by slapping fins on the surface. 以此相互传送声音信号

141. These are colder, rougher, and more dangerous waters.
     这些是更冷、更狂暴、更多危险的水域
142. Mother and calf must stay close.
     母鲸和小鲸鱼必须靠得很近
143. They can send sound signals to one another, above the roar of the ocean
     他们可以通过拍打海面 制造超越海洋轰鸣的的声音
144. by slapping fins on the surface.
     以此相互传送声音信号
145. In winter, the temperate seas are lashed by violent storms.
     在冬季 气候温和的海域被风暴肆虐着
146. The turbulence stirs the water, and draws nutrients up from the depths
     湍流激起海水 将深处的养分搅上来
147. but nutrients alone can not support life.
     但只有养分并不能维持生命

来自《行星地球 第一季 第九集 Planet Earth S01E09 海洋》第 144 行