. Commercial fisheries review. Fisheries; Fish trade. 21. Fig, 1 - Schematic drawing of Lampara trawl rigged for bottom fishing. Door Spread versus Warp Length 40-] ^___^ g i''^- • j • 8 . c \,^^^^^..%--'-'-^^'''^ -"T §20- 1 __%-—--^ ^ 10- 1 c ) 50 100 150 200 250 300 Length of towing worp out in fothoms Fig, 2 - Relation of door spread and warp length for the Lampara trawl and 400-niesh Eastern. Both nets were towed at similar speeds over the bottom --Lampara at 310 and 400 Eastern at 240 Lampara net was always lower in compara- tive tows than 400-mesh Eastern trawl. Acoust
. Commercial fisheries review. Fisheries; Fish trade. 21. Fig, 1 - Schematic drawing of Lampara trawl rigged for bottom fishing. Door Spread versus Warp Length 40-] ^___^ g i''^- • j • 8 . c \,^^^^^..%--'-'-^^'''^ -"T §20- 1 __%-—--^ ^ 10- 1 c ) 50 100 150 200 250 300 Length of towing worp out in fothoms Fig, 2 - Relation of door spread and warp length for the Lampara trawl and 400-niesh Eastern. Both nets were towed at similar speeds over the bottom --Lampara at 310 and 400 Eastern at 240 Lampara net was always lower in compara- tive tows than 400-mesh Eastern trawl. Acoustic Spread Measuring System Acoustic measuring equipment was opera- ted during all tows in an effort to obtain in- formation on trawl door spread. Method and Materials: The measuring system consisted of the ship's echo sounder, 2 modified magnetostrictive transducers, and an oscilloscope. The transducers were in- stalled in streamlined fiberglass-reinforced epoxy housings and mounted facing each other, one attached to tailchains of each trawl door. Electro-mechanical towing cable provided a circuit from transducers to boat. The trans- ducers were connected in parallel through a transfer switch in wheelhouse to ship's sounder. An oscilloscope was connected across transducer leads to present a visual display of the signal. Results: The gear spread measuring sys- tem produced useful information on trawl door spread. Unfortunately, the oscilloscope readout system apparently did not function because signal was too weak. The sounder's amplifier, though, increased signal so during most drags a reading was obtained on the recording paper. Door Attitude Studies The results of the door attitude studies were inconclusive because the adjustments resulted in only minor variations in spread. Initial attempts indicate that large changes in tailchain length are needed to produce measurable changes in door attitude. Universal Trawl Evaluation The Universal trawl, designed to fish on and o
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