Repeated narwhal interactions with moorings challenge safety assumptions of passive acoustic monitoring in the Arctic.

Passive-acoustic monitoring is known as a non-intrusive and transformative tool for ecology and has been increasingly used for conservation and biodiversity monitoring. This study, however, identifies a high level of curiosity in narwhals (Monodon monoceros) with respect to scientific moorings and partially explains recent cases of narwhal entanglements. 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 (11 times per day), presumably out of curiosity or due to confusion with food items. It is a behavior previously unknown for odontocetes. These results imply that oceanographic monitoring might alter the behavior of whales and poses a risk to their well-being, which should be investigated and accounted for in design. Our findings reveal the intrusive nature of a key scientific method, with implications for the management and conservation of vulnerable marine mammals.