A CONTRIBUTION TO THE CONSERVATION OF MARINE BIODIVERSITY: EXPERIMENTAL SETUP FOR THE STUDY OF THE EFFECT OF NOISE ON FISH

Abstract

Recognising noise as one of the main pollutants in the marine system (Kunc, 2016; Weschke, 2019), it is important to determine the type of noise (amplitude and range of frequencies) and how it affects the marine ecosystem and the different species (MAURO, 2020; VAZZANA, 2020). The role sound plays in the live of fish has been established relatively recently and it affects many essential processes for their survival . Although it is known their sensitivity both to the sound pressure level (SPL) and to the particle motion (PM), and despite the fact that differences between sound pressure and acoustic PM field at low frequencies were reported years ago (Banner, 1968), most of the works limit their results to the impact of SPL. Recently, the relevance of PM in the impact of sound waves on fish and invertebrates has been claimed and the challenge to define standard protocols to measure it has been stressed (Popper and Hawkings, 2018; Nedelec 2016). Amongst others, the SONORA project (Filling the gap: Thresholds assessment and impact beyond acoustic pressure level linked to emerging blue-growth activities) aims to evaluate the effects at behavioural and biochemical, cellular and molecular levels of underwater anthropogenic noise on two commercial fish species in two different experimental condition. The behavioural effects will be evaluated on adults and/or juvenile fish. For this purpose, an experimental setup and methodology for the study of the effect of noise on fish in tanks has been implemented. The dimensions of the tanks are 2x2x0.75 m. The first step has been to carry out a vibro-acoustic study of these tanks taking into account the noise sources (airborne and vibration) existing in the laboratory. This experimental study was complemented with a finite element simulation to estimate the spatial distribution of sound pressure levels and particle velocity inside the tank as a function of the sound radiated by the sound source. Two types of sound sources have been developed to carry out the experiments. The first is a conventional electrodynamic loudspeaker with a carbon fibre diaphragm. The second is a DML (Distributed Mode Loudspeaker) type. An accelerometer has been installed on both diaphragms so that it is possible to determine the radiated power of the loudspeaker from the vibration measurements. One or two hydrophones and a PM sensor based on a miniature hydrophone array will be used.