The "Sea Monsters" Expeditions
Researchers Track a Top Predator
Think it's easy to record the utterances of a 50-ton behemoth?
 | Dr. Adam Frankel, postdoctural associate in BRP, found this "sperm whale" in New Zealand less vocal than the lifesized ones. |
Armchair adventurers around the world looked on via the Internet in 1997 as an international team of biologists and oceanographers explored the abyss of the Kaikoura Canyon, off the coast of the South Island of New Zealand. The 1,000-meter-deep canyon, located a kilometer offshore, is home to a rich variety of sea creatures, including sperm whales and their most remarkable prey, the legendary giant squid (Architeuthis).
Adam Frankel, a postdoctoral associate at the Cornell Lab of Ornithology's Bioacoustics Research Program (BRP), joined the research team to track the movements of sperm whales as they dove into the depths of the canyon. The expedition, the original working title for which was "Sea Monsters", was organized by the Smithsonian Institution and the National Geographic Society, in cooperation with several other research institutions and the U.S. Office of Naval Research. A web site operated by the National Geographic Society (see links below) provided daily coverage of the adventures of the research team and background information about the expedition.
Sperm whales were a focal point of the expedition because of their role as predators on one of the most mysterious creatures in the ocean, the giant squid. Giant squids, which can grow up to 60 feet long, are known only from dead specimens that have washed ashore or been hauled up in fishing nets. Although scientists have never succeeded in finding a live giant squid, sperm whales do it regularly: most sperm whale stomachs examined by scientists have contained parts of the squids. One of the major goals of the expedition was to give scientists their first view of a living giant squid in its natural habitat. In their quest for the squid, the researchers hoped to take advantage of the sperm whales' skill at finding their elusive prey.
Frankel's mission was to record the clicking sounds made by the whales, and to use the sounds to track the whales as they dove into the depths of the canyon to feed. The whales produce the loud clicks around once per second during each dive, presumably to detect obstacles and prey by listening to the echoes of the clicks. "Once we know where the whales are feeding," Frankel explains, "we'll have a better idea where to send the cameras in search of squid." The team's video "CritterCam" cameras were carried aboard an autonomous underwater vehicle, or robot submarine, and suspended on a cable that could be lowered deep into the canyon in search of squid and other creatures.
Sperm whales near New Zealand typically dive for 40 to 50 minutes at a time, presumably to feed, and then spend about 10 minutes at the surface before diving again. The first step in tracking a whale is to maneuver the research boat to within 200 meters of a whale at the surface. Frankel would then deploy a vertical array of four underwater microphones (hydrophones). The hydrophones are strung at intervals of 10 to 40 meters along an 80-meter-long cable that hangs down into the water from a buoy floating on the surface near the research boat. Sounds from all four microphones are recorded with a multichannel tape recorder on the research vessel for later analysis at a laboratory on shore. Recording starts when the whale dives and continues until the whale resurfaces or its sound is lost among the clicks of more distant whales. In some cases recordings were cut short because of bad weather.
Frankel explains how the click recordings are used to determine the whale's range and depth from the hydrophone array. "As a whale dives near the array, the four hydrophones record each click at slightly different times. Each click is recorded first by the hydrophone nearest to the whale, and then, fractions of a second later, by more distant hydrophones in the order of their closeness to the whale. From the difference in arrival time between any two hydrophones we can calculate a bearing line that points at the whale. By repeating this process for each possible pair of hydrophones, we get a set of lines that intersect at the whale's location."
Specialized software developed at BRP for tracking whales measures the time delays from the click recordings and calculates the whale's range and depth. Researchers use this information to plot a dive profile, showing the whale's depth at successive times during a dive.
Frankel discovered that on average, sperm whales around New Zealand were diving to approximately 325 meters, or about 40 percent of the water depth. The expedition's scientists and photographers used information from the whale dive profiles in deciding where to send their underwater cameras.
The thousands of images that were collected by their cameras continue to be analyzed at the Smithsonian Institution and National Geographic Society headquarters in Washington, D.C. Some results appeared in National Geographic magazine article: "Deep Mysteries of Kaikoura Canyon", June 1998.
A preliminary expedition to the Azores in July 1996, which included BRP assistant director, Kurt Fristrup, resulted in a National Geographic Television special, which debuted February 25, 1998.
A second expedition to New Zealand in Spring 1999 included BRP doctoral candidate Bernard Brennan. It was chronicled in a Discovery Channel program, "Quest for the Giant Squid", which debuted on June 4, 2000.
Physeter catodon and Architeuthis "eye to eye" in the depths: an artists's rendition of an ancient struggle for survival. |  |
For more information on these expeditions, visit the following sites:
- National Geographic Society coverage of the 1997 expedition.
- Learn More about National Geographic's CritterCam expeditions
- Smithsonian Institution coverage of the 1999 expedition.