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Giant salamanders, the world's largest amphibian, almost two metres long.
大鲵——世界上最大的两栖动物，几乎能长到2米长
They're the only large predator in these icy waters. They begin their hunt at night.
它们是这些冰水中唯一的大型掠食动物。夜幕降临，它们开始捕猎
These salamanders have an exceptionally slow metabolism.
大鲵的新陈代谢十分缓慢
Living up to 80 years, they grow into giants.
它们能活80多年，因此长得十分巨大
The fish they hunt are scarce and salamanders have poor eyesight.
可供大鲵捕食的鱼非常稀少，而且它们的视力也很差
But sensory nodes on their head and body detect the slightest changes in water pressure.
可是它们头上和身上的感官突起能觉察出最轻微的水压变化
Free from competition, these giants can dine alone.
由于没有竞争，这些大家伙得以独自享用美食
Pickings are usually thin for the salamanders,
大鲵的收获通常都比较少
but every year some of the world's high rivers are crowded by millions of visitors.
而世界上的高山河流每年都将迎接成千上万的来访者
The salmon have arrived. This is the world's largest freshwater fish migration.
鲑鱼来了。这是世界上规模最大的淡水鱼洄游
Across the northern hemisphere, salmon, returning from the ocean to their spawning grounds,
鲑鱼穿越整个北半球，从海洋回到它们的产卵地
battle their way for hundreds of miles upstream.
奋力逆流而上数百英里
Up here there are fewer predators to eat their eggs and fry.
只因上游很少有捕食鱼卵和鱼苗的掠食者。
