Sperm whales in the Mediterranean: on the sound trail of the marine giant

In the observations section of his logbook there are wonderful findings. Txema Brotons goes through the pages with her finger in search of her encounters with sperm whales on the deck of the sailboat Irifi (your home and your office for many weeks of the year). There is annotated the birth of a calf; or the two enormous males who were for a long time trying to get the attention of a female by shoving; wave kindergarten of sperm whales that he ran into north of Menorca…

All these encounters, in addition to recording them, have been recorded with drones by this doctor in Biology who specializes in cetaceans in general and, in particular, in sperm whales, the largest predator on the planet. This giant —Physeter macrocephalus— was the leviathan of the 19th century novel Moby Dick. Although in reality it was the victim of a fishing industry that decimated this species until, at the end of the last century, an international agreement was signed to end commercial fishing. Today it 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 Mediterranean, and Brotons, 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”, sums up this biologist expert in acoustics.

Although at first glance those drone videos may seem the most spectacular of his work, the real treasure is stored in dozens of hard drives where he accumulates thousands of hours of audio recordings that help to understand the sound universe in which he moves. this enigmatic species listed as endangered by the IUCN. What we see when it is on the surface is only a small percentage of its life. Underwater lies the mystery and the way to get closer is through the hydrophones that record the clicks, the clicks produced by these toothed cetaceans to, among many other things, hunt squid hundreds of meters deep. “They are difficult animals to observe, because they have very low densities and live in inhospitable places. We do not see his life, we listen to it”, sums up the person in charge of Tursiops.

acoustic footprint

Below deck, next to where he keeps the binnacle, the sailboat Irifi hides a recording equipment. With headphones on, Brotons and the rest of the Tursiops members and collaborators scour the seabed each campaign to try to locate the sound trail of sperm whales. One week on land, another week on board in search of these giants.

A 100 meter long cable hangs from the stern. At the end of the cape, to avoid the noise pollution generated by the boat’s engine, there is the hydrophone with which they look for these animals in a kind of sea cliff located in the southeast of the Balearic Islands: the Emile Baudot Escarpment, which reaches 2,000 meters. deep and 200 kilometers long. That’s where these cetaceans—the deepest-diving marine mammal—come to hunt for squid. They make dives of 45 minutes on average in which they reach 1,000 meters deep. The click they emit helps them to track the seabed and capture their prey where light no longer reaches. “They live in an acoustic universe, not a visual one,” says the biologist.

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

Brotons admits that humanity is still “light years away from being able to interpret all its sounds”, but science is beginning to decipher part of this click. After years of studies, the biologist points out, it has been possible to identify codas (repetitions of clicks) that are used by individuals from the same population group. “Each clan has its own codas,” details this ecologist.

Listen below to the coda of one of the clans.

that’s how it sounds

“They have a non-human culture and they are clicking continuously,” says the person in charge of Tursiops, who explains that “acoustics has 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 seen.

that’s how it sounds

Colossal animal

The sperm whale is an animal of records. Not only because of their size —males reach 16 meters in length and 41,000 kilograms in weight, females reach 11 meters and 14,000 kilos— or because they are the deepest marine mammals that can dive. Also for the power of your click. It is the animal that produces the most intense sound in the entire animal kingdom: the one known as big clang, which reaches up to 223 decibels one meter from the emitting source. “As of 150, a sound already generates pain in the human being,” says Brotons.

What sound is more powerful?

LISTEN AND CHOOSE WHICH OF THE TWO SOUNDS YOU THINK IS LOUDER

SPERM WALK

CONCERT

NEXT SOUND

The big clan of the sperm whale is the most powerful sound developed by an animal. One of 223 db has been recorded.

The big clang se It resembles a brief, dry blow on a metal surface and male sperm whales (the only ones that emit it) can repeat them every six or 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 is a socialization tool. “To attract females or to repel or locate other males. Perhaps, something like saying to the rest: ‘here I am, what a macho I am’.

Slope

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 the cetacean biologist Margalida Cerdà. The Tursiops association, for which she also works, has asked the Ministry for Ecological Transition to modify the Spanish Catalog of Threatened Species to increase its protection. Currently in this catalog the situation of the sperm whale in Spain is considered as “vulnerable”. This is due to the fact that the document does not distinguish between the populations of the Atlantic and the one of the Mediterranean, more punished. Cerdà and Brotons have requested that a specific section be created in the Spanish catalog for the Mediterranean population of sperm whales and that their situation be compared to that which the IUCN (International Union for Conservation of Nature) includes on its red list. This would mean that it would go from being considered “vulnerable” to “endangered” of extinction. Those responsible for Tursiops believe that this change would help increase the protection of a species that humans have been harassing for decades.

In its 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, also to make candles and to keep the lamps lit. “The whaling industry is a clear example of bad practice, it almost led the population to extermination,” laments Cerdà.

Some countries continue to hunt sperm whales – such as Japan and Norway, which argue scientific reasons – 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 is slow, because these animals have few young every many years and are very slow growing. 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 animals.

Collisions in hypoxia

After the deep 45-minute dives, the sperm whales return to the surface in a state of hypoxia, Brotons explains. “Your brain is at that moment off”. They remain torpid for 10 or 15 minutes on the sea surface. “At that moment, they are very vulnerable,” says the biologist, and when a ferry approaches 35 knots of speed, they do not react and the collision occurs.

“It is difficult to know the dimension of the problem,” admits Brotons. “But we know that it is important because we found specimens mutilated by the propellers, and we believe that those that survive learn to avoid collisions, but it is a very complex problem”, explains the scientific director of Tursiops. In any case, Cerdà emphasizes that “technically the main solution is to slow down.” “It is the only effective method”, he stresses. The trace of these encounters, in the form of cuts on the fins or back, have been photographed by the 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.

This association, in addition to campaigning from the sailboat, has three fixed hydrophones anchored several hundred meters deep. 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 bodies so that they make decisions”, summarizes Brotons from the cover of the irifi, already anchored in front of the island of Cabrera, whose waters are part of a maritime-terrestrial national park that they helped to design with the data collected during two decades of research campaigns.

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