Fig. 9. The evolution of (A) x and (B) y positions of the projection of the vortex centroid on the transverse plane. Error bars indicate measurement uncertainty. Note that due to limitations on FTLE integration time, these plots are for the first 400 ms of a 600 ms fin beat cycle; see also Figs 10, 11, 12. Squares, calculated position of the vortex centroid; solid line, spline fitting of the data.