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Marine mammals such as whales, dolphins, and seals have an amazing ability to hold their breaths—sometimes for up to two hours—while they dive deep to search for food and evade predators. In the cold, dark waters hundreds of meters below the surface, animals rely heavily on sound to navigate, avoid danger, and locate prey.

D-tag
Scientists use "D-tags" to record sounds marine mammals make and hear underwater and to gather data about how they travel. Image courtesy: Woods Hole Oceanographic Institution

Because these deep ocean divers spend much of their time out of sight, scientists in the field of "bioacoustics" are using their ears to study and track the animals in some creative ways.

In the late 1990's, researchers at the Woods Hole Oceanographic Institution (WHOI) invented the D-Tag—a radio device that can be attached by suction cups to a whale's back. Using a tiny underwater microphone, the tag records sounds that the whale makes and hears underwater. It also records depth, water temperature, and other information, providing a travel log of the animal's movements. Each tag records for several hours before floating to the surface where researchers retrieve it and download the data.

whale listening buoys
An engineering assistant at WHOI's Coastal Research Laboratory puts finishing touches on a buoy for the right whale detection system. Image courtesy: Woods Hole Oceanographic Institution

Around the same time the D-Tag was being tested, scientists with the Bioacoustics Research Program at Cornell University started using gadgets known as "pop-ups." These larger instruments float near the seafloor like underwater ears, recording all nearby sound for months at a time before they are collected.

Both tools help researchers investigate the effects of underwater noise, such as ship engines, sonar, and other racket caused by humans. Not all marine animals react the same way. Some seem to ignore the clamor. Others change course or alter their mating calls. Scientists suspect that increased noise levels and sudden sounds can also confuse or startle marine mammals, possibly leading to injuries and strandings.

listening buoy network
A snapshot of right whale calls detected on April 8, 2008 by the listening buoys off the coast Massachusetts. Image courtesy: Cornell Lab of Ornithology, www.listenforwhales.org

The North Atlantic right whale (Eubalaena glacialis), which was hunted nearly to extinction in the mid-1600's, is among the animals scientists have been eavesdropping on. Even though they haven't been hunted since 1951, fewer than 400 right whales survived in 2006. And they remain extremely vulnerable to ship collisions and fishing gear entanglement.

To help prevent collisions, researchers from WHOI and Cornell installed a network of listening buoys in busy shipping areas off the coast of Massachusetts, where many of the whales spend time. The buoys record and transmit any sounds that are similar to right whale calls to a lab at Cornell where researchers carefully check them. If a right whale call is confirmed, nearby ships are alerted to slow down and watch for whales. With their numbers so low, saving even a few whales from collisions could be critically important in the species' survival.

Related Links...

The Tale of the Whale: Building the Ocean Hall's Ambassador
http://www.mnh.si.edu/exhibits/ocean_hall/whale_model.html
The Right Whale Listening Network—Cornell Bioacoustics Research Program

http://www.listenforwhales.org/netcommunity/Page.aspx?pid=430

North Atlantic Right Whale Consortium
http://www.rightwhaleweb.org/index.php?mc=2&p=2

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