Electric boat underwater radiated noise and its potential impact on species of conservation interest.

Electric boats are thought to be noiseless, but in-situ measurements are generally rare. The Underwater Radiated Noise (URN) of 8-m Trimaran Pontoon Boat with two outboard electric engines was measured in the Miramare Marine Protected Area (Trieste, Italy), together with the URN of a fibreglass 5-m boat, with a outboard gasoline engine, for comparisons. International standards and guidelines for shallow waters were considered. URN were provided in one-third octave band and in narrow band spectra. The electric boat produced a low input of underwater noise at low frequencies. Given a low-frequency hearing sensitivity, the listening space reduction (LSR) was lower when generated by the electric than by combustion engine boat for the brown meagre, a local Teleost fish. No difference was found for the bottlenose dolphin LSR although continuous, tonal, high frequency components generated by the electric boat are expected to be highly detrimental for the bottlenose dolphin.

First basin scale spatial-temporal characterization of underwater sound in the Mediterranean Sea.

Anthropogenic underwater noise is an emergent pollutant. Despite several worldwide monitoring programs, only few data are available for the Mediterranean Sea, one of the global biodiversity hotspots. The results of the first continuous acoustic programme run at a transnational basin scale in the Mediterranean Sea are here presented. Recordings were done from March 2020 to June 2021, including the COVID-19 lockdown, at nine stations in the Northern Adriatic Sea. Spatial-temporal variations of the underwater sound are described, having one third octave band sound pressure levels (SPLs) from 10 Hz to 20 kHz as metrics. Higher and more variable SPLs, mainly related to vessel traffic, were found close to harbours, whereas Natura 2000 stations experienced lower SPLs. Lower values were recorded during the lockdown in five stations. Median yearly SPLs ranged between 64 and 95 as well as 70 and 100 dB re 1 µPa for 63 and 125 Hz bands, respectively. These values are comparable with those previously found in busy shallow EU basins but higher levels are expected during a business-as-usual period. This is a baseline assessment for a highly impacted and environmental valuable area, that needs to be managed in a new sustainable blue growth strategy.

First assessment of underwater sound levels in the Northern Adriatic Sea at the basin scale.

The protection of marine habitats from human-generated underwater noise is an emerging challenge. Baseline information on sound levels, however, is poorly available, especially in the Mediterranean Sea. To bridge this knowledge gap, the SOUNDSCAPE project ran a basin-scale, cross-national, long-term underwater monitoring in the Northern Adriatic Sea. A network of nine monitoring stations, characterized by different natural conditions and anthropogenic pressures, ensured acoustic data collection from March 2020 to June 2021, including the full lockdown period related to the COVID-19 pandemic. Calibrated stationary recorders featured with an omnidirectional Neptune Sonar D60 Hydrophone recorded continuously 24 h a day (48 kHz sampling rate, 16 bit resolution). Data were analysed to Sound Pressure Levels (SPLs) with a specially developed and validated processing app. Here, we release the dataset composed of 20 and 60 seconds averaged SPLs (one-third octave, base 10) output files and a Python script to postprocess them. This dataset represents a benchmark for scientists and policymakers addressing the risk of noise impacts on marine fauna in the Mediterranean Sea and worldwide.

Is the Venice Lagoon Noisy? First Passive Listening Monitoring of the Venice Lagoon: Possible Effects on the Typical Fish Community.

Three passive listening surveys have been carried out in two of the three Venice lagoon tide inlets and inside the Venice island. The spectral content and the intensity level of the underwater noise as well as the presence or absence of Sciaena umbra and the distribution of its different sound patterns have been investigated in all the recording sites. The passive listening proved to be successful in detecting S. umbra drumming sounds in both Venice lagoon tide inlets. Our results indicate that the spectral content and the level of underwater noise pollution in the Venice lagoon could affect fish acoustic communication.

Underwater noise assessment in the Gulf of Trieste (Northern Adriatic Sea, Italy) using an MSFD approach.

