Under the Ice, Sounds of Spring - 05-18-2011, 05:15 AM
By KATE STAFFORD Kate StaffordAbove the ice, there is often little evidence of life. But down below, the ocean is alive with the sounds of whales and seals.
Kate Stafford, an oceanographer at the Applied Physics Laboratory at the University of Washington, writes from Alaska, where she is participating in a visual census of bowhead whales.
Friday, May 13
You can look across a vast expanse of ice, all white and blue and cold, and see nothing. The lead is choked with pack ice or sealed over with newly formed ice, and there is no movement or sound. With few birds, no whales and no bears, one might mistake the Arctic for a desert. But if you go down to the ice edge, pick a hole in the new ice deep enough to reach water and drop in a hydrophone (an underwater microphone), the cacophony is astonishing.
Bearded seals, bowhead whales and belugas.
Most of my research involves listening to the oceans, especially in the Arctic. While I am still excited to hear animals underwater, the din no longer takes me by surprise. What I have come to enjoy just as much as listening is passing the headphones to someone who has never heard springtime in the Arctic. It is a rite of spring that would stun even Stravinsky.
Kate StaffordA bearded seal surfaces in a lead.
Here in the Chukchi Sea the springtime soundscape is dominated, always, by the long trills of male bearded seals. These signals are believed to be a male display; whether of territorial defense or to attract a mate is unclear. Their trills are ubiquitous in every Arctic ocean. Though we have seen only one or two bearded seals off Barrow, it is clear from the acoustic data that there are many of them trilling all at once and within only a few kilometers of the perch.
Bearded seal trill.
Grunts and moans from bowhead whales.
Beluga whistles with a few bowhead moans.
During spring migration, bowhead whales produce a variety of sounds, including songs that may serve a similar function as the bearded seal trills. Bowheads also produce simpler sounds: moans and grunts and trumpets that most likely aid in communication among animals but also help individuals navigate in ice-choked waters.
Pods of beluga whales swim by and whistle and whinny and squeal as they pass. All this is happening even when the lead appears closed and there is no surface expression of the existence of these animals. The ice creaks and cracks and groans and whines. This is the case in all the world’s oceans; anywhere you put a hydrophone, you are likely to learn something new about the animals that pass unseen.
Kate StaffordAn adult beluga whale swimming north.
Acoustic communication is key in a dark, ice-covered environment. This sense, more than any other, provides whales with information about their habitat, and the presence and behavioral state of other animals nearby. Sound propagates well in water, so signals can be heard over much greater distances than animals can be seen. Higher-frequency sounds, like those made by belugas, travel only a short distance, while lower-frequency sounds made by bowhead whales can be heard many tens of kilometers away.
The low frequencies used by bowhead whales overlap the acoustic bandwidth in which large ships and oil and gas exploration produce sound. These manmade sources of noise are likely to increase background noise levels as summer sea ice continues to decline and shipping routes cross the Arctic during ice-free summers. It is possible that this increase in noise will affect bowhead whales in particular by causing them to change the frequencies they use to communicate or the duration of the calls they produce, or by restricting the ranges over which they communicate. Currently, acoustic data from long-term recordings (months to years) is being collected and analyzed to assess the extent of the effects of anthropogenic noise on bowhead whales in the Arctic and marine mammals elsewhere in the world.
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