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Space-Age Whale Monitoring
Researchers use satellite to track whales On a typical work day last summer, engineer and computer programmer Brian Corzilius stood three feet deep in a children's pool in his backyard, adjusting an underwater microphone and speaker. Cables lay draped over the pool edge, connecting submerged electronic instruments to the power supply, tape recorders, oscilloscope, and laptop computer on the poolside picnic table. From time to time eerie, lowpitched moans emanated from the pool. Corzilius, who works in the Cornell Lab of Ornithology's Bioacoustics Research Program (BRP), was using this backyard underwater sound laboratory to test an acoustic probe that will be part of a compact instrument package to be attached to large whales. Scientists are developing the device to study where the animals travel, how long and how deep they dive, and how often, when, and where they vocalize. Once a whale is equipped with the instrument package, the device will measure the volume and pitch of every loud sound it makes. An onboard computer will record data about the whale's vocalizations: the time the call occurred, the whale's depth when it was made, and other important information. When the whale surfaces to breathe, the stored information will be transmitted to a communications satellite orbiting far above the earth, then relayed to a receiving station on the ground. The satellite will also provide information on the whale's location when it surfaced. The "satellite tag project," as it's known around the Lab, is a collaborative effort involving scientists at BRP and Oregon State University (OSU), funded by the Office of Naval Research. For several years, Bruce Mate of OSU has been developing satellite tags that track whales' positions and provide information about the depths and durations of their dives. About a year ago, Mate teamed up with BRP director Christopher Clark to add sound-monitoring capabilities to the tags. Early in the project, Clark put Corzilius in charge of designing and building the acoustic sensor and electronic circuits that pass data to the tag's computer "brain." Corzilius's background in designing and programming special purpose microcomputer devices makes him well qualified for the job. The satellite tag itself is a cylindrical package about eight inches long by two inches in diameter, weighing about two pounds. Crammed into this space are sensors for sound, depth, and temperature, a clock, a computer that processes and stores the data from the sensors, and a radio transmitter. About half of the package is taken up by batteries, which power the device for 40 to 50 days. To attach the tag, scientists must maneuver a boat to within 20 feet of a whale just as it surfaces to breathe. As the animal's blowhole breaks the surface, they fire the tag from a crossbow. If the shot is successful, the tag embeds itself in the whale's 8- to 12-inch layer of blubber. Whales tagged this way typically show no signs of distress from the procedure. The first model of the acoustic tag will provide information on when and where each whale call occurs. Because of technical 1imitations in the commercia1 satellite system that relays the data, it won't actually record the sounds. Corzilius is already thinking about how future versions of the tag might provide more detailed information about a whale's calls. One possibility is to equip the tag's onboard computer with a miniature version of the hard disk used to store information in desktop computers. Once the disk is full of recorded sounds and other data, the tag would drop off the whale, to be recovered by researchers. Although scientists plan eventually to attach acoustic satellite tags to whales of several species, they will focus first on blue whales off the California coast. Blue whales, the largest animals that ever lived on Earth, may be as long as 100 feet and weigh over 150 tons. They are uncommon and usually live singly or in small groups far from coastlines, so they are hard to find. Once found, they're hard to observe for very long because they swim so fast. And like all whales, blues spend most of their time submerged, hidden from observers on the surface. So, until recently, biologists had made few recordings of blue whale sounds. In the last two years, Clark has made more recordings using the U.S. Navy's undersea surveillance system (see Birdscope, Winter 1994). Most of these whale sounds have been sequences of low moans, 15 to 20 seconds long, repeated at intervals of about one minute. The function of these sounds is still unknown. Clark and Mate hope that by attaching sophisticated electronic sensors directly to the animals, they can begin to unlock some of the mysteries of whale behavior. |
