How an Underwater Listening Network is Revolutionizing Ocean Conservation
Beneath the waves, a hidden network of ears is listening, and what it's learning is transforming how we protect marine life.
The ocean is far from silent. Beneath the surface lies a rich soundscape—a complex symphony of biological, geological, and anthropogenic sounds. Marine mammals, including whales, dolphins, and porpoises, along with many fish species, rely heavily on sound for survival. In the marine environment, where light penetrates only so far, hearing becomes one of the most critical senses. These creatures use sound for navigating vast distances, socializing, establishing dominance, attracting mates, avoiding predators, and finding food.
However, this acoustic habitat faces increasing disruption from human-made noises. Commercial shipping, recreational boating, offshore construction, and energy exploration introduce loud, persistent sounds that can interfere with animal communication, cause stress, and even displace species from critical habitats.
Enter an innovative solution: the U.S. Northeast Passive Acoustic Sensing Network, or NEPAN. This collaborative network represents a technological tour de force in monitoring marine life through sound. Stretching from the northern Gulf of Maine to the New York Bight, NEPAN employs an array of underwater listening devices to continuously track the presence and movements of vocal marine animals year-round. By listening in on the ocean's secret symphony, scientists are gaining unprecedented insights into marine ecosystems—information that's becoming vital for effective conservation and management in an increasingly noisy underwater world 2 6 .
The U.S. Northeast Passive Acoustic Sensing Network (NEPAN) is composed of numerous passive acoustic recorders that provide both archived and near-real-time data on acoustically active marine mammals and fish species throughout the northwest Atlantic Ocean. Established as a formal network in 2014, NEPAN represents a collaborative effort among multiple federal agencies and research institutions, with the National Oceanic and Atmospheric Administration (NOAA) playing a central role 2 4 5 .
NEPAN operates on a simple but powerful principle: instead of actively sending out sound signals like sonar, it passively listens to the natural and human-made sounds of the marine environment.
What makes NEPAN particularly innovative is its multi-platform approach. The network incorporates various technologies deployed across different regions and habitats.
Strategically placed in critical habitats
Cover larger areas and adapt to changing conditions
Serving different research and management needs
This comprehensive network addresses a critical gap in marine monitoring. Before NEPAN, researchers largely depended on visual surveys from ships and aircraft, which are limited by daylight, weather conditions, and budget constraints. These methods could only provide snapshots of animal presence rather than the continuous, year-round data that passive acoustic monitoring now delivers 6 .
NEPAN exemplifies how collaborative scientific efforts and strategic financial investment across multiple federal agencies can produce novel solutions to longstanding information gaps in marine ecosystem management. By integrating previously disconnected monitoring efforts into a coordinated network, NEPAN provides a more complete picture of marine life distribution and human impacts than had ever been possible 5 .
The ocean soundscape comprises three main components: biophony (sounds produced by marine life), geophony (environmental sounds from waves, rain, and earthquakes), and anthrophony (human-made sounds). NEPAN focuses primarily on biophony and anthrophony, monitoring the sounds produced by marine animals while simultaneously tracking human activities that generate underwater noise 3 .
Produce low-frequency moans, pulses, and songs that can travel hundreds of miles underwater
Use higher-frequency clicks and whistles for echolocation and social communication
Produce sounds during spawning or through feeding activities
Underwater microphones (hydrophones) detect sound waves traveling through water. These hydrophones are specially designed to capture the full range of marine animal vocalizations.
Acoustic data are recorded either continuously or through programmed duty cycles (e.g., recording 5-10 minutes of every 15-20 minute period).
Recorded data are processed using advanced detection and classification systems. The Low Frequency Detection and Classification System (LFDCS) is one such tool specifically designed to identify baleen whale calls in extensive acoustic datasets .
Processed detections are manually reviewed or automatically classified to confirm species presence. This step is crucial for reducing false positives and ensuring data quality.
One of NEPAN's primary applications is monitoring endangered marine mammals, particularly the North Atlantic right whale (Eubalaena glacialis). With only about 500 individuals remaining, this species faces critical threats from vessel strikes and fishing gear entanglements. NEPAN data help address these threats in several crucial ways .
| Region | 2004-2010 Detection Rate | 2011-2014 Detection Rate | Change Between Periods |
|---|---|---|---|
| Scotian Shelf (Region 3) | High | Low | Decrease |
| Gulf of Maine (Region 4) | High | Low | Decrease |
| Southern New England (Region 7) | Low | High | Increase |
| Mid-Atlantic (Region 8) | Low | High | Increase |
| Southeastern U.S. (Region 10) | Moderate | High | Increase |
The data also confirmed that North Atlantic right whales now use habitats along the entire eastern seaboard from Florida to Canada throughout winter months, contradicting previous assumptions that they primarily occupied southern calving grounds in winter. This expanded understanding of their year-round distribution has profound implications for conservation planning .
Beyond long-term studies, NEPAN enables real-time conservation applications. The network includes systems that can detect whale vocalizations and transmit alerts to maritime managers, who can then notify vessel operators of whale presence in sensitive areas. This capability is particularly valuable in regions like Stellwagen Bank National Marine Sanctuary, where ship strikes represent a major threat to whale populations 3 6 .
