Whales to be Tracked Globally With Earthquake Sensor Arrays

Researchers have found they can better track whales and know what they're doing by analyzing whale vocalizations caught by undersea seismometers, which record vibrations.

The seismic devices, primarily used to collect data on earthquakes, have proved an inexpensive and non-invasive way to monitor the whales.

The findings were presented in three papers published this winter in the Journal of the Acoustical Society of America.

The research, the first to match whale calls with fine-scale swimming behavior, and therefore the animals' movement and communication patterns,  began about decade ago, the offshoot of an effort to monitor earthquakes along the seismically-active Juan de Fuca Ridge, located more than a mile below the water surface off the coast of Washington state.

Eight seismometers, inserted into holes drilled into seafloor lava, were installed at an ocean spreading-center volcano 150 miles off Vancouver Island.

During its three years in operation, the small listening network detected about 40,000 small earthquakes and hundreds of thousands of fin-whale calls.

"Over the winter months we...had an awful lot of fin-whale calls," said principal investigator William Wilcock, a professor of oceanography at the University of Washington, who admitted that, at first, the fin whale calls, which overlapped the seismic data, "were kind of just a nuisance."

But, in 2008, Wilcock won funding from the Office of Naval Research to study the previously discarded whale calls.

Wilcock's team compared the calls recorded by all eight seismometers, an approach that previous studies had used to examine for just two or three animals at one time.

In much the same way a smartphone's GPS determines a person's location by comparing the distances to different satellites, scientists used the recorded calls of specific fin whale made by the eight seismometers to calculate whale position.

The technique allowed researchers to follow the animal's path as it passed through the instrument grid and within 10 miles of its sensory limits.

Michelle Weirathmueller, a UW doctoral student in oceanography, used triangulations of data from that first seismic listening network to determine the loudness of whale calls and the vocal sounds made by fin whales are surprisingly consistent at 190 decibels underwater, which in air in the air is about as loud as a jet engine.

Knowing the consistent loudness a whale's calls will help Weirathmueller and her colleagues  track whales with more widely spaced seismometer networks, such as the Neptune Canada project, the U.S. cabled observatory component of the Ocean Observatories Initiative and the huge 70-seismometer Cascadia Initiative array that's started to detect tremors off the Pacific Northwest coast.

"We'd like to know where the fin whales are at any given time and how their presence might be linked to food availability, ocean conditions and seafloor geology," Weirathmueller said.

"This is an incredibly rich dataset that can start to pull together the information we need to link the fin whales with their deep-ocean environments."