Narwhals hit moorings—passive monitoring might not be as non-invasive as beforehand assumed

Underwater passive acoustic recording is important for researchers to watch and research marine animals of their pure setting with minimal disturbance.

“Using passive acoustic monitoring to detect acoustically active animals helps to census biodiversity, understand animal behavior and habitat use, and reduce the negative impacts of human-made noise,” mentioned Associate Professor Evgeny A. Podolskiy of the Arctic Research Center at Hokkaido University in Sapporo, Japan.

“For these reasons, scientists increasingly rely on passive acoustic monitoring to answer fundamental ecological questions and manage conservation.”

Endemic Arctic whales, the narwhals, nevertheless, appear to have developed a robust curiosity in underwater passive recording gadgets. Over the course of a two-year research in Greenland, narwhals repeatedly approached, scanned, and hit deep-sea hydrophones.

In a research revealed in Communications Biology, Podolskiy and colleagues from Hokkaido University and the National Institute of Polar Research analyzed information from Inglefield Bredning Fjord in northwest Greenland. They collaborated with native Inughuit hunters to deploy and retrieve three underwater acoustic recording gadgets to depths starting from 190 m to 400 m.

Unexpected narwhal habits and research findings

The gadgets recorded sounds between August 2022 and May 2024, together with these of narwhals repeatedly knocking and rubbing towards them, of echolocation clicks, and of the foraging ‘buzz’ of narwhals, which received louder as they approached the gadgets.

Altogether, there have been 247 incidents of narwhal hits in additional than 4,000 hours of audio data. These hits have been detected on the 2 deepest recording gadgets positioned 25 km aside. Given that the recordings weren’t steady and had ~15 min pauses, the researchers estimated that the true variety of narwhal hits on the 2 gadgets might have been as a lot as 484–613 over the 2 months of narwhal presence within the space, representing a median of 10–11 hits a day, principally throughout daytime hours.

“Our results suggest that narwhals repeatedly dived to visit the moorings out of playful curiosity or, more likely, due to confusion with potential prey,” Dr. Podolskiy mentioned.

The research included an evaluation of the abdomen contents of 16 narwhals caught in the identical space in August 2022 and 2023 by Inughuit hunters as a part of their subsistence harvest. The evaluation revealed that the narwhal weight loss plan was primarily composed of cod, with smaller quantities of shrimp and squid. The staff additionally discovered stones within the stomachs.

Possible explanations and cultural insights

The researchers speculate that the narwhals would possibly confuse the recording gadgets with cod or halibut close to the seafloor, though they famous that narwhals would possibly have the ability to distinguish positive variations in texture and density by echolocation, like different toothed whales.

They additionally famous that the gadgets typically picked up a protracted “rubbing” sound after the foraging buzz and hit, which they recommended may very well be the sound of the animal’s pores and skin sliding previous the microphone. “Though little is known about molting in narwhals, mooring rubbing could be the associated behavior,” they wrote.

“Inughuit hunters were not surprised by the discovered interaction: they are familiar with narwhal entanglement in unattended gear. They also believe that narwhals like to play and are told so by their parents, and joked that narwhals might scratch their backs, like cats. While this is possible, and other Arctic whales are known to rub their bodies over rocks, it is unlikely due to the high energetic costs of deep diving,” Dr. Podolskiy mentioned.

Implications for conservation and monitoring

The findings elevate questions on whether or not passive acoustic monitoring is definitely as noninvasive because it’s regarded as. The paper demonstrates that narwhals are usually not deterred however somewhat interested in scientific moorings, exhibiting that the presence of those synthetic gadgets can have an effect on the habits of this species.

The authors counsel that quick mooring strains is likely to be a easy precaution to attenuate inadvertent results of observations indispensable for conservation and administration.

“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,” Podolskiy mentioned.