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

Abstract

SUMMARY 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.

Development of vocalization, auditory sensitivity and acoustic communication in the Lusitanian toadfishHalobatrachus didactylus

“…Individuals of these groups were probably just a few months, 1 year, 1-2 years, 2-3 years and 5-8 years old, respectively (based on J. L. Costa, unpublished). Hearing thresholds from the largest size group (G5) are reported elsewhere (Vasconcelos et al, 2007).…”

“…Moreover, this approach with hearing generalists has frequently been adopted in similar studies, e.g. the Lusitanian toadfish Halobatrachus didactylus (Vasconcelos et al, 2007), the oyster toadfish Opsanus tau (Yan et al, 2000), the bluegill sunfish Lepomis macrochirus (Scholik and Yan, 2002), the gobies Padogobius martensii and Gobius nigricans (Lugli et al, 2003), the European perch Perca fluviatilis (Amoser et al, 2004;Amoser and Ladich, 2005) and the damselfish Abudefduf saxatilis (Egner and Mann, 2005). Even so, the hearing thresholds should not be considered as absolute values.…”

A noisy spring: the impact of globally rising underwater sound levels on fish

“…Human invasion of the underwater acoustic environment Underwater sounds generated by human activities can be subdivided in two categories: sounds that are an unintentional byproduct and sounds that are used as a measurement tool. Dominant in the first category are low-frequency noises from vessels for container shipping, public transport, fishing and recreational activities [1,2,67,68,88]. For example, >80% of global freight transport takes place over water by motorized shipping, while passenger crossing occurs on many rivers, lakes and seas, often on noisy ferries that shuttle between harbours at frequent intervals.…”

“…Clearly, however, if fish sounds serve a communicative function in a reproductive context, problems of detection and recognition due to the presence of anthropogenic noise [65][66][67] could have fitness consequences. It should be clear that fish have not evolved in a quiet environment, and natural noise levels can also become loud, for example during fish choruses [58,59].…”

Novel underwater soundscape: acoustic repertoire of plainfin midshipman fish

“…Lugli, 2010) or anthropogenic (e.g. Vasconcelos et al, 2007;Popper and Hastings, 2009) sources. Background noise can enhance the detection of auditory stimuli through a mechanism known as stochastic resonance (Jaramillo and Wiesenfeld, 1998).…”