but are also concealed by the sound of waves breaking on the shore... 而且会被海浪拍击海岸的声音掩盖

147. The family keeps in constant contact with whispered calls.
     一家人会通过轻声低语保持联系
148. New research has revealed
     最新的研究表明
149. that in shallow coastal waters, their calls not only fade quickly,
     在沿海浅水区 它们的声音不仅会迅速消失
150. but are also concealed by the sound of waves breaking on the shore...
     而且会被海浪拍击海岸的声音掩盖
151. ..so they won't attract the attention of predators.
     因此不会吸引捕食者的注意
152. Not so long ago, these whales faced a graver threat.
     不久之前 这些鲸鱼面临着更严重的威胁
153. They were hunted to near extinction.
     它们遭到猎杀 濒临灭绝

来自《行星地球 第三季 第一集 Planet Earth S03E01 海岸》第 150 行