Study: Noisy tests offshore possibly scaring fish away from reefs

Avery Paxton, a marine ecologist with UNC's Institute for Marine Sciences, has for two years been studying the effects of loud manmade noises on fish in the ocean.

"These noises, on the reef, they're repetitive," Paxton said. "The sound levels on the reef that were heard by these fishes were loud enough that, in laboratory experiments, fish did have physiological damage."

Survey ships blast sound waves through the water to the floor of the ocean and use the reverberation to map the ocean and determine likely spots to drill for oil and gas.

Paxton mounted cameras and microphones on reefs off the North Carolina coast. While fish are present in large numbers, a steady din similar to being in a crowded room can be heard. But during the period of seismic surveying, most fish leave the area rather than be subjected to the 230-decibel booms – nearly three times the measured level of normal reef sound.

Paxton called the study's results surprising.

"We weren't expecting the fish to respond in that way. We were really surprised that four out of five fish were no longer on the reef," she said.

Because divers are not allowed in the water and ships aren't allowed in the area during seismic surveys, batteries on the researchers' cameras and microphones had died by the time they returned, which Paxton said leaves many questions needing further study.

"We don't know how long this decrease of fish on the reef lasts," she said. "I want to know how long the fish stayed away from the reef. What happened to them? What caused them to leave the reef? Was it that the noise was too loud? Was it that they were feeling the noises differently than we do?"

She said the impact of the sonic testing could be felt across North Carolina.

"If the fish don't come back to the reef or if there is a longer-term effect of the fish leaving the reef temporarily, it has potential to cause harm to our coastal citizens and our economy and our culture," she said.

The study was funded by the Bureau of Ocean Energy Management and produced with partners from UNC, Duke University and the National Oceanic and Atmospheric Administration.