Anthropogenic noise: the behavioural responses of Sparus aurata juveniles as the basis for a numerical model.

Abstract

Underwater noise is mainly produced by anthropogenic activities and has increased in recent years. The Marine Strategy Framework Directive aims to monitor “continuous low frequency sound” trends in ambient noise in particular at 1/3rd octave bands centered at 63 and 125 Hz. The aim of this work is to evaluate the possibility of using the results of Sparus aurata juvenile’s behavior for parameterizing a numerical model of the fish behavior. The fishes were stressed with white noise filtered with a band pass filter at 1/3 octave band centered respectively at 63 Hz, 125 Hz, 500 Hz, and 1 kHz (SPL: 140-150 dB re 1µPa). We performed three test replicas for the control (without any sound emission) and for each of the four frequencies. Each trial lasted 7:15 hours in total and included the following three periods in which two video cameras recorded: 30 min before the acoustic emission; 60 min in which the acoustic stress was dispensed; 6 hours after the acoustic emission divided into 6 periods of 1 hour. To obtain the behavioral data (cohesion, motility, swimming height) the fishes were video monitored 15 min before the sound exposure, one hour during the sound exposure and the final 15 minutes of each hour after the sound exposure. The bottom of the tank was divided into squares. Cohesion was evaluated by counting the number of squares occupied by the group; motility by counting the number of squares crossed by each fish; swimming height by counting the fish presence in three zones (deepest, intermediate, and highest). Using Kruskal-Wallis tests and multiple comparisons post-hoc tests we assessed different behaviors of the fishes reacting to different acoustic frequencies. Here, we propose the use of part of these data (the first hour of acoustic emission) for the parameterization of a numerical model using an adaptation of the Boids method. In the model the cohesion, motility and the swimming height are analyzed in the same way as they are analyzed for in vivo video recordings. Preliminary results showed that it is possible to reproduce in the new model the same qualitative behavior of the in vivo recordings with fish. In this way, it will be possible to understand the behavioural responses of fish in laboratory experiments and contribute to the prediction of the impacts of other possible acoustic sounds emitted by human activities through the application of the created numerical model.