Listening to the Ocean

© P.DeParscau/Tara Expéditions

2 July 2015

François Aurat (second capitaine) et Louis Wimotte (électricien) testent l’hydrophone avant sa mise à l’eau

François Aurat (first mate) and Louis Wilmotte (electrician) test hydrophone before launching

After sailing along the English coast for several miles, TARA took advantage of a 20-knot wind from the south to cut her engines and let the hull roll on soon-to-become Scottish waves. A climate conducive for encounters, as was the case yesterday with a pod of 5 Risso’s dolphins that came to greet the bow in turquoise waters. Tara has often observed these animals, but during the upcoming nordic campaign, we will listen to them for the first time. To do this, in Rouen the crew took aboard a special device: a hydrophone. A waterproof microphone, 50 meters of cable and a recorder: a rudimentary kit already tested by a duo well known to Taranautes: Louis Wilmotte, electrician aboard, and Douglas Couet, oceanography student. Having accomplished the MareNostrum adventure together, they were reunited aboard Tara during our route along the Brittany coast.

Arrivée de l'équipage MareNostrum à Istanbul après 14 mois de mer

Arrival of the MareNostrum crew in Istanbul after 14 months at sea

“It was a real challenge to voyage between Gibraltar and Istanbul by kayak” Doug told me as we passed the Cotentin Peninsula. “We were totally autonomous for 14 months, traveling these 8,500 kilometers of coastline, and participating in research on the marine environment.” MareNostrum carried aboard their kayak a type of hydrophone developed by Professor Hervé Glotin at the University of Toulon. “As soon as we could, we immersed the hydrophone to a depth of 30 meters and recorded sounds for a few minutes. Not many studies have researched this, neither cetaceans nor anthropogenic noise, that is, noise produced by man under water”. Thanks to this technique of sound observation, scientists are able to identify all so-called “vocalizing” species — over 60 cetaceans and certain molluscs and shellfish. Unlike surface observations, the hydrophone has a more extensive surface and depth range — up to several kilometers –  in registering certain frequencies. Occasional sounds are very recognizable, like the click of  the sperm whale which Doug let me discover with headphones. “This large animal, over 20 meters long, which hunts squid at great depths, will emit only this very small sound to communicate and locate itself underwater.” On the sound wave displayed by this signal, the 3 closely-spaced peaks definitely betray the presence of one of these sperm whales in the area being analyzed.

Dauphins de Risso rencontrés par TARA au large de l’Angleterre

Spinner dolphins encountered by TARA off England’s coast

These recordings have resulted in an unprecedented survey of underwater sounds throughout the northern Mediterranean. Thanks to the sound signature of each species, scientists were able to identify different populations present along the route of the 2 kayakers, and also quantify noise pollution in the marine environment. “Noise pollution, depending on level and frequency, disrupts inter-individual communications and thus reproduction,” explains Professor Glotin. “The sounds produced by man also disrupt their hunting and therefore feeding.” The example of dolphins found stranded in the Adriatic with pierced eardrums also highlights physiological effects possibly related to overly loud noises. The impact of man-made noise on the marine population is still under study, but certain elected officials have begun questioning the state of their coasts. The municipality of Villefranche-sur-Mer has commissioned Professor Glotin and his team to analyze the sounds of the port to better understand the effects of development on life in the depths.

Chaque lieu d'enregistrement est soigneusement inscrit dans le carnet de bord de l'hydrophone

Each recording location is carefully noted in the hydrophone’s logbook

To extend these analyses, TARA will make new recordings during the campaign in northern latitudes. “With these sound samples, we hope to analyze the song-structure of humpback whales in the area, and collect data on the behavior and status of other species we’ll detect.” A scientific adventure that promises to mobilize TARA’s crew during the coming weeks — listening to the world of silence.

Pierre de Parscau

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