A new study by scientists at the University of St Andrews has found that beaked whales are particularly sensitive to unusual sounds, such as sonar.
Sonar linked to whale strandings
The use of sonar for naval communication has been linked to beaked whales stranding in the past, with concerns that the whale deaths may be directly linked to the mid-frequency signals.
Strandings along the coast are thought to occur when whales become disorientated and are unable to follow their usual routes.
Working with some of the world’s marine experts, the scientists investigated how sonar affected beaked whales in the Bahamas. They monitored the reaction of Blainville’s beaked whales (Mesoplodon densirostris) to both simulated sonar calls and live sonar calls during naval exercises in the area.
The researchers were able to listen to the group of whales using underwater microphones, called hydrophones, and electronic tags attached to the whales allowed the team to track the whales’ movements using satellites.
Loud noises disrupt whales’ behaviour
The scientists discovered that sonar caused the whales to stop making the clicking and buzzing calls which they use to navigate and communicate. The whales also ceased foraging and moved quickly away from the loud noises.
According to David Moretti, Principal Investigator for the U.S. Navy, the results indicate that “the animals prematurely stop vocalisations during a deep foraging dive when exposed to sonar. They then ascend slowly and move away from the source, but they do resume foraging dives once they are farther away.”
Although beaked whales are known to emit high-frequency calls, this study is the first to show the whales also react to mid-frequency sounds.
Professor Ian Boyd, chief scientist on the research project, says “We showed that the animals reacted to the sonar sound at much lower levels than had previously been assumed to be the case. We now think that, in some unusual circumstances, they are just unable to get out of the way and this ends up with the animals stranding and dying.”
Sensitivity of marine mammals to noise may have far-reaching implications
Perhaps one of the most important findings of this new research is the discovery that beaked whales are scared by virtually anything unusual. This may have wider implications for the marine environment, with offshore wind farms, oil rigs and passing ships potentially posing further threats to marine mammals.
Professor Boyd indicates that these other sounds may be more dangerous than sonar as they can be heard constantly, possibly affecting the feeding and reproductive cycles of marine mammals such as whales.
Read the full study, published in the journal PLoS One.
Find out more about beaked whales on ARKive.
Helen Roddis, ARKive Species Text Author