Sound and the Marine Environment
Light doesn’t travel well underwater, but sound travels efficiently and across great distances. For many marine mammals, hearing is the primary sense for communicating, navigating, finding food, mating, and avoiding predators.
Today, the ocean is increasingly noisy from ship traffic, sonar, construction, seismic exploration, and industry. This excess sound can cause hearing loss, disrupt communication, raise stress, and interfere with vital behaviors like foraging and mating.
At NMMF, we study how marine mammals use sound and how human-generated (anthropogenic) underwater noise affects their survival. Our work provides critical information to ocean noise regulators, shaping conservation strategies to reduce noise pollution and protect vulnerable species.
Understanding Marine Mammal Hearing
NMMF scientists use two methods to study hearing:
- Behavioral testing – working with animals trained to respond when they hear a sound
- Auditory Evoked Potential (AEP) testing – measuring brain activity in response to sound
AEP testing is especially valuable for stranded or wild animals. It helps ensure that an animal’s hearing isn’t severely compromised before release, and allows researchers to compare hearing across species, track changes with age, and study the impact of ocean noise.
Through partnerships with NOAA Fisheries and stranding networks, we are expanding AEP research and training new technicians, building capacity to test more animals and strengthen conservation strategies in a changing ocean.
New Research Informs Marine Mammal Conservation
Minke Whale Hearing: Groundbreaking Research
Baleen whales rely on hearing to communicate, navigate, and likely find food. But rising noise from ships, sonar, and industry threatens these essential behaviors. Until recently, no one had ever measured a baleen whale’s hearing.
In a groundbreaking multi-year study, NMMF scientists and the Norwegian Defense Research Establishment (FFI) revealed the first direct insights into how minke whales perceive sound – an important step toward stronger protections against noise pollution.
Eavesdropping on Marine Mammals: How Much Noise Does it Take to Affect Their Communication?
To understand how dolphins communicate in noisy environments, NMMF researchers developed a hydrophone array that continuously records the vocalizations of U.S. Navy dolphins in the San Diego Bay.
The three-year study, conducted with the U.S. Navy Marine Mammal Program, found that dolphins maintain consistent whistle rates despite moderate noise exposure, highlighting their resilience. These results improve our understanding of dolphin communication and inform efforts to protect wild populations.
Acoustic Monitoring in the Amazon
Just as we listened to dolphins in the San Diego Bay, NMMF scientists are now monitoring Amazon river dolphins, including the endangered boto (Inia geoffrensis) and tucuxi (Sotalia fluviatilis).
In collaboration with the Universitat Politècnica de Catalunya (UPC), we deployed passive acoustic recorders to capture their echolocation clicks. This research fills key gaps about habitat use and overlap with human fishing, which is critical for future conservation. Our long-term goal is to create a real-time monitoring network across the Amazon Basin.
The Science of Dolphin Echolocation
How Dolphins Use Biosonar
Dolphins rely on echolocation to navigate, hunt, and explore. They emit rapid clicks that travel through water, bouncing off objects and returning as echoes. With extraordinary hearing, dolphins interpret these echos with precision, forming detailed representations of their surroundings and even detecting buried objects or hidden prey.
Listen to dolphin echolocation
Advancing Biosonar Research
For decades, the U.S. Navy Marine Mammal Program has studied dolphin echolocation and its application to detect and identify objects that challenge human-made sonar systems.
Cutting-Edge Research and Applications
In collaboration with the U.S. Navy Marine Mammal Program, NMMF researchers study how dolphins classify objects, detect subtle sound changes, and interpret acoustic environments. Funded by the Office of Naval Research, these studies reveal how dolphins construct complex soundscapes – knowledge that inspires next-generation sonar technologies. This research also informs conservation, showing how dolphins might be affected by fishing gear entanglement and helping guide sustainable fisheries.
