In the realm of marine ecology and conservation, the use of underwater passive acoustic monitoring has revolutionized the way scientists observe and analyze marine animal behavior. This technique, valued for its non-invasiveness, enables researchers to capture the natural sounds produced by marine fauna, thereby providing critical insights into their biodiversity, habitual patterns, and responses to environmental stressors, particularly anthropogenic noise pollution. However, a recent comprehensive study led by Associate Professor Evgeny A. Podolskiy from Hokkaido University reveals an intriguing deviation from this assumed non-intrusive interaction paradigm, specifically in the context of Arctic narwhals.
The study, conducted over a two-year period in the icy waters of Northwest Greenland’s Inglefield Bredning Fjord, challenges the conventional belief that passive acoustic monitoring does not influence marine mammals. Using a collaborative approach, the research team worked alongside the indigenous Inughuit hunters to deploy three hydrophones at depths ranging from 190 to 400 meters. These devices recorded continuously through significant portions of 2022 to 2024, capturing over 4,000 hours of underwater acoustic data. Intriguingly, the narwhals exhibited repeated physical interactions with these scientific instruments, a behavior that was unexpected given the anticipated wariness of wildlife toward unfamiliar objects.
Narwhals, often referred to as the ‘unicorns of the sea,’ exhibited a persistent curiosity or possibly confusion as they engaged in various behaviors such as knocking and rubbing against the hydrophones. The devices detected 247 distinct incidents of these interactions, with extrapolations suggesting the real frequency may have been nearly double due to intervals when recordings were paused. Most of these encounters occurred during daytime hours and were spatially distributed between two hydrophones separated by 25 kilometers, indicating that this behavior might be widespread rather than isolated occurrences. This repeated physical engagement is particularly remarkable considering the energetic costs for narwhals to perform such deep dives repeatedly.
From an acoustical perspective, the hydrophones recorded an array of narwhal sounds, including the species-specific echolocation clicks and intense foraging buzzes. These vocalizations crescendoed as the animals approached the moorings, perhaps indicating a heightened state of interest or investigation. Notably, the researchers observed a distinct ‘rubbing’ sound post-foraging buzz, theorized to be the whales’ skin gliding along the device surfaces, a phenomenon that could be associated with molting—a poorly understood biological process in narwhals.
Parallel to the acoustic data analysis, the research team examined the stomach contents of sixteen narwhals, which were harvested by the Inughuit hunters concurrently with the acoustic study. The dietary analysis revealed that cod constituted the primary food source, supplemented by shrimp and squid. Surprisingly, the presence of stones was noted in all sampled stomachs, hinting at possible gizzard-like functions or dietary habits that might influence foraging behavior. The researchers posited that the hydrophones’ shape and placement near the seabed might mimic the physical characteristics of flatfish species such as cod or halibut, potentially misleading the narwhals into mistaking the devices for prey items.
The implications of this finding extend beyond behavioral curiosity to a critical reassessment of the integrity and impact of passive acoustic monitoring methodologies. Traditionally considered non-invasive, these instruments in fact alter the behavior of narwhals, thereby introducing a novel dimension to ecological data interpretation. The authors point out that this attraction could affect the spatial presence and foraging habits of narwhals, thereby potentially biasing the very ecological assessments these devices are intended to facilitate.
In light of these unexpected behavioral responses, the study highlights the necessity of re-evaluating the design and deployment strategies of acoustic monitoring equipment. One suggested mitigation measure involves shortening the mooring lines to reduce physical contact opportunities, thereby minimizing the inadvertent impact on narwhal behavior while preserving data collection efficacy. This recommendation underscores a broader call within marine research to contextualize technological interventions within the framework of animal welfare and ecological validity.
The local knowledge held by the Inughuit hunters provided a valuable ethnobiological perspective that supported the scientific observations. These hunters, accustomed to narwhal behavior in the region, were not surprised by the animals’ interactions with submerged equipment. Their insights helped frame the narwhals’ behavior as potentially playful or akin to scratching movements observed in other cetacean species. However, the scientific team emphasized the unlikelihood of these behaviors being purely recreational due to the substantial energy investment required for deep dives, suggesting that confusion due to prey resemblance remains the most plausible explanation.
This intersection of traditional ecological knowledge and advanced scientific research exemplifies the benefits of integrating indigenous perspectives in contemporary marine studies. Such partnerships facilitate a nuanced understanding of animal behaviors that may otherwise be overlooked or misinterpreted, enhancing both conservation and management strategies.
Furthermore, understanding how marine megafauna interact with both natural and artificial objects underwater advances our comprehension of anthropogenic effects on the Arctic ecosystem. Scientific and industrial infrastructures increasingly populate marine environments, making it imperative to assess their ecological footprints rigorously. The findings from this study advocate for a precautionary approach in deploying monitoring and industrial equipment to mitigate unintended behavioral disruptions in vulnerable species such as narwhals.
In conclusion, the compelling research conducted in the Arctic unveils a fascinating narrative wherein narwhals exhibit unexpected attraction to underwater monitoring moorings, challenging assumptions about observational neutrality in passive acoustic studies. This discovery beckons a broader discourse on the ethics and methods of remote wildlife monitoring and underscores the dynamic interface between technological innovation and natural animal behavior. The study paves the way for refining marine research methodologies to both respect animal welfare and enhance the fidelity of ecological data essential for successful conservation in rapidly changing polar environments.
Subject of Research: Animals
Article Title: Repeated narwhal interactions with moorings challenge safety assumptions of passive acoustic monitoring in the Arctic
News Publication Date: 12-Nov-2025
Web References: http://dx.doi.org/10.1038/s42003-025-09106-4
Image Credits: E. A. Podolskiy, August 2023
Keywords: Life sciences, Marine biology, Marine ecology, Ecosystems
