Sperm whales in the Mediterranean: Following the trail of sound of this giant of the seas

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Sperm whales in the Mediterranean: On the sound trail of the giants of the seas

About 2,000 of these fascinating aquatic mammals survive near Spain’s Balearic Islands after suffering a huge decline in the last 90 years. Researchers are using acoustics to delve into their hidden universe and bolster conservation efforts

Txema Brotons runs his finger through the pages of his logbook in search of his encounters with sperm whales on the deck of the Irifi, a sailboat that doubles as his home and office for many weeks of the year. In the observations section, there are wonderful findings.

Noted down is the birth of a calf, and the sighting of two enormous males who spent a long time trying to get the attention of a female by shoving each other. There are also notes about the nursery of sperm whales that he came across, north of the island of Menorca.

Brotons, a doctor in biology, has recorded all of these encounters – both in handwritten ledgers and with drone images. He specializes in the study of cetaceans (aquatic mammals) with a particular focus on sperm whales, the largest predators on the planet.

This giant of the seas – Physeter macrocephalus – was the leviathan of the 19th-century novel Moby Dick. Although, in reality, the sperm whale was the victim of a fishing industry that decimated the species until the late 20th century, when an international agreement was signed to end commercial fishing of the creature.

Today, however, the sperm whale is still at risk due to collisions with large ships and marine pollution generated by nets and plastic. A population of around 2,000 survives in the western area of the Mediterranean Sea. Brotons – the scientific director of the Tursiops association – has been tracking them since 2003, to help get them out of the danger zone. “The best conservation tool is knowledge,” says the biologist, who is also an expert in acoustics.

At first glance, his drone videos may seem to be the most spectacular element of his work, but the real treasure is stored in dozens of hard drives, where he has accumulated thousands of hours of audio recordings that help him understand the sound universe in which sperm whales live and communicate.

This enigmatic species – listed as endangered by the International Union for Conservation of Nature (IUCN) – reveals only a small percentage of its life on the surface. Underwater lies the real mystery, and the way to get closer is through hydrophones, which record the clicks produced by these aquatic predators to, among other things, hunt squid hundreds of feet beneath the ocean’s surface.

“They are difficult animals to observe, because they have very low density and live in inhospitable places. We don’t see their lives, we listen to them.”

Acoustic Footprint

Under the deck, next to where the logbook is kept, the sailboat Irifi hides some recording equipment. With headphones on, Brotons and the rest of the Tursiops members scour the seabed, trying to locate the sound trail left by sperm whales. One week is spent on land, while another week is spent on board in search of these giants.

The sailboat 'Irifi' with the hydrophone to locate sperm whales.

A 300-foot-long cable hangs from the stern. At the end of it – to reduce the noise pollution generated by the boat’s engine – there’s a hydrophone, with which they look for these animals around a kind of sea cliff located in the southeast of the Balearic Islands. The Emile Baudot Escarpment – which is 6,500 feet deep and 120 miles long – is where the deepest-diving marine mammals come to hunt for squid. They make dives that last 45 minutes on average, during which they go down more than 3,000 feet. The clicks they emit help them to track the seabed and capture their prey in places where light doesn’t reach.

“They live in an acoustic universe, not a visual one,” the biologist notes.


“We searched for them at 1,000 meters, in total darkness. That’s why they hunt with their clicks”, adds Brotons. Thanks to the return they receive in their enormous head, they manage to make a map of the area, just like sonar systems. But these clicks are not only used by cetaceans to feed and see everything that surrounds them. “It is also a communication and socialization system.”

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Brotons admits that humanity is still “light years away from being able to interpret all the sounds,” but science is beginning to decipher part of them. After years of studies, the biologist points out that it has been possible to identify identical codas (repetitions of clicks) used by the members of a specific group. “Each clan has its own codas.”

Listen below to the coda of one of the clans:

This is what is sounds like

“They have a non-human culture and they are clicking continuously,” says Brotons, who explains that “acoustics have been a revolution” for the study of this animal. In his archives, he keeps hours and hours of audio recordings of sperm whales, like this recording in which the tension between various specimens can be appreciated:

This is what it sounds like

A colossal animal

The sperm whale is an animal of records. Not only because of their size – males reach 52 feet in length and 90,000 pounds in weight, while females reach 36 feet and 30,000 pounds – or because they’re the marine mammals that can dive the deepest. The power of their click is also a record-breaker. The sperm whale produces the most intense sound in the entire animal kingdom: the one known as “the big clang,” which reaches up to 223 decibels three feet from the emitting source.

