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Distribution of Fishes in the Red River of the North Basin on Multivariate Environmental Gradients

Mapping of Fish Distribution

Stream digitizing

All nonintermittent streams and lakes in the Red River basin were digitized from USGS 1:250,000 scale quadrangle maps using a Summagraphics Microgrid II digitizer and TOSCA (1993) software. Streams were entered as lines and lakes as polygons with separate files created for each quadrangle map. The VCONCATE module of TOSCA was used to combine all stream files and all lake files into two complete coverages (layers). These layers served as the base map upon which species distribution points were plotted.

Species distribution

For each fish species, a file containing the year and coordinates in latitude and longitude of all sites where the species occurred was created from the Quattro Pro data base. The coordinates were sorted by year into three periods (early, middle, and late), saved as separate files, and downloaded into an IDRISI (1993) geographic information system (GIS). In IDRISI, the files were saved as vectors in binary data format using the CONVERTV module. Hard copies of distribution maps for 79 fish species were created by overlaying vector files and printing from TOSCA (1993).

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