February 8, 2012
Whales Briefly Benefited From Decrease In Shipping Traffic After 9/11
According to a new study, baleen whales suffered less stress from ship noise after the September 11, 2001 terrorist attacks on the World Trade Center.
A study conducted in Canada's Bay of Fundy has revealed that a lull in ship noise after the attacks eased stress on right whales, a type of baleen whale.
They analyzed underwater noise levels during a period of reduced ship traffic in the bay after the attacks, and compared the data with levels of stress-related hormone metabolites in the fecal samples of right whales before and after the attacks.
Douglas P. Nowacek, Repass-Rodgers University Associate Professor of Marine Conservation Technology and Electrical & Computer Engineering at Duke University, said there was a six-decibel decrease in underwater noise in the bay following September 11.
"This correlated to reduced baseline levels of stress-related hormone metabolites in samples collected from whales later that fall," Nowacek said in a statement. "In subsequent years, ship traffic — and noise — were higher, along with the whale's stress-hormone levels."
Scientists have become concerned about the effect that increased underwater noise pollution might be having on whales and other marine mammals over the past 50 years.
These animals rely on sound to help communicate with each other, locate prey, and navigate through the waters.
Nowacek said the sounds made by large ships are particularly concerning because their propellers and engines generate low-frequency noise that overlaps with the frequency band used by baleen whales for communication.
Until this study, there was little evidence about whether exposure to the noise resulted in physiological responses that could be harmful to the whales.
"Essentially, the animals' stress levels dropped when the underwater ship noises did," Nowacek said.
BBC reported that the researchers used trained dogs to help locate bobbing fecal matter in the waters.
This feces gathered showed a lower level of metabolites of glucocorticoid hormones, which are associated with stress, than in subsequent summers when marine traffic returned to normal levels.
"Past studies have shown they alter their vocalization pattern in a noisy environment just like we would in a cocktail party, but this is the first time the stress has been documented physiologically," Dr Rosalind Rolland of the New England Aquarium in Boston told BBC.
Despite the positive effects of the drop in noise levels for the whales, global shipping has risen substantially in recent decades, with noise levels reaching 10 to 12 decibels louder than in the 1960s.
The researchers would like to extend their study to other locations, such as moving to study the Southern right whales in the southern hemisphere.
The findings were published in the journal Proceedings of the Royal Society B.
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