Fig. 6. Regression equation of vertical descent speed (relative to the bottom; solid line) and effective swim speed relative to the fluid (calculated using vector geometry; see Materials and methods), over a range of current speeds. The dashed line is regression of effective swim speed at a dive angle of 10° with 95% confidence intervals. The shaded area indicates regression equations from sensitivity analysis of dive angle from 0° (lower edge of shaded area) to 20° (upper edge of shaded area). Effective swim speed was regulated across currents at a relatively constant value of 1.24±0.14 m s^–1 while vertical descent velocity decreased non-linearly. Regression equations are presented in Table 1.