
Pilot Whales the ‘Cheetahs of the Deep Sea’
Researchers reveal first glimpse of whales' high-speed, deep-diving hunts for squid
Until now, what happened in the depths, where many whales hunt, stayed there.
A new study has revealed that pilot whales are “the cheetahs of the deep sea,” making 15-minute, high-speed, all-or-nothing dives up to 3,280 feet (1,000 meters) deep to chase and catch large squid, before surfacing to catch their breath.
“They make colossal dives and must come back exhausted,” said Natacha Aguilar de Soto, the study’s lead author. “They have to spend time at the surface catching their breath before undertaking a new sprint to catch prey.”
The pilot whales’ hunting tactics contrast with beaked whales, another family of similar-sized, deep-diving squid-eaters that ply nearby waters in the Canary Islands, a research team involving scientists in three countries reported online in the Journal of Animal Ecology. Beaked whales dive slowly, conserving their breath so that they can remain at depth for 20 to 30 minutes hunting for smaller squid. Their dives can last up to 50 to 90 minutes.
“We didn’t expect such differences in tactics between deep-diving squid-eaters,” said Mark Johnson, an engineer at Woods Hole Oceanographic Institution (WHOI) who designed innovative tagging devices that record whale sounds and movements in the deep and allowed this first glimpse of their hunting behavior. Perhaps the different species can coexist in the same territory because they have evolved different hunting styles, just as cheetahs have done to carve a niche on the same Serengeti Plains where other big cats hunt, he said.
Rather than expending energy in a sprint for a big, one-time payoff as pilot whales do, beaked whales are more like endurance runners. Moving more slowly, they gather more, though smaller, prey. “It’s more like picking berries,” said Aguilar de Soto of the University of La Laguna in Tenerife, Canary Islands.
The new research also helps explain and reinterpret thinking about the whales’ behavior at the surface. Beaked whales are seldom seen because—moving more slowly and expending less energy—they can spend most of their time in the depths. Meanwhile, pilot whales often congregate in groups at the ocean surface and have a reputation for being calm, approachable, and not bothered by boat activity. Instead, they may be too tired to react.
The new understanding about whale diving and feeding behaviors should also inform policies to better manage whale-watching and shipping movements in areas with whales, said the researchers, who also included Peter Madsen of the University of Aarhus in Denmark, Francisca Diaz, Iván Dominguez, and Alberto Brito, all from the University of La Laguna, and Peter Tyack of WHOI.
Technology reveals the hunt
Unlike scientists studying predators on land or in the air, whale biologists could not observe their subjects or attach radio-transmitting collars to track them. To overcome these barriers, Johnson developed a non-invasive tag, called a D-tag, which temporarily attaches to whales. It digitally records their movements and the sounds the whales make and hear on their dives, from start to finish.
In the dark depths, sound takes the place of light. To perceive their surroundings and locate prey, whales send out sound signals and receive sound reflected back from objects.
Pilot whales, for example, produce regular “clicks” after reaching a certain depth, and sense what’s near them from sound echoes. When the whales get close to prey, the clicks become more rapid, turning into a “buzz” of more than 300 clicks per second.
The whales can “look” further with the more powerful clicks, spaced farther apart, but they get that information more slowly. The rapid buzzes provide less range, but can give the whale fast-paced updates about whether its prey is taking evasive action, for example.
Over the last few years, the research team has pioneered a method using D-tags to capture whale sounds echoing off objects that the whales encounter. The team has been able to follow prey as whales chase them, sometimes trying to escape at the last minute or schooling together to gain strength in numbers. So far the method only works for beaked whales, Johnson said. “Pilot whales have a square head that gets in the way of the returning sound.”
“The D-tag was the first instrument to capture an echo from prey in the wild, one of the great challenges in studying echolocation,” said co-author Peter Madsen, a professor at the University of Aarhus inDenmark. “It is a really unprecedented chance to study how whales find and capture their dinner.”
Putting it all together, Aguilar de Soto and Johnson believe that the whale buzzes, followed sometimes by the sound of a bump or crash, indicate the moment that whales are capturing prey. The D-tags also records the sounds of the whales “fluking”— pumping their tail flukes to power forward, as well as the sound of water flowing fast over tag during the pilot whales’ chases (“it sounds like a train approaching,” Johnson said). By analyzing the recorded “clicks,” “buzzes,” and other whale sounds together with the whales’ recorded speeds, orientations, and depths, scientists can reconstruct a picture of the whales’ dives and hunts.
“What’s cool,” Johnson said, “is to ‘see’ how whales hunt at depth using their own sounds, —without the intrusion of lights and a camera.”
