Effects of Dam Removal on Fish Assemblage Structure and Spatial Distributions in the Baraboo River, Wisconsin

Abstract

We evaluated the effects of dam removal on fish assemblage structure and spatial distributions after four low-head dam removals in the Baraboo River, Wisconsin, using data collected at 35 study sites over 7 years. After dam removal, biotic integrity scores (possible range ¼ 0-100) increased by 35-50 points at three of the four former impoundments as a result of decreases in percent tolerant species, increases in the number of intolerant species, and in some cases, increases in species richness. Fish assemblage shifts were muted at a fourth, lower-gradient impoundment site, indicating that responses differ among dam sites within a river system. In tailwater areas, postremoval assemblage shifts were transient; biotic integrity and species richness declined initially but then recovered at two of the three sites within 2 years after dam removal. An analysis of spatial distributions before dam removal revealed 11 fish species that were found below, but rarely or never above, the downstream-most dam. After dam removal, 10 of the 11 species were collected at new sites upstream from the dam, indicating that recolonization of reconnected upstream sites had occurred. Some species recolonized rapidly and in large numbers. For example, emerald shiners Notropis atherinoides recolonized 16 upstream sites and were collected 123 km upstream from the dam within the first year after removal. One of the nine recolonizing species, the spotted sucker Minytrema melanops, was only detected during spring, suggesting that these fish recolonized seasonally, perhaps for spawning. Recolonizing species were generally lacustrine or large-river fishes known to undergo overwintering and spawning migrations. Our study suggests that dam removal is a viable option for restoring lotic fish communities, but further study is needed on recovery patterns as they relate to channel morphology, hydrologic characteristics, impoundment sediment storage capacity, and the distance to source populations of recolonizing taxa.

Fragmentation and dewatering transform Great Plains stream fish communities

“…point to previous examples of reestablishment or increased dispersal following barrier removal or mitigation as proof of concept that increasing connectivity benefits fishes known to respond negatively to fragmentation (Catalano et al 2007, Archdeacon and Remshardt 2012, Walters et al 2014). …”

“…However, small-bodied lithopelagophilic fishes have received considerably less attention than the pelagophilic guild. The two species classified as small-bodied lithopelagophilic in our study, silver chub (Macrhybopsis storeriana) and emerald shiner (Notropis atherinoides), are both known to decline in response to fragmentation, but not to the extent of known pelagophilic species (Winston et al 1991, Catalano et al 2007, Perkin and Gido 2011. One ecological characteristic shared by small-bodied lithopelagophilic species is their ability to inhabit lentic habitats such as reservoirs created upstream of large impoundments, habitats that generally do not support pelagophilic fishes (Dudley and Platania 2007).…”

Historical Changes in Fish Assemblage Structure in Midwestern Nonwadeable Rivers

“…In addition to hydrologic alterations, anthropogenic disturbances can also fragment habitats. In particular, dams fragment river corridors and act as dispersal barriers that truncate fish distributions (Santucci et al, 2005;Catalano et al, 2007) and isolate and contribute to the extirpation of fishes upstream of dams (Sheldon, 1987;Quist et al, 2005). Other than physical changes to lotic habitat, the introduction of nonindigenous species from various stocking practices have also led to negative consequences for native ichthyofauna in Iowa (Bernstein and Olson, 2001).…”

Method to support Total Maximum Daily Load development using hydrologic alteration as a surrogate to address aquatic life impairment in New Jersey streams

“…Increased awareness of the adverse effects of dams in concert with an aging infrastructure and dam maintenance costs has led to a heightened interest in dam removal in the United States (Orr and others, 2008), where more than 500 dams have been removed in the past two decades (Stanley and Doyle, 2003). The ecological benefits of dam removal include increased fish passage and broader access to spawning habitats, reestablishment of riverine taxa, declines in nonendemics, and restoration of stream integrity (for example, Catalano and Bozek, 2007); however, large amounts of trapped sediment released after dam removal can adversely affect biotic integrity for months or even years after dam removal (Thomson and others, 2005). This effect is temporary, however, as aquatic assemblages will continue to recover as fine sediments are reduced in downstream habitats.…”