Beaked whales are one of the most poorly understood mammals. That’s because these mysterious cetaceans are some of the deepest-diving whales, and rarely spend any time at the ocean’s surface. A new study has combined visual and acoustic monitoring to track these elusive creatures in the deep Foz de Amazonas basin off the north-eastern coast of Brazil.
Study author Raphael Barbosa Machado, a researcher at the Juiz de Fora Federal University in Brazil, said, “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,” in a press release. Machado and a team of Brazilian researchers published their findings in The Journal of the Acoustic Society of America.
Listening for the Mostly Silent Whale
Tracking down the whales was no easy feat. The animals can spend over two hours underwater, reaching depths of 3,000 meters (about 9,800 feet), where they feast on deep-water squid and crustaceans. Machado and his colleagues knew that the whales could be identified by their distinctive echolocation pulses, which they use to talk with other whales.
The whales, however, stay silent for up to 80 percent of their lives. Researchers believe this is a cryptic defense mechanism to avoid detection by roving packs of killer whale predators. When the whales do make noises, it is usually at depths below 170 meters (about 560 feet), rather than nearer the ocean’s surface, posing a challenge for the team.
The researchers boarded a 25-meter-long (about 82 feet) research tugboat, the Urano, and took off to systematically search the basin. Their visual search involved two lookouts placed along either side of the Urano, who peered out over the ocean for the whales with binoculars. They looked for the whales’ distinctive head shape, crescent-shaped blowhole, and dorsal fin position.
The team combined these visual searches with acoustic profiling. They deployed underwater microphones called hydrophones, placed in cages that they lowered down to a depth of 150 meters (about 492 feet). These listened for the whales’ distinctive frequency-modulated pulses.
A Dozen Recordings Reveal Brazilian Beaked Whales
Ultimately, the team recorded 12 whale detections — three sightings, eight audio recordings, and a single matched simultaneous recording. The audio recordings included 395 echolocative “clicks.” Interestingly, they didn’t record any whistles or so-called “buzz sounds,” which these whales have previously been recorded making. The team concluded that this was likely due to these distinctive sounds only being used in limited social contexts and at certain depths.
The team estimated that they had recorded from at least three different species of beaked whale over the course of the study.
“This study provides the first documentation of acoustic parameters of beaked whales in Brazilian waters,” said Machado in a press release. By capturing the most observations through acoustic monitoring, the study highlights the importance of tracking the most elusive species in our deep oceans using sound, a task that the team intends to continue across the South Atlantic.
“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 in the release. “Addressing these knowledge gaps is essential for informing public policies and guiding conservation and management efforts aimed at safeguarding these elusive species.”
Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
- The Journal of the Acoustic Society of America. Finding beaked whales in the Foz do Amazonas basin: Visual and acoustic records of a deep diving cetacean
- The Journal of the Acoustic Society of America. Sounds recorded in the presence of Blainville’s beaked whales, Mesoplodon densirostris, near Hawai’i