When biologist Terrie Williams checked the heart-rate monitors she had put on wild narwhals in Greenland, she found bizarre readings. They showed that after interacting with humans, the animals’ heartbeats plummeted from 60 per minute to just three or four. At the same time, the animals were swimming fast, moving their fins as quickly as possible. Williams compares the paradoxical reaction to ‘trying to run away while holding your breath’ and scientists speculate it might be putting the narwhals’ health at risk.
When a mammal meets a threat, it tends to show one of two reactions: active or passive. Active reactions are usually a fight or flight response, while passive can mean the animal goes into a frozen or a sleep state. Usually, a narwhal reacts actively. As one of the deepest diving cetaceans it can flee to deeper water. ‘These are deep-diving marine mammals,’ says Williams, ‘but we were not seeing normal dives during this escape period.’ Its sluggish heart rate after encountering humans suggests it is also trying a passive reaction at the same time.
The responses are complicated by the narwhals’ limited access to oxygen underwater. Williams calculated that the narwhals used 97 per cent of their oxygen stores in these escapes from humans, well exceeding the 53 per cent of stores they use in escape from other threats. It is possible that restriction of oxygen to their brains could confuse or disorientate them in the face of new and unfamiliar threats. ‘The Arctic seascape has changed for marine mammals with the rapid degradation of ice cover,’ writes Williams. Less ice means the narwhals are being quickly exposed to activity they did not evolve with, such as more shipping, oil exploration and – a key concern – more noise. ‘Unlike threats from predators such as killer whales,’ says Williams, ‘noise from sonar or a seismic explosion is difficult to escape. Problems can start if the whales try to outrun it.’
This was published in the February 2018 edition of Geographical magazine.
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