Boat noise reduces acoustic active space in the lusitanian toadfish Halobatrachus didactylus

Anthropogenic noise is considered of global concern since increasing ocean background noise due to human activities is impacting aquatic lifeforms. One of the most prevalent anthropogenic noise sources are boat engines. Although motorboat traffic has increased in the last decades, the impact of boat noise on the communication of aquatic animals is still poorly known. Impact of boat noise on the communication active space of a vocal teleost, the Lusitanian toadfish (Halobatrachus dydactilus), was tested. To achieve this goal a comparison between the maximum distance a fish can perceive the conspecific advertisement signal – the boatwhistle, before and after embedding the acoustic signal in boat noise, using the AEP technique, was made. Noise from two different types of boat, a small motorboat and a ferryboat, was used. At about 2 m water depth, active space ranged between 6 and 13 m, depending on boatwhistle spectral characteristics. Noise from the small motorboat and from the ferry boat reduced the communication range to 2.5-4 m and 7-8.5 m, respectively. These results demonstrate that boat noise can severely reduce the acoustic active space of this fish and, with heavy boat traffic, it may influence mate finding, depending on the boat noise characteristics.