Elusive Beaked Whales May Dive Over 3,000 Feet to Forage Near the Seafloor

Deep below the ocean surface off the coast of Louisiana, some goose-beaked whales forage near the seafloor. New acoustic tracking shows that during dives exceeding about 3,200 feet (1,000 meters), they can approach within roughly 300 feet (about 100 meters) of the seafloor.

Beaked whales are difficult to study because they spend little time at the surface, and detailed dive data from the Gulf have been limited. By reconstructing three-dimensional dive paths from echolocation clicks, researchers could document how these whales move.

The findings, published in PLOS One, come from six months of acoustic monitoring conducted between 2021 and 2022. The results provide new details on how goose-beaked, Gervais’, and Blainville’s beaked whales use deep Gulf waters.

“This study provides the first direct information on the diving behavior of any beaked whale species in the Gulf of Mexico. Our results confirm that, at the deployment site in the Gulf of Mexico, goose-beaked whale diving behavior is constrained by seafloor depth, with several individuals foraging at or near the seafloor for part of their dives,” lead author Héloïse Frouin-Mouy told Discover.

Tracking Deep-Diving Beaked Whales

Instead of tagging whales, researchers placed two sets of underwater microphones on the seafloor, spaced about 2,500 feet (772 meters) apart. Known as High-Frequency Acoustic Recording Packages (HARPs), the devices continuously recorded the whales’ echolocation clicks. By comparing tiny differences in when each click reached the microphones, researchers calculated the whales’ positions in 3D.

Beaked whale dive infographic showing acoustic detection on the seafloor — Goose-beaked whale emits an echolocation click while foraging.
(Image Credit: Dr. Héloïse Frouin-Mouy/CC-BY 4.0)

Over roughly 200 days of recording, the team tracked 24 goose-beaked whale dives, 24 Gervais’ beaked whale dives (which are a species of goose-beaked whales), and two Blainville’s beaked whale dives. Only high-quality tracks were used for dive analysis.

Each dive was divided into descent, foraging, and ascent phases when possible. From these tracks, researchers measured dive depth, swim speed, and pitch angle. The result was a detailed description of how each species moved through the water column.

Goose-beaked whales typically made long, steep descents, then spent time foraging at their deepest point. Gervais’ and Blainville’s whales followed a similar pattern but did not dive as deep.

Beaked Whales Foraging Near the Seafloor

Goose-beaked whales dove to an average depth of about 3,225 feet (983 meters), with maximum depths averaging about 3,536 feet (1,078 meters). At the study site, the seafloor lies at roughly 3,600 feet (about 1,100 meters), meaning some individuals were foraging at or near the bottom.

They also descended more steeply than the other species. Goose-beaked whales dropped at an average pitch angle of 68.5 degrees, compared with 35.7 degrees for Gervais’ beaked whales. During these dives, goose-beaked whales clicked for longer periods, averaging 20.5 minutes vs. 12.7 minutes for Gervais’ whales.

The other species remained higher in the water column. Gervais’ beaked whales reached a mean depth of about 2,837 feet (865 meters), while Blainville’s beaked whales averaged about 2,608 feet (795 meters).

According to Frouin-Mouy, the three species’ use of different depths likely reflects differences in how and what they hunt. Previous stomach content studies support this idea, showing that goose-beaked whales tend to feed on larger squid and other cephalopods that live deeper than the prey targeted by other beaked whales.

Vertical Habitat Differences Among Gulf Beaked Whales

The study was designed to improve acoustic monitoring in the Gulf, but the dive tracks also clarify how these species share the same deep habitat while using it differently, offering insight into how environmental pressures may affect them.

“Enhanced passive acoustic density estimation will allow for more effective long-term monitoring of beaked whale populations in the Gulf of Mexico and will improve our capacity to assess and track the impacts of anthropogenic stressors,” Frouin-Mouy told Discover.

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