Magazine article Oceanus

Run Deep, but Not Silent: A New Tagging Device Lets Scientists 'Go along for the Ride' into the Underwater World of Whales

Magazine article Oceanus

Run Deep, but Not Silent: A New Tagging Device Lets Scientists 'Go along for the Ride' into the Underwater World of Whales

Article excerpt

Whales are among the most elusive animals that humans have ever hunted. Pursuing whales across the seas and centuries, whalers made careful observations of whale behavior whenever and wherever they surfaced. But sperm whales, for example, spend about 95 percent of their time beneath the waves. Studying five percent of their behavior was enough to learn how to kill them, but it has taught us very little about how they live.

But now, for the first time in history, we can accompany a whale on its dive, hear what it hears, and observe its normal, natural, previously hidden behavior in the depths. Working closely together, scientists and engineers have created an innovative device--the digital acoustic recording tag, or D-tag. It attaches to a living whale and records nearly everything that happens on its dives, without disturbing the animal. (See "Playing Tag with Whales," page page 57.)

On land, behavioral scientists spend years carefully observing animals such as wolves, lions, or chimpanzees to build up a detailed record of how they behave in response to social or environmental circumstances. Often the researchers remain hidden, or they acclimate the wild animals to their presence, before they can trust that their observations reflect natural behavior.

We cannot do that with whales. We can't be unobtrusive, because boats can't be hidden. And we can't observe whales for long, because most of the time, we can't see them at all. Scientists have had no practical way to follow along on a sperm whale's epic dives, 600 to 1,200 meters down into the cold, dark depths, on their all-consuming mission to search for enough food to keep their massive bodies fueled. Until now.

Pioneering whale studies

Whales live in a world of sound, not sight. Like bats, they send out and receive sound signals and are guided through the sea by what they hear--using both sounds reflected back from objects and sounds made by other whales. Sound is the currency of their lives; they rely on it for knowing where the bottom is, for finding food, and for communicating with each other.

Researchers also use sound for locating whales. Nearly 50 years ago, biologist William Schevill and physical oceanographer Valentine Worthington at Woods Hole Oceanographic Institution were the first to record the sounds of sperm whales, using underwater devices called hydrophones. WHOI biologist William Watkins made enormous advances in identifying which sounds are made by which species of marine mammal.

So careful were these pioneering scientists' methods that we still use their results 45 years later. They still represent some of the best data sets available, accurately measuring and attributing sounds to the different whales that made them, and I have avoided many wrong turns by being attuned to this resource.

With hydrophones, scientists could listen to sounds in the sea and begin to know where, what kind, and how many whales there are in an area. But what the whales were doing below the surface has remained hidden.

The D-tag's origin and evolution

Ecologists place tags on a variety of animals to track their movements, and they have tagged marine animals, too: whales, dolphins, seals, turtles, and even a great white shark. Such tags record depth a few times each minute and can transmit data only when near or at the surface, giving scientists a record of the tagged animal's location and depth over time.

I came to WHOI originally to develop a small tag for captive dolphins that would light up when a dolphin made a sound, allowing us to tell which individual made which sound. It worked well for captive dolphins, but I had not considered using it in the wild. In the early 1990s, a graduate student at the University of Guelph named Andrew Westgate developed the first tag that could be used on wild porpoises to record time and depths of their dives. Unlike earlier tags used on seals, it was not on a collar, but temporarily attached to the porpoise. …

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