2007 NORTHEASTERN NATURALIST 14(1):125–138 Effects of Lowhead Dams on Unionids in the Fox River, Illinois Jeremy S. Tiemann1,*, Hope R. Dodd2,5, Nick Owens3, and David H. Wahl4 Abstract - We sampled 9 sites (5 free-flowing and 4 impounded) to investigate effects of lowhead dams on the habitat characteristics and the freshwater mussel assemblage of the Fox River in Illinois. We used 2 habitat indices, the Qualitative Habitat Evaluation Index (QHEI) and the Stream Habitat Assessment Protocol (SHAP), to determine effects of lowhead dams on habitat quality. Free-flowing sites had higher QHEI and SHAP scores than impounded sites, indicating higher quality stream habitat. We calculated 3 variables, catch-per-unit-effort (CPUE), extant species richness, and percent missing species, to establish effects of lowhead dams on freshwater mussels. Free-flowing sites had higher CPUE and extant species richness and lower percent missing species than impounded sites. We also examined literature reviews and museum collection holdings to determine species distributions within the basin. These data suggest that dams limit the upstream distribution of 5 species. Introduction Freshwater mussels (Bivalvia: Unionidae) are important components of stream ecosystems (Strayer et al. 1994). Not only does their sensitivity to stream disturbances make them good biological indicators of stream integrity, but they also provide habitat or a food source for many animals. During the past century, freshwater mussels have become one of the most imperiled groups of organisms in North America, where nearly 70% of the approximately 300 species have become extinct or are endangered, threatened, or in need of conservation status (Williams et al. 1993). Among factors affecting freshwater mussels are anthropogenic disturbances that result in habitat destruction/fragmentation and environmental degradation. Impoundments are one of the major sources of anthropogenic disturbances on streams (Baxter 1977). Dam effects include converting lotic habitats to lentic habitats, changing flow regime, altering physicochemical parameters, increasing siltation upstream from and scouring substrates downstream from the dam, and altering fish assemblages and/or blocking movement of host fishes (Baxter 1977, Tiemann et al. 2004, Watters 1996). The resultant dam effects can alter the freshwater mussel fauna, including restricting distributions and isolating populations (Watters 1996), reducing 1Illinois Natural History Survey, Center for Biodiversity, 1816 S. Oak Street, Champaign, IL 61820. 2Illinois Natural History Survey, Center for Aquatic Ecology and Conservation, 1816 S. Oak Street, Champaign, IL 61820. 3Illinois Natural History Survey, Center for Wildlife and Plant Ecology, 1816 S. Oak Street, Champaign, IL 61820. 4Illinois Natural History Survey, Center for Aquatic Ecology and Conservation, Kaskaskia Biological Station, RR 1 Box 157, Sullivan, IL 61951. 5Current address - National Park Service, Missouri State University, 901 S. National Avenue, Springfield, MO. *Corresponding author - jtiemann@inhs.uiuc.edu. 126 Northeastern Naturalist Vol. 14, No. 1 native species richness and abundance (Parmalee and Hughes 1993), increasing non-native species richness and abundance (Parmalee and Polhemus 2004), and altering evenness (Dean et al. 2002). Several studies have documented effects of large dams on freshwater mussels (e.g., Bates 1962, Blalock and Sickel 1996, Suloway et al. 1981, Williams and Fuller 1992), but few have addressed effects of lowhead dams (< 4 m in height) (e.g., Dean et al. 2002, Watters 1996). Data on how lowhead dams affect freshwater mussels are important for the protection of this imperiled fauna. The objectives of this study were to investigate whether lowhead dams affect the habitat characteristics, freshwater mussel fauna, and unionid species distributions in the Fox River in Illinois. We predicted that habitat quality and freshwater mussel abundance and extant species richness would be lower, while percent missing species would be higher in impounded sites than free-flowing sites; we also presumed that some species of freshwater mussels would be restricted in their distribution due to dams. To test these hypotheses, we calculated indices for habitat quality and conducted timed searches for unionids at 9 sites upstream from 5 lowhead dams in the Fox River in Illinois; in addition, we examined literature reviews and museum collection holdings to determine species distributions within the Fox River basin. Study Area The