Do whales have ears?

It’s a pretty crappy time to be a cetacean—killer whales are hungry, beluga whales are contaminated, right whales are getting smacked by ships, bottlenose dolphins are getting caught in fishing gear and then of course, minke, sperm, sei and brydes whales are being hunted under Japan’s scientific whaling program.

As if that wasn’t bad enough, scientists have now discovered something else that might make life a little harder for whales and dolphins. The ocean is getting noisier, thanks to an old friend. (Nope, not the Navy.) It turns out that carbon dioxide, that ubiquitous greenhouse gas, is pumping up the volume in our oceans. Confused by the connection? So are scientists, but they know this much:

Oceans absorb carbon dioxide. They always have. But because we’re pumping more carbon dioxide into the atmosphere now than ever before, more CO2 is landing in the ocean as well. When CO2 mixes with seawater it forms carbonic acid (the stuff that makes fizzy drinks fizz) and as the amount of carbonic acid in the ocean increases, the ocean becomes more acidic. (For more on ocean acidification see The Ocean’s Big pHat Problem.)

Sound travels farther in more acidic seawater because—for some reason—seawater absorbs less sound as it becomes more acidic. Right now, researchers say that underwater sound is probably traveling 10% farther than it did 100 years ago, but they predict that sounds could travel up to 70% farther in some parts of the ocean by 2050.

And what does that have to do with whales and dolphins?

Sound travels way faster underwater than in air. And so marine mammals depend on sound for pretty much everything. They use sound to communicate locally and over long distances—humpback songs can be heard 100 miles away and blue whale sounds can reach more than 1,000 miles. Some cetaceans also use sound to identify objects (like prey and icebergs) through a process called echolocation. But being so sound-centric isn’t all it’s cracked up to be.

Por que? Because the ocean is noisy and some of the noises—those from military sonar—are so loud and scary that the whales want only one thing: to get the hell outta dodge. For the whales, that means stranding. And that’s what they do. Since 1989, at least 10 mass stranding events have been linked to military sonar use. Some of the stranded animals have shown signs of physical trauma, including signs of  “the bends”—the illness that can kill scuba divers who surface too quickly.

Sonar isn’t the only noise in the ocean. Ship engines make noise, as do blasts from seismic exploration. There are plenty of natural sounds too, like earthquakes, noisy parrotfish chomping on coral and of course, the whistles, clicks and melodies of whales and dolphins.

As sound travels farther and farther underwater, the ocean will become even noisier.  Whales may be able to communicate with one another over longer distances, but the level of background noise will increase. What once sounded like a quiet bistro will come to resemble Chuck E. Cheese’s. How will this affect the whales? Will they be able to accurately assess their environment through the chaos? Will the sounds of sonar threaten whales hundreds of miles away?

So many questions, but one still lingers: umm, do whales have ears? Yes, but they don’t have external ears—that would be completely impractical for any deep diving animal—instead, they hear through their lower jaw bone. That’s right, the lower jaw acts like an antenna. Sound travels along a fat channel within the jawbone directly to the inner ear.