In March, the water between Canada and Greenland, called Baffin Bay, is covered with sea ice. Scientists in a helicopter fly over, searching for narwhals (独角鲸). The narwhal is one of the most mysterious whale species on the Earth. Each male sports a single tusk (长牙) 6 to 10 feet long. Narwhals are the only whales with tusks. They feed on fish, squid and shrimp. By staying under the ice, they avoid killer whales and other predators.
The helicopter lands on the frozen ocean, and Dr. Jens Koblitz climbs out. He studies animal sounds at the BioAcoustics Network. And he works with Dr. Kristin Laidre, a biologist who studies mammals that live in the Arctic.
Dr. Koblitz lowers a weighted line into the icy water. Attached to the line are 16 underwater microphones strung together, about a yard apart. Each sound from a narwhal hits each microphone at a slightly different time. When Dr. Koblitz records, he captures information about how the whales dive and rise as they hunt for food.
"The windchill is minus 5 to minus 22 degrees Fahrenheit. I have to quickly get everything back inside the helicopter so my equipment isn't destroyed by the cold and ice," he says.
Narwhals use echolocation. The whales buzz, click, and creak. When that sound wave hits an object, like a fish, it bounces back, producing an echo. They use sonar to find holes in the ice and prey in the dark.
But as the average global temperature increases, the Arctic ice is shrinking. The narwhals will face a severe threat as the ice melts. For centuries, sea ice has blocked most ships from the Arctic Ocean. But scientists predict the ocean will be ice-free in a few decades. Then ships will roam the narwhals' habitats. The noise of the ships may drown out the whales' clicks.
Dr. Laidre says, "If we understand what sounds they use, we can better understand how human impacts." That understanding can show humans how to help narwhals survive.
