“For some of us, it’s just been, ‘ugh, these dang whales are in my data,’” Dr. Caplan-Auerbach said. Humpback whales have interrupted her research in the past on Lō‘ihi Seamount, an underwater Hawaiian volcano. “We had tons and tons of whale song, and to me it was just total noise in my data.”
But as this new study shows, this noise can be used to study the planet’s interior. “And that’s awesome,” she said.
“It’s never going to replace air guns,” Dr. Kuna said. Fin whale seismic waves are somewhat weak, which means their imaging of the subsurface is of relatively low resolution. “But it is a complement. And it’s free.”
Although seismologists are careful to avoid marine life, a recent report detailed just how noisy the oceans have become in recent years as a result of human activity. Finding more ways to use fin whale seismology could mean adding less to the cacophony. “It’s win-win,” Dr. Kuna said.
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 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.
This paper may be about the seismological benefits of fin whales, but this method may prove useful to marine ecologists, Dr. Wilcock said. In recent years, seismometers on land have been trying to track elephants and estimate their populations. The same principle could apply to fin whales, animals endangered by climate change, habitat loss and the grim legacy of commercial whaling. And like those elephant-eavesdropping seismometers, machine learning may one day listen for signature fin whale songs and autonomously detect different pods of fin whales, or individuals within those groups.
“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.”