Fig. 4. Wake flow at three different swimming speeds and three different phases during the tail beat cycle. Black arrows represent flow velocity magnitude and direction. Vorticity is shown in color in the background, and contours of the discriminant for complex eigenvalues at -200, -500 and -1000 are shown in white. The eel's tail is in blue at the bottom. Note that the vector scale is different for each swimming speed but the length and vorticity scales are the same in all plots. Mean jet magnitude in L s^-1 is written beside each jet. Horizontal lines are provided to facilitate comparisons of jet diameter.