Here’s what narwhals sound like underwater | Science News for Students

Here’s what narwhals sound like underwater

Multi-day eavesdropping reveals a range of clicks, calls and buzzes
Jul 20, 2018 — 6:45 am EST
researchers stand in the water with a narwhal

Researchers put a sound recording device on a male narwhal to capture its underwater clicks, buzzes and calls.

S. Blackwell

Listen to the narwhals.

Narwhals are among the most elusive of whales. But for the first time, researchers have been able to listen in on their chatter for days at a time. A team eavesdropped on these “unicorns of the sea” as they dove, fed and socialized.

Susanna Blackwell is a biologist who studies ocean mammals. One of her interests is underwater sounds and how they affect marine animals. She works at a company called Greeneridge Sciences, Inc., in Santa Barbara, Calif. She wants to know how narwhals use different sounds in their daily lives.

Blackwell and her colleagues listened in on the clicks, buzzes and calls of the East Greenland narwhal. What they learned could help future studies of whether the whales might be disturbed by human-made noise from fishing or oil drilling, the scientists hope.

Narwhals rely on sound in the dark Arctic waters where they live. Like other species of toothed whales, narwhals use echolocation to hunt. “They’re like wet bats,” says Kate Stafford. She studies whales and their songs at the University of Washington in Seattle. but was not part of the new study.

Whale sounds are often recorded using hydrophones (HIGH-druh-fohnz). These special underwater microphones dangle in the water to collect sounds. But these devices have a few drawbacks. They can’t sense the depth or direction from which noise comes. And they can’t tell which animal is making what sound.

So Blackwell and her colleagues came up with a different solution. They attached acoustic recording devices 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.

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narwhal pod in the water
Narwhals use a variety of sounds to hunt and communicate with each other.
Kristin Laidre, Polar Science Center, UW NOAA/OAR/OER

How to eavesdrop on a narwhal

With the help of native Greenland hunters, the researchers tagged six of the skittish creatures between 2013 and 2016. The devices stuck to the whales with suction cups. Nylon string threaded through a ridge of cartilage on the narwhals’ backs. This string held the devices in place. Special links to the string were designed to degrade fairly quickly. After three to eight days in the water, the links broke apart. This released the devices from the whales. The recorders then floated to the surface, where researchers could track and retrieve them.

The whales were very quiet on the first day they wore those devices. That’s probably because tagging was stressful for them, says Blackwell. But after that, the narwhals resumed their normal behavior — and chatter.

The acoustic devices captured a rich repertoire of narwhal sounds. And the whales made them during different activities and at different water depths.

“We were very surprised that they actually have a very specialized way of using sound,” says study coauthor Mads Peter Heide-Jørgensen. He is a biologist at the Greenland Institute of Natural Resources based in Copenhagen, Denmark.

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Several whales socialize with each other at a depth of 65 meters (210 feet), using clicks, whistles and trumpet sounds.

A female narwhal communicates using pulselike sounds as she swims near the surface of the ocean.

Audio: S. Blackwell

Narwhals search deep waters for squid and fish such as Arctic and polar cod. And they clicked while diving to locate such prey. As a whale closed in on a meal, its clicks turned into a rapid buzzing. At the surface, the narwhals instead used whistles and trumpetlike calls to communicate.

The part of East Greenland where the narwhal research took place is very remote. But it likely won’t be for long, says Jens Koblitz. He studies animal sounds at the University of Konstanz in Germany. Global warming is melting Arctic sea ice. As that ice recedes, fishing boats, oil-seeking ships and others are expected to spend more time in the region. Thanks to climate change, human presence in the Arctic is already on the rise , Koblitz says. And all those ships and people bring more noise.

It’s vital to learn about the whales’ behavior while their habitat is still fairly isolated, says Stafford. Such information, she says, will help researchers see any changes caused by more human activity in the area.

If scientists discover that human sounds disturb narwhals, they may recommend limiting human activity in some areas, Heide-Jørgensen says.

His team described the narwhale sounds June 13 in the journal PLOS ONE.

