The Sperm Whale’s Deadly Call

Scientists have discovered that the massive mammal uses elaborate buzzes, clicks and squeaks that spell doom for the animal’s prey

Whalers pursued sperm whales for the rich oil in their oversized heads. Now biologists are on the tail of these deep-diving, long-lived, sociable and mysterious sea creatures. (Gerard Soury / Oxford Scientific / Getty Images)
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The most celebrated natural antagonism between sperm whales and squid, conjuring up images of the Leviathan grappling with the Kraken in the abyssal trenches, almost certainly involves the jumbo squid’s larger cousin, the giant squid, a species that grows to 65 feet long and closely resembles the creature described in Moby-Dick. In the novel’s “Squid” chapter, Starbuck, the first mate, is so discomfited by a squid that floats up in front of the Pequod—“a vast pulpy mass, furlongs in length and breadth, of a glancing cream-color, lay floating on the water, innumerable long arms radiating from its centre”—that he wishes it were Moby-Dick instead.

The nonfictional relationship between sperm whales and squid is pretty dramatic also. A single sperm whale can eat more than one ton of squid per day. They do eat giant squid on occasion, but most of what sperm whales pursue is relatively small and overmatched. With their clicks, sperm whales can detect a squid less than a foot long more than a mile away, and schools of squid from even farther away. But the way that sperm whales find squid was until recently a puzzle.

The orange octagonal box in Kelly Benoit-Bird’s office at Oregon State University is an echo sounder transducer. At sea, it hangs under a boat and sends out waves of sound at four different frequencies. The time it takes each of the waves to return tells her how far away an object is; the waves’ intensity tells her the object’s size. Each organism has a different acoustic signature, and she can often figure out what sort of creature the waves are bouncing off of. To do so requires a certain interpretive knack. Once, in the Bering Sea, her boat came upon a flock of thick-billed murres, diving seabirds, as they were feeding. The acoustics showed a series of thin, vertical lines in the water. What did they represent? Murres pursue their prey by flying underwater, sometimes to great depths. Benoit-Bird figured out that the lines were columns of tiny bubbles the murres expelled when their feathers compressed as they dove.

“Acoustics is a great way to see what’s going on where you can’t see,” Benoit-Bird says. To understand sperm whale sound, she had to first establish how the whales use their clicks to find squid. Unlike fish, squid don’t have swim bladders, those hard, air-filled structures that echolocating hunters such as spinner dolphins and harbor porpoises typically key in on. “Everyone thought squid were lousy sonar targets,” she says. But she thought it unlikely that the whales would spend so much time and energy—diving hundreds or thousands of feet, clicking all the way down—only to grope blindly in the dark.

In a test, Benoit-Bird, Gilly and colleagues tethered a live jumbo squid a few feet under their boat to see if the echo sounders could detect it. They found that squid make fabulous acoustic targets. “They have plenty of hard structures for sonar to pick up,” she says. Toothy suckers cover their arms; the beak is hard and sharp; and the pen, a feather-shaped structure, supports the head. Benoit-Bird was thrilled. “You could say,” she says, “that I’m learning to see like a sperm whale.”

To see like a sperm whale is to get a glimpse of a world inhabited by much smaller animals. “In the Sea of Cortez,” Benoit-Bird says, “you know that what sperm whales do is driven by what the squid do. So you expand. You ask: What is driving the squid?”

The squid, it turns out, are following creatures whose behavior was first noted during World War II, when naval sonar operators observed that the seafloor had the unexpected and somewhat alarming tendency to rise toward the surface at night and sink again during the day. In 1948, marine biologists realized that this false bottom was actually a layer of biology, thick with small fish and zooplankton. Instead of the seafloor, the Navy’s depth sounders were picking up many millions of tiny swim bladders, aggregated so densely that they appeared as a solid band. The layer is composed of fish and zooplankton that spend the day between 300 and 3,000 feet deep, where almost no light can penetrate. At night, they migrate upward, sometimes to within 30 feet of the surface. The fish are well suited to life in the dim depths, with enormous, almost grotesquely large eyes and small organs, known as photophores, that produce a faint glow.

The mobile band of life was named the deep scattering layer, or DSL, for the way that it scattered sound waves. In the Sea of Cortez, the fish that inhabit it, called myctophids or lanternfish, are among the jumbo squid’s preferred prey. The squid follow the fish’s daily vertical migration, spending the daylight hours between 600 and 1,200 feet and then pursuing them toward the surface at night.

Biologists assumed that the DSL creatures were at the mercy of currents, drifting haplessly, helplessly along. But Benoit-Bird and colleagues have found that even microscopic plants and animals can lead active and finicky lives. Phytoplankton, seeking out particular conditions of biochemistry and light, will form sheets that can stretch for miles but are only a few feet high. Slightly larger zooplankton take advantage of this great conveyor of food. Lanternfish likewise fight against prevailing currents to reach the feast. Things gather to eat or not be eaten—by fish, by squid, by sperm whales. What was thought to be at the whim of physics turns out to act on its own biological imperatives.

“I always go in with the same question,” says Benoit-Bird, who in 2010 was awarded a MacArthur Fellowship for her work on sensing biological activity in the deep ocean. “How come things are found where they are? And so what? I think of it as the Big Why and the So What. All the pieces make the full picture.” More than trying to see like a sperm whale, she is trying to see—to understand—everything. “Sometimes, you get a little swept away,” she says. “It’s fun just to watch and go, ‘Cool!’ ”


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