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Missouri Trawler

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Published on: Dec. 13, 2012

sampling in small to large waters. While the Missouri Trawls are particularly useful to sample small, rare fishes in deep, swift-water habitats, they are now used throughout the United States and internationally in smaller rivers and large creeks. They can also be used by detaching them from a boat and pulling by hand in water that is too shallow to motor through.

Trawling has become widely used since the creation of the Missouri Trawl in 1997 and has been incorporated into many sampling protocols. As a large-river scientist from Illiniois told us, “This technique will forever change how we sample large rivers.” A Canadian researcher who works on smaller rivers and lakes reported that the trawl also helped enhance the knowledge of small fishes in the lower Great Lakes and tributaries.

Independent researchers are now creating new variations of older trawl designs that sample throughout the water column and some are attempting to chase down invasive species like the Asian carps. Sampling technique books now suggest trawling as part of a thorough fish-sampling protocol, further identifying the importance of the technique.

The Missouri Trawl is an effective sampling gear in deep, swift rivers. It was designed to skim the bottom of streams and rivers where no other gear can be effectively deployed. The trawl has helped scientists better understand what kinds of organisms live in such places and where they are distributed. Following are some examples of rare and unusual organisms captured by the trawl in Missouri.

Pseudiron Mayfly (Pseudiron centralis)

Localized common names for this rarely seen mayfly are white sand-river mayfly and flat-headed mayfly. The species is widespread across North America, but is not known from the St. Lawrence River and some drainages west of the Rocky Mountains. It is generally considered to be rare and is often listed as a state endangered or threatened species. However, because this species lives in large, sandy rivers, which are difficult to sample, it is probably more common than records indicate. In the Mississippi River bordering Missouri, it is frequently encountered when using the trawl and can be abundant in the river above St. Louis. Unlike most mayflies, this species lives primarily on the surface of sandy-bottomed rivers.

The nymphs are mostly yellow with black eyes but males are darker, having browns and reds over the body and bluish eyes. It is a ferocious predator eating mostly fly (chironomid) larvae (also

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