Narwhal population affected by underwater noise pollution海洋噪音污染导致一角鲸数量下降

　　Of all the creatures on the planet, the narwhal is one of the strangest looking. It's a whale which has a large protruding tusk coming out of its head; that's how it got its nickname, the unicorn of the sea. They live in the Arctic Ocean off the coast of Canada, Russia and East Greenland. However, experts say some populations of narwhal could be extinct by 2025, and it's all because of noise pollution.

　　Narwhals rely on echolocation, which they use to find food and navigate their surroundings. The animal produces a sound wave which bounces off an object. They pick this reflected sound up through their lower jaw, and information on features like size and speed passes to their ears.

　　However, increase in human marine activity, as well as climate change, has resulted in the Arctic Ocean becoming noisier, which means it's more difficult for narwhals to rely on sound. Susanna Blackwell, who studies the effects of underwater noise on marine animals, told the BBC that there is noisier activity in the Arctic Ocean than ever because, as sea ice melts, new navigation routes are opening. And while icebergs breaking and creaking have been part of the ocean soundscape for hundreds of years, man-made noise is much harder for animals to adapt to, particularly as these changes are so sudden.

　　Research published in Science Advances in 2023 recorded the reactions of narwhals to the simulated noises of oil expeditions made by a patrol vessel. The scientists tagged and tracked the creatures and found that, on hearing these sounds, they ended deepdives and stopped clicking, the echolocation signal they use for finding food underwater. This is the same reaction narwhals have to orcas, who hunt them, meaning human-made noise could trigger the creature's 'threat button'.

　　So, what can we do? Charlotte Findlay, a postdoctoral fellow at Aarhus University, says "noise is actually quite easy to solve. We need to either turn it off or turn it down."词汇表

　　narwhal 一角鲸

　　protruding 突出的，鼓出来的

　　tusk （动物的）长牙

　　unicorn of the sea 海洋独角兽

　　extinct 灭绝的

　　echolocation （动物的）回声定位

　　bounce off 从…反弹

　　lower jaw 下颌骨

　　marine activity 海洋活动

　　marine animals 海洋动物

　　navigation route 航线

　　soundscape 声景

　　adapt to 适应

　　tag 标记，给动物植入定位芯片

　　track 跟踪

　　deep dive 深潜

　　click （鲸鱼等动物）发出短而尖的声音

　　orca 虎鲸

　　hunt 捕猎