Acoustics

Passive acoustic monitoring (PAM) is a non-invasive technique that allows us to study marine mammals by recording and analyzing the sounds they produce and the soundscapes they inhabit. Many species rely on complex vocal repertoires—including clicks, whistles, songs, and low-frequency calls—for communication, navigation, and foraging. Because many species vocalize regularly and sound travels efficiently underwater, PAM allows researchers to monitor species presence, seasonal distribution, and behavior even when animals are not visible. Acoustic approaches also enable us to quantify anthropogenic or human-made noise (from shipping, construction, or military activities) helping assess how human activities can alter communication space and influence behavior. Long-term acoustic datasets provide powerful insights into population trends, habitat use, and the cumulative impacts of changing ocean soundscapes. Advances in automated detection, machine learning, and PAM technologies now allow us to process large volumes of data efficiently and monitor remote habitats continuously. PAM is therefore an essential tool for both ecological research and conservation management.

How it Works:

Hydrophones are deployed on the seafloor or moorings to continuously record underwater sound across months or years. Non-invasive tags can also be deployed on animals and can record several hours of acoustic data.
Acoustic recordings are processed to detect marine mammal calls using automated detectors or manual review.
Ambient noise levels are quantified to assess potential overlap with marine mammal frequency range
Species are identified using call characteristics such as frequency, duration, and temporal patterns.
Detection data are used to model spatial and seasonal distribution and evaluate relationships with human activities and environmental conditions.

Soundscape monitoring: integrating biological and human noise

Soundscape analyses combine marine mammal calls, physical ocean noise, and anthropogenic sources to understand how species share acoustic space. By comparing call rates, noise levels, and habitat features, researchers evaluate how shipping, construction, and other changes alter communication ranges and behavior across multiple species.

Deriving species distribution from acoustic detections

Long-term PAM datasets allow researchers to map when and where marine mammals are present by analyzing patterns of acoustic detections. By combining detection rates with environmental variables such as sea surface temperature or prey availability, scientists can model habitat preferences and identify important feeding or breeding areas. For instance, the acoustic monitoring of endangered or protected species such as false killer whales or Hawaiian monk seal help identify relevant areas for management and conservation.

Monitoring behavioral responses to human activities

PAM can be used to evaluate how marine mammals respond to episodic noise sources such as naval sonar exercises or construction. Changes in vocal behavior, such as reduced calling or shifts in call frequency, may indicate disturbance. Understanding these responses helps managers develop mitigation measures such as time-area restrictions or noise reduction strategies.

Archival non invasive acoustic tags: fine scale behavior and sound exposure

Archival acoustic tags (such as Dtags or CATS tags) attach temporarily to whales and dolphins using suction cups and record both the sounds animals produce and the sounds they receive. These tags provide high resolution data on vocal behavior, movement, and even exposure to anthropogenic noise. By combining acoustic recordings with depth, acceleration, video and orientation sensors, researchers can reconstruct dive profiles, foraging events, and potential responses to environmental or human-generated sounds. Because the tags detach on their own and are recovered at the surface, they offer a non invasive way to study individual behavior at fine temporal scales while minimizing disturbance.

Acoustics

How it Works:

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