The Use of Soundscapes to Monitor Fish Communities: Meaningful Graphical Representations Differ with Acoustic Environment

Rita Carriço,Gui Menezes,Mónica Silva,Manuel Vieira,Pedro Afonso,Paulo Fonseca,Maria Amorim

doi:10.3390/acoustics2020022

Abstract

Many marine animals produce sounds in several phases of their life cycles, either actively or as a byproduct of their activities, such as during mate attraction or when moving. Recent studies of underwater soundscapes have proved passive acoustic monitoring to be a cost-effective, non-invasive tool to understand ecological processes, especially when sampling in adverse conditions or at great depth. Four days of sound recordings at three seamounts from the Azorean archipelago were examined to assess the suitability of different sound graphical representations to characterize different acoustic environments that contrast in the contribution of vocal fish communities. Long-term spectrograms, sound pressure level, spectral probability densities and the Acoustic Complexity Index (ACI) were computed for two shallow seamounts (Formigas and Princesa Alice, c. 35 m) and one deep seamount (Condor, 190 m) using graphics with different time spans. Only in Formigas, which presented the highest occurrence of fish sounds, was it possible to observe temporal patterns of fish vocal activity in the graphical representations. We highlight that habitats with a higher diversity and abundance of sounds are the most suitable targets for these methods, while in locations with a low prevalence of fish sounds a combination of several methods would be recommended.

Highlights

In the marine environment, sound is a more efficient source of information than vision, touch, taste or smell
The presence and diversity of fish sounds were tallied for the three seamounts by manual scrolling of a subsample of four days from June 2010
This study contributes to highlight the usefulness of some currently used graphical representations of acoustic data to study different ecosystems, and how much information they can relay according to the biological sound contribution to the soundscape type and characteristics of the habitat

Summary

Introduction

Sound is a more efficient source of information than vision, touch, taste or smell. Sound provides fast (around five times faster than in air), long-distance information to marine animals during day and night [1,2,3]. The acoustic scene (or soundscape) that encompasses biotic, abiotic and manmade sounds is explored by animals as a source of information and may reveal biodiversity, ecosystem dynamics and ecological processes, and habitat health [10,11,12,13]. PAM allows cost-effective, long-term studies with a negligible impact in the biota while revealing information on acoustic sources, their amplitudes, the interaction between the different sources and how marine species may interpret and react to sounds [14]

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