Field Notes
U.S. Fish & Wildlife Service
Field Notes Entry   
New Procedures to Rank Low-Water Crossings in Threatened Niangua Darter Range
Midwest Region, December 13, 2006
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Nick Frohnauer measures culverts in Missouri stream crossing. 
- FWS photo
Nick Frohnauer measures culverts in Missouri stream crossing.

- FWS photo

- Photo Credit: n/a

Fishery Biologists Joanne Grady and Nick Frohnauer met with Missouri Department of Conservation fishery biologists, stream specialists and Niangua darter researchers to assess data collected from low-water crossings throughout the range of the Niangua darter.

The group examined data collected from 54 road crossings which occur over streams within the range of the threatened Niangua darter. The crossings were examined to determine if they were jump barriers, velocity barriers or behavioral barriers for the darter.

Jump barriers were any culverts perched above the water level. Velocity barriers are tentatively defined as culverts with velocities exceeding 2 feet per second. Behavioral barriers will exist at crossings which have culverts within the water but at some distance from the stream bottom, as darters are benthic fish without swim bladders.

A new index proposed at this meeting is Percent Passable Face. Where wetted culverts do not present a jump barrier to the darter, the sum of the culvert width corrected for percent blockage, is divided by the length of the crossing. It is theorized that the smaller this number, the harder fish will have to work to find an opening.

This analysis in combination with Niangua darter population information gathered by MDC will be used by the group to rank crossings and watersheds for structure replacement projects.

This project supports multiple Fisheries Strategic Vision Goals including: Partnerships and Accoutability, Aquatic Species Conservation and Aquatic Habitat Conservation.

Contact Info: Larry Dean, 612-713-5312, Larry_Dean@fws.gov
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