Fig. 1. Sample sonomicrometric and electromyogram (EMG) traces from swimming I. oxyrinchus. (A) Lateral view of a 91 cm mako swimming at 1 L s^–1 in the swim tunnel. Red and blue arrows correspond to the axial positions shown in B–D. (B) Mako cross sections at 0.4 and 0.6L, showing the difference in size and location of the red muscle mass at the two axial positions. Sample of EMG and sonomicrometric data recorded simultaneously over several consecutive tailbeat cycles in the anterior (C) and posterior (D) axial positions.