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."
