How Sound Reveals Gervais’ Beaked Whale Diving and Hunting in the Gulf of Mexico

Trying to study a beaked whale by conventional means is no easy task. These animals are exceptionally skilled at avoiding detection. They pass much of their lives at great depths, surface only briefly to breathe, then disappear beneath the water once more.

Rather than attempting to see them, scientists in the Gulf of Mexico took a more effective approach: they listened.

Using underwater recordings, a research team created a three-dimensional reconstruction of beaked whale diving and hunting activity without directly seeing a single whale.

Based solely on sound, this is the first detailed account anywhere in the world of deep-diving, foraging behaviour in the Gervais’ beaked whale (Mesoplodon europaeus).

This is important because Gervais’ beaked whales rank among the world’s most poorly understood whales. They are not ‘rare’ because they are absent; they are rare because observing them is extraordinarily difficult.

Attempts to assess their numbers, feeding habits or even the basic ways in which they use their habitat soon encounter the same obstacle: these whales do not remain in places where people can easily watch them.

Why sound is the best “camera”

Beaked whales locate prey through echolocation, producing rapid clicks that reflect from prey and return in a biological sonar-like system.

These clicks are far more than incidental noise. They are unique to each species and provide clues about both the whale’s location and its activity. By accurately recording them, researchers can begin to recreate a whale’s path through the water.

That was the basis of this research, which used passive acoustics. The word “passive” is important: the team did not transmit sound into the sea.

Instead, the researchers installed listening equipment to record sounds already occurring underwater. This makes the technique non-invasive and scalable, valuable qualities for long-term monitoring in a region as heavily used as the Gulf of Mexico.

“These findings come at a critical time for beaked whales in this heavily industrialized region,” said Dr. Héloïse Frouin-Mouy, lead author of the study and a bioacoustics scientist at the University of Miami.

“There is an urgent need for reliable data on the populations and behavior of these whales, which are believed to be in decline.”

Earlier research has indicated that Gulf beaked whale populations may have fallen sharply since the 2010 Deepwater Horizon oil spill. Some estimates have suggested declines of up to 83%.

Although the precise figure remains disputed, the overall trend is concerning enough to make improved data an urgent priority.

Underwater ears on the seafloor

The researchers positioned two high-frequency acoustic recording packages, known as HARPs, on the seafloor off Louisiana at a depth of roughly 1,100 metres.

Rather than containing just one microphone, each HARP included several sensors synchronised in time. This feature is what enables three-dimensional tracking.

When a whale produces a click, it arrives at each sensor at marginally different times, separated by tiny fractions of a second. These timing differences allow scientists to calculate the direction from which the click originated.

With two separate recording systems, researchers can merge those directional calculations and triangulate the whale’s location in the water at that instant. Repeating this process throughout a dive produces a track, much like mapping unseen footsteps.

Through this method, the team captured echolocation clicks from 50 deep foraging dives and recreated underwater movements using the recordings alone.

What sounds reveal about the whales

The team examined the diving behaviour of three species found in the region: goose-beaked whales, Gervais’ beaked whales and Blainville’s beaked whales.

A notable result was that goose-beaked whales were generally detectable for longer durations and frequently carried out deeper foraging dives than the other two species.

At times, they descended near the seafloor, pointing to a somewhat different hunting method or prey preference.

For Gervais’ beaked whales, the principal advance is that a detailed description of their dives now exists at all. Before this work, scientists had no movement-and-foraging map of this kind for the species anywhere.

The research offers the first substantial view of Gervais’ beaked whale activity during deep dives: the length of time they click, their movements while hunting and their use of depth in an ocean environment where direct observation is virtually impossible.

Significance beyond one species

This is not merely an impressive technique; it is a useful practical tool. Beaked whales face numerous human-caused pressures, including shipping, oil and gas operations, underwater noise, pollution and habitat disturbance.

Yet protecting animals is difficult when they cannot be measured. Passive acoustics, particularly when it can reconstruct movement in three dimensions, provides conservation and management organisations with a means of monitoring these whales where they actually spend their time.

The research also demonstrates that meaningful findings do not always require tags, boats following animals or chance encounters.

When the appropriate signals are recorded and carefully analysed, it becomes possible to “see” behaviour in complete darkness, 1 kilometre below the surface, using an approach that is gentle for the animals and feasible to repeat over time.

In a Gulf of Mexico that is industrialised, noisy and ecologically complex, such a method is not simply useful. It could be the only way to monitor certain species before they become still more difficult to find.