Narwhals get physiologically disrupted because of seismic survey ship noise

Researchers have found that narwhals get physiologically disrupted because of the loud noise from seismic air guns used in oil exploration. While the effect is not direct, the disruption is caused in response to the intense exercise as the animals try to escape the noise.

The findings are published in the Journal of Functional Ecology and it provides the first look at the impact of seismic noise on the physiological responses of a deep-diving cetacean. According to researchers the combination of extremely low heart rates, increased heart rate variability, and high-intensity exercise during deep dives presents a significant physiological challenge for narwhals, especially if the disruptions are prolonged as would be likely during extended oil exploration activities.

While the narwhals are generally out of reach as they live in high Arctic waters where sea ice has helped isolate them, the decline in polar ice is making the region more accessible to shipping, natural resource exploration, and other human activities.

The researchers recorded not only extremely low heart rates during noise exposure, but also increased variability, with heart rates switching rapidly between extremely low rates associated with fear and fast rates associated with intense exercise. Reduced heart rate, or bradycardia, is a normal part of the mammalian dive response, but during normal dives the heart rate still increases with exercise. In addition, narwhals and other deep-diving marine mammals usually save energy by gliding rather than actively swimming as they descend to depth.

During noise exposure, the narwhals performed 80% less gliding during diving descents, their swimming strokes exceeded 40 strokes per minute, their heart rates dropped below 10 beats per minute, and their breathing at the surface was 1.5 times faster. Overall, this unusual reaction is very costly in terms of energy consumption, Williams said.

Over the past two decades, noise from human activities such as military sonar has been linked to mass strandings of deep-diving cetaceans, mostly beaked whales. These deep-diving species are extremely difficult to study, and it was only through a partnership with indigenous hunters that researchers were able to attach monitoring devices to narwhals.

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