In the marine environment, underwater noise is one of the most widespread input of man-made energy. Recently, the European Commission has stressed the necessity of establishing threshold levels as a target for the descriptor 11.2.1 "Continuous low frequency sounds" in the Marine Strategy Framework Directive (MSFD). In 2012, a monthly underwater noise monitoring programme was conducted in the Gulf of Trieste (Northern Adriatic Sea, Italy); the collected acoustic samples (frequency range: 10-20,000 Hz) were analysed in the 1/3 octave bands. The stations have been further clustered following the 63 and 125 Hz bands noise levels. Average SPL levels resulted similar to those previously computed for proximate areas, indicating that the Adriatic Sea sub-region experiences high noise pressure in the marine waters. In its turn this claims for a scientific and technical international cooperation, as requested by the EU programme. No seasonal variation in local noise levels has been found.

Brown meagre vocalization rate increases during repetitive boat noise exposures: a possible case of vocal compensation.

This study investigated whether or not boat noise causes variations in brown meagre (Sciaena umbra) vocalizations recorded in a nearshore Mediterranean marine reserve. Six nocturnal experimental sessions were carried out from June to September 2009. In each of them, a recreational boat passed over vocalizing fish 6 times with 1 boat passage every 10 min. For this purpose three different boats were used in random order: an 8.5-m cabin-cruiser (CC), a 5-m fiberglass boat (FB), and a 7-m inflatable boat (INF). In situ continuous acoustic recordings were collected using a self-standing sonobuoy. Because boat noise levels largely exceeded both background noise and S. umbra vocalizations in the species' hearing frequency range, masking of acoustic communication was assumed. Although no immediate effect was observed during a single boat passage, the S. umbra mean pulse rate increased over multiple boat passages in the experimental condition but not in the control condition, excluding that the observed effect was due to a natural rise in fish vocalizations. The observed vocal enhancement may result either from an increased density of callers or from an increased number of pulses/sounds produced by already acoustically active individuals, as a form of vocal compensation. These two explanations are discussed.

Sound pressure and particle acceleration audiograms in three marine fish species from the Adriatic Sea.

Fishes show great variability in hearing sensitivity, bandwidth, and the appropriate stimulus component for the inner ear (particle motion or pressure). Here, hearing sensitivities in three vocal marine species belonging to different families were described in terms of sound pressure and particle acceleration. In particular, hearing sensitivity to tone bursts of varying frequencies were measured in the red-mouthed goby Gobius cruentatus, the Mediterranean damselfish Chromis chromis, and the brown meagre Sciaena umbra using the non-invasive auditory evoked potential-recording technique. Hearing thresholds were measured in terms of sound pressure level and particle acceleration level in the three Cartesian directions using a newly developed miniature pressure-acceleration sensor. The brown meagre showed the broadest hearing range (up to 3000 Hz) and the best hearing sensitivity, both in terms of sound pressure and particle acceleration. The red-mouthed goby and the damselfish were less sensitive, with upper frequency limits of 700 and 600 Hz, respectively. The low auditory thresholds and the large hearing bandwidth of S. umbra indicate that sound pressure may play a role in S. umbra's hearing, even though pronounced connections between the swim bladder and the inner ears are lacking.

Effects of ambient and boat noise on hearing and communication in three fish species living in a marine protected area (Miramare, Italy).

The WWF-Natural Marine Reserve of Miramare (Trieste, Italy) is located in a major industrial and vacation area in the Adriatic Sea. Consequently, noise emanating from boating and shipping is an inevitable factor for local fishes. This study investigates the effects of ambient and ship noise on representatives of three vocal fish families with different hearing abilities. Ambient and ship noise were recorded, their sound pressure levels measured and played back in the lab. Auditory sensitivity was determined in Chromis chromis, Sciaena umbra and Gobius cruentatus, utilizing the auditory evoked potential recording technique. Compared to lab conditions, hearing thresholds determined during ambient noise playbacks were barely masked. Contrary, the noise emanating from a cabin-cruiser substantially reduced auditory sensitivity relative to thresholds in ambient noise. This masking effect was most pronounced in the frequency range where acoustic communication takes place. Boat noise potentially affects acoustic communication in fishes inhabiting the reserve.