- Whales appear to react to human-made noise in the ocean, such as naval sonar, in a similar way to which they respond to the sounds of their predators like killer whales, according to recent research.
- The authors of the study played the sounds of sonar and killer whales when whales from four species were present.
- The whales responded by breaking off their feeding forays, leading scientists to conclude that noise pollution in the ocean could leave them weaker and more vulnerable to predation.
- The researchers also suggest that marine mammals in the Arctic may be especially at risk as climate change alters their environment in ways that may make them more vulnerable.
Generally, the word pollution conjures images of billowing smokestacks, oily water and trash-filled highway medians. But for whales, dolphins and porpoises, a subtler and perhaps more sinister source of pollution also poisons their realm: human-made sound.
A study published March 21 in the Proceedings of the National Academy of Sciences supports the theory that noise from technology such as military sonar systems causes problems for these cetaceans by spooking them into thinking predators are lurking nearby.
“Personally I became motivated to study the effects of noise on whales during my PhD, as I often heard very loud human sounds while I was recording sounds of killer whales,” Patrick Miller, a professor of biology at the University of St. Andrews in the U.K. and one of the paper’s lead authors, said in an email. “It was during this time that it became clear that whales were being negatively impacted by ocean noise.”
Whales occasionally beach themselves in connection with naval sonar, Miller said. Sometimes, dozens of whales will strand at a time, often leading to their deaths.
The scientists’ hypothesis held that cetaceans are especially vulnerable to human-caused noises in their environment because their hearing is adapted to identify specific sounds as dangerous, potentially indicating the presence of predators. Sounds made by killer whales, for example, are similar enough to human-created noises, such as naval sonar, that the animals may be unable to distinguish between them. Upon hearing these sounds, the animals stop feeding, possibly because they think they’re in danger. The loss of food leaves them weaker and more vulnerable to an actual attack by a predator.
The study focused on sperm whales (Physeter macrocephalus), long-finned pilot whales (Globicephala melas), northern bottlenose whales (Hyperoodon ampullatus) and humpback whales (Megaptera novaeangliae). When the team spotted a member of one of these target species, they boated closer and, with a long pole, affixed a tag to the animal that recorded its movements and sound from the environment. The scientists then played sounds of naval sonar and of predatory killer whales underwater and recorded the whales’ behavior.
Predatory killer whale sounds. Audio courtesy of the University of St. Andrews. Image by wolfganglucht via Pixabay.
Audio of navy sonar sound. Image of northern bottlenose whales (Hyperoodon ampullatus) swimming off the coast of Jan Mayen Island in Norway with research vessel HU Sverdrup II in the background. Audio courtesy of the University of St. Andrews. Image by Paul Wensveen courtesy of the University of St. Andrews.
The team monitored the whales throughout the experiment to make sure the sounds weren’t hurting them, Miller said, adding that “it is always a privilege to see these animals in their natural environment.”
The animals’ focus on searching for food dropped significantly in response to both the sonar and the killer whale sounds. The scientists also found that, for each species, the more an animal was exposed to underwater sonar sounds, the less it foraged for food.
The study’s authors conclude that human-created sounds are dangerous to the cetaceans and other marine mammals wherever they might encounter them in the wild. Scientists are even more concerned about populations living in the Arctic, however.
For example, the researchers write that human-created underwater noise likely causes free-ranging Arctic seals to break off feeding forays early. At the same time, these seals also face additional challenges like climate change, which may reduce the amount of ice they used as protection from predators like killer whales and can make them easier prey. That “looming double-whammy” puts them at even greater risk than their non-Arctic dwelling counterparts, the team adds.
The problems with sound in the ocean, whether from naval sonar, icebreaking ships, or seismic air guns used to search for oil and gas, are clear. The solutions, however, appear to be more complicated.
Companies and organizations could do a better job of documenting when and where they’re creating underwater noise, Miller said. Those types of records would then allow authorities in charge of monitoring the marine environment to determine if noise producers could reduce certain noises or at least plan them for times when they would have less impact on marine life.
“The starting point is for environmental regulators to recognize that these noises do have negative impacts so need to be taken seriously in planning and management,” Miller said.
Banner image: A mother sperm whale (Physeter macrocephalus) and her calf off the coast of Mauritius. Image by Gabriel Barathieu via Wikimedia Commons (CC BY-SA 2.0).
Citation:
Miller, P. J., Isojunno, S., Siegal, E., Lam, F. A., Kvadsheim, P. H., & Curé, C. (2022). Behavioral responses to predatory sounds predict sensitivity of cetaceans to anthropogenic noise within a soundscape of fear. Proceedings of the National Academy of Sciences, 119(13). doi:10.1073/pnas.2114932119
