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

Ecology of Stream Fishes

The following is a summary of contributions from the literature on ecology of stream fishes that relate to this paper and to the fishes of the Red River basin.

Early studies

The published notes of early naturalists in the 1800s, who rode horse-drawn wagons or followed the railways west, often remarked on conditions of streams and rivers and the fishes that were found (Cope 1879, Eigenman 1895, Evermann and Cox 1896). Observations such as these could be considered the beginning of the study of stream fish ecology in this country. An ecological study was published by Forbes (1907), who developed a coefficient to analyze the strengths of association between pairs of darters (Etheostomidae) collected from Illinois streams. Darter abundance was related to stream sizes, flow conditions, and substrate types. Degree of association among species varied between species pairs; and many species preferred one stream size, flow rate, or substrate type over another.

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.

Effect of flow variability on fish assemblages

Streamflow plays a central role in stream ecology (Hynes 1972). Streamflow controls several important stream characteristics such as depth, width, current velocity, and substrate composition (Horowitz 1978, Poff and Ward 1989). The effects of low flows on the distribution of stream fishes have been studied by researchers following drought conditions (Larimore et al. 1959, Deacon 1961). After virtually all the fishes and invertebrates were destroyed by drought in a small stream in Illinois from 1953-1954, remaining pools were treated with rotenone to eliminate surviving fish. After the stream resumed its flow, 21 of the 29 regularly occurring species returned to most of the stream reaches (Larimore et al. 1959). Young-of-the-year fishes were found to dominate the population. Similarly, in the Neosho and Marias des Cygnes rivers in Kansas, fish assemblages also adjusted in response to marked environmental changes (Deacon 1961). As rivers became low and clear, they assumed a fish fauna characteristic of smaller tributaries or ponds. As flow was resumed, "generalist species" capable of movement from more permanent waters moved in and quickly repopulated the reach. Species that occupied restricted habitats, such as many of the riffle dwellers, were slow to increase in numbers following the drought. Several of these species disappeared or became restricted to a single tributary in the stream system.

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.

Longitudinal succession and stream order

Several studies have been conducted that place stream fish species along a longitudinal environmental gradient from headwater reaches to stream mouth (Starmach et al. 1991, Przybylski 1993) since the physical variables within a river system follow a continuous gradient of physical conditions (Vannote et al. 1980) or (as applied to fishes) a continuum of abiotic and biotic regulatory factors (Zalewski and Naiman 1985). Zalewski et al. (1990) determined that species richness and diversity in two rivers increased downstream as a function of stream order (Horton 1945, Strahler 1957). Starmach et al. (1991) determined that abiotic factors regulated diversity of upstream fish communities and that fishes in downstream reaches were controlled by biotic factors. Hutchison (1993) found that species richness increased in a downstream direction with most changes in species composition due to addition rather than replacement of species. Schlosser (1987) proposed that in downstream reaches where habitat heterogeneity is greatest, fish communities are stable and diverse and that regulation in these areas was by biotic factors such as predation or competition.

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.

Temporal variability of fish assemblages

Studies to determine the temporal variation of stream fish communities are not as common as those to determine the spatial variation of fish assemblages, as they require the repeated sampling of established stream sites over time (Meffe and Berra 1988). Matthews et al. (1988) studied the long-term stability of stream fishes in three watersheds in Oklahoma and Arkansas. Over sampling periods as long as 17 years, the whole-stream fish faunas were persistent (regarding species presence or absence) and stable (as determined by indices of similarity and concordance of rank abundance of the common species in each stream across collection years). Similar results were shown by Ross et al. (1985) for the same streams. Likewise, Fausch and Bramblett (1991) determined that species composition and relative abundances remained constant at sites with deep pools with diverse habitats, but changed drastically at sites with shallow, less diverse habitats.

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.

Dispersal of fishes

The distributions of fishes in the upper midwest largely reflect postglacial reinvasion of drainages following the retreat of glacial ice at the end of the Wisconsinan glacial period, 8000-10,000 years before present (BP) (Eddy et al. 1963, Crossman and McAllister 1986, Underhill 1989, Mandrak and Crossman 1992b). Drainage of glacial Lake Agassiz, which once extended from the Arctic west to the Rocky Mountains of Alberta, east to the Lake Superior basin, and south into the Mississippi River basin (Teller and Bluemle 1983), occurred primarily through the River Warren, which formed the modern Minnesota River valley and provided a dispersal route for fishes from the Mississippi River drainage (Underhill 1989). A connection also occurred between Lake Agassiz and Lake Superior to the east, providing a temporary dispersal route for fishes from the Great Lakes drainage (Stewart and Lindsey 1983, Underhill 1989). Dispersal routes to Lake Agassiz from glacial refugia to the south were open from about 10,000-8500 BP (Underhill 1989). Following the final retreat of glacial ice and drainage of Lake Agassiz, land barriers to dispersal of fishes among drainage basins have existed (Eddy et al. 1963).

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).

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