The focal species of this study is the Gervais’ beaked whale (Mesoplodon europaeus), a species for which detailed behavioral data has been virtually non-existent until now. Through passive acoustic data alone, scientists have crafted a comprehensive picture of how these whales navigate, forage, and dive to extreme depths. This innovative approach captures the intricacy of their behaviors far below the ocean surface, revolutionizing our ability to study animals that remain concealed from conventional research methods.

Beaked whales spend the majority of their lives offshore in the deep ocean, surfacing only briefly to breathe before plunging once again into the dark abyss. Their elusive nature has made visual sightings incredibly scarce, and traditional tagging technologies are often impractical due to the animals’ sensitivity and deep-diving habits. The research team addressed these challenges using passive acoustics—deploying underwater listening stations capable of detecting species-specific echolocation clicks. These biologically generated clicks serve as acoustic signatures that can be precisely localized to track individual whales during their foraging descents.

Employing a network of High-Frequency Acoustic Recording Packages (HARPs) deployed at depths around 1,100 meters off the coast of Louisiana, scientists captured acoustic data during fifty distinct deep foraging dives. These HARPs consist of multiple time-synchronized sensors allowing for triangulation of the whales’ echolocation clicks. By measuring minute differences in the arrival times of sounds between sensors, the research team could estimate the direction and distance of individual whales, enabling the reconstruction of their three-dimensional movement paths underwater.

The application of this technology marked the first-ever detailed acoustic tracking of beaked whale dive behavior in the Gulf of Mexico. Three beaked whale species were studied: goose-beaked whales, Gervais’ beaked whales, and Blainville’s beaked whales. Among them, goose-beaked whales demonstrated longer detection durations and consistently deeper foraging dives, often approaching the seafloor. These new behavioral insights provide fresh understanding about species-specific diving strategies and habitat use.

This study’s innovative use of passive acoustics offers a scalable and non-invasive research methodology that can be applied across large marine areas. The ability to monitor these species continuously over long periods brings a significant advantage over traditional visual surveys or tagging, both of which are limited by weather conditions, observer availability, and the animals’ brief surfacing intervals. Such data acquisition is critical for robust conservation strategies, particularly as beaked whales face escalating threats from human activities.

The Gulf of Mexico, the site of this research, has experienced significant ecological disruptions over the past decade, most notably the 2010 Deepwater Horizon oil spill. Previous studies suggest that beaked whale populations in this region may have declined by up to 83% since the spill. The urgency to understand the behaviors and population dynamics of these whales amid mounting industrial impacts has never been greater. This research contributes vital baseline data to inform recovery and protection efforts in a heavily industrialized marine environment.

Héloïse Frouin-Mouy, Ph.D., lead author and bioacoustics scientist at the University of Miami’s Cooperative Institute for Marine and Atmospheric Studies (CIMAS), emphasized the critical timing of these findings. According to her, reliable, detailed behavioral data on these whales are necessary to monitor populations and address the potential declines caused by anthropogenic disturbances such as noise pollution and habitat degradation.

Data integration from two spatially separated HARPs allowed for more robust three-dimensional tracking capabilities. By comparing time-of-arrival differences of individual echolocation clicks at each sensor, researchers constructed a fine-scale map of whale movements and diving behavior. This approach not only uncovers spatial positioning but also temporal patterns in whale foraging, surfacing intervals, and movement dynamics within their deep-sea habitat.

The study’s comprehensive acoustic approach was conducted within the framework of the LISTEN project (Long-term Investigations into Soundscapes, Trends, Ecosystems, and Noise), a collaborative initiative led by NOAA’s Southeast Fisheries Science Center and partners, including the Scripps Institution of Oceanography. The project aims to expand understanding of marine soundscapes and the effects of anthropogenic noise on cetacean populations, which is increasingly pressing given the growth of offshore industrial activities.

