In the last three months, more than 3,000 dolphins have washed ashore in Peru, most likely due to offshore oil exploration. Oil companies in the region often use sonar or acoustic soundings to detect oil beneath the floor of the sea, and dolphins and whales can be affected because of their sensitivity to sound.
Toothed whales, including dolphins and porpoises, have evolved to be able to echolocate. Instead of having two nostrils like other mammals and baleen whales, toothed whales have only one which is used as their blowhole. A whale emits squeaks and whistles from its blowhole, and the sounds bounce off objects in the water, providing an echo. The other nostril has developed into a fatty tissue known as the melon, which is used to receive and focus the returning echoes.
Hearing is considered to be whales’ most important sense, used not only for navigating but also for feeding, bonding with offspring, and finding mates. Noise pollution cause changes in calling behavior, but can also cause whales to change their diving habits which can result in “the bends,” when nitrogen bubbles get trapped in the body.
Sonar can be extremely loud (imagine the sound of 2,000 jet planes), with sound waves travelling hundreds of miles through the ocean. Noise levels this high can cause fatal injuries, similar to those seen in many strandings around the world. As the world’s oceans become noisier, they also become more dangerous for whales and dolphins.
Editor’s Note: Guest blogger Shane Gero is a Ph.D. candidate at Dalhousie University in Nova Scotia and a lead researcher for the Dominica Sperm Whale Project.
I met Enigma when he was only a few months old. He was about three meters long and probably weighed over a ton.
That’s about average for a newborn sperm whale. When he reaches full size, in about 25 years, Enigma might be as long as 18 meters and weigh over 50 tons.
I have been following Enigma’s family since before he was born. I have spent literally thousands of hours at sea following them and about 20 other families of sperm whales which live in the eastern Caribbean Sea.
It has really been the first time that anyone has come to know these leviathans from the deep as individuals with personalities, as brothers and sisters or as mothers and babysitters, and as a community of families each with their own ways of doing things, their own dialects, and their own cultures.
Sperm whale relationships are very much like our social lives -- more so than many might like to admit. The main difference is the most obvious, they live in the ocean. You see, most of the ocean is actually dark. Only a thin layer at the surface gets any light from the sun. For a sperm whale, life is really in the darkness of the deep.
I jokingly call them “surfacers” rather than “divers” because an adult female, like Enigma’s mother Mysterio, will spend over 80 percent of her life in the darkness of the deep ocean feeding. She will only spend about 10 to 15 minutes of every hour in the part of the ocean that sunlight touches and where I can observe her interacting with other members of her family.
As a result, while Mysterio’s eyesight is good both above and below the water, her world is dominated by sound. Just like bats, sperm whales have evolved a system of echolocation to “see” in the dark. Their unique nose, which houses the most powerful natural sonar system, has allowed them to exploit the deepest parts of the ocean that very few other mammals can, and as a result has made them a significant part of the ocean ecosystem. Globally, sperm whales can eat as much squid as all of humanity’s fisheries combined.
Did you know there are about 40 species of dolphin? When you think of dolphins, you might just be picturing the bottlenose dolphin or the common dolphin, but what about the long-snouted spinner dolphin? (And did you know that the killer whale is actually a kind of dolphin too?)
Long-snouted spinner dolphins are relatively small for oceanic dolphins, growing only about 7 feet long (the bottlenose dolphin is about 10 feet long). Spinner dolphins are highly social and are often seen in pods of hundreds of dolphins. Like all dolphins, spinners communicate by echolocation, which is an elaborate series of clicks and whistles. Spinner dolphins also slap the surface of the water with their fins to communicate.
Bats and toothed whales share the ability to squeak and click their way to prey. And now two new studies in this week’s journal Current Biology reveal that their echolocation, which evolved independently in the two groups, has a similar underlying molecular mechanism.
There are plenty of examples of evolutionary convergence, such as the tusks of elephants and walruses, or the bioluminescence of fireflies and jellyfish.
But it’s highly unusual for convergence to occur at the molecular level. Turns out the inner ear hair cells of both the bottlenose dolphin (a toothed whale) and 10 species of bats contain a protein called prestin, which plays an important role in echolocation.
But not all echolocaters are created equal. Because the speed of sound in water is five times that in air, dolphins can use echolocation for more than 100 meters. Bats can only do so for a few meters.
(Hat tip to Monterey Bay’s Sea Notes blog for this story.)
Do me a favor and try this: stay where you are and click your tongue against the roof of your mouth. Now walk somewhere else, and click your tongue again. Can you hear a difference? Congratulations, you’re on your way to learning how to echolocate! Whales and dolphins use echolocation to navigate and locate objects in the dark ocean. According to acoustic experts in Spain, people can use tongue clicks to “see” things by listening to the way the noise reverberates off its surroundings. All you have to do is recognize changes in your tongue clicks based on what is around you. Apparently, two hours per day for a couple of weeks is enough to determine if something is in front of you, and it takes a couple more weeks to differentiate between a tree and pavement. The most ideal sound is the “palate click” where you place the tip of your tongue on the roof of your mouth just behind your teeth and quickly move your tongue backwards.