An ocean experiment that was accidentally conducted amid the shipping silence after the Sept. 11, 2001, terrorist attacks has shown the first link between underwater noise and stress in whales, researchers reported last week.

The analysis indicated that a drop in a stress-related hormone found in the right whales was tied to a dip in ocean noise that followed a near-standstill in ship traffic, due to security concerns after the attacks. The work indicates that whales and other sea life that use sound to communicate and travel can be harmed by the noise.

The report combined data from two unrelated experiments in Canada’s Bay of Fundy that happened to be occurring simultaneously. In one experiment, New England Aquarium scientist Rosalind Rolland was taking right whale fecal samples that September as part of a study on the health and reproduction of the endangered North Atlantic right whale.

She remembered getting word at the waterfront of the terrorist attacks. It was a brilliant day, and after a while the crew decided to go on with their work, as a measure of defiance and also because the bay was “calming for the soul,” Rolland said.

About the same time, another researcher, Susan Parks, was getting acoustic recordings on mothers and their calves for research on the social behavior of the whales.

The data didn’t come together until late 2009, when Rolland started researching stress and underwater noise to prepare for a workshop organized by the Office of Naval Research. She realized that Parks had four days of sound recordings from the bay, two days before and two days after Sept. 11, and she had five years of data on stress hormone levels for the whales that included that same period.

Some analysis showed a possible correlation between a drop in sound and the drop in whale stress hormone levels. The naval office eventually agreed to fund further research, which was published last week in the British journal Proceedings of the Royal Society B.

The more rigorous analysis showed a significant decrease in background noise in the bay post-Sept. 11, including a drop in the low frequency sounds that ships emit and which the whales use to communicate. Scientists compared the stress hormone levels found in the whale feces during the period and found them to be markedly lower.

Rolland said the study might prompt more research and eventually influence future ocean traffic.

Associated Press