High-speed chases are high-cost
The picture that emerges is this: Pilot whales dive down to about 1,640 feet (500 meters) and then level out to select a target—“sort of like acoustic window shopping,” Johnson said. Once they have picked their prey, a chase starts that can take the whales down to around 3,000 feet (1,000 meters) and reach speed of 20 miles per hour (9 meters per second). (Their terrestrial counterparts, cheetahs, run up to 60 miles per hours, but only for 20 seconds, before they have to rest for long periods—“and, of course, they can breathe all the time, whereas the pilot whales are working on just one lung-full of air,” Aguilar de Soto said.) Most deep-diving whales swim at only 1 to 2 meters per second, allowing them to conserve energy and oxygen and maximize hunting time in the depths where their prey dwell. “The sprints of these short-finned pilot whales open a new perspective into optimal foraging theories of deep-diving breath-holding mammals,” said Aguilar de Soto.
Running is harder than walking, even in air, and water exerts a much higher drag than air. Factor in the limited amount of oxygen whales can carry on the dive, and the whales must balance their needs for food and air.
So sprint-diving poses a calculated risk versus reward. The pilot whales’ speed offers them advantages to catch prey, but they expend much more energy and oxygen doing it. “The power needed to swim goes up with the cube of the speed,” Aguilar de Soto calculated. That means that when pilot whales swim at four times their normal speed in a chase, they could be using 64 times as much energy per second.
Working with the echolocation sounds made by the tagged pilot whales, the team concluded that the whales don’t always get a meal. For all their effort, pilot whales hunt unsuccessfully about 40 percent of the time, Aguilar de Soto estimated. Given the high energy cost of their sprints, they can afford only one or two capture attempts per dive. “A missed catch,” Aguilar de Soto said, “could cost them the whole dive.”
The food, then, has to be worth the risk and the energy spent to get it. What are pilot whales catching at 3,000 feet?
Pilot whales are known to eat several species of large deep-water squid, some of which get big enough to be worth chasing. Squid tehtacles four feet long have been seen trailing from pilot whales’ mouths after they have resurfaced. But even larger prey may be the whales’ quarry.
“We’ve found pieces of the arms of giant squid, Architeuthis dux, floating where the whales are coming up,” Johnson said. “We have always imagined sperm whales hunting giant squid but maybe these tough pilot whales, one third the size of a sperm whale, are the ones showing up for the fight.”
Rest and risks
Finding food is not the only challenge pilot and beaked whales face. Boats and sonar are two others.
A large whale-watching industry spotlights seemingly calm pilot whales that congregate at the surface off the Canary Islands.
“Because they don’t react, people think boat traffic doesn’t bother them,” Johnson said, but the pilot whales’ survival could depend on their ability to rest and recover, undisturbed, from sprint dives. “They’re not just relaxing there,” Aguilar de Soto said.
The more elusive beaked whales are considered sensitive to sonar, and several species have experienced mass strandings correlated with the use of sonar in naval exercises. Living in deep waters that are not usually considered coastal, they may not be subject to regulations, but Aguilar de Soto and Johnson believe there’s an urgent need to protect them.
“They fall into a hole in policy,” Johnson said. “They are so difficult to find that no one really knows how many there are, and under most regulations, if you can’t count them, you can’t protect them.”
D-tags may help scientists learn more about the mysterious deep diving species, and Johnson and colleagues are now working on similar acoustic recording devices installed on long-term moorings that could acoustically identify whale species, numbers, and locations, and help conserve whale populations.
This work was supported by the Strategic Environmental Research and Development program of the U.S. Department of Defense, the U.S. National Oceanographic Partnership Program, and the Canary Islands Government-Spanish Ministry of Defense. Research was conducted under a permit to La Laguna University from the Government of the Canary Islands and was approved by the Woods Hole Oceanographic Institution Animal Care and Use Committee.
