Tønnesen P, Oliveira C, Johnson M, Madsen PT. The long-range echo scene of the sperm whale biosonar. Biol Lett. 2020;16: 20200134. https://royalsocietypublishing.org/doi/10.1098/rsbl.2020.0134
Seeing with sound
What happens if you place a microphone on the tip of a sperm whale’s nose? Putting anything on the nose of a 50-foot (15-meter) giant is no easy task, but the reward is a glimpse of how the world’s largest toothed predator sees the world.
Led by their gigantic noses, sperm whales hunt for food in the dark depths of the sea. Diving down to where sunlight doesn’t penetrate, these magnificent predators search for prey using the most powerful sounds produced by any animal. The loud clicks that sperm whales produce while diving are used for echolocation. Just like sonar used by naval ships or fishing vessels, animals that echolocate emit sounds and then listen for the echoes. The sounds they emit will bounce off objects around them and return to the animal along with important information about how far away the object is and what it’s made out of. Piecing together echo after echo, sperm whales create a collage of sound, painting a picture of the world around them click by click.
Until recently, no one knew for sure what exactly sperm whales “saw” using echolocation. The idea that sperm whales use their clicks for echolocation comes from observations of other toothed whales, like dolphins and porpoises, which emit similar clicks and buzzes. Experiments with animals in captivity have revealed the echoes which can be used for navigation or hunting prey.
Studying the echoes received by a sperm whale is much harder than studying those received by smaller toothed whales. This is in part because sperm whales can’t be kept in captivity, but also because the size of their noses makes it very hard to record these echoes. Unlike the slender snout of a dolphin, sperm whale noses are almost rectangular and make up nearly a third of the whale’s massive body.
Tags containing microphones have been deployed on the backs of sperm whales before, but their huge noses create shadows, effectively blocking out any returning echoes from being recorded on a tag. When the echoes arrive, the whale hears them through the front of its nose, which also stops the sounds from moving any further. Aiming to record sperm whale sonar on its return trip, researchers decided to try moving their microphone-containing tags. For the first time, sounds were recorded from the tip of a sperm whale’s nose.
The resulting sound recordings were pieced together to render what the researchers called the “echo scene” of a sperm whale, which was recently reported in an article in the journal Biology Letters.
From this echo scene, the research team was able to draw two conclusions. First, sperm whales can locate prey in the deep sea at long ranges. In one recording, echoes from deep sea creatures were detected from 144m (about 472 feet) away. Given that sperm whale hearing systems are likely even more sensitive than the microphones used in the study, sperm whales can probably detect prey at even further ranges.
Second, contrary to previous theories, sperm whales do not use their loud clicks to debilitate prey. In the past, some scientists have wondered whether the incredibly powerful sounds produced by sperm whales could paralyze prey, rendering them immobile in the water and easy to catch and eat. But, based on the sound levels recorded from outgoing clicks and the average distances to prey, it appears that sperm whale clicks are not loud enough to stun fish or squid.
Innovative animal-borne tagging technology for tracking and recording behavior has provided important insight in studies across the animal kingdom. Combined with the ingenious and novel tag placement on the tip of a whale’s nose, this study gives us, for the first time, an idea of what a sperm whale sees on its deep hunting dives.
I am a PhD candidate at Syracuse University studying marine mammal communication. My research focuses on analyzing underwater recordings of whale calls in order to better understand whale behavior. I’m also interested in education, outreach, and science communication. When I’m not listening to whale sounds, you can find me curled up with a good book or complaining about how much it snows in Syracuse.