Shipping noise and seismic airgun surveys in the Ionian Sea: Potential impact on Mediterranean fin whale

Abstract

Many threats affect fin whale (Balaenoptera physalus) survival in the Mediterranean Sea and, among others, anthropogenic noise represents an issue of growing concern. In 2012, the cabled deep-sea multidisciplinary observatory, "NEMO-SN1", was deployed in the Ionian Sea, at a depth of 2100 m. NEMO-SN1 was equipped with a seismic hydrophone, that allowed us to monitor fin whale and low frequency noise. In this paper we present the analysis of the acoustic data continuously acquired from 2nd July, 2012 to 10th May, 2013. Both shipping noise and seismic airgun pulses highly contributed to the low frequency background noise. Average values and percentile distribution of noise Power Spectral Density were measured on all the acquired data and, separately, in a contour of each airgun pulse detected. Seismic airgun pulses were detected in 4 of the 10 analyzed months and they were presumably produced hundreds of km away from sensor's location. Airguns also were detected in presence of emitting fin whales. Although further observations are required, the study of the typical noise trends represents the first step in evaluating the impact of noise on fin whale ecology in the Ionian Sea.