How to find a cryptic animal: Recording the elusive beaked whale in the Foz do Amazonas Basin

WASHINGTON, Sept. 9, 2025 – Whale watching is a popular pastime on coastlines around the world. Cetaceans like blue whales, humpbacks, and orcas can be seen in the wild, and their characteristics are well categorized in science and popular culture. Other cetaceans, however, are less outgoing, preferring to stay out of the limelight.

Beaked whales are considered one of the least understood mammals in the world, which is due to their cryptic behavior and distribution in offshore waters. Predation pressure from their predators may be one of the factors driving these whales to exhibit inconspicuous surface behavior. They are also the deepest diving mammal on record, able to dive around 3,000 meters below the surface for over two hours.

In JASA, published on behalf of the Acoustical Society of America by AIP Publishing, researchers from Instituto Aqualie, Juiz de Fora Federal University, Mineral Engenharia e Meio Ambiente, and Santa Catarina State University set out to record these elusive whales.

“The motivation for this research arose from the need to expand knowledge on cetacean biodiversity in Brazilian waters, with particular attention to deep-diving species such as beaked whales,” said author Raphael Barbosa Machado.

Beaked whales, currently represented by 24 species, produce sounds that differ from those of other toothed whales, using echolocation pulses that enable them to perceive their surroundings. However, these pulses are generally not emitted at the surface, posing a challenge for reliably associating the sound with a visually confirmed species.

Machado and his colleagues began their search in 2022 in the Foz do Amazonas Basin off the coast of northern Brazil. Using passive acoustic monitoring, hydrophones, and autonomous recorders operating at 192-384 kilohertz, they were able to capture nine audio recordings, visually spotting the whales four separate times. After analyzing the data, they found they had recorded at least three different beaked whale species.

“This study provides the first documentation of acoustic parameters of beaked whales in Brazilian waters, while also contributing new information on cetacean biodiversity in northern Brazil,” said Machado.

Their results also demonstrated that acoustic monitoring is a viable strategy for categorizing evasive sea creatures. Machado and his team intend to continue studying the biodiversity of the western South Atlantic Ocean, which remains poorly studied to this day.

“As the number of detections increases — particularly simultaneous visual and acoustic records — our ability to reliably associate specific acoustic signals with visually confirmed species will also improve,” said Machado. “Addressing these knowledge gaps is essential for informing public policies and guiding conservation and management efforts aimed at safeguarding these elusive species.”

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The article “Finding beaked whales in the Foz do Amazonas Basin: Visual and acoustic records of a deep diving cetacean” is authored by Raphael Barbosa Machado, João Pedro Mura, Giovanne Ambrosio Ferreira, Franciele Rezende de Castro, Natália de Souza Rodrigues-Soares, Larissa Kelmer de Lima Kascher, Barbara Stefânea da Silva, Gabrieli Messias Rodrigues, Lúcia Alencar, Yasmin Viana, Daniela Ferro de Godoy, Pedro Volkmer de Castilho, and Artur Andriol. It will appear in The Journal of the Acoustical Society of America on Sept. 9, 2025 (DOI: 10.1121/10.0038973). After that date, it can be accessed at https://doi.org/10.1121/10.0038973.  

ABOUT THE JOURNAL

The Journal of the Acoustical Society of America (JASA) is published on behalf of the Acoustical Society of America. Since 1929, the journal has been the leading source of theoretical and experimental research results in the broad interdisciplinary subject of sound.  JASA serves physical scientists, life scientists, engineers, psychologists, physiologists, architects, musicians, and speech communication specialists. See https://pubs.aip.org/asa/jasa.

ABOUT THE ACOUSTICAL SOCIETY OF AMERICA

The Acoustical Society of America (ASA) is the premier international scientific society in acoustics devoted to the science and technology of sound. Its 7,000 members worldwide represent a broad spectrum of the study of acoustics. ASA publications include The Journal of the Acoustical Society of America (the world's leading journal on acoustics), JASA Express Letters, Proceedings of Meetings on Acoustics, Acoustics Today magazine, books, and standards on acoustics. The society also holds two major scientific meetings each year. See https://acousticalsociety.org/.

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