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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