Fox River begins near Menominee Falls in Waukesha County, WI, and flows approximately 315 km south-southwest before converging with the Illinois River near Ottawa in LaSalle County, IL (Schanzle et al. 2004). The basin, nearly 6900 km2, is predominately agricultural land (66%) and urban areas (18%) with some woodlands (9%), wetlands (5%), and lakes and streams (2%) (Santucci et al. 2005). The mainstem of the Fox River is impounded with 19 lowhead dams, 15 of which occur in Illinois (Schanzle et al. 2004). Dams, which range from 44–183 m long and 0.8–9.0 m high, impound small areas (2–346 ha); due to the number of dams, 47% of the length and 55% of the surface area of the river is impounded (Santucci et al. 2005). Historically, the Fox River basin contained at least 33 species of freshwater mussels (Schanzle et al. 2004 and references therein); 25 of these have been collected in the basin since 1969 (Illinois Natural History Survey [INHS] Mollusk Collection, Champaign, IL). Methods We sampled 9 sites in a 17.3-km stretch of the Fox River, Kane County, IL, in July 2003, to assess effects of lowhead dams on the habitat characteristics and the freshwater mussel assemblage (Fig. 1). Two of these sites (Geneva Free-Flowing and Aurora Impounded) were measured for habitat in April 2006; values obtained were similar to those reported in 2000 (V.J. Santucci, Illinois Department of Natural Resources, Spring Grove, IL, pers. 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 127 comm.). This area of the Fox River primarily drains urban areas. The 9 sites consisted of 2 site types (5 free-flowing and 4 impounded) upstream from each of 5 lowhead dams (Fig. 1). The South Batavia Dam was breached and no longer contained an impounded area; therefore, no impoundment data from this site were included in this study. Free-flowing sites were outside the zone of direct dam influence on flow, predominately had gravel/pebble substrates, and ranged from 55–100 m in width, 0.5–1 m in depth, and 100– 200 m in length. Impounded sites were inundated, primarily had silt substrates, and ranged from 140–200 m in width, 0.5–2 m in depth, and 150–400 m in length. No pre-impoundment data were available. We concluded impounded areas were more similar to free-flowing areas than wide, deep, silted pool areas before being dammed due to the steep gradient (0.85 m/km) of this section of the Fox River. Also, we considered free-flowing sites to be normal conditions for presently undammed portions of the Fox River. Therefore, we believed the sites we chose acted as suitable and valid standards for their respective areas presently found in the basin. We assessed habitat at each site using two qualitative habitat indices designed to evaluate stream integrity and habitat quality: the Qualitative Habitat Evaluation Index (QHEI) (Ohio EPA 1989) and the Stream Habitat Assessment Procedures (SHAP) (Illinois EPA 1994). Both indices are multi-metric and provide empirical, quantified evaluations of stream habitat (Holtrop and Fischer 2002, Santucci et al. 2005). They score and rate Figure 1. Study area in the Fox River, Kane County, IL, and locations of lowhead dams (bars) and study sites (Xs). 128 Northeastern Naturalist Vol. 14, No. 1 habitat quality based on visual observation data that describe channel morphology, substrate, and flow characteristics. The QHEI has 7 principal metrics (substrate, instream cover, channel morphology, riparian zone and bank erosion, pool-glide quality, riffle-run quality, and gradient), and the SHAP has 15 (bottom substrate, deposition, substrate stability, instream cover, pool-substrate characterization, pool quality, pool variability, canopy cover, bank vegetative protection/stability, top-of-bank land use, flow-related refugia, channel alteration, channel sinuosity, width/depth ratio, and hydrologic diversity). For each index, higher scores indicate better habitat quality for aquatic organisms. We collected live freshwater mussels and valves of dead specimens by hand-groping while wading for 1–4 collector-hours at each site. Handgroping has been documented to be an effective and efficient means of estimating abundance and species richness of freshwater mussels (Metcalfe- Smith et al. 2000, Obermeyer 1998, Vaughn et al. 1997). Variation in sampling effort was due to the differences in the size of the sample area and the ease of groping in silt versus gravel/pebble substrates. At each site, we recorded the number of live individuals of each species before returning the unionids to the stream reach