Fish and Ships: Impacts of Boat Noise on the Singing Fish, Porichthys notatus

As anthropogenic ocean noise rises, research into its impacts on marine life is intensifying. Recent studies show concerning effects of noise on a variety of taxa, including fish. However currently lacking are in situ studies: the majority of fish studies have been lab-based, which lack the natural conditions and interconnections that put results in context. Further, the dearth of baseline information on natural fish sounds, communication and behaviours, limits predictions of noise impacts. Here I investigated the highly vocal plainfin midshipman (Porichthys notatus) in its natural habitat to determine the effects of boat noise on wild fish. Porichthys notatus uses sound to communicate during courtship and aggression, and depends on paternal care to safeguard nests in intertidal zones over several months. I first described acoustic communication features of P. notatus in situ by quantifying its vocalizations from longterm audio recordings gathered via hydrophones near a nesting site. I then characterized behaviours associated with acoustic signals by analyzing audio and video data of nest-guarding P. notatus. Finally, I determined the response of P. notatus to live motor-boat noise by examining behavioural and vocal activity of P. notatus in boat noise, ambient and control conditions. In addition to the manual analysis, I used an automated approach to determine overall movement of P. notatus under boat noise, ambient and control conditions. Findings reveal that when exposed to boat noise, fewer P. notatus predators were documented in the vicinity of P. notatus nests, while P. notatus increased overall time spent moving inside nests. Thus, noise benefits P. notatus indirectly by decreasing predator pressure, yet has direct negative impacts on P. notatus by increasing stress and metabolic costs. Such results reveal fitness consequences at both species and ecosystem scales, and indicate the importance of accounting for ecological relationships when predicting noise effects.