Boat noise reduces vocalization rate and alters vocal characteristics in wild plainfin midshipman fish

Anthropogenic noise pollution has been accelerating at an alarming rate, greatly altering aquatic soundscapes. Animals use various mechanisms to avoid acoustic masking in noisy environments, including altering calling rates or the frequency (pitch) of their vocalizations or increasing the amplitude (loudness) of their vocalizations (i.e., exhibiting the Lombard effect), but few studies have examined this vocal plasticity in fishes. We tested the effects of in situ motorboat noise on the agonistic and mating vocalizations of nesting plainfin midshipman fish (Porichthys notatus), and found that midshipman fish reduce and alter their vocalizations in the presence of boat noise. During boat noise, fish produced four times fewer agonistic vocalizations compared to ambient control periods. The fish also increased the frequency of mating hums and the amplitude of grunts and growls during boat noise. This study is the first to experimentally demonstrate the Lombard effect in fishes using real motorboat noise.