from which they came. We vouchered and deposited valves of each species from each site into the INHS Mollusk Collection. We identified species using Cummings and Mayer (1992), with common and scientific names following Turgeon et al. (1998), except we did not recognize subspecies. We standardized freshwater mussel abundance at each site as catch-perunit- effort (CPUE), which was the number of live individuals per collector-hour. We determined extant species richness as the number of species found live at a given site during the survey. We calculated percent missing species using the formula: ([(number of historical species - number of extant species) / number of historic species] x 100), where the historical count was established as the number of species found at a given site either live or as valves during this survey or previous visits (data taken from the INHS Mollusk Collection). We pooled data for analysis at the site-type level. We used the Shapiro- Wilk test to evaluate distributions of means for normality and the Levene’s test to examine homogeneity of variance (Zar 1999). We preformed multivariate analysis of variance (MANOVA) using Wilk’s lambda (􀁨) (Zar 1999) to investigate effects of lowhead dams on the habitat characteristics and the freshwater mussel assemblage. We used analysis of variance (ANOVA) to examine effects of lowhead dams on individual habitat indices (QHEI and SHAP) and freshwater mussel assemblage variables (CPUE, extant species richness, and percent missing species). We used the Statistical Analysis System, Version 8.1 (SAS Institute, Incorporated, Cary, NC) to calculate all statistical tests and considered tests significant at P 􀂔 0.05. We conducted literature reviews (Baker 1906, 1928; Calkins 1874; Cummings and Mayer 1997; Eldridge 1914; Mathiak 1979; Schanzle et al. 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 129 2004) and inspected museum collection holdings (Academy of Natural Sciences of Philadelphia, Chicago Academy of Science, Carnegie Museum of Natural History, Field Museum of Natural History, INHS, Illinois State Museum, Museum of Comparative Zoology, Ohio State University Museum of Zoology, University of Michigan Museum of Zoology, National Museum of Natural History) of the Fox River basin to determine historical species distributions within the basin. To recognize whether dams affected unionid distribution, we determined presence of a given species and compared those data to locations of lowhead dams (Santucci et al. 2005, Watters 1996). A species was considered extant at a site if it had been collected there since 1970 (Cummings and Mayer 1997). Results Mean QHEI was 73.0 (SD = 8.58) in free-flowing sites versus 37.5 (SD = 6.94) in impounded sites, and mean SHAP was 121.8 (SD = 26.46) in free-flowing sites versus 64.8 (SD = 8.42) in impounded sites (Table 1). MANOVA showed that the habitat characteristics varied significantly between site types (􀁨 = 0.12, n = 9, F = 20.80, P = 0.002). ANOVA indicated that both QHEI (F1,7 = 44.66, P = 0.0003) and SHAP (F1,7 = 16.08, P = 0.004) were significantly higher at free-flowing sites than impounded sites. Post-hoc pooled t-tests (df = 7) with sequential Bonferroni correction of individual QHEI and SHAP variables showed that free-flowing sites had shallower depths (t = 4.64, P = 0.002), fewer channel alterations (t = 4.66, P = 0.002), less silt deposition (t = 5.82, P = 0.0006), higher gradient (t = 6.52, P = 0.0004), more riffle/run sequences (t = 5.92, P = 0.0006), more diverse substrate composition (t = 6.35, P = 0.0004), higher substrate stability (t = 6.75, P = 0.0003), and higher hydrologic diversity (t = 5.81, P = 0.0006) than impounded sites. We collected 104 individuals of 6 unionid species in 16 collector-hours at the 5 free-flowing sites; however, we found no live individuals in 7 Table 1. Freshwater mussel assemblage data and habitat-quality indices by site from surveys upstream from 5 lowhead dams in the Fox River, IL, July 2003. Site codes are Gv (Geneva), NB (North Batavia), SB (South Batavia), NA (North Aurora), and Au (Aurora). FF are free-flowing sites and Im are impounded sites. Site Mussel data GvFF GvIm NBFF NBIm SBFF NAFF NAIm AuFF AuIm Effort (collector-hours) 2 2 4 2 4 4 2 2 1 Abundance of live indiv. 