The noise emitted by ships' propellers distresses whales on the high seas and oceans, say marine scientists who have found a link between the two.
Researchers from the New England Aquarium in Boston studied the faeces of right whales and found that fewer ships nearby caused their stress hormone levels to drop. Right whales are large baleen whales that often approach close to shore. The northern and southern right whales are on the endangered species list.
The discovery came to light after the 9/11 terrorist attacks in the US, which led to a massive decrease in shipping traffic on the east coast of America, the Daily Mail reports. At that time a team led by New England Aquarium's Rosalind Rolland was looking at the health and reproduction of right whales in the Bay of Fundy and realised that the hormone data was tied in with shipping levels.
Rolland said: "We showed whales occupying oceans with high levels of ship noise have a chronic stress response. We knew whales changed the frequency of their calls to adapt to the ship noise, but this work shows it is not merely an annoyance - it is having a physical effect."
"The instant responses to stress -- like running away from a tiger -- can be life-saving. But if it becomes chronic, it causes profound depression of the immune system, making them vulnerable to disease, and it depresses reproduction," added Rolland.
Rolland believes that the issue can be addressed because it is mainly the ships' engines that aren't malfunctioning that produce excess noise. Susan Parks, assistant professor of acoustics and research associate at the Applied Research Lab, Penn State University, said: "The impacts of increases in ocean noise from human activities are a concern for the conservation of marine animals like right whales."