Validation of River Valley Segments Delineated for Bioassessment and Fisheries Management Using Fish Assemblages

One of the most common practices in river research and management is to divide river network into more ecologically meaningful and operationally manageable spatial units.  The Great Lakes Regional River Database and Classification System was developed for the four-state region of Illinois, Michigan, New York, and Wisconsin by dividing river network into confluence-to-confluence reaches, merging similar neighboring reaches into segments, and classifying segments into types.  This presentation describes how the river reaches, segments, and segments types were developed using Michigan’s data as an example; reports the major differences in some physical characteristics within and among river reaches and multiple-reach segments; and compare the variations in fish assemblages within and among river reaches, multiple-reach segments, and segment types where sampled fish data are available.  Because the patterns of changes in physical and biological characteristics of river systems are spatial-scale dependent, our study focused only at the spatial scales that are meaningful for environmental assessment using fish assemblages and for fisheries management.  We found that river reach within a segment explained the least, segment type explained moderate, and segment explained the most variances in fish assemblage metrics, fish abundance of all species, and fish abundance for the top-three dominant species.