Submersible recorders pick up the animals’ clicks, calls and buzzes
Narwhals are among the most elusive of whales. But for the first time, researchers have been able to eavesdrop on the creatures for days at a time as these unicorns of the sea dove, fed and socialized.
Biologist Susanna Blackwell and colleagues listened in on the clicks, buzzes and calls of the East Greenland narwhal (Monodon monoceros). The team’s findings, published June 13 in PLOS ONE, provide a peek into the daily behavior of the long-toothed whale. The research could help scientists determine how human-made noises may affect narwhals as the Arctic warms due to climate change and shipping lanes become more open.
Many whale sounds are recorded using hydrophones, underwater microphones that dangle in the water. But these acoustic devices have several drawbacks: They can’t sense the depth or direction from which noise comes, and they can’t detect which animal is making a sound.
Blackwell and colleagues skirted these issues by attaching an acoustic recording device to the narwhals themselves. “It is really like sitting on the back of a narwhal for a few days and experiencing the world,” Blackwell says.
Listen to two recordings of East Greenland narwhals collected by researchers from 2013 to 2016.
Several whales socialize with each other at a depth of 65 meters, using clicks, whistles and trumpet sounds.
A female narwhal communicates using pulselike sounds as she swims near the surface of the ocean.
With the help of native Greenland hunters, the researchers tagged six of the skittish creatures from 2013 to 2016. The devices were attached with suction cups, and held in place for several days by a nylon string threaded through a ridge of cartilage on the narwhals’ backs. After three to eight days in the water, magnesium links to the string degraded and released the device, which the researchers retrieved using GPS.
Tagging was stressful for the narwhals, says Blackwell, who works for Greeneridge Sciences, Inc., the Santa Barbara, Calif., company that manufactures the acoustic devices (SN Online: 12/7/17). But after a day of silence, the narwhals resumed their normal behavior.
Like other species of toothed whales, narwhals use echolocation to hunt in the dark arctic waters. “They’re like wet bats,” says Kate Stafford, an oceanographer at the University of Washington in Seattle who did not participate in the study. The researchers found that the narwhals clicked while diving to locate their prey, often arctic and polar cod or squid. When closing in on a meal, the clicking sounds turned into a rapid buzzing noise. At the surface, the narwhals used whistle and trumpetlike calls to communicate with one another.
“We were very surprised that they actually have a very specialized way of using sound,” says study coauthor Mads Peter Heide-Jørgensen, a biologist at the Greenland Institute of Natural Resources based in Copenhagen. The narwhals’ sounds varied not only with each activity the animals did, but also with their depth.
Eistla, a female narwhal with a young calf, was one of six narwhals that researchers listened in on. She remained fairly silent immediately after having an acoustic device attached to her and being released. But by the second day, she became more vocal, clicking (blue lines) as she dove and buzzing (black circles) as she closed in on prey. Yellow squares mark calls made by Eistla or other nearby narwhals. The device detached on the fifth day.
Types of sounds used by a narwhal vary with depth and time of day
“Having some of this baseline data from an area that is relatively pristine is going to be really valuable going forward,” Stafford says.
Though the Scoresby Sound where the narwhal research took place is very remote, it won’t be for long. Human presence in the Arctic is increasing thanks to climate change, says Jens Koblitz, a bioacoustician at the University of Konstanz in Germany. Fishing boats, ships of oil prospectors and others are expected to spend more time in the Arctic as global warming reduces the extent of sea ice in the region (SN: 12/10/16, p. 15).
“This study is a great stepping-stone,” Koblitz says. If scientists discover that human sounds negatively affect the ways that the whales communicate, researchers might be able to protect some areas from human activity.
S. Blackwell et al. Spatial and temporal patterns of sound production in East Greenland narwhals. PLOS ONE. Published online June 13, 2018. doi:10.1371/journal.pone.0198295.
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