DYNAMICS OF THE AERIAL MANEOVERS OF SPINNER DOLPHINS
AUTHOR: FRANK E. FISH et al,
Journal of Experimental Biology 209, 590-598
Publishers: The Company of Biologists 2006: doi:10.1242/jeb.02034
This paper examined the mechanism of spinning by the Spinner Dolphin. Spinner dolphins regularly jump out of the water and make a number of spins and fall back into the water but what causes the spin was not known. This became the subject of investigation by the authors. Another observation was that the dolphins spin was slower just when it came out water but the speed increased until it fell back into water.
The authors deduced that when a spinner dolphin jumped from water it rotated around its longitudinal axis up to seven times or more times and this was enabled by the morphology of the animal which produced a mechanical twist of the body. Meanwhile, it had been observed that under water, the spinner dolphins did some rolling or corkscrewing motions.
Having identified the forces that could possibly cause the leap and spin, the authors developed a robust mathematical model taking into account the angular momentum and the torque that could effect such a move. Data to test the model was obtained from a video recording of aerial maneuvers by spinner dolphin supplied by Natural History New Zealand. In all, 45 aerial maneuvers were analyzed.
According to the study:
“The spinner dolphins observed in the video performed aerial maneuvers similar to previous descriptions… The dolphin emerged through the water surface, rostrum first. The body was observed to rotate as the body moved upward. The rate of rotation appeared to increase once the dolphin was completely airborne. In the air, the dolphin rose to its maximum leap height and then fell back to the water, executing a parabolic trajectory. In addition to the axial spin and ballistic movement, the body would typically rotate to present the lateral aspect of the body to the water surface upon re-entry.”
It was further observed, that the number of complete spins was dependent on the relationship between the swim speed and angular speed while corkscrewing under water. High numbers of aerial spins were achieved with higher angular speeds compared to low spin numbers. With increasing swim speeds more spins were possible for a given angular speed. From these results, it was concluded that the motion of the spinner dolphin performing aerial maneuvers was a combination of translational and rotational motions.