Stream Fish Communities and Environmental Correlates in the Red River of the North, Minnesota and North Dakota

In the Red River of the North (Red River) drainage in Minnesota and North Dakota, there are strong east–west hydrological and chemical environmental gradients. Historical fish surveys indicated the presence of species with both widespread and restricted distributions, leading to unique fish communities in several streams. To determine the important physiochemical correlates of stream fish community structure, we partitioned 25 streams into 46 large reaches by ecoregion classification. The reaches were then characterized from sampling during 1962–1994 by the frequency of occurrence of 76 fish species and 12 landscape-level hydrologic and chemical factors. In canonical correspondence analysis, the first two axes explained 56% of the species–environment relationship, and indicated that coefficient of variation of mean monthly discharge, minimum discharge in May, and residue were the most important factors correlated with fish community composition. Important covariates of residue were specific conductance, dissolved sulfate, and total hardness of waters. Certain catostomids, Hypentelium nigricans and Moxostoma valenciennesi, cyprinids, Notropis anogenus and N. texanus, ictalurids, Ameiurus natalis, and percids, Etheostoma caeruleum and E. microperca, all correlated highly with habitats characterized by low-flow variability, high discharges, and low residue, conductivity, and hardness. Reaches with these characteristics included the Otter Tail River in the Red River Valley, North Central Hardwoods (NCH), and the Northern Minnesota Wetlands (NMW) ecoregions; the Pelican River in the NCH ecoregion; and the Red Lake River in the NMW ecoregion. The results of this analysis support the hypothesis that regional environmental conditions are important in structuring fish communities in northern streams. As conditions are altered in the future by anthropogenic factors at the landscape scale, our exploratory multivariate model can be used to predict fish community response and support conservation efforts aimed at preserving or restoring unique and/or rare small fishes in the Red River and other, similar stream systems.