From Wired (By Brandon Keim)
After years of growing concern about the effects of marine noise on whales, scientists are finally asking what noise could do to fish. Whether they’re harmed isn’t yet known, but it’s certainly a possibility.
The oceans are an increasingly clamorous place, with boat motors and sonar and explosions and construction creating a din at frequencies used by fish.
“If you’re walking down the street and someone is jackhammering, you walk across the street and go around. What happens to a fish?” said University of Maryland aquatic noise specialist Arthur Popper. “How fish respond to sound is the big question for all of us.”
Popper co-authored a review of the field’s patchy, question-filled literature in the June Trends in Ecology and Evolution, marking a shift in thinking about ocean noise.
Until recently, researchers and environmentalists who thought at all about aquatic noise were focused on marine mammals and especially whales, which can be debilitated by sonar and engine noise. But the world’s 21,000 fish species also rely on sound. Many use it to communicate, and almost all rely on acoustics to navigate a dark, often turbid world.
What Jacques Cousteau called “The Silent World” is actually full of natural noise, from fish calls to the sound of their bodies moving through water. To that natural din, human activity has added roughly 10 decibels of ambient commotion in the last half-century. At construction sites for offshore oil platforms, wind farms and river bridges, where explosions and pile drivers can hit 250 decibels repeatedly for months or years on end, the noise is even more intense.
All this has concerned researchers like Popper, who warn that scientists simply don’t know how fish respond.
“It might be that fish are well-adapted to noise. Maybe it’s not a problem. We don’t know,” said Rob McCauley, a marine biologist at Australia’s Curtin University of Technology. “The work that’s been done has only scratched the surface.”
Studies on the effects of noise in terrestrial animals may provide some guide for what’s happening to fish. In some bird species, traffic noise that overlaps with song frequencies has been linked to drops in population diversity and density, and seems to reduce reproductive rates. The same appears to happen with frogs. Those findings don’t necessarily apply directly to fish, but they’re suggestive.
As for the fish themselves, studies are mixed. Tuna appear disoriented by boat noise, while some reef fish stay in their homes during and after massive air gun blasts. In some species, ship noise seems to increase production of cortisol — a stress hormone with damaging long-term effects — and harm eggs and larva. Another study, however, found no evidence of harm.
“If fish are swimming up the Potomac, and get to a construction site for the Woodrow Wilson bridge, do they go around it? Swim back to where they come from? Stop? This is a question for all of us,” said Popper.
Research is hindered by the different qualities of various types of underwater noise noise, as well as the variability of fish species, he said. It’s also hard to study fish behavior. “The best method would be to put transmitters in the fish, have receivers all over the place, and keep track of every fish” in a specific area, said Popper. Nobody has yet accomplished such a complicated task, though that’s a result not just of technical difficulties, but lagging scientific curiosity.
“The first thing we need to appreciate is that sound is extremely important to the lives of fish,” McCauley said.
Image: 1) Test tank of fish exposed to high-intensity sonar./Arthur Popper. 2) Graph of frequencies used by marine animals and generated by human activity./Trends in Ecology & Evolution.
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