Sonar’s effect on marine mammals has been a hot-button topic for years, and recent research shows that loud sounds damage the balance organs of cephalopods.
But we also should worry about the potential effect of lower-level, constant noise on fish, Arthur Popper of the University of Maryland in College Park will warn the Acoustical Society of America at a meeting in Seattle, Washington, later this month.
Navy sonar, acoustic guns used in seismic exploration and pile driving can produce sound levels of 180 decibels in water. These sounds can seriously affect nearby marine animals. For instance, injuries or distress caused by such intense sounds have been blamed for the beaching of cetaceans. They can also drive whales from their feeding grounds. But the loud noises don’t last long, so uninjured individuals can swim away until they stop.
But what if they don’t stop? This is Popper’s concern: the constant lower levels of noise from shipping or offshore wind farms can increase background noise by 10 decibels over a very large area. Although this noise is less intense than sonar, Popper says that long-term exposure to this constant rumble stresses fish. Experiments have shown that exposure to recorded ship noise increases levels of the stress hormone cortisol in fish.
The constant din may have other repercussions. Another experiment showed that recorded ship noise blocked Lusitanian toadfish from hearing sounds produced by others of their species. The extra noise can also prevent fish from hearing natural sounds that alert them to predators or prey.
Imagine living near a busy highway to understand how a busy shipping lane or an offshore wind farm might affect fish. Like highway noise, low-level machinery noise can be relentless.
The effects have not been well studied, but Popper suspects they may be serious. “It’s very hard to do experiments in the lab,” he told New Scientist, because the laboratory environment itself stresses fish enough to obscure the effects of several decibels of noise. He’s giving his talk primarily to increase awareness, he says. “We need to be doing some very critical experiments to understand long-term effects on animals on the wild.”
[Also see: “Low-frequency sounds induce acoustic trauma in cephalopods” by Michel André, Marta Solé, Marc Lenoir, Mercè Durfort, Carme Quero, Alex Mas, Antoni Lombarte, Mike van der Schaar, Manel López-Bejar, Maria Morell, Serge Zaugg, and Ludwig Houégnigan, Frontiers in Ecology and the Environment, 2011, doi:10.1890/100124]
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