Part of a depth recorder's printout: heavy line near center is the bottom; 

 clustered specks at left turned out to be a school of Spanish mackerel; 

 those at right were king mackerel 



fish located, if the device is used 

 correctly. The wrong pulse length can 

 make a small fish look like a large fish 

 or schools of fish look denser than they 

 really are. Amos says a shorter pulse 

 length distinguishes smaller objects 

 better and provides a more accurate 

 representation of the fish's size. But 

 the shorter pulse length can not be 

 used continuously in deep waters 

 without sacrificing the seabed profile. 



For deeper waters, fishermen need a 

 recorder with a variable pulse length or 

 a phase-ranging feature. The variable 

 pulse length allows the fisherman to 

 temporarily shorten the pulse length to 

 look inside a school of fish. Using phase 

 ranging, the fisherman can focus on a 

 particular section of the water column. 



For fishermen buying a paper re- 

 corder, Amos suggests equipment that 

 uses paper no smaller than four inches 

 wide. The recorder compresses hun- 

 dreds of feet of sea information into a 

 few inches of recorder paper. For the 

 most detail possible, fishermen should 

 buy a recorder that uses wider paper. 



Correct installation of the 

 transducer can make a decided dif- 

 ference in how well the depth recorder 

 works. The transducer should be 

 mounted on the boat's hull in an area 

 with minimum noise interference from 

 the boat's machinery or from move- 

 ment through the water. Amos 

 suggests mounting the transducer one- 

 third to one-half of the vessel's length 

 from the stem post, preferably beneath 

 the fish-storage area. 



And, like a musical instrument, a 

 depth recorder may need a little fine- 

 tuning after installation. A fisherman 

 should make sure he is very familiar 

 with the recorder's variable controls 

 before adjustments are made. 



The gain control, probably the most 

 important variable control, requires 

 careful adjustment for the recorder to 

 operate at peak efficiency. The gain 

 control works like the volume control 

 on a stereo, picking up more sound and 

 from farther away as it is turned up. If 

 the gain control is turned up too much 

 it will register extraneous noises, such 

 as vibration from the boat's engines, as 

 schools of fish. 



For fishermen wanting more 

 detailed information about the seabed 

 or midwater regions, add-on functions 

 are available for some depth recorders. 

 The most common "extra" is the 

 seabed locked-scale expansion unit. 

 With this feature, a fisherman can 

 magnify the display of any area he 

 chooses over a seabed. The expansion 

 unit allows accurate measurement of 

 the fish echoes and their exact depth 

 above the seabed. Another expansion 

 unit, the midwater expansion, 

 magnifies an area of the water column, 

 but the data is not locked to the 

 seabed. Another add-on feature is the 

 net sounder or net monitor, used to 

 provide data on the performance of the 

 trawl nets. 



Depth recorders were developed 

 prior to World War II for navigational 

 purposes, says Amos. But during the 



war, depth recorders were refined and 

 used to look for enemy submarines and 

 mines. After the war, an industry 

 developed around these new elec- 

 tronics as manufacturers recognized 

 their value to commercial fishing. By 

 the late 1950s, most offshore commer- 

 cial fishermen had installed depth 

 recorders abroad their boats. Now 

 every commercial and many 

 recreational fishermen have at least 

 one depth recorder and sometimes as 

 many as four recorders, Amos says. 



In the future more automation and 

 computerization is likely for the com- 

 mercial fishing industry, says Dave 

 White, a manufacturing representative 

 for Epsco Marine Systems of Seattle. 

 "Instead of having six thousand boxes 

 hanging from the ceiling giving loran, 

 depth recorder and other information, 

 it's all going to be in a . . . video com- 

 puter console." he says. 



White says he already knows about 

 20 West Coast fishermen who are using 

 computers. "There is a fisherman in 

 Seattle who put a computer on his boat 

 and everybody laughed. What he did 

 was enter all the information gathered 

 while fishing into the computer," 

 White says. "After two to three years 

 of entering data, he was able to punch 

 the computer, and, based on the day's 

 conditions, determine the best places 

 to fish. His fish catch actually in- 

 creased 25 percent." 



—Kathy Hart 



