Science / Medicine : If this ‘Big Bang’ is true--that toothed whales used concentrated sound waves to stun waves to stun their prey, then it could help explain the social behavior, feeding habits and evolution of toothed whales. : The Other ‘Big Bang’ Theory

For more than 20 years, marine scientists have occasionally suggested that some whales and dolphins may use blasts of sound to help them catch their dinners. Now, researchers at the Long Marine Laboratory here are planning to test this theory by exposing fish to the low-frequency banging, crashing and popping noises that dolphins and killer whales sometimes produce during feeding.

No clear-cut case of such noise being used to stun prey has ever been documented, and only in the last few years have a few lucky researchers captured the suspected sounds on tape. But a mass of anecdotes and circumstantial evidence are increasingly leading Long Marine researcher Kenneth Marten and some of his colleagues to suggest that dolphins and several related species of whales may use the special sound-producing organs in their heads to generate deafening bangs that temporarily stun fish.

The zoologists at Long Marine have dubbed this hypothesis the “big bang theory.” If true, the theory could help explain the social behavior, feeding habits and evolution of toothed whales.

Toothed whales, known more formally as odontocetes, are a suborder of the whales distinguished by the fact that they have teeth and hunt a wide variety of fish and marine invertebrates. Dolphins, killer whales and sperm whales are all toothed whales. In contrast, the baleen whales, such as the blues and grays, have bone-like plates, or baleen, in their mouths that they use to skim plankton from the ocean.

Use Sound Two Ways

Scientists have long known that dolphins and whales use sound in at least two ways: as signals to one another and as a beam of sonar clicks, the echo of which allows them to “see” objects in even the murkiest of water.

In 1983, Long Marine Director Kenneth Norris and Bertel Mohl, a sperm whale researcher from Aarhus University in Denmark, collaborated on a review of the evidence that odontocetes might also use sound as a weapon.

Norris and Mohl failed to find any conclusive evidence for the hypothesis. What they did find, however, was a series of scientific mysteries where the missing clue always seemed to be some sort of invisible weapon, like sound.

Perhaps the most dramatic of these mysteries is the case of the unblemished squid found in the bellies of sperm whales. Whalers and scientists have made numerous reports of opening the stomachs of captured sperm whales and finding picture-perfect fish and cephalopods. No scratches. No tears. No teeth marks. Live squid have even been seen to swim out of the stomachs of recently killed sperm whales. The untraumatized condition of the squid suggests that the whales have some way of getting the squid into their stomachs without having to use their teeth.

Jaws Often All But Useless

Even if sperm whales wanted to use their teeth, their jaws are often all but useless. And the whale is so much slower than its prey that it seems unlikely that it could ever get close enough to make a quick grab.

Adult sperm whales, weighing in at 30 to 50 tons, swim at an average speed of 2 to 4 knots, while their favorite food, squid, can move at bursts of up to 30 knots. Norris and Mohl calculated that for a 30-ton whale, just getting up to a speed fast enough to catch the squid would burn more calories than the squid was worth.

The difficulties faced by the sperm whale are similar to the troubles faced by other large odontocetes trying to catch small, nimble fish. How, for example, does a 15-foot narwhal with an 8-foot tusk growing out of its head manage to snag a tiny shrimp when the shrimp is doing its best to scuttle out of the narwhal’s path?

If a shrimp or squid could be temporarily stunned, a lazy odontocete could then simply scoop it up while passing by.

Evolutionary Evidence

The theory that odontocetes use sound to stun their prey also fits well with evolutionary evidence. In the Miocene epoch, 20 million years ago, many odontocete species had very long snouts with slim, piercing teeth.

This “pincers jaw,” as it is called, was probably used to pluck small prey from the water with a quick snap. In many modern odontocetes, however, the snout has either disappeared or been greatly shortened. And the teeth have become shorter and wider. This leads scientists to think that the long jaw is no longer needed because the animals have found other ways to catch their food.

At the same time, whales and dolphins have evolved more and more sophisticated sonar systems. Air sacs in a dolphin’s head act as parabolic reflectors, allowing the dolphin to focus the echolocation clicks into a beam of sound.

In the process, dolphins can generate “jet airplane level noise, about 230 decibels,” Marten said. By listening to the echoes of those clicks, dolphins are able to locate objects as far as 100 to 150 meters away.

Although low-frequency sounds transmit more efficiently through water, dolphins and most odontocetes use high-frequency clicks for echolocation when they are focusing on a small object because their heads are too small to focus the longer wavelengths associated with low-frequency sounds. Only sperm whales, whose heads make up about a third of their bodies, are large enough to focus low-frequency sound, Marten said.

Knowing this and using evolutionary logic, Marten reasoned that at some point some dolphins might have developed a sound beam powerful enough to stun fish. This accidental byproduct of improved echolocation would give those dolphins a competitive advantage, providing evolutionary pressure to retain and further develop the new behavior.

Quiet Killer Whales

But, no one has ever seen a dolphin or killer whale stun a fish with sound. Some researchers who spend time watching odontocetes feed have yet to hear so much as a single low-frequency pop.

One of those who remains skeptical is John Ford, a marine zoologist at the Vancouver Aquarium in British Columbia. Ford has spent a decade observing killer whales off the coast of British Columbia and recording the noises they make while hunting salmon in the nooks and crannies of coastal rocks.

“Over 10 years, in situations where it would have been ideal (for the whales) to bang off a few salmon, I’ve never heard it,” Ford said. “If they can do it, they are carrying around all this ammunition, why don’t they do it?”

Ford said he would not be surprised, however, to discover that his whales could use sonic bangs if they wanted to. He said he has spent little time observing killer whales during the winter months when they feed on herring, a type of prey that might be more suited to sonic hunting.

Hunting Techniques

Yet another factor that makes it difficult to catch odontocetes in the act of stunning fish is the sheer variety of hunting techniques they employ.

“Those guys are clawing and tearing and doing everything they can do to get their lunch,” Marten said. Dolphins have been known to strike fish with their flukes and produce loud bangs by means of cavitation, a maneuver in which a rapid swipe of the tail causes water to implode into the resulting vacuum.

Even when bona fide bangs are recorded on tape, it has so far been impossible to determine exactly how loud they are, which whale or dolphin is producing the sound and what sequence of events led up to the noise, Marten said.

The solution to these difficulties, Marten added, would be comprehensive underwater observation of dolphin social behavior. But that requires a level of funding that the lab does not have.

For the time being, Marten plans to focus his efforts on testing the effects of low-frequency bangs on fish. Already, he has produced a noise that killed anchovies in Santa Cruz Harbor. A commercial application of that technique may someday make it possible to keep fish away from power plant intakes or other locations where their presence could interfere with machinery, Marten said.

Reproducing the exact noises produced by dolphins is much more difficult than killing anchovies, Marten said. Equipment that can play the sounds under water costs “hundreds of thousands of dollars,” he said.

Training dolphins to produce the bangs on demand, which is probably less expensive than playing the sounds on electronic equipment, has its own problems, Marten said.

For one thing, dolphins in captivity are reluctant to produce loud noises because of the painful effects of reverberations off tank walls. Also, social relationships seem likely to play a big role in dolphin hunting behavior.

Under a program being developed, Long Marine lab will “borrow” related dolphins from the wild for short periods of time and then return them to their native location, Marten said.