How Sperm Whales Dive Deep to Steal Fish From Longlines | Part 2 | SLICE EARTH

The sperm whale can also dive for up to two hours. Its whole anatomy is designed for diving for long periods. With each breath, we humans replace only 15% of the air in our lungs, while sperm whales are able to renew 90% of their breath. Its muscles are rich in oxygen-carrying proteins and can store ten times more oxygen than humans. As soon as it leaves the surface of the water, the sperm whale's metabolism slows down to save oxygen and its blood is concentrated on vital organs like the heart and its enormous brain, the largest in the animal kingdom. Its chest cavity is flexible, so it doesn't snap when the pressure mounts. Its huge head, a third of its body length, contains a yellowish wax called spermaceti. It is believed that whales can vary the density of this substance at will. By restricting the blood supply, the spermaceti solidifies, acting like a weight, and allowing the whale to dive deeper and with less effort. When it resurfaces, the sperm whale reheats its spermaceti, causing it to liquefy until it is lighter than water. To avoid decompression accidents in the bends, the whale is able to collapse its lungs. While still sending oxygen to the brain. So the sperm whale can stay underwater for up to two hours. But the maximum depths that it reaches when it dives remain a mystery. Detachs cannot be attached to sperm whales because their skin is constantly exfoliating. Far from El Hierro, researchers use a different approach to learn more about their diving abilities and study their movements. In the Indian Ocean, off the coast of Mauritius, a team of scientists from the Moby Dick Association scans the horizon in search of sperm whales. Their technique is to anchor tags on the sperm whale's backs. At the same time, they perform a biopsy, taking a small sample of skin, which allows them to identify each tagged animal by its DNA. For a comprehensive study, they need to tag and identify several sperm whales. Luckily, the deep, calm waters surrounding the island have become a gathering place for large schools of sperm whales. By coupling the geographical information with bathymetric data, they will be able to evaluate the maximum depths they dive. In order to place the tags, scientists, like the whalers of the past, take advantage of the sperm whale's weak spot, their limited field of vision, particularly behind them. The reason is simple. The sperm whale's eyes cannot turn in their sockets, so they can't see a boat approaching from behind, allowing the scientists to tag the first whale. But the other sperm whales are suspicious, and a tactical chase begins. The sperm whales that have been tagged will reveal their movements for up to two months. The tags placed reveal the six sperm whales' amazing diving capabilities to depths of over 4,000 feet. The male whales stay around Mauritius for the duration of the study, but may head to southern latitudes afterwards, to the land of the albatross, and constant winds known as the Roaring Forties. Thousands of feet separate these liquid mountains from the ocean floor. Only male sperm whales are found at these latitudes. In this no-man's land, the main attraction is fish-processing ships that spend several months at a time on the high seas. These groups of males wait for the ships to lower miles of long lines into the water. When they are hauled in, the lines bring a highly prized resource in the Asian market, Patagonian toothfish, also known as Chilean sea bass. Fishermen suspect the sperm whales are thieves, stealing the huge fish from lines that extend more than a mile below the surface. But they have never been caught in the act. Chilean fishermen have come up with a protective system using nets to safeguard their catch, but the sperm whales continue their thievery. The fishermen estimate that they lose up to 30% of their profit to predators. To confirm their suspicions, they're working with a marine biologist who is studying the whales' behavior. Gaetan Richard is on board for the next three months. By using long-line fishing boats, we can deploy our acoustic devices like this one, which is a recorder and two hydrophones. So this device allows us to record the sounds that sperm whales make. What we're interested in are the echolocation clicks. When the animal clicks, the sound arrives at our device, first at one hydrophone and then at the other. Since we know the distance between them and the speed of the sound in the water, we can then work out where the animal is in relation to our device. The long lines are placed at a depth of between 2,500 and 6,500 feet, a depth that sperm whales are capable of diving. To find out why the whales appear around the fishing boats just as fishermen haul in their catch, Gaetan places accelerometers on the lines, just above the hooks. These devices can detect and record the difference in tension on the lines. A rise in tension could reveal a thieving sperm whale. By combining the accelerometer data with the hydrophone information, he can reconstruct the sperm whale's modus operandi. As an opportunistic hunter, it saves its energy and dives to the shallowest depth possible. When it returns to the surface, it grabs the main line from the fishing boat between its jaws and runs them along the length of the line to unhook the fish that it will then gather up as they drift in the water. The whales only dive to the sea bottom to feed from lines that are in shallow water. They can then place their jaws in the mud to unhook the toothfish. Surprisingly, the whales are rarely seen within 1,000 feet of the surface, for a very good reason. Near the surface, they are in competition with a fearsome predator. Killer whales. Damn killer whales.