Noise Pollution Is a Big Problem for Little Fish
Growing scientific evidence indicates that noise from ships can harm whales, which rely on sound to navigate and find food and mates. Now, new research has discovered that such aural pollution also appears to affect the survival of the tiniest of fish.
Stephen Simpson, the study’s lead author and a marine biologist at the University of Exeter in the United Kingdom, wanted to find out how boats affect fish survival and behavior. He first took Ambon damselfish in their larval stage (just half an inch long and three weeks old) and monitored them on artificial reefs under various conditions.
Fish that heard normal reef noise—Simpson points out that reefs are noisy places compared with much of the ocean—survived 79 percent of the time. Fish exposed to motorboat noise had only a 21 percent survival rate, according to the study, which was published in the journal Nature Communications.
The researchers next wanted to test what was driving the differences in survival. Using small sealed containers, they played the fish different noises and monitored the oxygen level in the water. As fish become more stressed, their metabolic rate rises, and they consume more oxygen.
When the scientists played boat sounds, the fishes’ metabolic rate increased 33 percent.
Finally, the scientists tried to measure the fishes’ startle response to visual stimuli, such as predators. They shot a spear toward the fish and recorded their response. They found the fish were six times less likely to startle in the presence of boat noise, and when they did respond, they moved 22 percent slower.
“Either of those outcomes could mean the difference between life or death with a real predator,” Simpson said.
The noises played to the fish were equivalent to a 30-horsepower outboard engine operating at a distance of 33 feet to 650 feet.
The researchers noted that not all species may be affected in the same way by boat noise. “In this case, the prey lost out to predators, but damselfish are a very vocal family,” said Simpson. “It’s going to be a challenge to make predictions about the future, because it really depends on how susceptible you are to sound.”
A rule of thumb is that fish that produce noise usually have good hearing, Simpson added. Fish with a swim bladder are generally sensitive to noise, while flat fish on the ocean floor are typically not so affected.
But among the myriad threats to marine life, from ocean acidification to toxic pollution, noise is the simplest to fix.
“It’s the easiest pollutant to manage, because we know the source, we have the technology to change how much noise is being made, and we can move the noise and change when and where it’s being made,” Simpson said.
For example, if the fish are spawning at a known time, boats could be kept away to help them survive. Boat engines could also be designed to be quieter.
“If we can make advances, we are building capacity to deal with other threats and taking away one of the stressors in a multi-stress environment,” said Simpson. “We can actually do something about it with some fairly easy fixes.”