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

Species Associations of Stream Fishes

After placing streams into groups, the fishes occurring at sites in each stream were used to associate species and create meaningful assemblages of fishes that are typically found in different regions of the basin. Fifty-eight species from cluster A streams (Figure 7) were successfully placed into seven "assemblages" by CA (assemblages A1-A7) (Figure 9). Assemblage A1 included species such as the goldeye, mooneye, silver chub, and sauger, all typical of large rivers with turbid waters. Assemblage A2 included species such as the northern hogsucker and central stoneroller, found almost exclusively in the Otter Tail River region. Assemblage A3 included species such as the blacknose shiner, blackchin shiner, and pumpkinseed, typical of clear water streams associated with lakes. Assemblage A4 included large stream species such as the quillback and freshwater drum; and assemblages A5-A7 included common species such as the white sucker and common shiner, which are widely distributed in the streams of cluster A.

Rose and Echelle (1981) determined that even in streams which are widely separated and very different in terms of habitat conditions, similar species will tend to sort into similar species associations. In the present study, similar assemblages were noticed in the four groups of streams, but there were also several distinct differences among them. For example, the assemblages produced from streams of cluster B differed somewhat from assemblages produced from cluster A streams. In assemblage B1 (Figure 10), the sauger and freshwater drum were closely paired, whereas the same two species were completely unassociated in analysis of fishes of cluster A streams (Figure 9). The shorthead redhorse, walleye, trout-perch, and rockbass, however, are included in common assemblages in both analyses. Assemblage B2 (Figure 10) contains species which would seem to prefer a wide variety of habitats. In this assemblage, the spotfin shiner was most closely paired with the channel catfish, brown bullhead, and black crappie. These species are typical of downstream reaches with wide, deep channels. A second subgroup of assemblage B2, the pearl dace, northern redbelly dace, bluntnose minnow, and Iowa darter, is more typical of headwater reaches which are more shallow. The assemblages produced by these analyses should be a reflection of the regularity that species have occurred together in samples, and evidently the assemblages cannot always be distinguished from one another on the basis of observed habitat preferences of fishes. Increasing the value of the simple matching coefficient which was used to define assemblages may help to clarify some of these problems.

Assemblages produced from streams of cluster C (Figure 11) and cluster D (Figure 12) also differ somewhat from results of clusters A and B, possibly because of the way that CA "forces" pairing of species at low similarity even though they only rarely occur together naturally. Regardless, several meaningful assemblages were produced by these analyses. Most notable was assemblage D3, which consisted of the pearl dace, northern redbelly dace, finescale dace, central mudminnow, and brook stickleback. These species are typical of the streams of cluster 4 and are commonly found together in small headwater streams and ponds.

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