4 0 1 0 43 37 0 19 0 Catch-per-unit-effort 2.0 0 0.3 0 10.8 9.3 0 9.5 0 Extant species richness 2 0 1 0 4 5 0 3 0 Historic species richness 10 1 13 1 8 12 1 9 4 % missing species 80 100 92 100 50 58 100 67 100 Habitat quality index QHEI 59.5 34.0 74.5 46.5 76.0 83.0 39.0 72.0 30.5 SHAP 78 61 142 63 129 142 77 118 58 130 Northeastern Naturalist Vol. 14, No. 1 Table 2. Freshwater mussel assemblage data by site from surveys upstream from 5 lowhead dams in the Fox River, IL, July 2003. Species found at a given site during previous visits are indicated by an asterisk (*) (data from the INHS Mollusk Collection). Numbers represent individuals collected live and “V” indicates species collected only as valves. Site codes are Gv (Geneva), NB (North Batavia), SB (South Batavia), NA (North Aurora), and Au (Aurora). FF are freeflowing sites and Im are impounded sites. Site Scientific name Common name GvFF GvIm NBFF NBIm SBFF NAFF NAIm AuFF AuIm Anodontinae Alasmidonta marginata Say Elktoe * * * * Lasmigona complanata (Barnes) White heelsplitter 1 10 V Lasmigona costata (Rafinesque) Flutedshell V V Pyganodon grandis (Say) Giant floater 3 V V 36 2 V * V Utterbackia imbecillis (Say) Paper pondshell * V V Ambleminae Amblema plicata (Say) Threeridge V * Cyclonaias tuberculata (Rafinesque) Purple wartyback V* * Elliptio dilatata (Rafinesque) Spike V V V V * Fusconaia flava (Rafinesque) Wabash pigtoe V V V Pleurobema sintoxia (Rafinesque) Round pigtoe V V * Quadrula pustulosa (Lea) Pimpleback * Quadrula quadrula (Rafinesque) Mapleleaf 2 20 3 V Lampsilinae Actinonaias ligamentina (Lamarck) Mucket * V * 7 V Lampsilis cardium Rafinesque Plain pocketbook 1 1 3 7 6 V Lampsilis siliquoidea (Barnes) Fat mucket * Toxolasma parvus (Barnes) Lilliput 2 Venustaconcha ellipsiformis (Conrad) Ellipse ** V V Villosa iris (Lea) Rainbow * 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 131 collector-hours at the 4 impounded sites. An additional 8 species were represented as valves at free-flowing sites, and 4 species were collected as valves at impounded sites (Table 2). None of the species collected live are listed at the state (Illinois) or federal level; two species, Cyclonaias tuberculata (Rafinesque) (purple wartyback) and Elliptio dilatata (Rafinesque) (spike), collected as valves are listed as state-threatened, and these were found only at free-flowing sites. A state-endangered species, Villosa iris (Lea) (rainbow), previously had been recorded at a free-flowing site within the study area, but was not collected during this survey (Table 2). At free-flowing sites, mean CPUE was 6.4 (SD = 4.84) per-hour, mean extant species richness was 3.0 (SD = 1.58), and mean percent missing species was 69.5 (SD = 16.91) (Table 1). Because no live unionids were found at impounded sites, mean CPUE was 0.0 per-hour, extant species richness was 0.0, and mean percent missing species was 100.0. MANOVA showed that the freshwater mussel assemblage varied significantly between site types (􀁨 = 0.23, n = 9, F = 5.73, P = 0.04). ANOVA indicated a significantly higher CPUE (F1,7 = 6.69, P = 0.04) and extant species richness (F1,7 = 14.00, P = 0.007) and significantly lower percent missing species (F1,7 = 13.07, P = 0.009) in free-flowing sites than impounded sites. Examination of literature reviews (n = 7 articles) and museum collection holdings (n > 2000 specimens) of the Fox River basin indicated that lowhead dams appear to limit the upstream distribution of 5 species of freshwater mussels within the basin. The distribution of Leptodea fragilis (Rafinesque) (fragile papershell), Potamilus alatus (Say) (pink heelsplitter), Potamilus ohiensis (Rafinesque) (pink papershell), Tritogonia verrucosa (Rafinesque) (pistolgrip), and Truncilla donaciformis (Lea) (fawnsfoot) was related to the presence of dams in the Fox River. Records suggest that: 1) T. donaciformis is extant only downstream from the Dayton Dam, the downstream-most dam in the Fox River; 2) P. alatus and T. verrucosa currently are found only downstream from the Dayton Dam, but a historical record (pre-1900) for each species exists downstream from the Carpentersville Dam (there is no evidence that either species now exists at the Carpentersville Dam site); 3) P. ohiensis is extant from downstream from the Yorkville Dam (the second downstream-most dam) to the confluence of the Illinois River; and 4) L. fragilis is found from downstream from the Yorkville Dam to the confluence of the Illinois River, in addition to an isolated population downstream from the Carpentersville Dam (no records exist between the Yorkville and Carpentersville dams) (Fig. 2). These 5 species are widespread and fairly common in the upper Midwest (Cummings and Mayer 1992), and all have been collected live at several locations in the Illinois River basin both upstream and downstream from its confluence with the Fox River and in neighboring systems (INHS Mollusk Collection). The question of why there is such a large distribution gap (e.g., no records exist between the Yorkville and Carpentersville dams) for L. fragilis, P. alatus, and T. verrucosa could not be addressed in this study. 