic environment with distinct environmental pressures. Despite morphological differences the NZ sea lion’s locomotion on land is comparable with other terrestrial locomotors. Though the NZ sea lion has distinctive looking gaits they can be defined within the anteroposterior sequence (APS) method, a lateral walk and a transverse gallop. While the NZ sea lion does achieve many of the standards defining a run gait, it inconsistently achieves an aerial phase. Further consideration of the NZ sea lion gait suggests its forelimbs and hindlimbs may be using different gaits. The NZ sea lion uses a large sagittal flexion phase to allow its hindlimbs to match pace to its forelimbs. The NZ sea lion gait parameters more closely resemble that of the noncursorial mammals. If the NZ sea lion is non-cursorial it would be the largest on record. Descriptions of gait and locomotion allow for informed conservation and management decisions regarding this large “nationally critical” marine mammal.