Noise from ships may disturb animals such as killer whales and dolphins much more than we thought before. New research shows that underwater noise could stop these animals communicating and make it more difficult for them to find food. It is well known that noise from ships disturbs large whales. But, US researchers have found noise also disturbs smaller sea creatures such as killer whales, also known as orcas. Dolphins and porpoises may have the same problems. 
“The main problem is that even a small increase in sound may make it more difficult for whales to find food using echo,” said Scott Veirs, who led the research. “That’s worrying because their food, a kind of salmon, is already quite scarce. Hearing a salmon’s click is probably one of the most difficult things a killer whale does. It is harder to hear that click if there’s a lot of noise around you.”
The researchers used underwater microphones to measure the noise made by about 1,600 ships as they passed through Haro Strait, in Washington State, USA. The two-year study recorded the sound made by 12 different types of ship, including cruise ships, container ships and military ships, that passed through the strait about 20 times a day.
Some ships are quieter than others but the average noise next to all the ships was 173 underwater decibels, the same as 111 decibels through the air – about the sound of a loud rock concert. Whales are not usually right next to ships and so would hear noise of about 60 to 90 decibels – around the level of a vacuum cleaner.
Veirs said scientists already knew about the effect of underwater noise on large whales. But, the new research shows the danger to smaller whales, dolphins and porpoises. “We think that ships make low-frequency noise, like the sound of lorries or trains,” he said. “Most noise is at that low frequency but there is more background noise in the high frequencies, too. This might be causing a big problem that we need to study more.”
Lots of underwater noise can cause many problems. Whales may have to stay closer together to hear each other. And, if they cannot find food easily, they will need to use their extra blubber. This is a problem because this blubber often contains manmade pollutants that are poisonous to whales if they get into their bodies.
Veirs said ships that pass near whales need to be quieter. “It should be easy to reduce noise pollution,” he said. “Military ships are much quieter and there could be simple ways of using that technology on normal ships. Another way to reduce noise is to slow down. Reducing speed by six knots could decrease noise by half.”
Some whale species are safer now because there is less whaling but other types of whale are still in danger for many different reasons. The US has recently protected nearly 40,000 square miles of the Atlantic to save a species of whale with just 500 individuals left.
In Europe, killer whales have dangerously high levels of illegal chemicals in their blubber. Scientists are still trying to find out if pollutants caused the deaths of five whales that were found on beaches on the east coast of Britain in January 2016. And, around the coast of Australia, whales are in danger from oil and gas drilling, as well as Japan’s recent decision to start whaling again in the seas of Antarctica.