It Is Not Just a Matter of Noise: Sciaena umbra Vocalizes More in the Busiest Areas of the Venice Tidal Inlets

Boat noise is known to have a detrimental effect on a vulnerable Mediterranean sciaenid, the brown meagre Sciaena umbra. During summer 2019, two acoustic surveys were conducted at 40 listening points distributed within the inlet areas of Venice (northern Adriatic Sea). Two five-minute recordings were collected per each point during both the boat traffic hours and the peak of the species' vocal activity with the aims of (1) characterizing the local noise levels and (2) evaluating the fish spatial distribution by means of its sounds. High underwater broadband noise levels were found (sound pressure levels (SPLs)(50-20kHz) 107-137 dB re 1 mu Pa). Interestingly, a significantly higher background noise within the species' hearing sensibility (100-3150 Hz) was highlighted in the afternoon (113 +/- 5 dB re 1 mu Pa) compared to the night (103 +/- 7 dB re 1 mu Pa) recordings due to a high vessel traffic. A cluster analysis based on Sciaena umbra vocalizations separated the listening points in three groups: highly vocal groups experienced higher vessel presence and higher afternoon noise levels compared to the lower ones. Since the species' sounds are a proxy of spawning events, this suggests that the reproductive activity was placed in the noisier part of the inlets.

Automated summary

The study revealed high levels of underwater noise in the inlet areas of Venice, which negatively impacted the brown meagre Sciaena umbra in the Mediterranean Sea. Afternoon noise levels were significantly higher compared to night recordings, potentially leading to the reproductive activity of the fish occurring in the noisier parts of the inlets.