Some suggestions as to why the cetaceans show a
preferential swimming direction have been forwarded.
These include the distinct asymmetry of the brain of
cetaceans [9], suggesting that this will mean that one half
of the brain will be dominant and thus cause counterclockwise
swimming. Others have suggested that the
unihemispheric nature of cetacean sleep associated with
different levels of hemispheric neural activity will cause
biases in the direction of swimming; however, physiological
studies report that changes in the level of
hemispheric activity do not correlate to changes or biases
in the direction of swimming [10]. Social factors have
also been implicated in directional swimming preference
[5]. Despite these suggestions, the causal factors underlying
the counterclockwise directional bias of swimming
in captive cetaceans in the Northern Hemisphere are not
understood.
No studies examining the preferential direction of
swimming of captive dolphins in the Southern Hemisphere
have been undertaken. The present study reports the results
of several nights of observation of eight dolphins held at
Seaworld in Durban, South Africa. This is the first study of
rest behavior of dolphins in the Southern Hemisphere. The
results are discussed in terms of the causal factors underlying
directional swimming in captive cetaceans.