For aquatic animals, turning maneuvers represent a locomotor activity that may not be confined to a single coordinate plane, making analysis difficult particularly in the field. To measure turning performance in a three-dimensional space for the manta ray (Mobula birostris), a large open-water swimmer, scaled stereo video recordings were collected. Movements of the cephalic lobes, eye and tail base were tracked to obtain three-dimensional coordinates. A mathematical analysis was performed on the coordinate data to calculate the turning rate and curvature (1/turning radius) as a function of time by numerically estimating the derivative of manta trajectories through three-dimensional space. Principal component analysis (PCA) was used to project the three-dimensional trajectory onto the two-dimensional turn. Smoothing splines were applied to these turns. These are flexible models that minimize a cost function with a parameter controlling the balance between data fidelity and regularity of the derivative. Data for 30 sequences of rays performing slow, steady turns showed the highest 20% of values for the turning rate and smallest 20% of turn radii were 42.65+16.66 deg s-1 and 2.05+1.26 m, respectively. Such turning maneuvers fall within the range of performance exhibited by swimmers with rigid bodies.
Journal of Experimental Biology
Company of Biologists
Fish, F. E., Kolpas, A., Crossett, A., Dudas, M. A., Moored, K. W., & Bart-Smith, H. (2018). Kinematics of swimming of the manta ray: three-dimensional analysis of open water maneuverability. Journal of Experimental Biology, 221(jeb166041), 1-10. http://dx.doi.org/10.1242/jeb.166041