Abstract
Streams are complex systems that rely on connectivity to maintain natural ecological function. Low-water crossings are common in small-intermediate sized streams and can restrict longitudinal movement of fishes. The Current River in Missouri (USA) contains a single anthropogenic barrier to longitudinal connectivity: the Cedar Grove low-water crossing, which spans the main channel (10 culverts) and a side channel (4 culverts). In July 2017, we radio-tagged Northern Hog Sucker Hypentelium nigricans upstream (henceforth ‘above’; N = 24) and downstream (henceforth ‘below’; N = 26) of the crossing and followed their movements monthly for a year to assess fish passage and maximum displacement. Passage was limited to four below-tagged fish passing upstream of the crossing with one fish making an additional downstream and then upstream passage. Passage was more likely to occur during high flow. On average, below-tagged fish exhibited more than seven times greater maximum displacement (Mean (M) = 6.55 km, Standard Error (SE) = 2.91 km) than above-tagged fish (M = 0.92 km, SE = 0.33 km). The majority (71%) of fish exhibited stationary behavior (<1 km) compared to mobile behavior (>1 km). Among mobile individuals, maximum displacement was greatest away from the crossing, with above-tagged fish favoring upstream movements (100%) and below-tagged fish favoring downstream movements (67%). Our results suggest the crossing is a semi-permeable barrier in which fish passage primarily occurs during high flows. Alternatives to the low-water crossings at Cedar Grove should be considered to promote natural longitudinal movement of fishes. The side channel provides a potentially impactful and economically feasible management opportunity to act as a fish bypass channel on the Current River.
Highlights
Longitudinal connectivity provides material resources from upstream to downstream as well as a migration corridor for aquatic organisms to essential habitat (Ward and Stanford 1995; Ensign and Doyle 2006; McIntyre et al 2008)
Longitudinal connectivity is critical for promoting movement to feeding, spawning, and seasonal habitats that are often distantly distributed within stream networks (Calles and Greenberg 2009; Armstrong and Schindler 2013; Ettinger-Dietzel et al 2016; Wells et al 2017)
We anticipated that a velocity barrier within the culverts would be the limiting factor on upstream-directed movements past the crossing, but evidence suggests that elevated flows created a pseudo-fish ladder lateral to the main channel that was likely the mechanism for upstream passage
Summary
Longitudinal connectivity provides material resources from upstream to downstream as well as a migration corridor for aquatic organisms to essential habitat (Ward and Stanford 1995; Ensign and Doyle 2006; McIntyre et al 2008). Longitudinal connectivity is critical for promoting movement to feeding, spawning, and seasonal habitats that are often distantly distributed within stream networks (Calles and Greenberg 2009; Armstrong and Schindler 2013; Ettinger-Dietzel et al 2016; Wells et al 2017). A major anthropogenic effect on longitudinal connectivity and fish movement in lotic systems worldwide is the construction of barriers (e.g. dams, weirs, and road crossings). Smaller barriers (e.g. weirs and road crossings) and less economically important stream fishes such as Campostoma spp., Cyprinella spp., and Cottus spp. have received more attention over the past decade (Benton et al 2008; Helms et al 2011; Mueller et al 2011). High flows may temporarily reestablish stream connectivity through perched culverts or provide alternative pathways around barriers of other types (Perkin and Gido 2012)
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