A Moment of Silence

Break in ship noise after 9/11 reduced stress in whales.
April 1, 2012

The days after the September 11 terror attacks—a period of high stress and anxiety for most Americans—turned out to be a relief for at least one group.

Whales in Canada’s Bay of Fundy experienced less stress during the period after the attacks, when ship traffic came to a standstill, according to new research from the Nicholas School of the Environment. The research team relates the change to reduced noise from ships during the temporary lull.

“There was a six-decibel decrease in un- derwater noise in the bay following 9/11, with an especially signifi- cant reduction in the low-frequency ranges below 150 hertz,” says Douglas P. Nowacek, Repass-Rodgers Uni- versity Associate Profes- sor of marine conservation technology. He said scientists saw a simi- lar drop in stress-related hormone metabolites in whale fecal samples col- lected later that fall.

The low-frequency sounds made by the propellers and engines of large ships travel well through the ocean and sometimes overlap the frequencies of whale communication. Past studies have shown a connection between ship noise and behavioral changes in whales, including al- terations in the whales’ own calls, says Nowacek. This study is the first to docu- ment physiological changes in mammals that correlate with ship noise.