FOOD SHORTAGES AND THE SEA— MERRIMAN 377 



fatliometers on trawlers on the Banks, we would simply turn a switch 

 and a light would flash at short intervals opposite the appropriate 

 depth on a dial reading from zero to a hundred fathoms. With such 

 a mechanism the skipper could drag his net in a gully or depression 

 where he had reason to think there were heavy concentrations of fishes. 



The fathometer underwent rapid improvement, and the utilization 

 of supersonic frequencies made it a i^recision instrument so delicate 

 that it could detect much more than absolute depth. Double "echoes'" 

 began to show up on occasion, one clearly from the bottom and the 

 other from intervening layers at mid-depths or less. It became clear 

 that the second reflection, or false bottom, could only arise from con- 

 centrations of fishes or other organisms. In the herring fishery of 

 the Pacific coast, schools of varying size occur at mid-depths. 



In the old days the fisherman had to depend on a combination of 

 intuition, knowledge, and experience. When a herring seiner arrived 

 in an area where there might be fish, it was common practice to let 

 down a great length of piano wire with a weight attached ; a skilled 

 man could tell whether the concentration was light, medium, or heavy 

 by the frequency of pings as the schooling fish hit the wire, and on 

 his say-so was based the decision to set or not to set the net. Nowadays 

 the echo-sounder performs the same function; it, too, can judge the 

 size and concentration of the school by the intensity and depth of 

 the recorded echo. Amazing hauls are made on occasion, as this story 

 from The Pacific Fisherman for January 1950 shows : 



Something close to an all-tiiue record for a single set of herring off the British 

 Columbia coast was achieved by Nelson Bros. Fisheries' Seiner Western Ranger, 

 Nov. 2, with a haul of 1,180 tons of fish. . . . (This) was made possible through 

 the practical application of electronics to fishing. The great school of herring 

 was detected by Capt. Hans Stoilen on his vessel's echo-sounder in weather so 

 foggy that no sign of fish could be seen. Acting on information provided by 

 his sounder, he set his net blind and made this enormous catch. . . . Western 

 Girl, the flagship of the Nelson Bros, fleet, was close by. . . . The two boats 

 were in constant radio telephone communication with each other while the opera- 

 tion was being completed. 



But the echo-sounder alone has not served to bring about a vast 

 increase in the catch of Pacific herring. To be sure, it has replaced 

 a more time-consuming method, it has made fishing more mechanical, 

 and at times it has made possible the detection of herring that might 

 otherwise have escaped the fishermen. But it has not, singlehanded, 

 brought about an increase in the catch of the order of magnitude that 

 here concerns us. The fisherman's accumulated Imowledge, his gam- 

 bling instinct, and other personal factors will not quickly be subordi- 

 nated to mechanical aids of this sort. 



Another discovery resulting from the perfection of echo-sounding 

 devices is the "deep scattering layer," a new term in oceanography. 



