9 Enormous Facts About Sperm Whales, Gigantic Creatures of the Sea

The star of the Herman Melville novel "Moby Dick" was a giant white sperm whale, so it's no surprise so many connect the book to real-life sightings. "In my experiences on whale watches and discussing whales with people, it is a very common association," says Stewart, "especially after the movie 'In the Heart of the Sea' came out in 2015 and reignited peoples' curiosities with this legendary species."

Or at least Stewart thinks so! "I call them the hot dogs of the sea," he says. "At least when you see them at the surface, and you're only seeing their enormous head." Stewart says their gray-brown color and long bodies appear to be less round — or of less girth — than baleen whales of similar size. They also lack a true dorsal fin and have instead something more like a dorsal ridge like gray whales and humpback whales. Their fluke (or tail) is a wide triangle that gives them a lot of surface area to push their enormous bodies.

"The most curious thing I find about their appearance is that while they are the largest of the toothed whales, they have an extremely narrow lower jaw," says Stewart. "They only have teeth on that lower jaw, and in their upper jaw, they have recesses or even holes, in their gums where the lower jaw teeth sit when their mouth is pressed closed."

"Sperm whales are one of the few whales that have a very significant difference in size between males and females," says Stewart. Males typically range between 50 and 60 feet (15 and 18 meters) long and weigh between 86,000 and 110,000 pounds (39,008 to 49,895 kilograms), while females typically are 26 to 55 feet (8 to 17 meters) long and weigh 26,000 to 40,000 pounds (11,793 to 18,143 kilograms).

Not only are they the largest toothed whale, but the sperm whale's brain is considered the largest on the planet when it comes to weight and volume. "Based on collected samples, the largest sperm whale brain recorded weighed about 20 pounds [9 kilograms]," says Stewart. "Size alone does not determine intelligence, but it is one of the factors psychologists and neurologists use."

Those big brains are also housed in huge heads. "Sperm whale heads by ratio are huge, being about one-third of the body length," says Stewart. "But in terms of overall length, the blue whale probably has the largest, with specimens measuring 20 feet [6 meters] long in whales that are 100 feet [30 meters] in total body length."

In fact, they're louder than just about anything else in the ocean. Some of their clicks and calls have been measured at 230 decibels, according to Stewart, who conducted some research specifically for HowStuffWorks. "Interestingly, I found out that underwater versus in the air are not the same," he says. "A sound created underwater would be about 60 decibels less in the air. So, if a sperm whale could make a sound next to you at your desk, it would reach 170 decibels. And that is still louder than almost anything on land. The bulldog bat can reach 140 decibels. Now, with all that said, we can't hear any of those noises because they are being emitted at a frequency that we cannot hear, thankfully."

"Sperm whales will live in pods when they are younger, or if they are in a nursing pod, but otherwise, large whales tend to live alone," says Stewart. "Sometimes, a single large male will find a nursing pod that will invariably become his harem, as he may mate with multiple females in the nursing pod. After that, the adult male will venture off on his own again." Speaking of mating: They have calls with a unique sound signature that they use to search for a potential mate.

Sperm whales tend to stay away from humans, too. There are historical accounts from whaling ships that claimed some whale species would turn on the whalers, trying to flip their paddle boats, says Stewart. "Gray whales used to be nicknamed devil-fish because they would become aggressive toward whalers," he says. "Now, at the lagoons in Mexico where gray whales have their babies, eco-tourists are offered the chance to get up-close to the whales without that kind of danger. However, in the U.S., the Marine Mammal Act requires people keep a safe distance of 150 feet [45 meters] from all whales and marine mammals."

Echolocation is a method used by whales, bats and dolphins to determine locations of objects using reflected sound. It allows the animals to navigate and hunt in darkness, recognize friends and foes, and avoid obstacles. "Their echolocation is a little different and quite complex because of how the sounds travel through the skull and spermaceti organ," says Stewart. "Their clicks help them locate their food across longer distances, acting like biological sonar. Lower grumbly tones help once the food is very close and about to become a meal."

So, how much and what does a sperm whale eat? According to the National Audubon Society Guide to Marine Mammals of the World, ​sperm whales are estimated to eat up to 3.5 percent of their body weight every day. That means a 100,000-pound (45,359-kilogram) large male would eat around 3,500 pounds (1,587 kilograms) of food each day. And they feed primarily on medium to large squid, but also have been recorded noshing on rays, sharks, fish and octopus.

Stewart says large, mature adult sperm whales are found all over the world — close to the polar regions, specifically. Young adults and female sperm whales tend to hang around the middle region of the planet, diving as deep as 6,000 (1,828 meters) feet to feed. "In one case, a sperm whale was recorded to be on a dive for two hours," says Stewart. They're also quite fast, he adds. "Like many of the big whales, sperm whales cruise at about 3 to 9 miles per hour [4.8 to 14.4 kilometers per hour], but they can sprint and rush at speeds up to 28 to 30 miles per hour [45 to 48 kilometers per hour]."

And Stewart says, all this moving around helps cetaceans (and probably pinnipeds and birds, for that matter) that dive for food at any great depth fertilize the oceans. "They help recycle nutrients that are locked up in the depths of the ocean by diving and hunting prey hundreds to thousands of feet under the surface," he says. "Then, when they defecate at or near the surface, the waste becomes marine snow [organic material that falls from upper waters to the deep ocean]. Filter feeders at the surface and at depths can then consume the detritus and restart the cycle."

According to NOAA Fisheries, the sperm whale population is estimated at more than 300,000. Sperm whales were a prime target of commercial whaling between 1800 and 1987, and before that the population is estimated to have reached more than 1 million. "Sperm whales were highly prized in whaling because the spermaceti was higher quality than whale blubber for making smokeless candles, smokeless oils and lubricants," says Stewart. Whaling today is no longer a major threat to sperm whales but the population is still recovering.