Clark Lake Research Articles

Strike–Slip Fault Reactivation Triggered by Hydraulic-Natural Fracture Propagation during Fracturing Stimulations near Clark Lake, Alberta

Strike–Slip Fault Reactivation Triggered by Hydraulic-Natural Fracture Propagation during Fracturing Stimulations near Clark Lake, Alberta

Factors affecting walleye and sauger recruitment in Lewis and Clark Lake, South Dakota, 2001–2022

AbstractAbundance of adult walleye (Sander vitreus) and sauger (Sander canadensis), two important sport fishes, decreased significantly during 2001–2022 in Lewis and Clark Lake, a border water between Nebraska and South Dakota, despite walleye fingerling stocking and stable age‐0 abundance of both species. We sought to identify factors that drove variation in age‐0 abundance from 2001 to 2022 using an information theoretic approach. Age‐0 walleye catch per unit effort (CPUE) was correlated to mean monthly outflow, mean annual precipitation, and mean April gauge height in a delta. Age‐0 sauger CPUE was correlated to adult conspecific CPUE, mean April Heating Degree Days, and mean annual precipitation. Our findings suggest that both biotic and abiotic factors were important for explaining variation in age‐0 CPUE of sauger, but mainly abiotic factors for walleye. As such, manipulation of abiotic factors (i.e., outflow) by installing entrainment barriers may be more effective than manipulation of biotic factors (i.e., stocking).

From fragments to connections to restoration: A case history of emergent sociocultural services in the Clark Fork River and Lake Pend Oreille fishery

Abstract Lake Pend Oreille and the Clark Fork River provide essential ecosystem services, including fisheries and hydroelectric power, to residents of Montana, Idaho, and Washington. Although conflicts exist, these services are maintained in concert by emergent sociocultural services created by a multi-institutional, transboundary collaboration. This has been enabled by an innovative Federal Energy Regulatory Commission license settlement agreement among a multitude of stakeholders. The consensus-based agreement promotes connections among people, projects, waterways, and fish populations. Collaborative management efforts allow stakeholders to address controversial issues, such as invasive fish suppression. We demonstrate how reciprocal cultural ecosystem services and services to ecosystems can enable ecosystem-scale restoration that addresses invasive species, habitat protection, and water quality management. Continued ecosystem management success relies on sustaining the relationship-building and shared knowledge services that have emerged over the past 25 years.

Expansion of woody vegetation on a Missouri River reservoir delta‐backwater

AbstractConstruction of dams in the mid‐20th century reduced channel dynamism, sediment transport, and regeneration of riparian trees on the Missouri River. Opportunities for forest regeneration, however, may occur where the Missouri River or tributaries deposit sediments in reservoir headwaters, forming deltaic and associated upstream backwater areas. One such delta‐backwater occurs at the confluence of the Niobrara and Missouri rivers upstream from Lewis and Clark Lake in southeastern South Dakota and northeastern Nebraska. We investigated spatiotemporal patterns of tree recruitment through vegetation sampling in 2017–2018, dendrochronology, and analysis of aerial photography from 2006 to 2016. We sampled woody vegetation in 47 plots and took tree‐ring samples from one to two trees within each plot to determine establishment dates. Woody vegetation was dominated by Populus deltoides (cottonwood) and Salix amygdaloides (peachleaf willow) in the tree layer and Salix interior (sandbar willow) in the shrub layer. Tree establishment occurred primarily in 2010–2012 and was distributed throughout the study area, including at the delta‐reservoir interface. LiDAR data showed that most of the delta‐backwater experienced a 0.5‐m increase in elevation in 2005–2011, a period that included high flows in 2010 on the Niobrara River and 2011 on the Missouri River. Woody vegetation decreased 8% from 2006 to 2012, but doubled from 2012 to 2016, colonizing areas of previous sandbar and herbaceous vegetation. These woodlands represent early successional habitat that is in decline elsewhere along the river. Understanding vegetation dynamics within reservoir delta‐backwaters may be vital for forecasting changes in regulated riverine landscapes, assessing biodiversity values of these ecosystems, and informing sustainable reservoir management.

