The effect of boat noise on calling activity in the Lusitanian Toadfish

Anthropogenic noise has been increasing during the last decades, altering soundscapes throughout most aquatic environments. In estuarine shallow waters one of the most prevalent sources of underwater noise are motorboats and ferries. In this study we compared the effect of boat noise and ambient noise playbacks on the calling activity of Lusitanian toadfish males (Halobatrachus didactylus), a species that relies on advertisement calls for mate attraction. Two sets of 12 concrete nests that toadfish males occupy spontaneously in the Tagus estuary (Portugal), were exposed to sounds during a fortnight by playing back either ambient noise (control) or boat noise (treatment) during one reproductive season. Noise treatment mimicked the passage of 10 ferries and of 4 small boats per hour during 18 hours, similar to what fish experience in Tagus estuary. Acoustic activity of each nesting male was monitored during the experimental period. By analysing male vocal activity, we found that calling rate significantly decreased in males under boat noise treatment. These results suggest that exposure to anthropogenic noise may alter vocalization patterns and likely impact reproduction in vocal fish.