Scientists listen in on sounds of underwater life

TECHNOLOGY:THE UNDERWATER explorer Jacques Cousteau mistakenly called the sea the "silent world" before humans figured out a way to listen in, writes KARLIN LILLINGTON

We now know the oceans are full of clicks, chirps, rumbles, wails and warblings, with many of the most complex and beautiful noises generated by cetaceans – whales and dolphins.

A growing realisation that Irish seas are among the richest in the world for cetacean life – 24 species have been identified here, from little porpoises to the majestic blue whale – has led to groundbreaking acoustic research to learn more about these creatures, and to keep them safe.

“Irish whales and dolphins need to be conserved, but we don’t know a lot about them,“ says Dr Michael O’Toole, a programme manager at the Marine Institute with responsibility for several cetacean acoustic projects.

Advances in acoustic hardware and software are driving these developments, enabling Irish engineers and researchers to listen in on, locate and learn more about the cetaceans.

At the technical forefront is Galway company Biospheric Engineering, which builds the hydrophone (underwater microphone) arrays and links them to computer programmes that process the sound files they generate.

“You have to have the correct hardware, because you’re dealing with such a huge range of sounds at extremes of loudness and frequency,” says company founder Eugene McKeown.

At one end are species that emit soft, infrequent sounds, and at the other are loud, vocal cetaceans that could overload acoustic equipment with their comparative din.

Hydrophones for such purposes can be attached to buoys, fastened to the sea bottom where they rise to the surface months later, fixed to the bottoms of ships, towed behind on long lines, or used with sensor devices. The technique is called passive acoustic monitoring because the animals can be “observed” passively via the sounds they make, from a distance. No direct interaction or tagging is necessary.

Several cetacean projects are under way, involving partners including Biospheric, Dublin City University, IBM, the Marine Institute, and the Irish Whale and Dolphin Group (IWDG).

Simply learning to use acoustics to identify each species – via their unique frequencies – has taken months of collaborative work between McKeown and the IWDG.

Now, says Simon Berrow of the IWDG, the project is paying off. Using McKeown’s arrays, he was able to get some of the first recordings of minke, fin and humpback whales in Irish waters.

“Fundamentally, cetaceans are acoustic animals. They have highly developed acoustic senses of which we understand very little,” says Berrow. “We’re trying to develop a long-term data set on cetaceans.”

At the end of this month, a two-week voyage on the Celtic Explorerwill take 17 scientists, including cetacean specialists and McKeown, to the edge of the sea shelf off the Irish Atlantic coast. There, they will undertake the first dedicated survey of ocean species in the region. "We're targeting the canyon because we're looking for the beaked whale, a rare and elusive species that routinely dives to 1,000 metres," says Berrow.

“Some are only known from DNA samples and dead whales that wash ashore here.”

Beaked whales are believed to be particularly vulnerable to undersea blasting. The hope is that a network of acoustic monitoring devices will eventually be in place to allow those creating sound through sonar, construction or dredging to cease activities when sound-sensitive cetaceans are near.

Underwater blasting is loud enough to deafen a diver, says McKeown, and must jar sensitive cetacean hearing even at a distance, as sound waves can travel much farther under water than in air. Human-generated underwater noise is believed to be responsible for cetacean strandings and perhaps death in deep-diving whales who surface too quickly in fright and get the “bends” – bloodstream bubbles that can cause stroke.

Ireland is mandated by the EU to monitor its cetaceans in a zone extending 320km (200 miles) off the coast, and acoustic monitoring would make it far easier to fulfil this requirement, says O’Toole.

The partners also hope to obtain interesting results from a project in conjunction with IBM Ireland to use the sensors in Galway Bay as part of the existing SmartBay initiative to track cetaceans in real time and make that data available to anyone from scientists to whale-watching groups.

Berrow is fascinated by the complex view of cetacean life being generated by the projects. “The more we do, the more amazing we find things are here,” he says.

How to hear under the sea

Eugene McKeown, founder of Biospheric Engineering in Galway, has made building better underwater acoustic arrays one of his specialities.

McKeown, who has a background in environmental acoustic noise and vibration, uses hydrophones (underwater microphones) that are connected to computers. The computers store the acoustic data that is generated, and then process and analyse them.

“You need a system for hearing and a system for calibrating because you need to understand the noises you are hearing,” he says, though “hearing” is a bit of a misnomer.

Humans can perceive sounds in the 20 hertz to 20 kilohertz range. Porpoises, for example, communicate at 50 kilohertz, while some whale song is at very low frequencies, and both are imperceptible to the human ear.

And because some noises are very faint and some are loud, hydrophones have to be able to tolerate extremes.

For detection, McKeown uses arrays of four to six hydrophones, with two mounted on a ship at front and rear and some towed behind it. The location of a cetacean can be triangulated off the millisecond delays at which its calls hit the hydrophone array. Software calculates the angles and the location can be determined in real time. Sounds are processed into visual representations which identify a species, as each has its own unique frequency.

The amount of raw data is enormous. McKeown says four hydrophones generate a megabyte of data a minute. He brings several PCs and disk drives on board, one for low- and one for high-frequency sounds, and several for mid-range noises.