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![A converted ferryboat is used in the Potomac River by the Virginia Institute ofMarine Science to test the efficiency of a midwater trawl in catching alewivesas they migrate upstream to spawn fish7977.jpg A converted ferryboat is used in the Potomac River by the Virginia Institute ofMarine Science to test the efficiency of a midwater trawl in catching alewivesas they migrate upstream to spawn](/sites/default/files/styles/max_1300x1300/https/s3.amazonaws.com/s3-east-testmedia-noaa.woc.noaa.gov/dam/Photos/legacy/pl23_fish7977.jpg?itok=NF8mbG5u)
Description
A converted ferryboat is used in the Potomac River by the Virginia Institute ofMarine Science to test the efficiency of a midwater trawl in catching alewivesas they migrate upstream to spawn. (Image credit: NOAA Central Library Historical Fisheries Collection; P. 108 of Our Changing Fisheries 1970 Centenary NMFS centenary volume)