Science: Calling All Fish

Up the west coast of England last week crept the French Navy's minesweeper Siam, spying on schools of herring. Its assignment : to learn how to hunt fish with ASDIC (developed for the Allied Submarine Device Investigation Committee, from whose initials it took its name).

ASDIC, designed for submarine hunting, sends ultrashort sound waves through the water and any sizable object reflects them. During the war, this fact frequently caused depth-bombing of whales, torpedoing of schools of pilchards. But as ASDIC and its operators improved, they learned to distinguish skillfully between echo-making objects, could even tell big from little fish.

By using this principle, says hearty Jean Le Gall of the French Bureau of Fisheries, it may be possible to develop a practical, commercial fish-ASDIC. The captain of a fishing boat equipped with such a device would need to do little guessing. He would turn on his ASDIC, and all fish within range would echo back, "Here we are."

Several observers, M. Le Gall among them, have seen schools of fish turn toward the ASDIC-emitting vessel. Why they do it, he does not know, or even whether they do it regularly. He intends to find out. But if fish do—voilà! In future, schools of herring may be seduced by ASDIC right into kippering plants.