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First published online June 11, 2007
Journal of Experimental Biology 210, 2104-2112 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004317

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Effects of ship noise on the detectability of communication signals in the Lusitanian toadfish

Raquel O. Vasconcelos^1,2,*, M. Clara P. Amorim² and Friedrich Ladich³

¹ Departamento de Biologia Animal e Centro de Biologia Ambiental, Faculdade de Ciências da Universidade de Lisboa. Bloco C2 Campo Grande, 1749-0161 Lisboa, Portugal
² Unidade de Investigação em Eco-Etologia, I.S.P.A. Rua Jardim do Tabaco 34, 1149-041 Lisboa, Portugal
³ Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria

^* Author for correspondence (e-mail: raquel_vasconcelos{at}ispa.pt)

Accepted 28 March 2007

Underwater noise pollution is an increasing environmental problem which might affect communication, behaviour, fitness and consequently species' survival. The most common anthropogenic noises in aquatic habitats derive from shipping. In the present study we investigated the implications of noise pollution from a ship on the sound detectability, namely of conspecific vocalizations in the Lusitanian toadfish, Halobatrachus didactylus. Ambient and ferry-boat noises were recorded in the Tagus River estuary (Portugal), as well as toadfish sounds, and their sound pressure levels determined. Hearing sensitivities were measured under quiet lab conditions and in the presence of these masking noises at levels encountered in the field, using the auditory evoked potentials (AEP) recording technique. The Lusitanian toadfish is a hearing generalist, with best hearing sensitivity at low frequencies between 50 and 200 Hz (below 100 dB re. 1 µPa). Under ambient noise conditions, hearing was only slightly masked at lower frequencies. In the presence of ship noise, auditory thresholds increased considerably, by up to 36 dB, at most frequencies tested. This is mainly because the main energies of ferry-boat noise were within the most sensitive hearing range of this species. Comparisons between masked audiograms and sound spectra of the toadfish's mating and agonistic vocalizations revealed that ship noise decreased the ability to detect conspecific acoustic signals. This study provides the first evidence that fishes' auditory sensitivity can be impaired by ship noise and that acoustic communication, which is essential during agonistic encounters and mate attraction, might be restricted in coastal environments altered by human activity.

Key words: ship noise pollution, masking, hearing, auditory evoked potential, acoustic communication, fish

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SHIPPING NOISE IS BAD FOR TOADFISH

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