December 7, 2017—Narwhals swim the icy Arctic Ocean, and dive to its dark depths, so they're a challenge to study. To learn about their biology, scientists attached sensors to narwhals. Monitors tracked heart rate, swimming strokes, and diving depth, in a resting state, during a dive just after "escape," and later, in a normal dive. Suction cups on the sensors released, and they floated up for retrieval. Animal species tend to react to a threat in one of two ways: For some, stress raises the heart rate and activity level. Other species freeze up, and their heart rate lowers. Narwhals don't fit either pattern. When they're released from nets, narwhals' heart rate plummets, even as they speed away. So they burn through ready oxygen, pushing tissues' limits. Researchers fear low oxygen may hurt cognition, causing unsafe behaviors, and adding to the risk narwhals face from human presence. READ:
Heart Monitor-Wearing Narwhals Reveal the Dangers of Human Encounters