In 2014, NEPAN established a real-time monitoring buoy in Rhode Island Sound that detects baleen whale vocalizations and transmits this information to marine managers. Similar buoys have been deployed near Mount Desert Rock, Maine, where fin and humpback whales are commonly found.
NEPAN's applications extend beyond marine mammals to include commercially important fish species. Researchers have used gliders equipped with hydrophones to detect Atlantic cod spawning aggregations by listening for the distinctive sounds males produce during reproduction. This information helps identify critical spawning habitats that may warrant special protection from fishing pressure or habitat degradation 2 6 .
| Species Group | Monitoring Applications | Conservation Benefits |
|---|---|---|
| Baleen Whales (right, humpback, fin) | Migration timing, habitat use, population distribution | Dynamic management of shipping lanes, fishing activities, and noise-producing industrial operations |
| Toothed Whales (dolphins, porpoises) | Habitat preference, seasonal occurrence | Identification of critical habitats needing protection |
| Fish (cod, haddock) | Spawning aggregation identification, population monitoring | Fisheries management, protection of spawning grounds |
| Entire Soundscape | Ambient noise level assessment, anthropogenic noise impact | Evaluation of cumulative effects of human activities on marine ecosystems |
To understand how NEPAN generates transformative scientific insights, we can examine a key study that tracked North Atlantic right whale distribution from 2004 to 2014. This research exemplifies the power of passive acoustic monitoring to reveal long-term, large-scale patterns in marine animal movements .
The study synthesized passive acoustic data collected by 19 different organizations across the western North Atlantic Ocean, creating a massive dataset that would have been impossible for any single institution to assemble.
The study yielded several groundbreaking insights that have reshaped our understanding of right whale ecology and conservation:
| Platform Type | Deployment Duration | Data Delivery | Primary Applications |
|---|---|---|---|
| Bottom-Mounted Recorders | 6 months - 1 year | Archival (retrieved after deployment) | Long-term presence/absence monitoring, baseline data collection |
| Surface Buoys with Satellite Link | Several months | Near real-time | Dynamic management, vessel strike prevention |
| Autonomous Gliders | Up to 3 months | Near real-time | Large-scale spatial surveys, adaptive monitoring |
| Towed Arrays | Hours to days during ship surveys | Real-time | Combined visual and acoustic surveys, species identification |
| Animal-attached Tags | Hours to days | Archival | Fine-scale behavior studies, source level measurements |
The implications of these findings extend directly to conservation policy. Seasonal Management Areas (SMAs)—zones where vessels must reduce speed during specific periods to protect whales—were initially established based on historical whale distribution patterns. This research demonstrates that these management strategies must evolve as whale distributions change, highlighting the need for dynamic, responsive approaches to marine conservation .
NEPAN's effectiveness stems from its diverse array of acoustic monitoring technologies, each suited to particular research questions and operational constraints. These tools form an integrated technological toolkit that allows scientists to monitor marine life across multiple spatial and temporal scales 3 6 .
Anchored to the seafloor and typically deploy for 6 months to a year. They provide long-term, continuous monitoring at specific locations, making them ideal for understanding seasonal patterns.
Combine subsurface hydrophones with surface buoys that can transmit detection data via satellite or cellular networks. This real-time reporting enables immediate conservation responses.
These mobile platforms can survey large areas for up to three months, controlled remotely from shore. They're particularly valuable for monitoring remote or difficult-to-access regions.
Hydrophones towed behind research vessels allow scientists to correlate visual observations with acoustic detections during ship-based surveys.
These free-drifting systems capture acoustic data across moving water masses, providing insights into how sound propagates through different oceanographic conditions.
Tags attached to marine animals record both the animal's movements and the acoustic environment it experiences, offering unique insights into how individuals respond to anthropogenic noise.
NEPAN represents a transformative approach to understanding and protecting marine ecosystems. By listening to the ocean's natural sounds, this network provides invaluable data on animal distribution, human impacts, and the changing nature of marine environments. The collaborative spirit behind NEPAN—bringing together multiple agencies, institutions, and technologies—demonstrates how integrated approaches can address complex conservation challenges 5 6 .
The vision for NEPAN extends beyond its current reach. Researchers envision an expanded network spanning the entire U.S. East Coast, with eventual extension to waters around the United States.
Such a comprehensive system would provide unprecedented insights into migration patterns, climate change impacts, and the cumulative effects of human activities on marine life. This expanded capability would be particularly valuable as ocean industries grow and climate change continues to reshape marine ecosystems 6 .
However, this vision faces a significant challenge: the need for sustained funding and institutional support. As the creators of NEPAN noted, "the continued operation and/or expansion of this type of 'listening network' will only be possible in the long term with clear and direct support from NOAA" and other federal agencies 4 5 .
For the public, NEPAN offers a powerful reminder that the ocean has much to tell us if we learn to listen. Each recorded whale song or fish grunt represents not just an animal going about its daily life, but a data point in our collective understanding of marine ecosystems. As we face increasing challenges in managing our oceans sustainably, technologies like those employed by NEPAN will be essential for making informed decisions that balance human needs with the health of marine ecosystems.
Sometimes the most powerful thing we can do for science and conservation is to listen—attentively, continuously, and on nature's terms.