Lateralised swimming behaviour in the California sea lion

Lateralised motor behaviour in the pinnipeds has been subject to little investigation. This study examined the swimming behaviour of seven zoo-housed California sea lions to determine whether they exhibited a directional bias in their motor behaviour. Data were collected on the direction of the animals' swimming patterns from the point of entering a pool of water from dry land. Each animal was studied for 100 episodes of swimming. All seven of the sea lions showed significant (P<0.001) bias in the direction of their swimming, although unidirectional bias was not observed at the level of the population. The direction of the sea lions' swimming patterns varied significantly according to the animals' sex. Males showed a preference at the level of the population for swimming in a clockwise direction, while females showed a population-level counterclockwise swimming preference. Overall, the findings appear to suggest that California sea lions, like other marine mammals, exhibit motor bias in the direction of their swimming patterns, although further work using larger sample sizes is needed before more firm conclusions regarding motor laterality in this species can be reached.