In situ behavioural responses to boat noise exposure of Gobius cruentatus (Gmelin,1789; fam. Gobiidae) and Chromis chromis (Linnaeus, 1758; fam. Pomacentridae) living in a Marine Protected Area

The short-term behavioural effects of two types of boat noise were tested on Gobius cruentatus and Chromischromis, i.e. one permanently and one temporarily benthic vocal fish species living inside the WWF-NaturalMiramare Marine Reserve (Northern Adriatic Sea, Italy). The underwater noises produced by a 26-m touristferry and a 5-m fiberglass boat were recorded inside the core zone of the reserve. Each type of boat noise wassubsequently played back in situ to 10 animals per species (C. chromis males caring their nests or G.cruentatus in their shelters).The 1/3 octave spectra of recorded sound pressure levels were compared to the underwater ambient noiselevel and to sound pressure level measured at the hearing threshold of the two species. The boat noise levelshave been calculated in terms of particle acceleration for both field measurements and in situ playbackprojections and subsequently compared to the available measured values of particle acceleration at thehearing threshold.The animalswere free to move in all directions during thewhole experimental session. The behaviour of each fishwas videotaped by an underwater camera for a total of 10 min (5 min before and5 min duringthenoise playback).No short-termbehavioural reaction (aversion)was observed in any of the specimen of the two species during theplayback of the recorded noises, therefore suggesting no impact. However a time-budget analysis revealed asignificant change in the total time spent in caring their nests (C. chromis) or inside their shelters (G. cruentatus).This result highlighted how analyzing fish reaction on a short-term might underestimate the effects of noisedisturbance and indicated that the overall fish behaviour should be considered to assess noise impact