Modeling fish reaction to vessel noise, the significance of the reaction thresholds

Abstract

A simple model of fish reaction to vessel noise is made. The fish are assumed to swim directly away from the noise source. The main noise source is assumed to be the propeller. Parameters for endurance and swimming speed are obtained from the literature. The initiating stimuli in the model are the loudness and/or the change in loudness. A sensitivity analysis is used to check the importance of the parameters. The model is very sensitive to vessel noise and the fish reaction thresholds. This is an artefact of the dB-scale used in the loudness measure. However, if the fish interpret the dB-scale as almost linear, this may also explain some of the variability in vessel avoidance problems. A small change in the reaction thresholds, may lead to significant changes in the resulting behaviour. If the task is to model fish reaction to vessels, emphasis should be put on the reaction thresholds and noise field around the vessel, rather than swimming speeds and endurance. In general the parameters describing the physiology are less sensitive than the parameters describing the behaviour.