蓝鲸是地球上体型最庞大的动物。在印度洋的一片水域， 它们曾因捕鲸活动而几乎灭绝，而几十年后， 这片水域的蓝鲸数量已经恢复。 The deep very low frequency song of the blue whale is difficult for us to hear.Depending on what device you're listening on, it might be ...