What sound does a person make
Disturbed soundscape: How human noise changes the seas
The oceans are a strange world: They not only harbor extremely bizarre creatures, but also very special soundscapes. The most curious examples include the cracked crabs (Alpheidae): With specially shaped claws, these shrimp, which live on coral reefs, make gun-like noises when they catch their prey.
The toad fish is less loud Opsanus beta: At the bottom of the Gulf of Mexico, the up to 30 centimeters long brownish males with toad-like tones attract females. Cod shoals (Gadus morhua) emit grunts during the spawning season. And in spring the arctic sea echoes with the drawn-out whistling calls of the bearded seals(Erignathus barbatus). Most famous are probably the songs of the humpback whales. And blue whales not only sing to find a partner, but also to coordinate activities such as seasonal hikes.
The soundscapes of some marine areas are so characteristic that larvae and young animals of a number of species use them to find their habitat, writes an international team of researchers in the journal Science. "Animals produce sounds for many reasons, for example for orientation, for hunting, as a signal of readiness to fight, to defend the territory, to recruit partners and for reproduction," writes the group around Carlos Duarte from King Abdullah University in Thuwal, Saudi Arabia.
The oceans have become much louder since the Industrial Revolution
There are simple reasons why acoustic signals are of paramount importance to marine life: "Sound spreads relatively quickly under water and carries information over greater spatial distances than other stimuli such as light or chemical substances," explains the team. "As a result, marine animals have a wide range of receptors to perceive sounds." This even applies to jellyfish that do not have a central nervous system.
Another reason is given by the director of the Alfred Wegener Institute (AWI), Antje Boetius. “The oceans are on average around four kilometers deep, and there is only light in the upper 200 meters,” explains the expert, who was not involved in the article. «The largest living space on earth is therefore predominantly in complete darkness. There, too, the animals have to communicate - for example to meet each other for reproduction. The best way of communication is sound. "
In their inventory, the more than two dozen scientists from eleven countries describe the current state of knowledge about natural soundscapes, their importance for the animal world - and above all the increasing influence of humans.
"Before the industrial revolution, the soundscapes of the oceans consisted largely of biological and geological sources," writes the team, citing seaquakes, underwater volcanoes and the cracking of ice as examples. "Since then, the oceans have become much louder." Because the noise level is steadily increasing, the influence of human noise on the marine life urgently needs to be clarified.
Especially since hardly any marine region is spared: Expeditions search the sea floor for mineral resources with the help of seismic compressed air cannons. These airguns continuously emit loud shots over a wide frequency spectrum, the echoes of which provide information about the nature of the ground.
The human noise drowns out the animal noises
The military uses sound pulses to locate submarines, for example. And more and more ships are cruising the oceans: "In the last 50 years, the increased shipping traffic has increased the low-frequency noise along the main routes by an estimated 32-fold," writes the team.
But that's not all: During the construction of drilling rigs and offshore wind farms, anchors are rammed into the seabed, and mineral resources - such as sand for the construction industry - are extracted from the bottom of the oceans. And dynamite is used to fish in many coastal regions of Southeast Asia and Africa.
While humans make more and more noise, the animal soundscape has also changed, according to the researchers. This is due, for example, to the centuries-long hunt for whales, seals and fish, but also to the disappearance of many important habitats such as kelp forests, seagrass meadows and coral reefs.
In addition, the human noise superimposes the animal sounds. This is confirmed by AWI Director Boetius, whose institute maintains a number of acoustic observatories deep below the surface of the water in both polar regions and records noises - including in the Fram Strait between North Greenland and Spitsbergen: “On the recordings you can constantly hear the sound waves from technologies used in the search for oil and gas, ”she says.
When the noise occasionally falls silent - for example at Christmas - a completely different soundscape emerges: "Only then do you hear nature itself, for example the variety of whales that are singing."
Studies show: underwater noise influences animal behavior
Many species flee to calmer waters from human noise. However, the researchers emphasize that this is not possible for many marine animals. As an example, they cite the Maui dolphin, which is only native to New Zealand (Cephalorhynchus hectori maui)that is critically endangered.
The team emphasizes that noise now penetrates almost all marine regions. The Weddell Sea in Antarctica is one of the few exceptions, says co-author Ilse van Opzeeland from AWI. "This is one of the last soundscapes without much human influence." However, with reservations: once the number of whales was significantly higher - the number of blue whales has fallen by around 98 percent since the early 20th century.
An evaluation of 538 studies carried out by the researchers shows that underwater noise changes the behavior of animals. Around 90 percent of those studies that focused on marine mammals show clear consequences of human noise. For fish and invertebrates, it is more than 80 percent each. The data situation is poor for seals, reptiles such as sea turtles and sea birds such as penguins.
The sonic cannons used to search for raw materials could sometimes cause permanent hearing damage in marine life, says co-author van Opzeeland. This has been proven in harbor porpoises and seals, for example.
The “Science” report does not mention whale strandings, which environmental groups often associate with underwater noise. However, there is no clear evidence for the killing by sound, says Boetius. Because often dead marine mammals also have stomachs full of garbage. Cases are known in which whales and bottlenose dolphins perished as a result of military exercises or dynamite fishing. But there is no evidence that noise directly increases the mortality of marine life. Other consequences, however, are "very well documented".
Scientists call for regulation of shipping routes
“Our report on the existing knowledge shows that man-made noise should be included in evaluations of the growing pressure on marine ecosystems,” emphasizes the team in “Science”. The noise in the oceans is expected to increase.
"A continuation of the development of the ocean-based economy will inevitably lead to more and more noise from the development of coastal shipping, seismic explorations, military operations, dredging and pile driving as well as deep-sea mining, with a likely growing impact on marine life."
So far, noise has been ignored in international agreements such as the Convention on Biological Diversity (CBD), the team complains. "The topic is not so prominent because it is not as visible to people as a beach full of plastic waste," says Boetius.
The researchers cite the European Union's Marine Strategy Framework Directive (MSFD) as an exception: It expressly recognizes noise as a stress factor and calls on the member states to monitor and improve noise pollution.
Antje Boetius mentions another positive example: "The Antarctic Treaty also contains many conditions - not only for access for ships, but also for the exploration of resources - even for sound-wave-based research."
As concrete measures against noise, the researchers are calling for regulation of shipping routes and speed limits. In the eastern Mediterranean, for example, the speed limit for particularly noisy ships from 15.6 knots (almost 29 kilometers per hour) to 13.8 knots (25.5 kilometers per hour) has been estimated to halve the noise of these vehicles along the main routes from 2007 to 2013. In the future, electric motors or quieter propellers could also reduce ship noise.
The noise when building offshore wind farms can therefore be reduced with technical measures such as bubble curtains. The construction of such facilities in the Baltic Sea, for example, used to drive harbor porpoises - the only native whale species there - from their habitat, says Harald Benke, director of the German Maritime Museum in Stralsund. "Some did not come back."
In German waters it is now compulsory to use bubble curtains to dampen the noise when the piles are driven into the seabed. Rings are placed around the systems, from which compressors press air into the water column. The rising bubbles are supposed to reflect the sound waves. In this way, depending on the depth of the water and the current, the noise input can be reduced by up to 90 percent, says Benke.
Boetius also advocates protecting larger marine regions on the basis of research. For example, hotspots of social interaction, for example of marine mammals and sharks, as well as breeding areas could largely be closed to fishing and shipping.
In general, people can be more considerate, says Boetius: "We should adapt to the animal world at least as well as we ask the marine life to adapt to our activities."
Walter Willems, dpa#Subjects
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