Intermediate 
Noise from ships may disturb animals such as killer whales and dolphins much more than people previously thought. New research shows that underwater noise could disturb the animals communication and ability to  nd prey. The low rumble of passing ships has, for a long time, been connected to the disturbance of large whales. But, US researchers have also found noise at medium and higher frequencies, including at 20,000Hz where killer whales, also known as orcas, hear best.
These noises could be disturbing the ability of killer whales to communicate and use echo to  nd their prey. Dolphins and porpoises, which also hear at higher frequencies, may have the same problems. The  ndings suggest that the noise could affect the endangered population of killer whales that are found near the shipping lanes up the west coast of the USA.
The main concern of this is that even a slight increase in sound may make echolocation more dif cult for whales, said Scott Veirs, who led the research. Echolocation is the process of using sound to bounce off objects such as prey and identify where they are. Thats worrying because their prey, chinook salmon, is already quite scarce. Hearing a salmons click is probably one of the most challenging things a killer whale does. Hearing that subtle click is harder if theres a lot of noise around you.
The researchers used underwater microphones to measure the noise created 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 vessel, including cruise ships, container ships and military vehicles, that passed through the strait about 20 times a day.
Some ships are quieter than others but the average intensity of noise next to all the ships was 173 underwater decibels, equivalent to 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 lawnmower or a vacuum cleaner.
Veirs said scientists already knew about the impact of underwater noise on large whales. But, the new research shows the threat to smaller whales, dolphins and porpoises. Ships have been thought of as low-frequency sources of noise, like the rumbling of lorries or trains, he said. Most noise is at that low frequency but the background noise of the ocean is raised even in the high frequencies. This could be causing a signi cant problem that we need to look into more
There are several further consequences of a noisy underwater environment. Whales may have to group together more closely in order to hear each other. And, if they fail to  nd prey as effectively, they will need to use up their stores of extra blubber. This is a problem because this blubber often contains manmade pollutants that are toxic to whales if they are released fully into their systems.
Veirs said more work needs to be done to identify how badly the noise is affecting whales and also to quieten the ships that pass near them. It should be easy to reduce noise pollution, he said. Military ships are quite a bit quieter and there could be simple ways of transferring that technology to commercial ships. Another way to reduce noise is to slow down. Decreasing speed by six knots could decrease noise by half.
While some whale species, such as blue whales, the largest mammal on Earth, are safer now because whaling has declined, others are still under threat from a range of factors. The US federal government has recently protected nearly 40,000 square miles of the Atlantic to try to avoid losing a species of whale with just 500 individuals left.
In Europe, killer whales are carrying dangerously high levels of banned chemicals in their blubber. Scientists are still trying to  nd out whether pollutants caused the deaths of  ve whales that were found on beaches on the east coast of Britain in January 2016. Meanwhile, around the coast of Australia, whales face an increased threat from ship strikes and oil and gas drilling, as well as Japans recent decision to start whaling again in Antarctic waters.