Bigmouth shiner (Notropis dorsalis) COSEWIC assessment and status report: chapter 7
Habitat
In Manitoba, the bigmouth shiner appears to favour small streams, up to 12 metres in width and one metre in depth, although presence in larger rivers such as the Assiniboine has been documented. Stewart pers.comm., state that the bigmouth shiner commonly inhabits riffles and runs at moderately fast velocities, preferring faster water than the sand shiner. The bigmouth shiner is also found closer to upstream ends of riffles and runs than is the sand shiner (K.W. Stewart pers. comm. 2003). The bigmouth shiner seems to be most common in the Pembina and Cypress rivers. The Cypress River is a small stream (up to 12 metres in width) with a medium gradient and substrate characterized by shale outcrops. In one of the few detailed habitat sampling efforts conducted in the Cypress River, the bigmouth shiner was found in locations with channel widths between 2 and 12 metres (average 5.5 m), water depths between 0.11 and 1.0 metres (average 0.41 m) and velocities between 0.10 and 0.62 m/sec (average 0.39 m/sec). Substrates were composed of the following combinations: gravel/shale; cobble/boulder; shale/silt; cobble/shale; and sand/shale. The bigmouth shiner was the most abundant species (over 20% of the total catch) where wetted widths were between 3 and 4 metres, depths were between 0.28 and 0.5 metres, velocities were between 0.39 and 0.62 m/sec, and substrate was gravel and shale (B. Franzin, 1995 unpublished data).
In the Little Saskatchewan River, a single bigmouth shiner was collected over sand and gravel in 0.69 metres of water (Appendix 3 in McCulloch and Franzin 1996). The bigmouth shiner has been collected in similar habitat in Oak and Epinette creeks. In the Assiniboine River, the bigmouth shiner has always been collected in low numbers (<10 individuals) were they occur over gravel, sand and shale outcrops in water up to one metre in depth (Appendix 1 in McCulloch and Franzin 1996).
Elsewhere, the bigmouth shiner occurs mainly in small permanent prairie streams with unstable sandy bottoms (Mendelson 1975, Pflieger 1997). Becker (1983) and Mendelson (1975) found that the species was absent or rare from larger streams. In smaller streams, abundance decreased as stream width exceeded 3 metres. This tendency to favour smaller streams is not exclusive throughout its range, however, as Johnson and Becker (1970) reported it common in medium-sized sandy streams in the Mississippi drainage, while Starrett (1950) found it to be abundant in the Des Moines River. In tributaries of the Red River in North Dakota, Copes and Tubb (1966) found the bigmouth shiner to be most abundant in slightly turbid water over sand substrate. Other habitats occupied have included small streams with silt substrates (Eddy and Underhill 1974) and sand substrate overlain with silt (Gilbert 1980). Mendelson (1975) found that the bigmouth shiner exhibits a pronounced preference for shallow water upstream from pools. O’Shea et al. (1990) found bigmouth and sand shiners in wide river channels with abundant sandbars and low amounts of river-edge habitat in the Platte River in Nebraska.
While it is hard to determine rates of habitat change, Tompkins (1987) indicated that population trends in the United States have suggested that suitable habitat has expanded in the central plains, but has declined in the eastern part of the range. Pflieger (1971) suggested that channelization of prairie streams in the early part of the twentieth century created habitat conditions that were favourable for the bigmouth shiner. In fact, Scarnecchia (1988) found that bigmouth shiner populations were significantly higher in channelized sections than in unchannelized sections of Pillsbury Creek, Iowa. Percentage of total catch increased from 1-4% in unchannelized sections to 22-54% in channelized sections (Scarnechhia 1988). Typically, channelization of waterbodies occurs either to protect infrastructure and other properties from natural erosive features of active steam channels, or when a waterbody is crossed and a culvert is used to convey water under the roadway. Realignment of a portion of the stream channel usually involves minor channelization to accommodate flow through the culvert. In this way, flow becomes uniform, with little or no variation.
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