Pallid sturgeon are a bottom-oriented, large river obligate fish inhabiting the Missouri and Mississippi rivers and some tributaries from Montana to Louisiana (Kallemeyn 1983). Pallid sturgeon evolved in the diverse environments of the Missouri and Mississippi rivers.
Floodplains, backwaters, chutes, sloughs, islands, sandbars, and main channel waters formed the large-river ecosystem that met the habitat and life history requirements of pallid sturgeon and other native large-river fishes.
In many portions of the pallid sturgeon’s range, research into habitat usage has produced some useful insights. However, it should be cautioned that much of these data are based on habitat characterizations in altered environments, in some cases substantially altered environments, including an altered hydrograph, suppression of fluvial processes, stabilized banks, loss of natural meanders and side channels, fragmented habitats, and increased water velocities. Thus, the following information and current understanding of habitat use may not necessarily reflect preferred habitats for the species, but rather define suitable habitats within an altered ecosystem.
Within their range, pallid sturgeon have been collected from a variety of locations. These observations help inform habitat usage, but vary by age class and geographic location. In the upper portions of the species’ range, sub-adult hatchery-reared pallid sturgeon select main-channel habitats (Gerrity 2005). Conversely, adult pallid sturgeon select areas with frequent islands and sinuous channels while rarely occupying areas without islands or with straight channels (Bramblett and White 2001; Snook et al. 2002; Peters and Parham 2008). In the middle Mississippi River, pallid sturgeon select for areas downstream from islands that are often associated with channel border habitats and select against main-channel habitats (Hurley et al. 2004). Other Mississippi River capture locations tend to be near the tips of wing-dikes (an engineered channel training structure), steep sloping banks, and channel border areas (Killgore et al. 2007b; Schramm and Mirick 2009).
Pallid sturgeon have been documented over a variety of available substrates, but are often associated with sandy and fine bottom materials (Bramblett and White 2001; Elliott et al. 2004; Gerrity 2005; Snook et al. 2002; Swigle 2003; Peters and Parham 2008; Spindler 2008). Substrate association appears to be seasonal (Kochet al. 2006a; Koch et al. 2012). During winter and spring, a mixture of sand, gravel and rock substrates are used and during the summer and fall, sand substrate is most often used (Koch et al. 2006a). In the middle Mississippi River, Pallid sturgeon transition from predominantly sandy substrates to gravel during May which may be associated with spawning (Koch et al. 2012). In these river systems and others, pallid sturgeon appear to use underwater sand dunes (Bramblett 1996; Constant et al. 1997; Snook et al. 2002; Elliott et al. 2004; Jordan et al. 2006).
Depths and Velocity
Across their range, pallid sturgeon have been documented in waters of varying depths and velocities. Depths at collection sites range from 0.58 meter (m) to > 20 m (1.9 to > 65 feet (ft)), though there may be selection for areas at least 0.8 m (2.6 ft) deep (Bramblett and White 2001; Carlson and Pflieger 1981; Constant et al. 1997; Erickson 1992; Gerrity 2005; Jordan et al. 2006; Peters and Parham 2008; Wanner et al. 2007). Despite the wide range of depths associated with capture locations, one commonality is apparent: this species is typically found in areas where relative depths (the depth at the fish location divided by the maximum channel cross section depth expressed as a percent) exceed 75% (Constant et al. 1997; Gerrity 2005; Jordan et al. 2006; Wanner et al. 2007).
Bottom water velocities associated with collection locations are generally < 1.5 m/s (4.9 ft/s) with reported averages ranging from 0.58 m/s to 0.88 m/s (1.9 ft/s to 2.9 ft/s) (Carlson and Pflieger 1981; Elliott et al. 2004; Erickson 1992; Jordan et al. 2006; Swigle 2003; Snook et al. 2002).
Pallid sturgeon have been collected from a variety of turbidity conditions, including highly altered areas with consistently low turbidities (i.e., 5-100 nephelometric turbidity units (NTU)) to comparatively natural systems like the Yellowstone River with seasonally high turbidity levels (> 1,000 NTU) (Braaten and Fuller 2002, 2003; Erickson 1992; Jordan et al. 2006; Peters and Parham 2008). Currently, it is not fully understood if high turbidity levels are fundamentally important for individual sub-adult and adult fish. However, the general consensus is that the historically high turbidity levels in the Missouri and Mississippi Rivers is a component of natural ecological processes under which pallid sturgeon evolved. Given the small eye structure, presence of barbels with taste buds, taste buds on lips, and ampullary electroreceptors on the underside of the snout, the species appears to be highly adapted to low-visibility environments. Thus, rivers defined by high turbidity levels that fluctuate seasonally and annually are considered important because other life history traits (i.e., predator avoidance or feeding mechanisms) may have evolved specific to low visibility environments.