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Paradoxical escape responses by narwhals (Monodon monoceros)

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Science  08 Dec 2017:
Vol. 358, Issue 6368, pp. 1328-1331
DOI: 10.1126/science.aao2740

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The flight of the narwhal

Animals tend to respond to threats with the well-known behaviors of fight, flee, or freeze, each of which requires a different suite of physiological responses. Marine mammals face particular challenges because they may flee into an environment where oxygen is not available and pressure must be accommodated. Williams et al. placed a submersible electrocardiograph, depth, and acceleration recorder on narwhals after they were freed from entanglement. The animals displayed contrary cardiovascular responses simultaneously, which placed extreme stress on the cardiovascular system and the tissues that it protects.

Science, this issue p. 1328

Abstract

Until recent declines in Arctic sea ice levels, narwhals (Monodon monoceros) have lived in relative isolation from human perturbation and sustained predation pressures. The resulting naïvety has made this cryptic, deep-diving cetacean highly susceptible to disturbance, although quantifiable effects have been lacking. We deployed a submersible, animal-borne electrocardiograph-accelerometer-depth recorder to monitor physiological and behavioral responses of East Greenland narwhals after release from net entanglement and stranding. Escaping narwhals displayed a paradoxical cardiovascular down-regulation (extreme bradycardia with heart rate ≤4 beats per minute) superimposed on exercise up-regulation (stroke frequency >25 strokes per minute and energetic costs three to six times the resting rate of energy expenditure) that rapidly depleted onboard oxygen stores. We attribute this unusual reaction to opposing cardiovascular signals—from diving, exercise, and neurocognitive fear responses—that challenge physiological homeostasis.

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