November 7, 2019 — The following was released by NOAA Fisheries:
The 2019 twin-trawling experiment aboard the F/V Karen Elizabeth in late September tested scientific survey net performance at different “spreads”—or how widely the net is open.The differences in capturing fish at different water depths that can be attributed to that spread.They found subtle differences between the two options.
In a twin-trawl study, one vessel tows two trawl nets as closely together as possible through the same body of fish at the same time. This makes the two samples comparable. In this study, one net had a constant opening while the other tested various openings.
Both nets were otherwise the same, and are the survey nets and rockhopper sweeps used on the NOAA Ship Henry B. Bigelow twice-yearly bottom-trawl survey since 2009. “Sweeps” are the gears attached along the bottom of trawl net openings that help target different types of species on different types of bottoms. Rockhoppers are big rubber disks that help a trawl net more easily tow over rocky bottom.
The four fish targeted in the study were flatfish:
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Gulf of Maine witch flounder and American plaice found in deeper waters.
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Southern New England winter flounder and windowpane flounder found in shallower waters.
Fishermen and researchers want to know more about Bigelow net underspread (being open less widely than desired) in shallower water. They are also interested in net overspread (or being open more widely than desired) in deeper water, and how different spread affected flatfish catch.