Noise from ships stresses out the whales, new research has shown.

Experts based at the Duke University and the New England Aquarium in the U.S. found that noise generated by engines of large ships overlaps the frequency range that some whales use for communicating, thereby increasing their stress level.

During the experiment, the scientists had studied the right whale's stress levels when ship traffic in the U.S. was dropped because of the September 11 attacks. They found out that stress level of the whale was quite low compared to the normal days. This clearly shows how whales are getting affected by shipping noise.

A rise in noise generated by ships can result in habitat displacement, behavioural changes and alterations in the intensity, frequency and intervals of whales' calls, according to the UPI.

"There was a six-decibel decrease in underwater noise in the bay following 9/11, with an especially significant reduction in the low-frequency ranges below 150 hertz," Douglas P Nowacek, researcher from the Duke University, told the UPI.

"This correlated to reduced baseline levels of stress-related hormone metabolites in samples collected from whales later that fall," he said.

"Essentially, the animals' stress levels dropped when the underwater ship noises did," Nowacek said in a statement.

Right whales have been called America’s urban whale. Their primary habitats up and down the East Coast of North America are all in or near major ports and shipping lanes. Here a right whale dives near a large ship in Canada’s Bay of Fundy.New England Aquarium
Right whales are the most endangered large whale in the Atlantic. There are only about 450 of these baleen whales left. Their low population is thought to be a product in part of multiple stressors in their environment. Unexpectedly after 9/11, whale researchers at Boston’s New England Aquarium discovered the first evidence of the effects of noise pollution on the chronic stress levels of these whales.New England Aquarium
Right whale mothers give birth to their calves near the Florida/Georgia border during the winter months near the ports of Jacksonville and Savannah. In the spring, they bring their calves to Cape Cod Bay adjacent to the shipping lanes into Boston, and in the summer, they bring their calves to feed in the Bay of Fundy and the major shipping lanes into St. John, New Brunswick.New England Aquarium