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Tuesday, July 6, 2010

Tuning In To Whale Sounds

Interesting news from the world of cetacean science, where researchers are homing in on why specific sounds come from specific Sperm Whales (not pictured!), physically and perhaps socially.

Courtesy of Wired Science:
“The whales communicate by patterns of clicks. The clicks reverberate in the head. If you listen to it carefully, there are these pulses. The time between pulses reflects the time it takes for sounds to reverberate, to go from one end of the head and back. Because the heads are all different length, they have different reverberation times,” study co-author Hal Whitehead, also a Dalhousie University biologist. Until now, “just figuring out who makes which sound underwater was tough,” he said.
That's the physiological bit. Now for the behavioral part:

...While the whales tended to possess the same basic repertoire of “codas” — the technical name for each distinctive series of clicks — one female had a completely different set. She happened to be a mother. The distinctive sounds could be what she used to communicate with her calf.

Apart from the mom, the researchers found that half of each individuals’ vocalizations followed one of two patterns.

One pattern is formed by two consecutive, slowly-paced clicks, followed by three faster clicks. It has been found only in the Caribbean. While the pattern varies slightly between groups, this study suggests that it’s consistent within the group. According to Gero, it could function as a family identifier, letting other whales know who is around. “It says, I belong to this family, I belong to this vocal clan,” he said.

The other common pattern is composed of five regularly-spaced clicks, and has been heard in sperm whales all over the world. Preliminary research suggests that the pattern may vary slightly between each individual, said Gero. If so, the pattern could function as an individual identifier — or, from another perspective, a name.
There was another, unrelated great contribution to the topic of cetacean sound recently, when TED invited Woods Hole Oceanographic Institution's Peter Tyack to talk about marine mammal sounds and humans' inability to shut up.

Tyack talks about dolphins imitating trainers' whistles. OK, parrots can mimic sounds, too. But the complexity and functionality of "vocal" art in cetaceans goes so much further. (Here's a great interactive sampler of whale "Voices in the Sea" courtesy of UC San Diego.)

In one example, Tyack points out that Humpback Whale populations each have their own distinct sounds; but songs are regularly transferred, with individuals on the move introducing a song that catches on and displaces the new group's old song. Tyack (see from around the 10-minute mark in the video) uses the example of Australian east-coast whales adopting a west-coast whales' song -- and completely, to an individual, abandoning their old song. (But you might also think of The Beatles' famous propagation of their sound across the Atlantic and beyond, releasing "Sergeant Pepper's Lonely Hearts Club Band" and utterly transforming the musical landscape.)

Something in Tyack's lecture -- maybe it was the implied fragility of cetacean songs and sound -- made me think of a "meeting" I'd read of somewhere. Turns out it was a description by David Powell, the Californian diving pioneer and aquarist extraordinaire, of dives in the Revillagigedos off the southernmost tip of Baja California (probably in the 1970s or 1980s, though chronology is an afterthought in his excellent memoirs "A Fascination for Fish"). He describes a "mysterious moaning sound" during night dives that a Mexican fisherman had once laughingly described as the "cry of the hungry tiger shark."

The morning after one such dive at Isla Socorro, Powell says:
"[W]e looked out from our cove and were astonished to see a humpback whale leap from the water and come crashing back down with a giant splash. All of a sudden the strange sounds made sense: they must have been the song of the male humpback! We were familiar with the recordings Roger Payne made in the late 1960s in the Caribbean, but what we'd heard underwater didn't sound anything like Payne's record. One striking feature that was missing was the echo of the whale song from the bottom of the deep ocean. Since we were in shallow water next to an island, we must have received the sound directly from the whale, without an echo....

We later learned that the Revillagigedo Islands are the winter home for a large number of humpbacks, a little-known fact, mainly because of the islands' remoteness. (pp. 136-137)
Tyack's talking about the potential damage of oceanic noise pollution, for the most part. But it's a fascinating window on the world of marine mammal communication (he deals more with communication than echolocation, which is present among whales only in the so-called toothed whales, as far as scientists can tell).

It also brings to mind a recent claim that Blue Whales are sliding down the musical scale. The jury's still out on whether it's somehow to escape our deafening racket, keep up with the way sound travels in ever-warmer waters, grab attention among growing populations of whales, get the girl, or for an entirely different reason.

There are reasons for optimism on the issue of noise from commercial shipping, although there's also a great counterweight in the form of public indifference and obstacles to international cooperation. Tyack points out (at around 15 minutes) that the UN's International Maritime Organization is tasked with issuing standards for commercial shipping noise levels and, hopefully, "quieting down ships."

Here's some of what the U.S. National Oceanic and Atmospheric Administration has to say about it:
Interference with (or "masking" of) such communications could have significant impacts on marine life. As a result of the potential significance of incidental noise to commercial shipping interests and the marine environment, the International Maritime Organization (IMO) has charged its Marine Environment Protection Committee (MEPC) with investigating and developing papers on these issues. GCIL worked with the National Marine Fisheries Service Offices of Ocean Acoustics Program and Protected Resources, NOAA's Office of International Affairs, as well as other federal agencies in developing the U.S. Noise and Marine Mammals Information Paper (MEPC 57/INF.4). The paper notes the ongoing work of NOAA on this issue and invites participation in NOAA’s ongoing dialogue regarding identification of potential adverse impacts associated with incidental vessel noise and the potential mitigation of those impacts.
Tyack does some of the reasoning for us, and notes that two easy improvements that might even be cost neutral are slightly adjusting shipping lanes and easing up on the throttle. But it's far from a no-brainer.

"They've already found that by being more intelligent about propeller design, you can reduce that (propeller) noise by 90 percent," Tyack says. "If you actually insulate and isolate the machinery of a ship from the hull, you can reduce that noise by 99 percent. So at this point it's primarily an issue of cost and standards."

We humans aren't the greatest of neighbors to begin with; and even if we started implementing dramatic changes, the improvements would come only gradually. But alas, it's hard to imagine this particular topic getting its due at the best of times, much less amid the current (and overdue) hue and cry over global warming.

But the next time one of your dives is spoiled by the liquid-jelly grind of a passing motorboat, put yourself in the flukes of marine mammals trying to doze, woo, croon, mingle, coddle or hunt with the human cacophony blasting away from above.

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