SEASONAL VARIATION OF RIFFLE AND POOL FISH ASSEMBLAGES IN A SHORT MITIGATED STREAM REACH

We sampled a series of contiguous riffles and pools throughout one year to examine spatial and temporal variation in stream fish assemblages on a short, mitigated reach of the Cotton- wood River, Kansas. One of three riffles sampled was an artificial riffle constructed as habitat restora- tion in an area previously dredged of gravel. Canonical correspondence analysis demonstrated differ- ences between riffle and pool fish assemblages, and indicated seasonal assemblage variation with no influence imparted by the artificial riffle. Current speed, water depth, substrate character, total alka- linity, and season explained most assemblage variation. Fish assemblages were similar spatially, but were seasonally variable. Riffle fish assemblages exhibited more seasonal variability than did those of pools; 59% of the total number of fishes captured in riffles were seasonally variable compared to 12% in pools. Patterns of variability in this mitigated stream reach were similar to those reported for natural streams.