The melting of sea ice in the Arctic is expected to result in a greater presence of humans and infrastructure in the region. However, little is known about the likelihood of Arctic-endemic animals becoming entangled or interacting with human-made objects. Understanding animals' interaction with industrial and scientific infrastructure can help reduce impacts on wild animals and improve our ability to implement and interpret autonomous field observations.

Here, we applied passive acoustic monitoring to study narwhals (Monodon monoceros) in Northwest Greenland. This method is known as a transformative tool for applied ecology and has been increasingly used for conservation and biodiversity monitoring. Its application is based on a belief that (contrary to active acoustics) it does not interfere with animals' behaviour.

However, the present study identified a high level of curiosity in narwhals with respect to deep-water scientific moorings in Greenland and explained recent cases of lethal entanglements in narwhals. Using acoustic data from different locations and years together with stomach content analysis, it is shown that foraging narwhals engaged in repeated hits on seafloor moorings (on average, 11 times per day), presumably out of playful curiosity or due to confusion with food items. It is a behaviour previously unknown for unconfined odontocetes.

These results imply that oceanographic monitoring might alter the natural behavior of narwhals and pose a risk to their well-being, which should be further investigated and accounted for in the design. Our findings reveal the intrusive nature of a key ecological method (passive acoustic monitoring) and should inform policy-making concerned with the management and conservation of narwhal habitats. As a precaution against entanglement, we suggest using the shortest lines possible.