land, the average decibel level would be deafening to a human. But the sound is
so deep _ deeper than thunder or the biggest bass drum _ that only the sharpest
human ears could detect it.
In order to listen to the sounds in the lab, Weirathmueller and her colleagues have to speed up the recordings.
That low-frequency, rumbling quality is why the calls of fin and blue whales register on underwater seismometers, which are tuned to detect the rumblings of the Earth. Scientists have used the instruments to track whales before, but never in such large numbers or over such an extended period of time as in the UW studies.
Doctoral student Dax Soule analyzed a year's worth of data _ more than 300,000 whale calls _ recorded by eight seismometers on the ocean bottom off the coast of Vancouver Island.
Wilcock and his colleagues installed the instruments beginning in 2003 to record geologic activity at the Juan de Fuca Ridge, where molten rock rising from the Earth's interior creates new seafloor and fuels underwater volcanoes and hydrothermal vents.
In the winter, the number of whale calls was stunning.
"There are days when it's really like whale soup out there," Soule said.
Using a computer program of his own design, Soule was able to tease out the paths followed by 154 individual whales or groups as they passed through the area.
The conventional wisdom holds that only males sing, with the goal of attracting females _ but even that isn't known for sure, Calambokidis said.
Soule's data revealed two distinct types of calls, one slightly higher pitched than the other. Most of the animals he tracked were moving south in the winter and early spring, as expected. Some seemed to travel solo, while others moved in pairs or clusters. Why some animals opted to head in the opposite direction is an open question, Soule said.
One suggestion is that they might be bachelor males, with no incentive to visit the breeding grounds. But that's just guess, he cautioned.
Seismometers only detect the loudmouths, Calambokidis pointed out, which is one of the technique's shortcomings. That's why it would be ideal to mount a research blitz, where the signals from the seafloor instruments could be correlated with observations of the whales' behavior and even some tagging, he said.
Similar studies of blue whales revealed that most of the animals were silent, with just a small number of voluble males making all the racket.
Weirathmueller is expanding the UW studies by tapping into new seismic networks.
As part of a project called the Cascadia Initiative, scientists recently deployed 70 seismometers off the Northwest coast, where they've been gathering earthquake data for more than a year. An underwater observatory called NEPTUNE Canada includes seismometers, and a similar array of instruments will be installed soon off the Washington coast.
The additional sensors will allow Weirathmueller to follow the whales over a larger area and identify where they congregate and feed.
"If we want to prevent things like ship strikes and entanglements," she said, "the most important thing is to know where the whales are."
(c)2013 The Seattle Times
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