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Listening to Whales: Hydrophones, Headphones, and Singers in the Sea

Karen B.'s avatar

Education

Tuesday, January 06, 2015

Karen

Listening to Whales: Hydrophones, Headphones, and Singers in the Sea
One of the large floating buoys attached to the anchored hydrophones.

Whales live in a world full of sound. The ocean was a noisy place even before humans started making a ruckus underwater with boat engines, blasting, construction, drilling, and seismic air gun noise; surf smashes against the beach, underwater volcanoes erupt, wind kicks up foamy white-capped waves, fish grunt, shrimp snap, dolphins click and whistle, and the list goes on. In the midst of all this racket, male humpback whales are trying to stage a romantic serenade. They pose half on their heads in the water, swim very, very slowly, and sing. Within a population (population: noun. a group of animals that live in a particular place), each year, every male humpback sings the same song – the 2014 hit single, if you will. The song changes from year to year, and is passed between populations. How did the song travel? Who carried it? Who listened to it? How did it change? Does being exposed to seismic air gun noise affect their singing? What does that teach us about the whales? Answering these questions may help us better protect whales and understand when, where, and how that protection is most needed.

It’s mid-afternoon on the ocean a few kilometers offshore from BRAHSS project headquarters at Peregian Beach. The research vessel Proteus, a small “tinny,” a metal-sided boat, bobs up and down on the waves, held in place by the sea anchor. A scientist sits cross-legged on the boat’s deck, grinning with her eyes closed. Large headphones cover her ears, and she’s holding the end of a long, black cord, no wider than a pencil. Dangling over the side of the boat, the cord terminates in a waterproof black cylinder, only a few inches long. This is a hydrophone (“hydro” meaning water, “phone” meaning sound). It’s recording a singer, an adult male humpback performing his solo, and playing the recording through to the headphones, giving our girl on the deck such a broad grin.

This year’s whale song would not sound like Frank Sinatra to you and I; personally, I think it sounds spooky, both beautiful and sad, with occasional comical squeaks. But it’s just what the female humpback whales are listening for, along with the BRAHSS acousticians (acoustician: noun. a scientist who studies sound). Recordings of whale song are made with the hand-held hydrophones, like the one we’re using today on Proteus, and with hydrophones attached to the big floating buoys, pictured below. Back at headquarters, these recordings will be run through a computer program that turns the song into a picture. This picture is called a spectrogram; it’s essentially the sheet music of whale song. Studying these recordings and images, the acousticians can work out the pattern of the 2014 Australian east coast humpbacks’ song. Next year, if things go as usual, another group of humpbacks will sing this pattern, and the population here will sing a new song, transmitted to them from another ocean.

Back on the deck of Proteus, the scientist wearing the headphones opens her eyes. “It’s getting fainter,” she says. “He’s about to surface.”

Everyone on board, skipper, scientist, deckhand, and research assistant, looks for signs of a whale surfacing. A few long moments pass.

“Blow! Eight o’clock!”

Our singer has swum a fair distance away in those few minutes. Quickly, we reel up the hydrophone, and Proteus motors to the new location, marked by a still patch on the water’s surface. The hydrophone is deployed and we begin recording again. This time we are lucky, and are very close to our singer. He is deep enough that we can’t see him, but his song echoes up through the water, resonating through the metal hull of the boat. We sit in awed silence and listen.

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