Identification codes in Southern Hemisphere fin whale songs

Drop a microphone into the Atlantic Ocean, and it will amplify a chorus of leviathans: fin whales, Antarctic minke whales, blue whales, and more. At 20 hertz, the pulses of the fin whales dominate.

The turbulent weather conditions of the Atlantic Ocean make visually tracking fin whales, whose populations were heavily depleted by commercial whaling, challenging. Their acoustic signals, however, remain detectable.

Wöhle et al. studied songs of the Southern Hemisphere fin whale at two locations in the Weddell Sea, finding two high-frequency components that are distinct and recognizable across region and year. These reliable acoustic markers, produced simultaneously with 20 hertz calls, provide insight into population distribution.

The signals, 86 hertz at Elephant Island and 99 hertz at the Greenwich Meridian, show both inter- and intra-annual variabilities. The calls decrease in peak frequency from March to July each year, and from 2011 to the present.

Intra-annual variation may be related to hormonal cycles and cultural transmission, while long-term signal frequency decline may be related to increasing population density. Despite the decline, the two high-frequency signals remain spectrally distinguishable.

High-frequency signal population identification requires less time and effort than the conventional inter-pulse-interval analysis.

“I would say this could be the foundation of probably easier identification of acoustic populations,” said author Svenja Wöhle.

Rather than measuring the time between each 20 hertz pulse to find the repeating patterns that define a population-specific song, researchers can search for the presence of the high-frequency signal. The method enables long-term study of acoustic populations, as the signals remain easily identifiable in the shifting rhythm of whale song.

Source: “Shifts in acoustic signature of Southern Hemisphere fin whales: Declining peak frequency of high-frequency components,” by Svenja Wöhle, Laura Parker, Elke Burkhardt, Ilse Van Opzeeland, and Elena Schall, JASA Express Letters (2025). The article can be accessed at https://doi.org/10.1121/10.0039500 .