Cool science: how to protect dolphins and whales through hearing tests
Have you ever listened under water?
When diving or snorkeling, I am always amazed at just how much noise there is underwater.
Sometimes it is the sounds of fish (like croaker) or snapping shrimp, other times it's the splashing of other swimmers, or the hum of a boat engine.
Pretty cool, huh?
Now imagine you live there…and you can never turn that noise off.
Maybe not so cool.
For dolphins and whales, this is the reality. Noise that is a natural part of the environment isn’t a problem. But whales and dolphins rely on keen hearing for communicating, navigating and locating prey.
Anthropogenic, or human-made noise, can interfere with these important processes. Noise from ships, industrial activities, seismic work, and sonar (which can be something as simple as a depth finder or as complex as military sonar) can make it difficult for these very social animals to communicate with one another.
Whales communicate over very long distances underwater. Their songs can carry for miles. Unfortunately, the noise from ships that can mask, or cover, the whale sounds acts the same way. The inability to communicate can impact feeding and reproduction.
Seismic testing, explosions and other loud noises can have more acute effects.
In some cases animals may suffer a physical trauma from the noise and in others the effect can be a behavioral one- causing animals to panic. This can result in changes in dive patterns that can have physical effects (think of divers who rise too quickly and get the bends), or can cause a “fight or flight” response in which animals panic and move out of known habitat and can strand or be unable to return to open water.
While the connection between the sounds we make and the effects on marine mammals may be logical, the ability to document them with hard, scientific evidence is challenging.
The International Fund for Animal Welfare (IFAW) Marine Mammal Rescue and Research team is doing our part to help understand the impact of underwater sound on marine mammals.
We have tested the hearing of many of the dolphins that strand on Cape Cod to better understand the normal hearing ranges for their species. We now have the hearing data for Atlantic white-sided dolphins, and we’ve contributed to the data on common dolphins and pilot whales as well.
We use Auditory Evoked Potential testing (AEP) to determine what the dolphins can hear. This is the same technology used to test hearing in infants.
Like human infants, dolphins cannot raise their hand in response to heating a sound. Instead, we use electrodes to receive the electrical response from the brain and measure levels at which animals can hear certain frequencies.
Basically, we play a sound to the animal through a jawphone (a suction cup placed on the animal’s jaw, since that is where they receive sound). Several sounds can be played at the same time at different rates, and we can capture the animals response, eventually determining the threshold, or lowest sound pressure level (think volume) at which the animal can hear a certain frequency (think tone or pitch).
It’s really pretty cool stuff. The best part is that it is completely non-invasive, and the animals rarely respond in any outwardly noticeable way.
By collecting these data, we hope to further our collective understanding of what cetaceans can hear and, by doing so, better understand how anthropogenic ocean noise is affecting them.
Hopefully, the result will be more informed conservation policies to protect these animals from an unseen, but very real threats.