Predicted probabilities of eel bypass passage without hesitation (p(P_wh), mean with 80% confidence interval in shaded areas) as a function of the tangential velocity Vt (m s⁻¹) in the proximity of the rack and the bypass discharge Q_bp% (expressed as a proportion (%) of exploited HPP discharge), resulting from logistic regression Model 1 (a and b) and Model 2 (c and d, including Vt and Q_bp% interaction); TL − fish total length (mm), site as factor, straight lines on b and d indicate Q_bp% of 3%, set by French authorities.