Figure 1.
Coordinate system. The Earth frame-of-reference is defined by the position of the fish's centre of mass (origin Oearth) and orientation of the fish before the C-start (-Yearth), the fish frame-of-reference follows the fish throughout the swimming bout and is defined by the tangential direction of the trajectory of the centre of mass (Yfish) and the position of its centre of mass (Ofish); the escape angle is defined as the angle between the Earth frame-of-reference and the fish frame-of-reference at the end of stage 2.