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The oceans are noisy and getting stronger and stronger. And marine mammals must live in the din. These animals have different approaches to noise: dolphins perform the equivalent of shouting. Humpback whales, when competing with a nearby boat, are silent.
"Many people imagine that this underwater place is really calm, but it's not the case," said biologist Helen Bailey, who studies marine mammals and sea turtles at sea. University of Maryland. The sounds of the ocean are more than just breaking waves. Acoustic noises, such as sonar used in oil exploration or explosive war games of the navy, can damage the ears of whales. Crowded freight lanes are teeming with maritime traffic. And as the Arctic heats up and more ships and industrial developments develop in previously ice-free areas, northern marine mammal populations are exposed to more noise.
The increase in ocean noise has been identified as a potential problem more than 20 years ago. Near California, the volume of maritime traffic has nearly doubled every decade since the 1960s. But the specific effects of this human cacophony are still being replenished.
Bailey and his colleagues, in a new report published Tuesday in the journal Biology Letters, used underwater microphones to listen to bottlenose dolphins about 20 miles off Ocean City, Maryland. The scientists recorded 77 different animals, which distinguished themselves by their "signature whistles," Bailey said. (The ability to identify wild dolphins by their whistles, rather than relying on visual markings, is a new and powerful development in dolphin research, Bailey said.)
Sound is a cornerstone of the dolphin society. Their calls convey important identity information and may even use whistles to alert others of the presence of fish. Dolphins form what Bailey described as "fission fusion" companies, weaving social bonds. As it happens, it's "a bit like a family reunion, talking to each other," Bailey said. "They are very vocal and like to chat."
When the background noise of the sea – the ambient noise of the offshore shipping lanes, which resemble static radio brouhaha – began to crescendo, the dolphins used informative whistles, discovered Bailey and his co-authors. The outlines of their calls became flat, rather than the richer and more curvy whistles.
Bailey used an example of a missing house key. Imagine that your friend lost her keys: at home, you could say, "Hey, your keys are between these cushions." But in a noisy bar, you just shout, "Keys!" A similar loss of information is occurring with these flatter whistles, she said.
It is known that human noise can mask animal calls as long as the frequencies overlap. But in the new study "this adjustment was not just about noise in the same frequency as their calls," Bailey said. This surprised her and her co-authors. "We were making badumptions that were just not true," she said. "We have to think a little differently about the impact of noise on these animals."
Janet Mann, an expert in large-print dolphins at Georgetown University who was not involved in this research, said she suspected the calves would stay close to their mother while the ambient sounds were strong. Otherwise, they risk permanent separation. "This means that the calf has fewer opportunities to explore the environment or to create links by itself," Mann said.
Only a few studies have examined the effects of ambient sounds like this one. "Marine research on the impact of sound on marine mammals involves controlled studies with loud sounds, where animals are observed and recorded," Mann said. "The ambient noise of ships is omnipresent and it is difficult to conduct controlled research."
Another study, published in 2012, examined a relative period of ambient calm, when maritime traffic ceased after the terrorist attacks of September 11, 2001. In addition to a noise reduction of 6 dB, stress hormones were eliminated in the feces of Right Whales in the North Atlantic. This suggests that "when the ambient noise dropped precipitously, the whales were much less stressed," said Mann.
Researchers have recently monitored humpback whales near a remote shipping lane, halfway up the Maryland coast in Japan. Only one cargo / freighter liner cruised the area once a day. Two recorders captured the sounds of the cargo and whales nearby. When the ship pbaded, "humpback whales seemed to stop singing temporarily," the study's authors reported in their study published Wednesday in PLOS One.
This document was unusual because "there are not many studies based on a direct and quantitative approach," said Sadaharu Koga, senior scientist at the Japan Ship Technology Research Association. (Koga was not directly involved in this research, but members of his organization were.) It is unclear to what extent the cessation of cetaceans is detrimental, but previous studies show that "singing behavior is related to breeding strategies of male whales, "said Koga. Songs are a way for men to announce their presence and attract whales.
"Water is a great way to direct the sound, which is great if you're a fin whale that needs to find a partner a hundred miles away," said Mann, "but not as great if there is raw sounds created by the man that hinder your attempts to find a date. "
In 2016, the Obama White House called on the National Oceans and Atmosphere Administration to create high level guidelines to reduce the noise of the ocean. NOAA finalized its roadmap in September 2016. NOAA's Ocean Noise Strategy is a "10-year vision" for understanding and managing ocean noise, said Jason Gedamke, Chief Environment Officer. Ocean Acoustics Program.
NOAA has already established a network of noise reference stations, consisting of 12 monitoring sites in US waters, as well as an archive of pbadive acoustic data including a map allowing the public to observe the location. data collection sites. "The implementation is still ongoing," said Gedamke. It "will continue in the foreseeable future".
But there are no rules for marine sounds comparable to those that limit noise pollution on land, Bailey said. A specific permit is required for some noisy activities, such as seismic surveys of an oil company. For the general sound of the boat, "there is no regulation," she said. "If we can do everything," like the ship engines, she said, "a little quieter, we can reduce this problem."
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