Fig. 3. Enlarged records of acceleration and body angle during phases of the same dive as in Fig. 1. (A) High frequency component of heave (XH: foot stroke), that of surge (YH: forward thrust) and body angle at the start (0–1 m depth) and, (B) middle of descent phase (28–30 m depth) and (C) those at the bottom phase (40 m depth). The high frequency components were obtained using the three types of low-pass filter, where the end of the first band/the start of the second band were 0.1/0.5 Hz, 1/1.5 Hz and 2/3 Hz, and shown by different types of lines. Thick horizontal bars in heave show power strokes. Circles in the figures for high frequency component of surge indicate forward thrusts (see the text for definition).