132 Northeastern Naturalist Vol. 14, No. 1 Discussion The habitat characteristics and the freshwater mussel assemblage within the Fox River study area varied significantly between site types, suggesting that these lowhead dams have negative effects on habitat and freshwater Figure 2. Distribution of (a) Truncilla donaciformis, (b) Potamilus alatus and Tritogonia verrucosa, (c) Potamilus ohiensis, and (d) Leptodea fragilis in the Fox River basin, IL. Solid circles (●) denote sites where specimens have been found since 1970, solid triangles (▲) denote sites where specimens were found pre-1900, and open circles (O) denote sites where specimens were not found. Solid rectangles (❚) are lowhead dams and include Dayton, Carpentersville, and Yorkville. 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 133 mussels similar to those reported for large dams and lowhead dams in other lotic systems. Impounded sites had lower QHEI and SHAP scores than freeflowing sites, indicating that these areas had poor habitat quality and degraded conditions. Impounded sites had greater depths, channel alterations, and silt deposition, and less gradient, riffle/run sequences, diverse substrate composition, substrate stability, and hydrologic diversity. These characteristics are often found in impounded areas upstream from large dams (Baxter 1977) and lowhead dams (Tiemann et al. 2004), and cause alterations in freshwater mussel faunas (Dean et al. 2002, Parmalee and Hughes 1993, Vaughn and Taylor 1999). Reductions in the freshwater mussel assemblage likely are the result of modifications in habitat in the impounded areas. The freshwater mussel assemblage variables for the free-flowing areas were within the ranges reported by Schanzle et al. (2004) for the Fox River mainstem. Free-flowing sites had higher CPUE and extant species richness and lower percent missing species than impounded sites. Although we found valves at impounded sites, we found no live specimens and therefore zero extant species richness and 100% missing species in these areas. The 6 species we collected at freeflowing sites are widespread and common in the Fox River (Schanzle et al. 2004), yet we did not collect them in impounded areas. Reductions in freshwater mussel abundance and/or extant species richness are common in impounded areas, as reported for both large dams (Combes and Edds 2005) and lowhead dams (Dean et al. 2002). CPUE and extant species richness of freshwater mussels in the Fox River free-flowing areas is lower compared to similar areas in other streams in the Illinois River basin. Schanzle et al. (2004) stated that the decline in abundance and species richness parallels the increased urbanization of the Fox River watershed, despite the passage of the Clean Water Act in 1972. Even though the Fox River has had water quality problems (e.g., high nutrient loads) due to urban runoff, municipal wastewater discharges, and other domestic and industrial sources, water quality has been shown to be improving over the last few decades (Santucci et al. 2005). However, recolonization by freshwater mussels could take decades and is dependent upon source populations of both unionids and host fishes (Sietman et al. 2001, Watters 1996). Given the large number of lowhead dams in the Fox River, their negative effects on the stream ecosystem could be widespread. Lowhead dams might contribute to the overall reduction of the freshwater mussel fauna by not only creating unsuitable and fragmented habitat, but also by artificially restricting freshwater mussel distributions. The 5 species that appear to have distributions limited by dams in the Fox River basin have been collected in the headwaters of neighboring unimpounded systems, including the Mazon River and Aux Sable Creek (INHS Mollusk Collection), both of which are Illinois River tributaries that are in the same physiographic region as the Fox River basin. Watters (1996) reported a similar distribution pattern for L. 134 Northeastern Naturalist Vol. 14, No. 1 fragilis and P. alatus in 5 midwestern stream systems. Both species appeared to have their distributions limited by lowhead dams, but were collected throughout neighboring unimpounded systems. Watters (1996) stated that the