Reaction of two sciaenid species to passing boats: Insights from passive acoustic localisation

Meagre ( Argyrosomus regius ) and weakfish ( Cynoscion regalis ) are two soniferous sciaenid species that use the Tagus estuary (Portugal) to breed. In this highly urbanized environment, fishes must deal with multiple anthropogenic stressors that include high noise levels caused by the intense boat traffic. We investigated how these sciaenids react to ferry boat and small boat passages, by assessing both changes in breeding calling activity with passive acoustic monitoring and escape responses with passive acoustic localisation. We found that meagre reduced calling activity after boat passages, but no such effect was observed in weakfish. Instead, weakfish moved in response to boat passages suggesting an escape response. Meagre also changed positions and dispersion patterns, but movements were more modest. This study uses a cost-effective and non-invasive passive acoustic localisation method to elucidate the behavioural response of soniferous fish to anthropogenic noise for the first time, contributing to our understanding of the way fish react to this stressor. Such knowledge is especially important in contexts where fish are exposed to highly prevalent human-generated noise during the breeding season, such as in busy estuaries and coastal areas. • We developed a passive acoustics localisation system to assess vocal fish escape responses to boats. • Meagre and weakfish movements and calling activity were evaluated while chorusing. • Boat passages triggered changes on the position of the detected calls (proxy for shoal position). • Weakfish positions changed noticeably, while modest movements were observed in the meagre. • Meagre reduced vocal activity after boat passages, in contrast with weakfish.