Uncovering Secrets of Blue Whale's Song
for National Geographic News
|February 6, 2004|
This story is one of a series looking at National Geographic
Crittercam research. Crittercam is a research instrument worn by wild
animals and equipped with a video camera and other
information-gathering equipment. Crittercam is used on animals both
in the ocean and on land.
To learn more about the Crittercam's field test in California, tune in to the Crittercam: Blue Whales episode on the National Geographic Channel in the United States on Friday, February 6 at 8 p.m. ET. Got a high-speed connection? Click here to watch previews of the Crittercam television documentaries on the National Geographic Channel Web site.
The haunting call of the blue whale is the most intense of any animal alive. These rhythmic pulses and deep moans are so loud they travel across entire oceans, yet the frequency of these calls is often so low that they are totally inaudible to human ears.
Though marine biologists are still at a loss to explain exactly what purpose blue whale calls serve, deciphering this lonely song could assist in conserving the endangered species. Despite being perhaps the largest animal ever to have lived on Earth, the blue whale's low numbers, elusive nature and tendency not to follow consistent migration paths make it difficult to study.
"One of the challenges in understanding the status of this species is knowing how many are out there," said National Geographic in-house marine biologist John Francis, based at Society headquarters in Washington D.C. Remotely listening to and measuring whale song, which travels for thousands of miles, is one off-beat option. "But first we need to know who is calling, how often and under what circumstances," he said.
Now, in an effort to glean new insights into calling and other behaviors, National Geographic Crittercam documentary makers have teamed up with Francis and whale expert John Calambokidis to capture both audio and video footage from blue whale-worn cameras for the first time. That unique footage, captured off the coasts of California and Mexico, has helped shed light on vocalizations, and provided novel insights into swimming dynamics and feeding behavior.
Brush with Extinction
Monitoring blue whales (Balaenoptera musculus) off the coast of California by taping vocalizations and other methods is an important task. These animals have barely rebounded from the brush with extinction dealt by whaling.
There may have been 300,000 blue whales at the end of the 19th century. Incredibly by 1966, when their hunting was banned by the International Whaling Commission, that number had dwindled to just a few thousand.
"Blue whales are so large and fast, that prior to the widespread use of explosive harpoons and modern ships [in the 20th century] whalers couldn't go after them," said Calambokidis, one of the world's foremost blue whale biologists with nonprofit institute Cascadia Research in Olympia, Washington.
Blue whaleseach of which can measure 90 feet (27 meters) or more in length, weigh up to 150 tons (136,000 kilograms), and yield 120 barrels of oilbecame the focus of the whaling industry in around 1900. That slaughter peaked in 1931 when 29,000 blue whales were killed in one season. "Forty years ago there was uncertainty as to whether the blue whale was doomed to extinction, because populations had been reduced so dramatically," said Calambokidis. Recovery has been slow, and 10,000 to 12,000 blue whales are estimated to survive today.
One of the least threatened populations (numbering up to 3,000 whales) spends the summer off the coast of California, and it is to these animals that Calambokidis has turned his attention.
Calambokidis' team has photographed and recognized around 1,500 blue whales by tail fluke and back markings. It also collects data on population size, whale calling, and other behaviors.
Scientists wants to monitor population growth remotely by listening out for voices in the deep, but so far have managed only to measure relative changes in numbers (from one August to the next for example). The amount of whale-calling detected varies by season, and researchers do not yet know whether that reflects real differences in population numbers, or if whales sing less at different times of year.
The whale-worn cameras provided by the Crittercam team have provided unprecedented opportunities to capture whales calling, and answer basic questions on feeding and swimming behavior. Crittercams automatically detach and float to the surface after around six hours and are equipped with radio transmitters for location and retrieval.
Not that attaching the devices was an easy task. Thirty miles from the shore, Francis, Calambokidis and the Crittercam team had to get within a few feet of fast-moving, surfacing whales, with only an inflatable boat to protect them.
Successfully deployed 17 times, these video cameras provided new insights into feeding behavior. Previously, time-depth recorders had revealed unusual "saw-tooth" patterns of diving: whales would repeatedly dive deep and lunge upwards again before resurfacing for air. "It turned out these were upwards lunges into dense swarms of krill," said Francis, who is also the National Geographic Society's Vice President for Research, Conservation and Exploration.
Not only did Crittercam film clouds of the shrimp-like prey swarming past the camera lenses as whales came to a full stop, mouths agape, but it also captured a whale's neck pleats expanding as its throat distended to several times its normal size.
Crittercam also revealed that during dives, blue whales stop flapping their huge tail flukes, instead compressing their lungs to decrease buoyancy and glide effortlessly towards deep waters.
However, some of the most interesting findings come from data collected with both Crittercam and other types of underwater data loggers used in collaboration with the Scripps Institute of Oceanography. Crittercam first hinted that blue whales don't make long calls during feeding, said Calambokidisone previously suggested purpose of the call.
In fact, his team's research using several types of whale-attached tags has revealed that "blue whales are not vocalizing anywhere near as often as we thought they would be." Instead, males alone produce the longer types of call, said Calambokidis. "It could be that males are advertising to other males or attracting females."
Researchers still have a long way to go to perfect methods for estimating whale numbers by vocalization alone. Some animals appear to vocalize much more regularly than others do for example, and Calambokidis still has little idea why.
In the meantime, though commercial whaling is no longer a threat, there may be new and less obvious dangers bringing the species' recovery into doubt. "There are a number of very low frequency sounds produced by human [technology], that are within the range of blue whale calls," said Calambokidis.
These sounds are produced by shipping among other sources, and a new type of low-frequency U.S. Navy sonar. Another type of mid-frequency sonar has been linked to mass strandings of other species, but researchers are at a loss to explain why. It could be that the low-frequency sounds confuse whales, damage their hearing or disrupt communication, said Calambokidis.
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