Narwhals: Photos Show Decline of "Unicorn" Whales
for National Geographic News
|April 13, 2004|
Digital snapshots from above the Arctic have helped a researcher spot
declining narwhal populations. The narwhala small Arctic whale
known for its six-foot-long (1.8-meter-long) tuskhas dropped in
numbers by an average of 6 percent per year during the last 17 years,
said marine biologist Mads Peter Heide-Jørgensen.
In Heide-Jørgensen's study, published in the April issue of Marine Mammal Science, he used aerial surveys of narwhals (Monodon monoceros) in 2001 and 2002 at their major summering ground in northwest Greenland. The biologist used two large-format digital cameras that continuously download images to laptop computers.
When the resulting photographs were compared to narwhal counts taken in the 1980sthe last time a species count had been conducted in this areathe results were surprising.
"We thought there was a good supply," said Heide-Jørgensen, a researcher for the Greenland Institute of Natural Resources.
In 2001 Heide-Jørgensen's aerial survey counted 360 narwhals over 324 square miles (840 square kilometers). In 2002, 566 narwhals were sighted in 853 square miles (2,200 square kilometers).
Hunting may be one reason for the narwhal's slow disappearance, Heide-Jørgensen said. Narwhals are hunted by local Inuit populations for their tusks, meat, and skin. The narwhal's skin is particularly valuable, as it has an extremely high vitamin C content, he said.
In addition, climate change and a growing halibut fishery may be playing a role in the changing numbers, Heide-Jørgensen said.
The Voyage of the Narwhal
The narwhal's tusk, a spiraling extension from a male narwhal's lip and upper jaw, is actually an overgrown tooth. While the tusk's primary use may be to attract or impress females, researchers have also witnessed males jousting with their tusks. There are also theories that the tusk may be used by narwhals as a way to sense sound or electromagnetic waves.
The narwhal has often been associated with another one-horned creature, the unicorn. In medieval times traders would pass narwhal tusks off as unicorn horns, thought to have magical disease-curing powers. Queen Elizabeth I reportedly paid 10,000 pounds for a single narwhal tusk in the 16th centurythat's about what it would have reportedly cost to build an entire castle at the time.
"It's a very peculiar animal," said Heide-Jørgensen, who has been studying arctic marine mammals for 20 years. "We know very little about them."
To uncover a few of the narwhal's secrets, Heide-Jørgensen and Kristin Laidre, a research scientist at the University of Washington in Seattle, have been fitting the marine mammals with satellite tags. The tags help the researchers track narwhals' movements and behavior from a distance.
From their studies, these researchers have revealed the species' seasonal migration, in which they move from high Arctic fjords in the summer to the pack ice of Baffin Bay and Davis Strait in the wintera round-trip journey of more than 1,243 miles (2,000 kilometers). Baffin Bay and Davis Strait are between northeastern Canada and Greenland.
The whales' migration follows nearly the exact same path each year. "It's really amazing," Laidre said. "Their schedule is the same, often down to the same day each year."
The satellite tags can also provide clues to the narwhal's diving habits by recording water pressure. Pressure is a reliable guage of how deep an object is underwater.
Over the past few years Laidre has learned that during summertime and migration, the narwhals' dives are fairly shallow, down to about 1,300 feet (400 meters). But in the winter the whales head to the depths, more than doubling their downward swims to 2,953 feet (900 meters), usually 20 times a day.
Often the satellite tags would send back a signal that the narwhals had gone down more than 4,900 feet (1,500 meters). At that depth, the tag stops recording, so it's possible they may even be heading deeper, Laidre said.
"We think they're diving to the bottom to prey on Greenland halibut," Laidre said.
Marine biologist John Francis, who is also vice chairman of the National Geographic Society's Committee for Research and Exploration, said he was particularly intrigued by Heide-Jørgensen's combination of two technologies to document narwhal numbers and behavior.
"Aerial surveying and tagging to measure depths of dives are important in their own right, but the combination of the two looks very promising as a way to make a remote census of these animals," Francis said.
Researchers estimate that 50,000 narwhals live in Greenland and Canada. Another narwhal group lives along Greenland's eastern coast, but the population there may only number a few thousand. Currently there are few regulations on narwhal hunting in Greenland and Canada.
Apart from hunting, two other factors may also be playing into the narwhal's decline. In Canada and Greenland, an inshore fishery for the Greenland halibut is looking to move to offshore waters, so boats would be pursuing the narwhal's dinner. "They're competing with people for that fish," Heide-Jørgensen said.
In addition, changing sea-ice conditions may be affecting narwhal survival. While warming trends have generally caused sea ice to shrink, it has been increasing over the last several decades in Baffin Bay, one of the narwhal's wintering grounds.
"Narwhals aren't usually in trouble when they're migrating, because they're constantly moving ahead of the ice," Laidre said. But the species spends the winter in areas thick with pack iceoften more than 95 percent covered. With increasing sea ice, these close quarters could be getting even closer, and wintering narwhals could become trapped in the ice more often.
This fall Laidre and Heide-Jørgensen plan to tag another group of narwhals, living in northern Greenland, to get a better sense of narwhal behavior, numbers, and overall status.
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