Northern bottlenose whales: The mysterious deep divers of Jan Mayen
17 July 2018
In the early 2000s, mass strandings of beaked whales during military exercises in temperate and tropical waters put the issue of navy sonar and marine mammals on the map. As Paul Wensveen tells us, recent research expeditions to Jan Mayen, a Norwegian volcanic island in the Arctic ocean, suggest northern bottlenose whales—the beaked whales of the Arctic—are also very sensitive to underwater noise.
Against the dramatic backdrop of Jan Mayen’s glacier-covered volcano, Beerenberg, a group of four northern bottlenose whales surfaces to breathe. The animals have been diving for almost an hour, reaching depths of more than 1,500 metres. In this other-worldly environment where sunlight does not penetrate, the whales rely on their hearing and ultrasonic clicks to find food and stay in contact with each other. The clicks function as an acoustic flashlight.
Suddenly, an unusual sound is produced near the surface of the sea several kilometres away from the whales. The sound is barely audible to them at first, but it repeats every 20 seconds and grows louder each time. Curious by nature, the animals stop foraging and move in the direction of the source. Soon, however, the synthetic sonar sound is loud enough to provoke a large-scale avoidance response. Many whale groups in the area travel dozens of kilometres away from the source of the noise, and only return to their normal feeding behaviour hours later.
This scenario is based on actual events observed during an experiment in 2013 near the remote island of Jan Mayen (71° N), located on the North Atlantic ridge; the sonar sounds were being played by researchers. The results of subsequent experiments in 2015 and 2016 suggest that the whales’ avoidance response was not a fluke. The scientists who were lucky enough to study these magnificent animals used controlled playbacks and careful monitoring along with on-animal tags and passive acoustic receivers. The sonar sounds they played for the whales were softer than real sonar and played for shorter periods. The concern is that actual sonar operations many lead to even longer and larger-scale behavioural responses than those observed.
Extreme lifestyle makes bottlenose whales hard to study
We know very little about northern bottlenose whales because they spend only minutes at the surface and often dive to depths greater than 1,000 metres, disappearing for up to an hour at a time. Dives lasting as long as two hours have been reported. However, it is believed that populations are still recovering from the whaling era. While only one report of a sonar-induced mass stranding involved a northern bottlenose whale, other forms of disturbance may be more concerning from a conservation viewpoint.
Researchers think beaked whales regularly exposed to predictable noise may learn to tolerate it. But this may not be the case for bottlenose whales that have spent their lives in the largely pristine acoustic underwater environments of the Arctic.
The northern bottlenose whales of Jan Mayen are representative of other beaked whales living in areas without frequent exposure to sonar, so they provide an important case study. The evidence suggests that beaked whales near navy training ranges respond less to distant and predictable sound sources than to close and unpredictable ones at the same decibel level. From this, we infer that they may have learned to tolerate certain noise exposures based on previous experience. But this might not be the case for whales that have spent much of their lives in the largely pristine acoustic underwater environments of the Arctic, such as narwhals and northern bottlenose whales, which both seem highly sensitive to man-made noise.
Navy operations and oil and gas exploration both rely on sound to “see” under water, and this is unlikely to change any time soon. The North Atlantic Treaty Organization (NATO) is also showing renewed interest in the Greenland–Iceland–UK gap, and the Arctic is strategically important in anti-submarine warfare. In addition, climate change is likely to lead to increases in oil and gas exploration and heavy shipping in the Arctic. Given the scale of the challenges ahead—and the difficulties involved in studying marine mammals—all stakeholders need to continue to work together to minimize the impact of man-made noise in the area and protect the marine mammals that live there.
Paul Wensveen is a University of Iceland researcher focusing on the impacts of noise on marine mammals. He is also a member of the “3S Project,” an international research consortium studying the effects of navy sonar on cetaceans.