The Underwater Soundscape at Gulf of Riga Marine-Protected Areas

Muhammad Saladin Prawirasasra,Mirko Mustonen,Aleksander Klauson

doi:10.3390/jmse9080915

Muhammad Saladin Prawirasasra, Mirko Mustonen + Show 1 more

Open Access

https://doi.org/10.3390/jmse9080915

Copy DOI

Abstract

Passive acoustic monitoring (PAM) is widely used as an initial step towards an assessment of environmental status. In the present study, underwater ambient sound recordings from two monitoring locations in marine-protected areas (MPAs) of the Gulf of Riga were analysed. Both locations belong to the natural habitat of pinnipeds whose vocalisations were detected and analysed. An increase of vocal activity during the mating period in the late winter was revealed, including percussive signallings of grey seals. The ambient sound spectra showed that in the current shallow sea conditions ship traffic noise contributed more in the higher frequency bands. Thus, a 500 Hz one-third octave band was chosen as an indicator frequency band for anthropogenic noise in the monitoring area. It was shown that changes in the soundscape occurring during the freezing period create favourable conditions for ship noise propagation at larger distances. Based on the monitoring data, the environmental risks related to the anthropogenic sound around the monitoring sites were considered as low. However, further analysis showed that for a small percentage of time the ship traffic can cause auditory masking for the ringed seals.

Highlights

The pressure on marine ecosystems from anthropogenic underwater noise has been recognised as a challenging problem during the last decades
The initial step towards assessing the environmental pressure posed by anthropogenic sound is passive acoustic monitoring (PAM)
To assess the masking potential, we focused on the frequency band that is important for anthropogenic sound (500 Hz third of octave bands (TOBs)) in the area and the critical ratio (CR) interpolated value for the pure tone of 500 Hz

Summary

Introduction

The pressure on marine ecosystems from anthropogenic underwater noise has been recognised as a challenging problem during the last decades. This cross-border issue can be solved only with an international joint effort. The directive sets qualitative descriptors for GES that list Descriptor 11 as relevant to the energy introduced to the marine environment, including underwater sound. The initial step towards assessing the environmental pressure posed by anthropogenic sound is passive acoustic monitoring (PAM). One-third of octave bands (TOBs) with nominal frequencies of 63 Hz and 125 Hz have been suggested as most relevant to monitor the anthropogenic continuous low-frequency sound in water [2]

Objectives

Results

Conclusion