distribution pattern of L. fragilis and P. alatus in relation to the locations of dams could be coincidental; however, that these species were found in the headwaters of neighboring, unimpounded systems implies that their distributions cannot be attributed to the size of the stream reach or distance from the mouth of the stream. The 5 species listed above are expanding their ranges in the Illinois River basin (Cummings and Mayer 1997, Sietman et al. 2001; INHS Mollusk Collection). However, colonization of upstream portions of the Fox River might not occur due to lowhead dams. Watters (1996) reported that the distributions of L. fragilis and P. alatus might be restricted because lowhead dams prohibit upstream movement of their host fish, Aplodinotus grunniens Rafinesque (freshwater drum). These patterns also might occur for P. ohiensis and T. donaciformis because they also use A. grunniens as a host; T. donaciformis also uses Sander canadensis (Griffith and Smith) (sauger) as a host (Watters 1994). Watters (1996) suggested that the distribution pattern of Quadrula quadrula (Rafinesque) (mapleleaf) might be limited due to lowhead dams prohibiting the upstream movement of its host fish, Pylodictis olivaris (Rafinesque) (flathead catfish). The same also might occur for T. verrucosa because it also uses P. olivaris and other ictalurids as a host (G.T. Watters, Ohio State University, Columbus, OH, pers. comm.). Sander canadensis is found only downstream from the Dayton Dam, whereas A. grunniens and P. olivaris are present throughout the Fox River, including impounded areas (Santucci et al. 2005). Because the 5 freshwater mussel species listed above are not distributed throughout the Fox River, or are in small, isolated populations, their chances of parasitizing host fishes are low. Even if the host fishes do become parasitized, the lowhead dams could act as physical barriers and impede the upstream movement of the fishes, and thus limit freshwater mussel distribution and range expansion within the watershed. Therefore, restricted dispersal capabilities, coupled with suboptimal habitat in inundated areas, limit the potential of freshwater mussels for sustaining their populations in portions of the Fox River. Other anthropogenic disturbances (e.g., water quality) often co-occur with dams to cause alterations in a freshwater mussel fauna (Vaughn and Taylor 1999). Lowhead dams play a notable role in the widespread occurrence of substandard water quality in the Fox River (Santucci et al. 2005). Dissolved oxygen concentrations in the river have been shown to widely fluctuate on a daily basis in impounded areas; these concentrations often reach substandard levels, last for most of the day, and occur when water temperatures are high and discharge is low (Santucci et al. 2005), creating unsuitable conditions for freshwater mussels. Also, pollutants could settle in the sediments of impounded areas and further compound the unfavorable conditions for the freshwater mussel fauna in these areas (Harman 1974). 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 135 Given the proportion of impounded waters in the Fox River, lowhead dams are having an adverse effect on the ecological condition of the stream (Santucci et al. 2005). We recognize the limitations of our study (e.g., limited number of sites and limited sampling effort). However, our results suggest a negative effect of lowhead dams on habitat characteristics and freshwater mussel assemblages similar to those found in other studies on lowhead dams (e.g., Dean et al. 2002, Tiemann et al. 2004, Watters 1996). Future studies could address water quality and pollutants in their relations to dams/dam removal and freshwater mussels. Our data, coupled with those of other dam studies, can be used in the protection of stream ecosystems. Future Considerations Dam removal is one management option for improving the condition of streams. The North Batavia Dam and South Batavia Dam in the Fox River might be removed in the near future. Over the short term, dam removal has been shown to result in desiccation of freshwater mussels within the former impounded areas and suffocation of freshwater mussels from the release of trapped sediments in downstream reaches (Sethi et al. 2004). However, over the long term, dam removal has been shown to improve biotic integrity and habitat quality upstream and downstream from the formerly impounded areas and enhance fish passage in streams (Kanehl et al. 1997, Orr and Stanley 2006, Stanley et al. 2002). With proper dam-removal