Slideshow

Slideshow
- A short-finned pilot whale (Globicephala macrorhynchus) surfaces explosively after its rapid dive, trailing a 4-foot-long squid tentacle from its mouth. The tentacle's length indicates that the whale is catching very large, deep-living squid. (Pablo Aspas)
- During their field work off the Canary Islands, researchers on the newly published study found tentacles of giant squids (Architeuthis) floating in the water where pilot whales surface — tantalizing evidence of what the whales are hunting at depth. (Francisca Diáz, University of La Laguna)
- Lined up for a nap: Pilot whales are social animals that lie in groups at the surface during daytime. They seem calm and untroubled by boat traffic, but actually they may be too exhausted from their strenuous dives to move when approached. (Francisca Diáz)
- A trio of pilot whales underway at the surface, off the island of Tenerife, Canary Islands. Beneath the surface on a feeding dive, they make downward sprints of up to 20 miles per hour, remarkable speeds that consume up to 64 times more energy than a normal swim. (Nick Tregenza)
- Short-finned pilot whales are small toothed whales found around the world. They are about 4 to 6 meters (13 to 20 feet) long, with a large rounded head that distinguishes them from other small toothed whale species. Though the whales are often visible at the surface, scientists don't know how many exist in the world. They believe that small local populations of the whales are threatened by human activity. (Frants Jensen, Aarhus University, Denmark)
- A rare photo of a mother pilot whale and her calf, breaking the surface off Tenerife. Small populations of these whales live year-round in the very deep waters between the Canary Islands. (Teo Lucas, Balfin)
- Blainville's beaked whales are similar in length to pilot whales and share the same deep waters off the Canary Islands. But they have a different lifestyle. They are the deepest divers of all known whales, making hour-and-a-half dives to a mile down &mdash on one breath. (Victor Gonzalez Otaola, University of La Laguna)
- A rare Cuvier's beaked whale leaps near the island of El Hierro, Canary Islands. Here the seafloor drops off into very deep canyons where all three species of small toothed whales hunt squid. Using a different hunting style, sprinting pilot whales live in the same area as the slower-diving beaked whales, just as cheetahs carve out a niche in a habitat where other big cats hunt. (Natacha Aguilar de Soto, University of La Laguna )
- The third little-known whale tagged and studied by the research team, Cuvier's beaked whales (Ziphius cavirostris) also shares deep water off the Canary Islands. Like other beaked whales, they are mysterious, extremely deep-and-long-diving whales that spend only about 8 percent of their time at the surface. (Marta Guerra, University of La Laguna)
- Beaked whales are mysterious, seldom-seen animals. Because they dive slowly, 1 to 2 meters a second (2.2 to 5 miles per hour), they are able to conserve their breath and surface infrequently—but sometimes dramatically. (Iván Dominguez, University of La Laguna)
- Mark Johnson, an engineer at Woods Hole Oceanographic Institution, is poised to attach a D-tag to a pilot whale off the island of El Hierro in the Canary Islands. Johnson, who developed the non-invasive tag to record whale movements and sounds in the deep, is co-author of a study (published online in May 2008) that used D-tags to reveal the distinctive way that pilots whales hunt.
- Natacha Aguilar de Soto, lead author of the new (May 2008) report on pilot whale hunting behavior, coordinates whale-sighting and tagging efforts from a small boat off El Hierro, Canary Islands. She is a whale biologist at the University of La Laguna, Canary Islands. (Marta Guerra, University of La Laguna)
- From an inflatable boat, Peter Madsen (University of Aarhus, Denmark), a co-author of the new study, keeps track of whale locations reported by spotters ashore. (Marta Guerra, University of La Laguna)
- The work starts from above: Researcher Alejandro Padron from the University of La Laguna spends hours in blazing heat on the volcanic highlands of El Hierro, patiently locating whales for the whale-tagging scientists in boats. (Victor Gonzales Otaola, University of La Laguna)
- In one clean lunge, WHOI engineer Mark Johnson applies a D-tag to the back of a fast-diving, short-finned pilot whale (Globicephala macrorynchus) that is resting on the surface. (Francisca Diáz, University of La Laguna)
- Previous work on D-tagged Blainville’s beaked whales (Mesoplodon densirostris), such as this one, showed that their and pilot whales' feeding styles differ. Beaked whales make slow, long, deep foraging dives, while pilot whales make fast deep sprints. (Victor Gonzalez Otaola)
- Mark Johnson holds a D-tag retrieved from the water. Suction cups on the tag keep it attached to the whale for several hours and then it pops off and floats to the surface, where a small antenna signals its position to researchers. (Courtesy of Mark Johnson, Woods Hole Oceanographic Institution)
- In Johnson?s lab at WHOI, he and Aguilar de Soto spend hours analyzing the large files of numerical data collected by the tags on each whale?s dive, including depth and water temperature, the whale?s body orientation and tail strokes, the sounds emitted from and reflected back to the whale, and other sounds in the ocean. From these, they construct a picture of each dive. (Tom Kleindinst, Woods Hole Oceanographic Institution)
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See Also
- Cheetahs of the Deep Sea Journal of Animal Ecology 'online early' article describing pilot whales' hunting behavior
- The Deepest Divers An article on using D-tags to learn about beaked whales from Oceanus magazine
- Eavesdropping on Whales' Mealtime Conversation An articles on using D-tags to learn about orca whales from Oceanus magazine
- Playing Tag with Whales An article from Oceanus magazine on the development of D-tags, by WHOI engineer Mark Johnson
- Put the D-tag on the Manatee An article on using D-tags to learn about manatees from Oceanus magazine
- Run Deep, but Not Silent An article on using D-tags to learn about sperm whales from Oceanus magazine
- Marine Mammal Center (MMC) See what the MMC is all about.
- Universidad de La Laguna