Characterization of underwater operational sound of a tidal stream turbine

By Denise Risch, Ben Wilson (SAMS), Nienke van Geel and Douglas Gillespie (University of St Andrews)

The underwater sound emitted during the operation of the Atlantis AR1500 turbine, a 1.5 MW three bladed horizontal axis tidal-stream turbine, was measured in the Pentland Firth, Scotland. Most sound was concentrated in the lower frequencies, ranging from 50 to 1000 Hz. Within 20 m of the turbine, third-octave band sound pressure levels were elevated by up to 40 dB relative to ambient conditions. In comparison, ambient noise at these frequencies fluctuated by about 5–10 dB between different tidal states. At the maximum recording distance of 2300 m from the turbine, median sound pressure levels when the turbine was operational were still over 5 dB higher than ambient noise levels alone. A higher frequency, tonal signal was observed at 20,000 Hz. This signal component appeared at a constant level whenever the turbine was operational and did not change with turbine rotation rate. It is most likely produced by the turbine’s generator. This study highlights the importance of empirical measurements of turbine underwater sound. It illustrates the utility and challenges of using drifting hydrophone systems to spatially map operational turbine signal levels with reduced flow noise artefacts when recording in high flow environments.

“Posidonia meadows calling”: a ubiquitous fish sound with monitoring potential

By Lucia di Iorio (Chorus Institute), Xavier Raick, Eric Parmentier (University of Liège), and Pierre Boissery (Agence de l’Eau Rhône-Méditerranée-Corse)

In the Mediterranean Sea, the seagrass Posidonia oceanica plays a key ecological role, and is protected by a range of legislation. Standard Posidonia monitoring programms generally focus on the plant at different spatial and short temporal

Acoustic behaviours of large crustaceans in NE Atlantic coastal habitats

By Laura Coquereau (UBO), Laurent Chauvaud (CNRS), and Aurélie Jolivet (SOMME)

Although many studies have investigated the benthic environment of temperatemarine waters, little is known about the acoustic behaviour of the organisms in these habitats,particularly crustaceans. This study focused on the acoustic behaviour of large crustaceans inNE Atlantic coastal regions. A total of 11 crustacean species were recorded in tank-basedexperiments to identify sound-producing species and the behaviours associated with theirsounds as well as to quantitatively characterise and compare the sounds. A total of 34 soundswere associated with behaviours such as moving, feeding, mandible rubbing, swimming, spe-cies-specific behaviour and other unidentified behaviours. The sounds included single pulseand pulse train signals that were distributed across a peak frequency spectrum of 3 to 45 kHzwith received levels between 93 and 142 dB re 1 μPa (peak to peak). The resultsdemonstrated that Brachyura had the most diverse sound types. Using a combination of sev-eral acoustic features, 24% of the recorded sounds appeared to have a high potential to be differentiated in field recordings: the feeding sound of Cancer pagurus, Carcinus maenas,Necora puberand Pachygrapsus marmoratus; the species-specific sound of C. pagurusandGalathea squamifera; and the pulse train sound associated with unidentified behaviours ofLophozozymus incisusand N. puber. These findings extend the existing crustacean acousticlibrary in marine ecosystems and contribute to our understanding of in situacousticrecordings in temperate regions.

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Mapping the diversity of spectral shapes discriminates between adjacent benthic biophonies

By Julie Lossent, Lucia Di Iorio (Chorus Institute), Cathy-Anna Valentini-Poirier and Pierre Boissery (Agence de l’Eau Rhône-Méditérranée-Corse)

Coastal soundscapes are dominated by broadband transient sounds primarily emitted by benthic invertebrates. These sounds are characterized by a very large dynamic of amplitude. The loudest ones propagate further and interfere with the detectability of benthic sounds by invading other more distant habitats. Acoustic diversity assessment is therefore biased when applying acoustic indices related to the signal’s power. Here, we propose new acoustic indices (IDSS: Indices of the Diversity of Spectral Shape) capable of extracting the diversity of the Benthic Invertebrate Biophony (BIB) despite the interference of loud and abundant sounds. A passive acoustic ecological survey was conducted in a shallow water Mediterranean bay with a small-scale mosaic of biocenosis. Sound pressure level and spectrum of the BIB revealed that the rocky fringe has the most powerful biophony propagating up to 3680m, thus “invading” other habitats. These power-based indices failed in depicting BIB diversity. The IDSS allowed to discriminate the BIB diversity despite the interfering rocky fringe biophony and including low-power sounds not depicted by traditional power-based methods. Four main categories of Benthic Invertebrates Sounds (BIS) spectra were found. Two categories (high-power, peak frequencies ~3kHz, 4kHz) were mainly linked to the rocky fringe. Their contribution to the diversity (56%) decreased with increasing distance to the fringe where low-power BIS (peak frequencies above 15kHz) predominantly contributed to the BIB (42%) and may be specific to coralligenous reefs. The IDSS enable a better characterization and quantification of the BIB diversity and of the soundscape structure with a fine spatial resolution (~200m).

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Sound characterization of the European lobster Homarus gammarus (L.) in tanks

By Youenn Jézéquel (UBO), Julien Bonnel (WHOI), and Laurent Chauvaud (CNRS)

Experiments in marine behavioural ecology rely heavily on observations made in tanks. However, when studying acoustic behaviours of marine animals in confined volumes, the effects of reverberation must be characterized, something that has been overlooked in parts of the marine ecology literature.
In this study, we characterized reverberation in tanks using an artificial sound source and examined the implications for bioacoustic studies using sounds emitted by the European lobster Homarus gammarus during feeding and in response to stress. Broadband and transient sounds commonly produced by crustaceans were severely impacted by reverberation such that their spectral characteristics and pulse width durations could not be assessed. In contrast, low-frequency
sounds could be characterized in tanks, but not their source level. Based on these observations,
we describe a simple methodology to identify which sound characteristics can be measured in tanks.
When feeding, the lobsters produced broadband and transient sounds called ‘rattles’, similar to sounds reported for tropical spiny lobsters Palinurus longipes and P. argus. When stressed, H. gammarus vibrated its carapace, producing a low-frequency sound analogous to the ‘buzzing’ sound of the American lobster H. americanus. The potential role of species-specific sound is discussed; however, although our observations represent the first bioacoustic characterization of H. gammarus, additional behavioural studies are necessary to understand their ecological meaning.

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