Publishing their findings in the open-access journal PLOS One, the research team has set a new standard for marine mammal study methodology. The paper, “Beaked whale dive behavior and acoustic detection range off Louisiana using three-dimensional acoustic tracking,” outlines the technical innovations and biological discoveries enabled by these acoustic techniques and underscores their implications for conservation science.

Funding for this research was provided through NOAA’s RESTORE Science Program as part of a grant focused on monitoring long-term trends in cetacean populations throughout the Gulf of America. Additional support came from the Deepwater Horizon Open Ocean Trustee Implementation Group’s project aimed at reducing the impacts of anthropogenic noise on cetaceans. This combined support highlights the collaborative and multidimensional effort to mitigate human impacts on marine ecosystems.

In sum, this study demonstrates the remarkable potential of passive acoustic monitoring to pierce the veil of the deep sea and illuminate the lives of some of its most enigmatic residents. Through unprecedented acoustic tracking of beaked whales’ deep-diving behavior, researchers are opening doors to new understanding and more effective stewardship of the ocean’s fragile ecosystems amid an era of increasing anthropogenic pressures.

Subject of Research: Animals

Article Title: Beaked whale dive behavior and acoustic detection range off Louisiana using three-dimensional acoustic tracking

News Publication Date: 4-Feb-2026

Web References:
https://doi.org/10.1371/journal.pone.0340398

References:
Frouin-Mouy, H., Frasier, K.E., Hildebrand, J.A., Snyder, E.R., Wiggins, S.M., Garrison, L.P., Soldevilla, M.S. (2026). Beaked whale dive behavior and acoustic detection range off Louisiana using three-dimensional acoustic tracking. PLOS One. https://doi.org/10.1371/journal.pone.0340398

Image Credits:
Heloise Frouin-Mouy, Cooperative Institute for Marine and Atmospheric Studies (CIMAS), University of Miami Rosenstiel School of Marine, Atmospheric, and Earth Science

Keywords:
Mammals, Marine life, Cetaceans, Aquatic animals, Marine mammals

The principal investigator, Kirby Parnell, a doctoral candidate with the Marine Mammal Research Program, meticulously analyzed over 4,500 hours of continuous acoustic recordings collected from multiple key monk seal habitats ranging from the inhabited island of Molokaʻi to the sparsely populated Northwestern Hawaiian Islands. His team identified more than 23,000 individual vocal events classified into at least 25 unique call types, thereby demonstrating a far richer and nuanced vocal repertoire than previously anticipated. This upturn in detected vocalizations challenges the longstanding assumption that monk seals relied on relatively simple acoustic signals, suggesting that underwater sound production plays a far more integral role in their social and ecological interactions.

The deployment of passive acoustic recorders allowed this unprecedented insight into an otherwise cryptic behavioral aspect of Hawaiian monk seals, which spend most of their lives underwater where direct human observation is impractical. The study revealed not only a significant expansion of call diversity but also unexpected combinational vocal behaviors. Unlike previous understandings, the seals are capable of linking discrete call elements in sequences, effectively creating “combinational calls.” This phenomenon, previously undocumented in any pinniped species, points to a hitherto unknown level of complexity in marine mammal communication systems, akin to syntax in human languages, and opens new avenues for exploring cognitive capacities in these marine mammals.

Among the newly characterized vocalizations is a novel call type designated the Whine, uniquely produced during foraging activities. Until now, the behavioral context of seal vocalizations has been predominantly associated with social interaction, mating, or territorial displays. Observing an elemental call correlated with active prey pursuit is especially significant, as this is only the second recorded example across seal species that links vocal activity explicitly to foraging. This finding suggests that Hawaiian monk seals may employ acoustic signals not only for reproductive or social purposes but may also utilize sound as an ecological tool for hunting, potentially aiding in prey detection or coordination in complex underwater environments.

