1. It is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo.
    不仅能够确定鱼群的位置，而且可以根据鱼群回声的特点分辨出是鲱鱼、鳕鱼，这是人们所熟悉的其他鱼。

2. A shoal of fish will do this.
    鱼群也反射声音。

3. So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
    从测定海深到测定鱼群，这一进展比较容易。