After capturing six narwhals in Scoresby Sound, which is the world's largest and probably least-known fjord system, the team tagged them with special acoustic and GPS satellite instruments. They recorded 533 hours of audio, matching the sounds with their location and likely activity.
They noted three types of sounds: clicks, buzzes and calls. Calls, likely how they communicate, tend to happen closer to the surface at less than 100 meters (but often less than 7 meters). Clicks and buzzes, used as echolocation to find food, often occur between 350–650 meters below the surface.
The research team was surprised "[t]hat these whales are more specialized than we thought initially. They depend on very specific water depths in relatively small areas for feeding on a few prey species," says Mads Peter, who works for the Greenland Institute of Natural Resources.
The concern amongst many scientists is that two main climate change effects on the Arctic — warming sea temperatures and increased human and industrial activities from disappearing sea ice — could affect the small population of narwhals. These creatures rely on sound for communication, navigation and feeding.
Mads Peter says:
"Narwhals may abandon areas with increased warming and loss of their preferred prey species, but they may also avoid areas with underwater noise from seismic explorations, oil drilling, shipping, sand dredging, mining and fishery."
This research "is inspiring," says UC-Santa Cruz' Terrie Williams, who was not part of the study. She says it's important to gather more information on the potential impact of human noise:
"There are concerns that anthropogenic noises will cause changes in critical vocal behaviors of the animals — imagine not being able to locate members of your pod, or locate fish to eat. For deep-diving cetaceans such as narwhals these sounds are vital to their survival."
Dive deeper: Listen to rare narwhal recordings captured by the team and read the study published in PLOS ONE on Wednesday.
