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Missouri Trawler

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Published on: Dec. 13, 2012

Science sometimes makes big leaps in response to small questions. Our question was: How can we capture more fish species, and smaller members of those species, in large rivers? The answer was a simple merger of a standard large-meshed trawl with small mesh. This gear, and the technique for its use, have since become popular around the world.

Trawls (a net pulled by boat, similar to a shrimper’s trawl used in the oceans) were being used by some large-river scientists to sample fish populations, but they were not catching many rare or small fish.

To estimate what kinds of fish, how many, and of what sizes were passing through a standard trawl, the small mesh material was placed outside the trawl body. As fish passed through the larger inner-panel mesh, they were captured in the smaller-meshed, outer panel (and funneled to the end of the net, called the cod-end). This experimental dual-mesh trawl was implemented as part of a research effort and was shown to greatly increase the number of species and individual fish caught compared to the original trawl.

The unique pass-through design of the experimental trawl allowed us to demonstrate that we were catching fish with the old trawl, but most of the fish were simply passing through the large mesh and never made it to the cod-end. The new design became known as the Missouri Trawl by the late 1990s.

Initially the technique of trawling was considered too similar to a deep-water seine to justify consistent use. However, that thought changed based on the many new fish records that were being captured when using the trawl.

For example, in 1998 the first known “young-of-the-year” (less than 1-year-old fish), federally endangered pallid sturgeon was captured in a Missouri Trawl. Then, from 2000–2001, the Missouri Trawl was used to obtain unprecedented information on the abundance and distribution of sicklefin chub and sturgeon chub, which at the time were candidate species for federal protection. The data was critical to the U.S. Fish and Wildlife Service in determining the status of the populations.

The effectiveness and ease of use of the Missouri Trawl continued to gain it popularity as Big Rivers and Wetlands Field Station staff completed several how-to-trawl workshops. During this time, we began developing variations of the original 16-foot-wide Missouri The Missouri Trawl is an effective sampling gear in deep, swift rivers. It was designed to skim the bottom of

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