Underwater Acoustic Monitoring

Acoustic monitoring is used to study sound and its behavior in the sea. Sound are waves created essentially when objects vibrate. Underwater, these sound-pressure waves compress and decompress the water molecules as it travels through the medium. The compressions and decompressions are detected as changes in pressure by receptors like hydrophones which are underwater microphones.

Some hydrophones are cabled where it is connected to an underwater communication cable, while many are autonomous in that they are portable and can be deployed anywhere in the ocean. Most hydrophones are ceramic that go through a piezoelectricity process. This is a process where small electrical currents are produced when exposed to pressure changes. When ceramic hydrophones are submerged in water, they produce small-voltage signals over a range of frequencies due to the exposure to underwater sounds from all directions. Sound in the sea is measured through the amplification and recording of the electric signals created by hydrophones. Deploying multiple hydrophones in an area can increase the sensitivity of hearing sound from all directions.

Why is the study of ocean acoustics important?

Marine animals use sound to communicate underwater. Many also use their hearing to find food, mate and navigate through their surroundings. With the addition of human-made noise, they are facing challenges in their everyday behavior. With vessels greatly altering the local soundscape, scientists have noticed that some commercial shipping fleets expel low frequency noise, similar to fin whales and blue whales. By measuring and recording ocean acoustics, scientists can produce maps of where animals are located understand where human-made noise overlap. This in the future can lead to better noise regulation and monitoring. Within the Puget Sound area, especially around port cities like Seattle, more research needs to be done to understand how much anthropogenic noise is affecting local species.

What is happening locally around the Puget Sound?

In recent years, projects through programs like Quiet Sound has launched to make efforts to protect marine mammals from vessels. By incorporating a whale report alert system, mariners are notified to slow down. By slowing down when near wildlife, underwater noise is reduced by about 50 percent. A buoy equipped with hydrophones was deployed in Puget Sound, where Southern Resident orcas frequent, to monitor their behavior as well as record underwater noise. By sharing the data taken with the hydrophone, researchers hope to decrease the noise level created by humans and expand the number of participants taking part in the alert system program.

Acoustic monitoring not only picks up sound that animals make but also noise created by humans that can be disruptive to marine mammals. Some cetaceans are known to stop feeding and vocalizing around certain anthropogenic noises like sonar, even becoming disoriented and strand (Alberts, 2021). Watch the videos below to learn more about marine mammal communication and local conservation efforts being made to monitor underwater sound.