methods (e.g., notching of the dam to control sediment- flushing or dredging of sediments), freshwater mussels could have a chance to recolonize regions of the Fox River without being artificially supplemented if habitat conditions are optimal, host fishes are extant, and source populations are in close proximity (Sietman et al. 2001). Reconnecting the river should allow improved habitat characteristics and water quality conditions and corresponding improvements to fish and freshwater mussel assemblages. Acknowledgments The Office of Water Resources, Illinois Department of Natural Resources (IDNR), Environmental Protection Trust Fund of the IDNR, and the Illinois Department of Transportation provided funding for this study; R. Lee coordinated activities with the Office of Water Resources; J. Butler, S. Butler, A. Defore, and B. Sauder assisted in data collection; V. Santucci and G. Watters shared experiences; and K. Cummings, G. Levin, D. Thomas, B. Tiemann, C. Warwick, and two anonymous reviewers offered constructive comments on the manuscript. Literature Cited Baker, F.C. 1906. A catalogue of the Mollusca of Illinois. Bulletin of the Illinois State Laboratory of Natural History 7:53–136. 136 Northeastern Naturalist Vol. 14, No. 1 Baker, F.C. 1928. The fresh water Mollusca of Wisconsin. Part II. Pelecypoda. Bulletin of the Wisconsin Geological and Natural History Survey, Vol. 70, No. 2. University of Wisconsin, Madison, WI. 495 pp. Bates, J.M. 1962. The impact of impoundment on the mussel fauna of Kentucky Reservoir, Tennessee River. American Midland Naturalist 68:232–236. Baxter, R.M. 1977. Environmental effects of dams and impoundments. Annual Review of Ecology and Systematics 8:255–283. Blalock, H.N., and J.B. Sickel. 1996. Changes in mussel (Bivalvia: Unionidae) fauna within the Kentucky portion of Lake Barkley since impoundment of the lower Cumberland River. American Malacological Bulletin 13:111–116. Calkins, W.W. 1874. The land and fresh water shells of LaSalle County, IL. Proceedings of the Ottawa Academy of Natural Sciences. H. McAllaster and Co., Printers, Chicago, IL. 48 pp. Combes, M., and D. Edds. 2005. Mussel assemblages upstream from three Kansas reservoirs. Journal of Freshwater Ecology 20:139–148. Cummings, K.S., and C.A. Mayer. 1992. Field Guide to Freshwater Mussels of the Midwest. Illinois Natural History Survey, Manual 5, Champaign, IL. 194 pp. Cummings, K.S., and C.A. Mayer. 1997. Distributional checklist and status of Illinois freshwater mussels (Mollusca: Unionacea). Pp. 129–145, In K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo (Eds.). Conservation and Management of Freshwater Mussels II: Initiatives for the Future. Proceedings of a UMRCC Symposium, 16–18 October 1995, St. Louis, MO. Upper Mississippi River Conservation Committee, Rock Island, IL. 293 pp. Dean, J., D. Edds, D. Gillette, J. Howard, S. Sherraden, and J. Tiemann. 2002. Effects of lowhead dams on freshwater mussels in the Neosho River, Kansas. Transactions of the Kansas Academy of Science 105:232–240. Eldridge, J.A. 1914. The mussel fishery of the Fox River. Report of the US Commissioner of Fisheries for 1913. Appendix VII:1–8. Harman, W.N. 1974. The effects of reservoir construction and canalization on the mollusks of the upper Delaware watershed. Bulletin of the American Malacological Union, Inc. 1974:12–14. Holtrop, A.M., and R.U. Fischer. 2002. Relations between biotic integrity and physical habitat in the Embarras River basin, Illinois. Journal of Freshwater Ecology 17:475–483. Illinois EPA. 1994. Stream Habitat Assessment Procedures (SHAP). Illinois Environmental Protection Agency. Springfield, IL. 8 pp. Kanehl, P.D., J. Lyons, and J.E. Nelson. 1997. Changes in the habitat and fish community of the Milwaukee River, Wisconsin, following removal of the Woolen Mills Dam. North American Journal of Fisheries Management 17:387–400. Mathiak, H.A. 1979. A river survey of the unionid mussels of Wisconsin 1973–1977. Sand Shell Press, Horicon, WI. 75 pp. Metcalfe-Smith, J.L., J. Di Maio, S.K. Staton, and G.L. Mackie. 2000. Effect of sampling effort on the efficiency of the timed-search method for sampling freshwater mussel communities. Journal of the North American Benthological Society 19(4):725–732. Obermeyer, B.K. 1998. A comparison of quadrats versus timed snorkel searches for assessing freshwater mussels. American Midland Naturalist 139:331–339. 