Fig. 6. Velocity transects through vortices in the eel's wake over time. The center of the first vortex is shown by the vertical dotted lines, and zero velocity is indicated by the horizontal dotted lines. Representative flow fields are shown to the right, indicating the position of the transect, with vorticity shown in color. The cross identifies the position of the first vortex, and the circle identifies the position of the second. Standard error around each velocity trace is shown by a lighter-colored region. (A) Transects through the primary vortex and, once it is formed, the secondary vortex. Idealized profiles through a single Rankine vortex and two same-sign Rankine vortices are shown in black at top and bottom. The position of the secondary vortex, plus or minus standard error, is shown as a bar along the zero line. Before the secondary vortex is completely formed, this bar indicates the position of the inflection point in velocity where the vortex will be formed. (B) Transects across the lateral jet, from the secondary vortex of one half tail beat to the primary vortex of the next. An idealized profile through a small-core vortex ring is shown in black above.