“As of 150 decibels, a sound already generates pain in human beings,” says Brotons.

Which sound is more powerful?


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The big clang of the sperm whale is the most powerful sound developed by any animal. One 223-decibel clang has been recorded.

The big clang resembles a brief thud on a metal surface. Male sperm whales – the only ones that emit it – can repeat it every six to eight seconds. But what is it for? Although at some point it was speculated that they could be used to stun their prey, Brotons maintains that it’s a socialization tool.

“To attract females, or to repel or locate other males. Perhaps, something like saying to the rest: ‘Here I am, look how macho I am.’”

Species in decline

The Mediterranean sperm whale population has experienced a brutal decline in the last 90 years. “In only three generations, it has suffered a decrease of at least 70%,” explains Margalida Cerdà, a biologist who specializes in cetaceans.

The Tursiops association – where she also works – has asked the Spanish Ministry for Ecological Transition to modify its Catalog of Threatened Species to increase protection for the sperm whale. Currently, the catalog notes that the sperm whale’s situation in Spain is considered to be “vulnerable.” This is due to the fact that the document does not distinguish between the populations of the Atlantic Ocean and the one within the Mediterranean Sea, which have been more severely impacted.

Cerdà and Brotons have requested that a specific section be created in the Spanish catalog for the Mediterranean population of sperm whales. Their situation should be compared to how it is documented by the IUCN, which includes it on its red list. This would mean that it would go from being considered “vulnerable” to “endangered” – at risk of extinction. Members of Tursiops believe that this change would help increase the protection of a species that humans have been harassing for decades.

In the sperm whale’s head – in addition to the complex sonar system – is spermaceti, a whitish oil that helps the animal control buoyancy. But this substance has also been its undoing, because, for decades, whalers hunted sperm whales to extract it. The precious oil was used as a watch lubricant, or to make candles and keep lamps lit.

“The whaling industry is a clear example of bad practice: it almost led the population to extermination,” Cerdà laments.

Some countries continue to hunt sperm whales – such as Japan and Norway, who claim to do so for scientific research purposes – but the problem has not reached the dimension that it had before 1986, when the moratorium on commercial fishing was decreed. The recovery of the species has been slow, because these animals only have a few calves (who grow slowly) every several years. In addition, some dangers still persist, such as collisions with large ships. Tursiops has several projects underway – financed with public and private funds – which seek, among other things, to avoid collisions by studying the behavior of the animals.

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Collisions with ships

After the deep 45-minute dives, the sperm whales return to the surface in a state of hypoxia, Brotons explains.

“At that moment, their brain is turned off.”

They remain inactive for 10 or 15 minutes on the sea surface. “During that time, they’re very vulnerable,” says the biologist. If a ferry approaches at a speed of 35 knots, they don’t react and a collision can occur.

“It’s difficult to understand the dimension of the problem,” admits Brotons. “But we know that it’s important, because we found specimens mutilated by the propellers. We believe that those that survive learn to avoid collisions, but it’s a very complex problem.”

In any case, Cerdà emphasizes that “technically, the main solution is to slow down… it’s the only effective method,” she stresses. The traces of these encounters – in the form of cuts on the fins or backs – have been photographed by members of Tursiops.

In addition to collisions, sperm whales in the Mediterranean face other dangers, such as driftnets, an indiscriminate fishing system in which these cetaceans are trapped, like many other species. Sperm whales are also vulnerable to plastic pollution and noise pollution.

The Tursips association – in addition to campaigning from the sailboat – has three fixed hydrophones anchored several hundred feet deep beneath the ocean floor. And soon, they will launch another project to place GPS tracking markers on various specimens.

“Our job is to provide the information to the managing [government] agencies, so they can make decisions,” summarizes Brotons from the deck of the Irifi, which is anchored off the island of Cabrera, whose waters form part of a maritime-terrestrial national park that the team helped design with the data collected over two decades of research.


Design and art direction: Fernando Hernández 
Video edition: Olivia López Bueno, Eduardo Ortiz and Rodrigo Merino
Acknowledgments:  We would like to thank Tursiops for providing the drone images, photographs and audios. And Banco Santander Foundation, one of the organizations that funds this association. 

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