So little light makes it to the deep, dark waters where sperm whales do their hunting that the aquatic beasts are essentially blind as bats.
The good news for these whales is that like bats, they can use echolocation to find their prey, according to new research.
The sperm whale is the world's largest deep-diving toothed whale and feeds mainly on squid. Until now, little was known about the hunting behavior, especially prey detection, of these massive beasts.
A team of researchers from Woods Hole Oceanographic Institution and the University of St. Andrews in Scotland used suction cups to attach acoustic recording tags to the backs of sperm whales. The tags were used to both track the whales and record the sounds they emitted while foraging.
As the whales began their dive from the surface, they emitted a regular series of "clicks." When they reached the bottom of the dive, the clicks were emitted more often, eventually combining to form a "buzz" sound.
When the pattern of spaced out clicks turning to a continuous buzz, the researchers said, the whale is homing in on the location of its meal. As the creature closes in on the squid, it switches to this buzz, which bounces more sound waves off the squid, providing the whale with more precise information on where the prey is.
The study is detailed in the May issue of the British Ecological Society's Journal of Animal Ecology.