Undersea Recorders Locate Large Whales in Unexpected Places

SEATTLE, Washington, January 2, 2006 (ENS) - Blue whales off the Pacific Northwest coast sound different than blue whales that live in the western Pacific Ocean, and those sound different from blue whales off Antarctica. And they all sound different than the blue whales off Chile, according to scientists listening to whale sounds recorded by undersea microphones moored to the ocean floor.

The blue whale is the largest mammal ever to inhabit the Earth. Blue whales can weigh over 100 tons and measure more than 100 feet in length. (Photo courtesy IWC)

They have found whale species in unexpected places, such as critically endangered North Pacific right whales in the Gulf of Alaska, where they were formerly abundant but have not been seen in decades.

"There has been only one confirmed sighting of a right whale in the Gulf of Alaska since 1980, so discovering them is not only surprising, it is fairly significant," said David Mellinger, an assistant professor at Oregon State University's Hatfield Marine Science Center in Newport. "We picked up the sounds of one whale off Kodiak Island, and several others in deep water, which is also something of a surprise, since most right whale sightings have been near-shore."

The autonomous data-recording devices, equipped with underwater microphones called hydrophones, have been used to track many whale species - blue, fin, humpback, North Pacific right, bowhead, and sperm whales - an article in the January 2006 issue of the journal "BioScience" reports.

Oceanographer Dr. Sue Moore (Photo courtesy Arctic Research Consortium of the U.S.)

In the "BioScience" article, Moore and her colleagues describe how they tracked the seasonal occurrence of large whales by detecting their calls on the hydrophones deployed in the Gulf of Alaska, the Bering Sea and the Beaufort Sea.

She describes the use of two types of undersea recorders, one developed by NOAA's Pacific Marine Environmental Laboratory and the other by the Scripps Institution of Oceanography, where Moore completed her doctorate with a dissertation on whale habitats in the Alaskan Arctic.

The recorders are attached to hydrophones that are held at different distances from the ocean floor and are equipped with disk drives able to store tens of gigabytes of data, she writes. This allows them to operate for months before they are recovered and the data accessed.

The sound patterns picked up by the hydrophones have yielded much new information and raised many questions as well.

"The whales in the eastern Pacific have a very low-pitched pulsed sound, followed by a tone," Mellinger explained. "Other populations use different combinations of pulses, tones and pitches. The difference is really striking, but we don't know if it is tied to genetics, or some other reason."

"There are also some hybrid sounds that are rare," he said. "We don't know if they are part of a common language that different populations of whales use to communicate with each other, or if they come from a confused juvenile who hasn't completely learned the complexities of communicating."

Researchers deploy an acoustic recording package that will pick up whale sounds for more than one year at a time without servicing. ((Photo courtesy Marine Physical Laboratory) )

Another Oregon State researcher, Christopher Fox, first received permission from the Navy to use the hydrophones at his laboratory at the Hatfield Marine Science Center to listen for undersea earthquakes. While listening for earthquakes, the researchers begin picking up sounds of ships, marine landslides, and whales.

An engineer at the Hatfield center, Haru Matsumoto, then developed an autonomous hydrophone that can be deployed independently of a ship or other structure.

Matsumoto says the titanium case containing the data recorder can withstand pressure to at least 1,000 meters (3,280 feet) below sea level. These instruments are capable of recording frequencies from 1 - 20,000 Hz, and depending on the sampling rate, can record data for over a year before servicing is required.

Also collaborating on the whale acoustics study is Professor John Hildebrand with the Scripps Institution of Oceanography who heads the Marine Physical Laboratory (MPL), a research unit of the University of California, San Diego. The lab used the hydrophone as the basis for acoustic recording packages that are used for multi-year studies of whales.

The researchers placed seven of these packages in the Gulf of Alaska about five years ago.

These acoustic recording packages are used to detect whale sounds. (Diagram courtesy Marine Physical Laboratory)

"There are a handful of records of people spotting sperm whales in the region – and they're all in the summer," Mellinger said. "Likewise, all of the historic whaling records are from the summer. The Gulf of Alaska is not a place you want to be in the winter. But apparently, sperm whales don't mind."

Some species, he said, have different "dialects" depending on where they are from.

The most readily detected signals are made by the blue whale, which produces sweeping calls over a several Hertz range around 17 Hz with durations of up to 16 seconds. The call of the blue whale in the northeast Pacific is often loud enough to be detected on more than one hydrophone array.

This distinctive call allows the use of mathematical matched filters to detect the signal within the ocean's ambient noise and allow localization of calls to within a few miles from ranges of hundreds of miles, the researchers said. This technique provides a remote means of acoustically surveying thousands of square miles of open ocean for the presence and movements of large whales.

The research is funded by the North Pacific Research Board, created by Congress in 1997 to recommend marine research initiatives to the Secretary of Commerce, who makes the final funding decisions. The funding support derives from the Dinkum Sands Case decided by the U.S. Supreme Court in 1997 in which the state of Alaska lost its claim to the ownership of submerged lands along Alaska's Arctic coast, including submerged lands offshore of the Arctic National Wildlife Refuge.

The results from these acoustic whale surveys could pave the way for more sophisticated acoustic surveys that would provide data in close to real time.

More advanced recording packages are in the works that will pick up the sounds of odonotocetes, such as dolphins and porpoises.

"Currently," says Hildebrand, "we are developing another more capable autonomous bottom mounted instrument, high frequency acoustic recording package for recording odonotocetes at frequencies over 100 kHz."