Northern Prairie Wildlife Research Center
Hankinson (1910) determined the local distribution and habitat preferences of fishes in a small stream in Illinois. He found that determining preferred habitats was difficult, because of the "great variation in distribution of fish noted at different times" and that there were "not only annual and seasonal fluctuations in (fish) numbers, but also daily and even hourly ones" (Hankinson 1910). The study noted the effects of barriers as obstacles to fish movement. Changing current flow was observed to quickly change bottom substrates, transforming one habitat type into another; and overhanging grassy banks held more fish than did other shore types.
Shelford (1911) studied the distribution of fishes in streams near Chicago, Illinois. Species distributions were related to migration patterns and environmental extremes such as flood and drought. The study noted that fish species have definite habitat preferences, and these preferences are the reason that species are arranged in streams "along a gradient from mouth to headwaters" (Shelford 1911).
These early studies were almost entirely qualitative, but are quite meaningful biologically and represent the birth of fish ecology in this region. More recent studies utilize a quantitative approach and statistical techniques to determine "significance" of relationships; however, questions still exist about the relationship between stream fishes and their environment (Aadland 1993). The following discussion involves studies of stream fish distributions as they relate to flow variability, longitudinal succession, temporal variability, and dispersal patterns.
Flow variability has been found to have profound effects on fish diversity. Horwitz (1978) calculated the CV of daily stream discharge from long-term records of 15 river systems in Illinois, Missouri, Ohio, and Wyoming and found that, in general, variability of flow was lowest in downstream reaches. Diversity patterns of fishes in these streams were then examined, and species richness gradients were correlated with flow variability. In all rivers, diversity increased from upstream to downstream reaches. Headwater species diversity was lowest in those rivers with the most variable headwaters.
Since many regulated rivers have variable and unpredictable flow patterns, Bain et al. (1988) studied the effect of artificially fluctuating the streamflow on fish communities. Results indicated that a group of small-fish species that were restricted to microhabitats with shallow depth and slow current along stream margins were reduced in abundance under highly regulated flows and were eliminated from a study site with high flow fluctuation. A second group of fish species that used a broad range of habitats or microhabitats that were deep and fast in the midstream areas had higher densities in the regulated river and peaked at sites with the greatest flow variability.
Poff and Allan (1995) studied the relationship of flow variability on the organization of stream fish assemblages using data from 34 sites in Minnesota and Wisconsin for each of 106 species. Results defined two distinct groups of fish assemblages, with one group associated with streams with high flow variability and another group associated with hydrologically stable streams.
Several investigators have correlated longitudinal fish assemblage patterns with stream order. Whiteside and McNatt (1972) related fish species diversity to stream order and physical and chemical conditions such as dissolved oxygen, pH, alkalinity, turbidity, conductivity, and temperature of Plum Creek, Texas. It was determined that higher order streams had greater stability as fluctuations in physical and chemical conditions declined with increasing stream order. Species diversity generally increased with increasing stream order up to and including fourth order streams. A decline in diversity of fifth order streams was attributed to fish migration and/or poor seining success. Hutchison (1993) determined that stream order was strongly and positively correlated with species richness in an Australian river system, and Morin and Naiman (1990) determined that stream order in watersheds of northern Quebec accounted for 61% of total variation in total fish biomass of streams. However, there was no evidence that stream order had any influence on the species composition of fish communities.
Matthews (1986) analyzed the distribution of fishes in 23 streams in the eastern and central United States for evidence of any "distinct longitudinal breaks" in the fish fauna, since several investigators have suggested that stream orders may represent distinct "biological units" for fishes (Kuehne 1962, Harrel et al. 1967, Whiteside and McNatt 1972, Lotrich 1973). Results indicated a lack of any relationship between stream order and fish faunal changes along the course of streams. The study supported work by Evans and Noble (1979) who determined that "stream orders do not serve as strong organizers of stream fish communities" (Matthews 1986). Also, Przybylski (1993) determined that anthropogenic modification of streams such as pollution and channelization had a larger role than stream order in controlling fish zonation in the Warta River, Poland.
Schlosser (1990) correlated the temporal variability in physical and chemical conditions with species life-history characteristics and temporal variability in fish community structure. It was determined that upstream fishes experienced greater environmental variability than downstream fishes, especially in intermittent streams, and fish species composition was more variable in upstream than in downstream reaches. His results suggested that upstream fish assemblages can exhibit a more rapid recovery from severe anthropogenic disturbances than can downstream fish assemblages.
During Wisconsinan glaciation, the most important refugium for fishes of the Hudson Bay watershed was the Mississippi River drainage south of the glacial ice sheet (Stewart and Lindsey 1983). Crossman and McAllister (1986) reported 57 fish species (>50%) found in the Hudson Bay watershed were derived from the Mississippi refugium alone. Several of these species presently occur in the Red River basin. The Red River in the United States shares over 70 species with the Minnesota and lower Mississippi River basins, suggesting the importance of the River Warren outlets of Lake Agassiz to the dispersal of fishes from a Mississippi refugium (Underhill 1989). Radke (1992) determined that the fishes and mussels of the Otter Tail and Pelican Rivers were more similar to the fauna of the Pomme de Terre River, a tributary to the Minnesota River, than to the fauna of other tributaries to the Red River. Results of her study also suggested a past connection between the Otter Tail (Red River) and Minnesota River drainages following glaciation.
Even though studies of postglacial fish dispersal patterns are important in understanding modern-day distributions, of equal or greater importance is the degree to which humans have altered these systems by introductions of nonnative species (Afton 1959) or other disturbances (Resh et al. 1988) such as interconnections between drainages (Stewart et al. 1985), dam construction, stream channelization (Gorman and Karr 1978, Scarnecchia 1988), livestock grazing (Armour et al. 1994), agricultural practices (Gorman and Karr 1978), or various kinds of pollution (Larimore and Smith 1963). It is highly unlikely that the warmwater fish species of this region (Centrarchidae, Ictaluridae, and Cyprinidae) could withstand the extreme low temperatures and swiftness of the River Warren glacial meltwaters (Stewart and Lindsey 1983). Crossman and McAllister (1986) reported that several fish species have probably entered the Red River from the upper Mississippi after the final draining of Lake Agassiz. Many centrarchids are found today in unusual locations as a result of introductions by humans (Crossman and McAllister 1986).