Power Words

(for more about Power Words, click here)

acoustic     Having to do with sound or hearing.

Arctic     A region that falls within the Arctic Circle. The edge of that circle is defined as the northernmost point at which the sun is visible on the northern winter solstice and the southernmost point at which the midnight sun can be seen on the northern summer solstice. The high Arctic is that most northerly third of this region. It’s a region dominated by snow cover much of the year.

Arctic sea ice     Ice that forms from seawater and that covers all or parts of the Arctic Ocean.

bat     A type of winged mammal comprising more than 1,100 separate species — or one in every four known species of mammal.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

biology     The study of living things. The scientists who study them are known as biologists.

cartilage     (adj. cartilaginous) A type of strong connective tissue often found in joints, the nose and ear. In certain primitive fishes, such as sharks and rays, cartilage provides an internal structure — or skeleton — for their bodies.

climate     The weather conditions that typically exist in one area, in general, or over a long period.

climate change     Long-term, significant change in the climate of Earth. It can happen naturally or in response to human activities, including the burning of fossil fuels and clearing of forests.

coauthor     One of a group (two or more people) who together had prepared a written work, such as a book, report or research paper. Not all coauthors may have contributed equally.

colleague     Someone who works with another; a co-worker or team member.

echolocation     (in animals) A behavior in which animals emit calls and then listen to the echoes that bounce back off of solid things in the environment. This behavior can be used to navigate and to find food or mates. It is the biological analog of the sonar used by submarines.

global warming     The gradual increase in the overall temperature of Earth’s atmosphere due to the greenhouse effect. This effect is caused by increased levels of carbon dioxide, chlorofluorocarbons and other gases in the air, many of them released by human activity.

Greenland     The world’s largest island, Greenland sits between the Arctic Ocean and North Atlantic. Although it is technically part of North America (sitting just east of Northern Canada), Greenland has been linked more politically to Europe. Indeed, Vikings arrived in Greenland around the 10th century, and for a time the island was a colony of Denmark. In June 2009, Greenland became an independent nation. Ice covers roughly 80 percent of Greenland. Indeed, the Greenland ice sheet is the world’s largest. If its frozen water were to melt, it could raise sea levels around the world by 6 meters (about 20 feet). Although this is the 12th biggest nation (based on surface area), Greenland averages the fewest people per square kilometer of its surface area.

habitat     The area or natural environment in which an animal or plant normally lives, such as a desert, coral reef or freshwater lake. A habitat can be home to thousands of different species.

hydrophone     A microphone that detects sound waves under water.

journal     (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

link     A connection between two people or things.

mammal     A warm-blooded animal distinguished by the possession of hair or fur, the secretion of milk by females for feeding their young, and (typically) the bearing of live young.

marine     Having to do with the ocean world or environment.

native     Associated with a particular location; native plants and animals have been found in a particular location since recorded history began. These species also tend to have developed within a region, occurring there naturally (not because they were planted or moved there by people). Most are particularly well adapted to their environment.

prey     (n.) Animal species eaten by others. (v.) To attack and eat another species.

repertoire     A stock of regularly performed songs

sea     An ocean (or region that is part of an ocean). Unlike lakes and streams, seawater — or ocean water — is salty.

species     A group of similar organisms capable of producing offspring that can survive and reproduce.

squid     A member of the cephalopod family (which also contains octopuses and cuttlefish). These predatory animals, which are not fish, contain eight arms, no bones, two tentacles that catch food and a defined head. The animal breathes through gills. It swims by expelling jets of water from beneath its head and then waving finlike tissue that is part of its mantle, a muscular organ. Like an octopus, it may mask its presence by releasing a cloud of “ink.”

tagging     (in biology) Attaching some rugged band or package of instruments onto an animal. Sometimes the tag is used to give each individual a unique identification number. Once attached to the leg, ear or other part of the body of a critter, it can effectively become the animal’s “name.” In some instances, a tag can collect information from the environment around the animal as well. This helps scientists understand both the environment and the animal’s role within it.

whale     A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.

Citation

Journal: 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.