The narwhal (Monodon monoceros) is one of the Arctic's most iconic and least-understood cetaceans. Its dependence on sea ice for feeding and protection makes it one of the most climate-vulnerable marine mammals, despite a current population estimated at approximately 170,000 individuals.
Narwhals respond to boat disturbance and killer whale predation with a paradoxical stress response: heart rate drops dramatically while they swim away rapidly, creating dangerous oxygen demand. This response — thought to be an evolutionary freeze reflex — may cause cardiac events in extreme disturbance situations. As sea ice retreats, narwhals lose refuge from killer whales and spend more time in open water where they are vulnerable. Entrapment in rapidly freezing leads during autumn — where narwhals can be trapped in ice before they migrate — causes mass mortality events through suffocation as breathing holes freeze over. Climate change is increasing the frequency of these events.