But global changes now threaten the great blooms of plankton on which the whales depend. 但是全球环境的变化 让蓝鲸赖以生存的浮游生物急剧减少

298. They take many tons of water into their ballooning throats in a single gulp and sieve out what it contains.
     它们一口可吃进几吨的海水 然后再过滤出想要的东西
299. Every day, each one swallows some four million krill.
     每天一头蓝鲸可以吃进400万条磷虾
300. Such gargantuan harvests depend on the continuing fertility of the oceans
     这样巨大的食量依赖富饶的海洋的不断提供
301. But global changes now threaten the great blooms of plankton on which the whales depend.
     但是全球环境的变化 让蓝鲸赖以生存的浮游生物急剧减少
302. Once and not so long ago
     曾经在不久以前
303. three hundred thousand blue whales roamed the oceans
     30万头蓝鲸让海洋看上去充满生气
304. now, less than three percent of that number remains.
     现在,只有不足9000头

来自《行星地球 第一季 第十一集 Planet Earth S01E11 海洋深处》第 301 行