These findings carry substantial ecological and conservation implications, particularly considering that the Hawaiian monk seal is one of the most endangered marine mammals globally and Hawaiʻi’s only endemic seal species. The discovery that their vocalizations predominantly occupy low-frequency acoustic bands—overlapping significantly with anthropogenic noise sources like vessel traffic—raises urgent concerns about acoustic interference, which could impede critical communication behaviors. Mitigating noise pollution and protecting acoustically favorable habitats become essential for ensuring the survival and reproductive success of this vulnerable population.

Lars Bejder, Director of the Marine Mammal Research Program and a co-author of the study, emphasizes that this research establishes the first robust baseline for underwater acoustic behavior in free-ranging Hawaiian monk seals. Understanding how these animals utilize sound during crucial life-history stages—including foraging, territoriality, social bonding, and reproduction—is foundational for developing effective management strategies. This research enhances the ability to detect subtle behavioral changes in response to increasing ocean noise, thereby informing policymakers and conservationists aiming to preserve soundscapes vital to the seals’ ecological needs.

The long-term goal of the research team is to develop sophisticated, automated acoustic detection algorithms capable of real-time monitoring of monk seal vocalizations across their range. Automated systems would dramatically improve data acquisition efficiency, allowing continuous, non-invasive surveillance of population dynamics, behavioral states, and stress responses induced by environmental changes. This technological advancement represents a paradigm shift in marine mammal monitoring, facilitating conservation actions that are both timely and spatially comprehensive.

From a methodological standpoint, this study exemplifies the power of interdisciplinary collaboration, combining expertise from marine biology, bioacoustics, data science, and ecology. Graduate and undergraduate students from the University of Hawaiʻi at Mānoa led the labor-intensive annotation of over 23,000 calls, a process that involved meticulous manual classification supplemented by developing initial automated tools. Additionally, international cooperation was fostered with colleagues from France and NOAA Fisheries’ Pacific Islands Fisheries Science Center, highlighting the global importance of Hawaiian monk seal conservation.

The deployment of acoustic recorders in remote and sensitive habitats such as the Papahānaumokuākea National Marine Sanctuary was facilitated by NOAA Fisheries’ Hawaiian Monk Seal Research Program. These protected areas provide invaluable natural laboratories for studying these animals away from intense human activity, allowing the capture of authentic behavioral acoustics essential to rigorous ecological inference. However, as human maritime traffic and ocean noise increase worldwide, ongoing monitoring within these sanctuaries will serve as a critical indicator of anthropogenic impact on marine ecosystems.

This research not only enriches scientific understanding but also resonates culturally within Hawaiʻi, where the monk seal is a treasured endemic species intertwined with local tradition and environmental identity. The progressive uncovering of their hidden acoustic world invites deeper appreciation and a renewed call for stewardship. The study’s revelations about the complexity of seal vocal communication enhance public engagement and underscore the urgency of protecting marine ecosystems from noise pollution and other anthropogenic threats.

In summary, this pioneering study dramatically expands the known vocal repertoire and communication ecology of Hawaiian monk seals, revealing a sophisticated acoustic network characterized by intricate call combinations and foraging-related sounds. It sets a new benchmark for marine mammal bioacoustics and offers vital insights for the protection of one of the ocean’s most endangered pinnipeds. Future research will further elucidate the behavioral contexts of these vocalizations, paving the way for innovative conservation technologies and enhanced ecosystem management approaches.

Subject of Research: Animals

Article Title: [Not provided]

News Publication Date: 11-Nov-2025

Web References:

• Marine Mammal Research Program, University of Hawaiʻi: https://www.mmrphawaii.org
• NOAA Hawaiian Monk Seal Research Program: https://www.fisheries.noaa.gov/species/hawaiian-monk-seal/science
• Papahānaumokuākea National Marine Sanctuary: https://sanctuaries.noaa.gov/papahanaumokuakea/

Image Credits: Krista Jaspers

Keywords: Hawaiian monk seal, Neomonachus schauinslandi, marine mammal bioacoustics, underwater vocalizations, endangered species, combinational calls, foraging vocalizations, passive acoustic monitoring, ocean noise pollution, marine conservation, Papahānaumokuākea, pinniped communication