2007 J.S. Tiemann, H.R. Dodd, N. Owens, and D.H. Wahl 137 Ohio EPA. 1989. Biological criteria for the protection of aquatic life: Volume III. Standardized biological field sampling and laboratory methods for assessing fish and macroinvertebrate communities. Ohio Environmental Protection Agency, Columbus, OH. 10 pp. Orr, C.H., and E.H. Stanley. 2006. Vegetation development and restoration potential of drained reservoirs following dam removal in Wisconsin. River Research and Applications 22:281–295. Parmalee, P.W., and M.H. Hughes. 1993. Freshwater mussels (Mollusca: Pelecypoda: Unionidae) of Tellico Lake: Twelve years after impoundment of the Little Tennessee River. Annals of Carnegie Museum 62:81–93. Parmalee, P.W., and R.R. Polhemus. 2004. Prehistoric and pre-impoundment populations of freshwater mussels (Bivalvia: Unionidaue) in the South Fork Holston River, Tennessee. Southeastern Naturalist 3:231–240. Santucci, V.J., S.R. Gephard, and S.M. Pescitelli. 2005. Effects of multiple low-head dams on fish, macroinvertebrates, habitat, and water quality in the Fox River, Illinois. North American Journal of Fisheries Management 25:975–992. Schanzle, R.W., G.W. Kruse, J.A. Kath, R.A. Klocek, and K.S. Cummings. 2004. The freshwater mussels (Bivalvia: Unionidae) of the Fox River basin, Illinois and Wisconsin. Illinois Natural History Survey, Biological Notes 141, Champaign, IL. 35 pp. Sethi, S.A., A.R. Selle. M.W. Doyle, E.H. Stanley, and H.E. Kitchel. 2004. Response of unionid mussels to dam removal in Koshkonong Creek, Wisconsin (USA). Hydrobiologia 525:157–165. Sietman, B.E., S.D. Whitney, D.E. Kelner, K.D. Blodgett, and H.L. Dunn. 2001. Post-extirpation recovery of the freshwater mussel (Bivalvia: Unionidae) fauna in the upper Illinois River. Journal of Freshwater Ecology 16:273–281. Stanley, E.H., M.A. Luebke, M.W. Doyle, and D.W. Marshall. 2002. Short-term changes in channel form and macroinvertebrate communities following low-head dam removal. Journal of the North American Benthological Society 21:172–187. Strayer, D.L., D.C. Hunter, L.C. Smith, and C.K. Borg. 1994. Distribution abundance, and roles of freshwater clams (Bivalvia, Unionidae) in the freshwater tidal Hudson River. Freshwater Biology 31:239–248. Suloway, L., J.J. Suloway, and E.E. Herricks. 1981. Changes in the freshwater mussel (Mollusca: Pelecypoda: Unionidae) fauna of the Kaskaskia River, Illinois, with emphasis on the effects of impoundment. Transactions of the Illinois State Academy of Science 74:79–90. Tiemann, J.S., D.P. Gillette, M.L. Wildhaber, and D.R. Edds. 2004. Effects of lowhead dams on riffle-dwelling fishes and macroinvertebrates in a Midwestern river. Transactions of the American Fisheries Society 133:705–717. Turgeon, D.D., A.E. Bogan, E.V. Coan, F.G. Hochberg, W.G. Lyons, P.M. Mikkelsen, J.F. Quinn, Jr., C.F.E. Roper, G. Rosenberg, B. Roth, A. Scheltema, M.J. Sweeney, F.G. Thompson, M. Vecchione, and J.D. Williams. 1998. Common and Scientific Names of Aquatic Invertebrates from the United States and Canada: Mollusks. 2nd Edition. American Fisheries Society, Special Publication 26, Bethesda, MD. 536 pp. Vaughn, C.C., and C.M. Taylor. 1999. Impoundments and the decline of freshwater mussels: A case study of an extinction gradient. Conservation Biology 13:912–920. 138 Northeastern Naturalist Vol. 14, No. 1 Vaughn, C.C., C.M. Taylor, and K.J. Eberhard. 1997. A comparison of the effectiveness of timed searches vs. quadrat sampling in mussel surveys. Pp. 157–162, In K.S. Cummings, A.C. Buchanan, C.A. Mayer, and T.J. Naimo (Eds.). Conservation and Management of Freshwater Mussels II: Initiatives for the Future. Proceedings of a UMRCC Symposium, 16–18 October 1995, St. Louis, MO. Upper Mississippi River Conservation Committee, Rock Island, IL. 293 pp. Watters, G.T. 1994. An annotated bibliography of the reproduction and propagation of the Unionoidea (primarily of North American). Ohio Biological Survey, Miscellaneous Contributions Number 1, Columbus, OH. 158 pp. Watters, G.T. 1996. Small dams as barriers to freshwater mussels (Bivalvia, Unionoida) and their hosts. Biological Conservation 75:79–85. Williams, J.D., and S.L. Fuller. 1992. Effects of impoundments on freshwater mussels (Mollusca: Bivalvia: Unionidae) in the main channel of the Black Warrior and Tombigbee rivers in western Alabama. Bulletin of the Alabama Museum of Natural History 13:1–10. Williams, J.D., M.L. Warren, Jr., K.S. Cummings, J.L. Harris, and R.J. Neves. 1993. Conservation status of freshwater mussels of the United States and Canada. Fisheries 18(9):6–22. Zar, J.H. 1999. Biostatistical Analysis. 4th Edition. Prentice-Hall, Upper Saddle River, NJ. 663 pp. + appendices.