Swimming in Circles Clockwise direction preferred by Southern Hemisphere dolphins Counterclockwise direction preferred by Northern Hemisphere dolphins

November 23, 2004 Dr. Paul Manger at the University of Witwatersrand (Republic of South Africa) knew that dolphins in the Northern Hemisphere swim mostly in the counterclockwise direction. Researchers have suggested that dolphin brain anatomy, social behaviors or sleep patterns may be responsible for this counterclockwise preference. To investigate this topic further, Dr. Manger and Guinevere Stafne studied swimming behavior of dolphins in the Southern Hemisphere. Surprisingly, they found that these dolphins spent the majority of their time in clockwise behaviors. Stafne and Manger studied four male and four female adult bottlenose dolphins (Tursiops truncatus). These dolphins lived at the Seaworld facility in Durban, South Africa. Each dolphin was observed for four hours on four different nights. The researchers measured the time each dolphin spent in four different behaviors: Swimming Counterclockwise: forward motion in counterclockwise direction. Hanging Counterclockwise: no motion, but the dolphin was facing in the counterclockwise direction. Swimming Clockwise: forward motion in clockwise direction. Hanging Clockwise: no motion, but the dolphin was facing in the clockwise direction. The eight dolphins spent a total of 86% of their time in clockwise behaviors. Swimming in the clockwise direction took up 49% of the dolphins' time and hanging in the clockwise direction took up 37% of the time. The dolphins spent only 14% of their time in counterclockwise behaviors (swimming, 7%; hanging, 7%). Dolphin Behavior It is still unknown why Northern Hemisphere dolphins prefer counterclockwise behaviors while Southern Hemisphere dolphins prefer clockwise behaviors. Because the brains of dolphins are the same regardless of where they live, it is unlikely that brain differences account for the directional preferences. Stafne and Manger point out that dolphins may be capable of sensing magnetic fields. Differences in the Earth's magnetic fields in the Northern and Southern Hemispheres may cause the dolphins to swim in different directions. Alternatively, the scientists propose that differences in Northern and Southern ocean currents may influence dolphin behavior. Future experiments may clear up this mystery. For example, what would happen if you transported a Southern Hemisphere dolphin to the Northern Hemisphere? Would this dolphin still continue to swim in the clockwise direction or would it switch to prefer counterclockwise directions? What is the behavior of dolphins in their natural environments? How does the size and shape of the swimming tank influence dolphin behavior?

Did you know? Dolphin Brain Image courtesy of Comparative Mammalian Brain Collection

Brain weight: dolphin = 1.5-1.6 kg; human = 1.4 kg. Cerebral cortex thickness: dolphin = 1.3-1.8 mm; human = 1.5-4.5 mm. Hearing Range: dolphin = 200 to 150,000 Hz; human = 20 to 20,000 Hz (Reference: S.H. Ridgway, The Cetacean Central Nervous System)

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