Acoustic Recordings Reveal Possible Comeback for Critically Endangered Antarctic Blue Whales

Researchers have found promising signs for a possible increase of Antarctic blue whales, based on surveys spanning from 2006 to 2021.

A team of scientists analyzed data they collected from seven acoustic surveys conducted in the Antarctic region over the 15-year timespan. They used “sonobuoys” to detect marine sounds and ultimately gathered about 3,900 hours’ worth of sounds to review. 

In the analysis, the researchers specifically sought out calls of Antarctic blue whales (Balaenoptera musculus intermedia), which are the largest animals on the planet but are currently critically endangered, according to the IUCN Red List.

The researchers explained that the whales’ song sounds are considered a 3-unit vocalization (written as A, B and C throughout the study), and together, the full call is referenced as the Z-call.

They found that Unit A calls were the most widely distributed in the recordings from the sonobuoys. Unit A calls and Z-calls were more prominent in late summer and early fall. D-calls, or non-song calls, were detected most in the summer, during the feeding season. The results were published in the journal Frontiers in Marine Science.

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“Antarctic blue whales are critically endangered, and this makes them difficult to find in the vast Southern Ocean, but they make very loud, low frequency calls that we can detect from hundreds of kilometers away, using acoustic technology,” said Brian Miller, lead author of the study and marine mammal acoustician at the Australian Antarctic Division of the Australian Marine Mammal Centre, as reported by Phys.org.

According to the World Wildlife Fund (WWF), Antarctic blue whales are not just the largest animal on the planet, but also the loudest. Their calls can reach about 188 decibels, making them louder than a jet engine, and they can be heard hundreds of miles away. This makes it easier and more cost-effective for researchers to use audio to study the whales.

While the findings reveal regular calls from the whales and give hope for a potential increase in the population, the study authors emphasized that more research is needed to determine whether that means the whale population is actually rebounding.

“Maybe they’re getting louder, or maybe they’re calling more frequently. Maybe this population is increasing and that’s why we’re hearing them more often,” Miller told the Australian Broadcasting Corporation. “It’s going to take a bit more work for us to be able to answer that conclusively.”

In addition to the acoustic data, the researchers are also using other tools like satellite, video and even artificial intelligence (AI) to build a bigger database on the Antarctic blue whales. This could help provide more information about the whales, their calls and their behaviors, especially relating to the krill they eat. This primary food source for the whales is under stress from fishing and climate change, the study authors noted. 

“Passive acoustic monitoring is poised to play a crucial role in future research addressing knowledge gaps about Antarctic blue whales,” Miller said.