Understanding Sound in the Ocean

Both natural and human-made sounds occur in the ocean. Natural sounds come from marine life and naturally occurring events like underwater earthquakes. Human-made sounds come from many sources, such as ships, underwater energy exploration, military sonar, and underwater construction, among others.

Learn more about sound in the ocean.

Sound is essential to many types of marine animals and is one of the main tools they use to survive in the ocean. Light can only penetrate a few hundred feet underwater, but sound can travel much farther. As a result, cetaceans (whales, dolphins, and porpoises) have evolved over millions of years to send and receive a variety of complex sounds. They rely on sound to communicate with each other, navigate, find mates and food, defend their territories and resources, and avoid predators. Fish and invertebrates also use sound for basic life functions.

Because water is denser than air, sound travels faster and farther in the ocean. Its speed and distance depends on the density of the water (determined by its temperature, salinity, and depth) and the frequency of the sound, measured in hertz (Hz). Some sounds, particularly low-frequency ones, can cover vast distances, even across ocean basins.

People produce some sounds intentionally, such as military sonar and seismic tests for oil and gas exploration. Other sounds are an unintentional by-product of an activity, such as shipping and underwater construction. Many human-produced sounds in the ocean are intermittent, whereas shipping creates an almost constant rumble in the ocean. Even the motor of a fishing boat creates extra sound underwater.

All of these sounds add to overall ocean noise and contribute to the “soundscape,” which scientists define as the combined sounds made by humans, natural events, and marine animals. Because sound travels so well underwater, many of these sounds can be heard miles from their sources.

Depending on the sound source, duration, and location, human-caused sound has the potential to affect animals by:

• Causing temporary or permanent hearing loss.
• Causing a stress response.
• Forcing animals to move from their preferred habitat.
• Disrupting feeding, breeding/spawning, nursing, and communication behaviors.

The impacts may be immediate and severe, or they may accumulate over time.

We are engaged on several fronts to better understand and manage ocean sounds, specifically in regard to cetaceans and other types of marine life. Most recently, we published the Ocean Noise Strategy Roadmap which defines a 10-year plan for the agency to address ocean noise.

In 2011, we started the CetSound mapping project. CetSound provides two mapping tools: SoundMap and CetMap. SoundMap allows us to map the time and location of noise, and CetMap shows how many cetaceans are in a given area at a specific time. This information is used to determine where marine animals go to breed and find food, what routes they use to migrate, and where small or fixed populations are concentrated. We then have a better understanding of how ocean noise affects them.

NOAA Fisheries is also part of an interagency partnership that established a set of undersea listening stations around the United States to measure levels of background noise in the ocean.

Among many efforts to protect marine species, NOAA Fisheries administers the Endangered Species Act to recover threatened and endangered species and prevent their extinction. Through consultations under the ESA, we develop biological opinions to determine how the actions of federal agencies may affect ESA-listed species and critical habitat.

We also are responsible for authorizing the “take” of marine mammals that can result from the sounds produced by human activities. These Incidental Take Authorizations are issued under the Marine Mammal Protection Act. The MMPA limits the numbers of animals that can be “taken” (disturbed or hurt) as a result of human activities and ensures that those activities result in a negligible impact on marine mammal species and stocks.

By knowing how much underwater noise humans produce around the world, scientists can develop ways to reduce or prevent it, as well as ways to protect marine animals from it.

Learn more about sound in the ocean and what NOAA is doing to reduce it to protect marine animals:

• NOAA's Ocean Noise Strategy 
• NOAA Fisheries' Ocean Acoustics Program 
• Marine Mammal Acoustic Technical Guidance