Living in a world of water, sound is as important to whales, dolphins and porpoises as sight is for humans, says the experts at Whale and Dolphin Conservation.
As well as using sound to navigate and hunt, whales communicate with each other over vast distances using their extraordinarily sensitive hearing. The low frequency calls of a blue whale can travel thousands of kilometres through the water in favourable conditions.
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One of the best-known examples of social learning and culture in whales and dolphins is the haunting song of humpbacks. But one thing that can interrupt their ocean discourse and drive them away from key feeding and breeding grounds is pollution. Not the plastic or toxic variety, but noise pollution.
What exactly is underwater noise pollution?
‘Anthropogenic’ underwater noise pollution refers to the human-made sounds that disrupt the natural acoustic environment of the ocean. The main sources of this kind of noise are:
- Impulsive pile driving: Steel pillars are often hammered into the seabed to anchor turbines. This process sends deep, booming pulses through the water.
- Construction and shipping: Big ships, dredging and machinery all generate a constant, low frequency hum underwater.
- Sonar and survey equipment: Tools used to map the seabed and military sonar can produce loud pulses that ripple through the ocean, sometimes travelling hundreds of kilometres.
Why are whales and dolphins particularly vulnerable to noise pollution?
Whales and dolphins rely on sound far more than humans do. In the dark and murky underwater world, sight is limited, so sound is their primary sense.
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They use it to find food, navigate and communicate with one another. When human-made noise fills the ocean, it can mask these vital sounds, disorienting creatures that depend on hearing to survive.
How does noise pollution interfere with their communication?
Each species of whale and dolphin has its own language of clicks, whistles, and songs. For instance, male humpback whales sing complex melodies during mating season, while orcas use distinct calls to coordinate with their pods. When the ocean is filled with constant man-made noise, these sounds can be drowned out. This makes it difficult for individuals to find mates, warn others of predators or stay connected with their pod.
Are there physical effects of noise pollution, not just behavioural ones?
Prolonged or intense exposure to loud sounds can cause stress, hearing loss and even physical damage and injury to sensitive ear structures.
Powerful naval sonar, for example, has been linked to mass strandings of whales. Scientific analysis of the UK’s largest common dolphin stranding off the coast of Cornwall in 2013 concluded that the most probable cause of the event were naval exercises in the area at the time.
The sudden, high-intensity sounds can cause disorientation and internal damage. Plus, constant exposure to lower-level noise can also lead to elevated stress hormones in North Atlantic right whales off the busy east coast of North America, which may weaken immune systems and reduce reproductive success.
Does noise pollution change where whales and dolphins go?
Absolutely. Studies have shown that whales and dolphins (including beluga whales, grey whales and bowhead whales) often abandon or avoid areas where noise levels are high.
Disturbance can force them out of important feeding or breeding grounds. Displacement from key habitats and alterations to migration routes can increase the energy they expend and reduce their access to food, impacting the survival of individuals and populations.
What is being done to reduce underwater noise pollution?
With increased awareness comes increased action. Some shipping companies are developing quieter propellers and hull designs. International efforts, including through the International Maritime Organisation’s guidelines, encourage "quieting technologies".
Naval forces are testing less harmful sonar practices, and researchers are mapping "acoustic sanctuaries", where marine mammals can live with minimal disturbance. In several countries, wind farm developers are also being required to reduce construction noise to less harmful levels, such as using bubble curtains to absorb sound.
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