Like a constant, maddening ringing in the ears, human-generated persistent sounds may stress and harm fish, according to a presentation scheduled for later this month at the annual meeting of the Acoustical Society of America in Seattle.
Most prior research has focused on the effect of extremely loud sounds, such as pile driving and seismic air guns, on fish and other marine dwellers. This latest presentation instead looks at less intense, but relentless, noises.
"There are many such sources," co-author Arthur Popper told Discovery News. "Long-term sounds come from shipping and barging, but also fishing boats and recreational boats. This is particularly prevalent in harbors, where there is a lot of boat traffic, or in shipping lanes."
Popper, a professor of biology at the University of Maryland, added that offshore wind farms, noise from aquaculture facilities, construction work and more could also hurt fish.
Until recently, little attention has been paid to the problem. One reason is because of challenges of conducting experiments and gathering evidence. It's generally accepted that studies on caged fish are not fully relevant to species in the wild, but with some high-tech equipment and ingenuity, Popper and colleague Brandon Casper are attempting to avoid those constraints.
For example, the researchers have placed fish in a large enclosed tank that can be lowered into lakes and other natural bodies of water. Attached PVC pipes hold video cameras and hydrophones that permit monitoring of the fish during experiments.
Such studies lead Popper to conclude that if the increase in background noise isn't much, fish may just ignore it or adapt to the sounds, similar to how they'd cope with natural continuous noises, such as driving winds. If the persistent sounds become louder, however, fish could be in trouble.
Popper and Casper are particularly worried about "masking," which can drown out fish communication, impair ability to listen for prey and predators, and cause other problems.
"Think of how in a room it gets harder to hear someone you are talking with as the number of people, and the noise level, increases," Popper explained.
We can usually move away from such noise, and there is evidence that fish are trying to get away as well. But some fish cannot escape human-generated sounds. Even when those sounds increase background noise by just 10 decibels or less, the health effects could be profound. The researchers, for example, suspect that continuous din may alter the hormone levels of fish. This, in turn, could impact mating and longevity.
Richard Fay, director of the Parmly Sensory Sciences Institute, agrees that the problems warrant concern.
"Masking, in particular, can make all the sources that a fish may normally listen to and need to know about rendered less audible or inaudible due to masking noise," Fay told Discovery News.
James Miller, chairman of the Department of Ocean Engineering at the University of Rhode Island, added, "The effect on fish populations would be greater if they are dispersed during the times of year when they would be naturally congregating or spawning for other purposes."
Some studies have found that sole increase their swimming speeds when exposed to low-pressure pile driving, while cod "were found to freeze their movements" when exposed to the same sounds. Sharks and rays, which don't even hear well, still use sound to hear prey, so there is further concern that human-caused noise may hurt their ability to hunt.
Popper and Casper indicate no blanket solution has yet been proposed, "but there has been talk of developing ways to quiet ships and boats and/or to mitigate the sounds of wind farms," Popper said. "While long-term and very expensive no doubt, there are ways to lessen the sounds produced by ships."