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FINNED SEISMOLOGISTS AID IN OCEANIC RESEARCH

THE FIN WHALE, Balaenotera physalus, grows to about 80 ft. in length, weighs up to 80 tons, lives more than 80 years, and chats with others of its species in astoundingly loud chirps. And such is the chirps’ sonic energy that it rebounds from below the seafloor through sediment and underlying volcanic rock.

The fin whale, Balaenotera physalus, endangered and protected throughout its range. Image from noaa.gov.

Hitherto, oceanic researchers have treated these reflected vocalizations as noise in their data. But, as described by Václav M. Kuna and John L. Nábĕlek in Science magazine, February 12, 2021, these fin whale songs have been used for seismic crustal imaging.

Traditional Soundings. Kuna and Nábĕlek observe,  “Probing the structure of the ocean crust requires a wave source. The most common source is an air gun, which is effective but potentially harmful for ocean life and not easy to use everywhere.” Another technique is monitoring seismometers placed on the ocean floor and recording tectonic events.

Listening Instead to Fin Whale Songs. Kuna and Nábĕlek write, “Fin whale vocalizations are among the strongest animal calls in the ocean. Reaching up to 189 dB, the source levels are comparable to those of noise produced by large ships. The calls can be monitored hundreds of miles away from the source, enabling studies of whale behavior, abundance, distribution, and migration patterns.” 

To put fin whale sonic energy in perspective, a jet plane taking off is measured at around 150 decibels at a distance of 80 ft.

Kuna and Nábĕlek continue, “Fin whale vocalizations include short, 1-second calls with a dominant frequency of around 20 Hz. Calls are characterized by a sinusoidal, downward frequency-sweeping signal, with about a 5-Hz drop in frequency over the duration of the call.”

Humans experience a 20-Hz sound at the lower range of audibility, felt as much as heard. 

Spectrogram of a 7-minute section of an unfiltered fin whale song. This and a following image from Kuna and Nábĕlek, Science, February 12, 2021.

“These calls repeat every 7 to 40 seconds,” the researchers say, “forming songs that last up to tens of hours, with short interruptions about every 15 minutes when the whale surfaces.”

A fin whale. Image from The New York Times, February 11, 2021.

In “Whale Songs Could Reveal Deep Secrets Beneath the Oceans,” The New York Times, February 11, 2021, Robin George Andrews quotes seismologist/volcanologist Jackie Caplan-Auerbach: “It’s a nice example of how we can make use of the data the planet provides for us.” 

“And it’s free,” says Dr. Kuna. “It’s a win-win.”

Seismological Tools to Study Biology. The technique may prove useful to marine ecologists: Andrews reports, “For this study, the researchers had to determine the location of the fin whales, a bit like searching for the epicenter of an earthquake. They looked at the arrival times of both the whale chirps’ sound waves heading directly to the seismometer and the sound waves ricocheting between the sea surface and the seafloor.”

The travel paths of waterborne chirp energy can be used to estimate the distance to the whale.

Andrews continues, “The time difference revealed the whale’s distance. Making some reasonable assumptions about the fin whale’s typical swimming depth, they could trace their journeys through the ocean.”

“We can use the tools of biology to study seismology,” Dr. Caplan-Auerbach said. “And we can use the tools of seismology to study biology.”

All from listening to fin whales having oceanic chats. ds 

© Dennis Simanaitis, SimanaitisSays.com, 2021 

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