A fascinating Smithsonian Piece from 2011 investigates how sperm whale echolocation works. The sounds are primarily produced by the same organ – a functional sound lens on their skulls, made primarily from the exceptionally fine oil that fueled the Industrial Revolution – which was the main target of the 19th and 20th century whalers, who briefly pursued them from extinction.
Biologists now believe that the sperm whale's massive head functions like a powerful telegraph machine, sending out sound pulses in different patterns. At the front of the head is the Spermaceti organ, a cavity that contains most of the roller, and a mass of oil-saturated fat called junk. Two long nasal passages branch off from the bony nostrils of the skull, winding around the spermaceti organ and the junk. The left nasal passage leads directly to the blowhole at the top of the whale's head. But the other twists and turns, flattening and widening to form a series of air-filled sacs that can reflect sound. Near the front of the head sits a clapper called "monkey lips".
Sound generation is a complex process. To make its clicking sounds, a whale pushes air through the right nasal passage to the monkey lips, which close. The resulting click! bounces off an air-filled sack and wanders back through the spermaceti organ to another sack that hugs the skull. From there, the click is sent forward through the garbage and amplified out into the watery world. Sperm whales may be able to manipulate the shape of both the spermaceti organ and junk so they may be able to aim with their clicks. The substance that made them so valuable to whalers plays an important role in communication today.
As the article explains, sperm whales primarily use this powerful sixth sense to locate their prey, which consists primarily of large squid, including, in some cases, the giant squid that lives deep in the oceanic trenches, of which the whales are among the only marine mammals can dive. The whales we saw off the coast of Kaikoura in August 2018 apparently sought such prey down in the Hirukangi Trench, which is 9,000 feet deep in places.
The sperm whales' ability to dive to extraordinary depths is enhanced by the deep wrinkles in their skin that are visible on their dorsal fins when they come to the surface to breathe.
At one point, scientists wondered if their echolocation sounds were used to stun or incapacitate the squid and perhaps even crush it into submission, as loud noises are known to be capable of underwater. However, further investigation into this question did not reveal anything to support the hypothesis.
"This was a beautiful idea that was killed by data," Peter Tyack, a senior scientist at the Woods Hole Oceanographic Institution in Massachusetts, told NYU Scienceline. Tyack and another scientist, who conducted separate experiments, found that the ultrasonic sounds of sperm whales had no effect on octopus or fish.
However, it's still likely that the sounds play a role in their ability to outrun their prey:
So ultrasound as a weapon is out. But there is a loophole. Sperm whales make some other powerful noises that have not been tested. These other sounds are within the range of human hearing and have a much lower frequency than those used in the two studies. However, researchers disagree on whether it is still worth testing the hypothesis that sperm whales are acoustically armed and dangerous.
"I think we shouldn't come up with the theory just yet," said Ted Cranford, sperm whale anatomist and professor of biology at San Diego State University. "It could be pretty easy for the sperm whale to overload the sensory systems of some living things."
When I listened to the hydrophone, I knew that the whales' echolocation noises were exceptionally strong. I'm used to hearing the echolocation sounds of killer whales (there are a lot of samples in this recording) which are shorter and less dense. Last but not least, the sounds can cover enormous distances under water. And who knows what they're saying to the whales?
The powerful surface blows of the sperm whales also enabled whalers in the 19th and 20th centuries to discover them and bring them almost to extinction.