【BBC地球脉动】淡水 04

英语自学网

The fish they hunt are scarce and salamanders have poor eyesight. But sensory nodes on their head and body detect the slightest changes in water pressure. Free from competition, these giants can dine alone. Pickings are usually thin for the salamanders, but every year some of the world's high rivers are crowded by millions of visitors. The salmon have arrived. This is the world's largest fresh water fish migration. Across the northern hemisphere salmon, returning from the ocean to their spawning grounds, battle their way for hundreds of miles upstream. Up here, there are fewer predators to eat their eggs and fry. A grizzly bear. From famine to feast, he's spoilt for choice. This Canadian bear is very special. He's learnt to dive for his dinner.它们能捕到的鱼类不多。它们视力很差，但是它们头上和身体上的感觉器可以感到水中压力最微弱的变化。它们没有竞争者，所以可以单独享受猎物。隐鳃鲵的食物来源很少，但世界上的某些高山河流每年都会涌来大量的来访者。
鲑鱼来了。这是世界上最大规模的鱼群迁徙活动。在整个北半球，鲑鱼都会经过近千公里的艰难回游，溯流而上，从海洋返回到产卵地。上游的这些地方，只有少数食肉动物来吃它们的卵和孩子。这是一只棕熊。它看到美餐，急不可耐了。加拿大的棕熊非常特别，它学会了潜水捕食。