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Effects of Flow Regulation Due to Hydroelectric Project Operation on the Structure of Fish Communities in Wisconsin's Large River Systems
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Date
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Piette, Randal R.
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University of Wisconsin-Stevens Point, College of Natural Resources
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Abstract
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EXECUTIVE SUMMARY:
Dams and flow regulation used to produce hydroelectric power have altered natural aquatic ecosystems
on all of the major large rivers in Wisconsin to various degrees. During the early to mid 1900's, there
was little concern about what effects dams would have upon the aquatic ecosystems and the consequences
of damming large rivers. Of particular concern is the effect dams have had on the native fish
communities of large rivers. Dams have fragmented habitat, blocked natural migrations, altered flow
regimes and physically changed habitat resulting in changes to the fish communities. There is concern
that over time the overall health of the fish communities has degraded in rivers heavily influenced by
dams and flow regulation.
In order to assess the effects dams and flow regulation have had on the fish communities, the warm-water
fish communities of two large river systems in Wisconsin were surveyed during summer months of 1996,
1997, and 1998 using a standardized sampling protocol. The Chippewa-Flambeau River is a moderately
to heavily regulated (17 dams/367 km) river system in north central Wisconsin while the St. Croix River
is lightly regulated (2 dams/166 km). Ecological indices for species richness, relative abundance, relative
biomass, diversity, evenness, modified index-of-well-being, index of biotic integrity, trophic levels,
tolerance, and spawning preference were compared to evaluate fish community health. The fish
community was examined both on a whole river scale and on a river-reach scale. At the whole river
scale, ecological indices for species richness, diversity (number and biomass), evenness (number and
biomass), and modified index-of-well-being were significantly greater (P < 0.05) for the unregulated river
St. Croix River compared to the regulated Chippewa-Flambeau River. In the unregulated river, the
overall fish community, especially riverine fish species, declined as flow regulation increased compared
to the unregulated river. In both rivers, insectivores were the dominant trophic level followed by top
carnivores, omnivores, herbivores and parasite/filter feeders. Insectivore species richness and abundance
were reduced (P < 0.05) as flow regulation increased. For fish classified as intolerant of environmental
degradation and species of intermediate tolerance, species richness was greater (P < 0.05) in the
unregulated river compared to the regulated river, while there were no differences for fish classified as
tolerant. Species richness for simple lithophilous spawning species was significantly greater (P < 0.05)
for the unregulated river.
Fish communities compared on a river-reach scale revealed similar declines in the apparent health of the
fish community as flow regulation increased, but was less evident than on a whole-river scale. At the
river-reach scale, differences in the fish community were attributed to reduction in fishes considered
riverine habitat specialists, intolerant of environmental degradation, insectivores, and simple lithophilous spawners. Habitat generalists, top carnivores, omnivores, and tolerant fishes were less affected by flow
regulation. Negative impacts of dams and flow regulation were also less apparent in longer riverine
segments in the regulated river.
Fish-habitat relations in near-shore lateral habitat of both river systems were examined using Canonical
Correlation Analysis (CCA). Water velocity at sites on the unregulated river was slower, depth shallower
but more variable, and bottom substrate consisted of more fine materials compared to habitat in the
regulated river. Substrate size in the unregulated river was strongly correlated with water velocity and
weakly correlated in the regulated river. Species richness and diversity in near-shore lateral habitats were
greater at unregulated river stations and decreased with increasing amounts of flow regulation. Obligate
riverine and habitat generalist species guilds overlapped in CCA biplots on both systems, but could be
distinguished from each other based on the distinct habitat preference for coarser substrates and moderate
flows in the unregulated river but not in the regulated river. In both rivers, CCA plots of fish community
diversity indicated diversity was higher at stations with shallower depths, moderate flows and mixed size
substrate. Highly regulated sites had the lowest diversity overall in near-shore lateral habitat. Riverine
fish species were strongly associated with natural stations, and lentic fish species more with heavily
regulated stations.
Study results suggest that dams and flow regulation have degraded fish community health at both the
whole-river, and river-reach scales leading to declines in biological diversity and biological integrity in
these large river systems. Flow regulation has disrupted typical fish-habitat associations of fishes
typically inhabiting near-shore lateral habitats leading to declines in the fish community. Current
regulations governing dam operations need to be re-evaluated to prevent the extirpation and possible
extinction of native large river fishes.
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Sponsorship
This study was funded in part by a gift from the Wisconsin Electric Power Company to the
Wisconsin Department of Natural Resources, and the Federal Aid in Sport Fish Restoration, Project F-85-
P, study SSDM.