Factors affecting the abundance of age‐0 sport fish in four mainstem Missouri River reservoirs

AbstractThe age‐0 abundance of eight sport fish species in the four mainstem Missouri River reservoirs in South Dakota was evaluated to estimate the influence of environmental and biological factors on age‐0 species abundance. Datasets (at least ten consecutive years) from each reservoir were analysed to evaluate the effects of both monthly (i.e. gauge height, temperature and precipitation) and annual (i.e. cooling degree days and heating degree days, minimum, average, and maximum temperature, and average precipitation) environmental and biological factors. Biological factors including age‐0 prey fish abundance (i.e. gizzard shad Dorosoma cepedianum [Leseuer] abundance), age‐0 sport fish abundance and adult sport fish abundance were examined. Factors were included that are known to have impacts on abundance of age‐0 sport fish in other systems. The abundance of all sport fish species was stable or increasing in all reservoirs, except for walleye Sander vitreus (Mitchell) and white bass Morone chrysops (Rafinesque) in Lewis and Clark Lake. Age‐0 white crappie was the most supported model for explaining age‐0 walleye abundance in Lewis and Clark Lake, and adult white crappie abundance was the most supported model parameter for explaining age‐0 white bass abundance in the reservoir. Findings of the current study highlight the need for species‐specific management of both environmental (i.e. flow manipulation) and biological factors (i.e. harvest limits for sport fish) to increase the abundance of age‐0 sport fish. Due to the dynamic nature of aquatic systems, resulting requirements for management agencies are system‐specific evaluations and management approaches.

A Review of Zebra Mussel Biology, Distribution, Aquatic Ecosystem Impacts, and Control with Specific Emphasis on South Dakota, USA

Zebra mussels Dreissena polymorpha are a native bivalve from eastern Europe. They were first detected in North America in Lake St. Clair in 1988 and were presumably introduced via infested ballast water. Zebra mussels have spread rapidly across the United States, with 31 states reporting infestations as of 2019. Zebra mussels were first detected in South Dakota, USA, in 2015 in Lewis and Clark Lake and McCook Lake, with subsequent infestations occurring in Lake Yankton in 2017, Lakes Francis Case and Sharpe in 2019, and Pickerel Lake, Kampeska Lake, and Lake Cochrane in 2020. This review paper presents information on zebra mussel biology and control, with specific information on the waters of South Dakota, USA.

Factors Related to Age-0 Native Fish Catch per Unit Effort in the South Dakota Missouri River Reservoirs

AbstractThe Missouri River in South Dakota was dammed in the 1950s and 1960s, altering the biotic and abiotic factors that potentially affect native species in the mainstem reservoirs. Little research has been conducted regarding what factors regulate age-0 catch per unit effort (CPUE) of native fish species since the damming occurred. Thus, we examined age-0 CPUE for 13 native fish species in the four Missouri River mainstem reservoirs. We analyzed data from 1995 to 2015 in Lake Oahe, 2002 to 2016 in Lake Sharpe, 1998 to 2008 in Lake Francis Case, and 2000 to 2013 in Lewis and Clark Lake. Not all species were sampled in all reservoirs. We evaluated potential environmental (inflow, gauge height, peak flow, precipitation, air temperature) and biological (CPUE of other native species, nonnative species, and predators) factors that have documented impacts on age-0 native fish. Significant relationships existed between age-0 native fish CPUE and both biotic and abiotic factors in all four reservoirs, but were species- and reservoir-dependent. Age-0 CPUE was either stable or increasing in all species examined in all reservoirs except age-0 Emerald Shiner Notropis atherinoides in Lewis and Clark Lake. Age-0 Emerald Shiner CPUE in Lewis and Clark Lake was most supported by biological models (e.g., total age-0 nonnative and adult White Bass Morone chrysops CPUE), and a positive relationship existed between age-0 Emerald Shiner and both factors. We believe our findings provide valuable insight into successful management of native fish populations.

Long-Term Data Suggest Potential Interactions of Introduced Walleye and Smallmouth Bass on Native Sauger in Four Missouri River Impoundments

Abstract Sauger Sander canadensis, Walleye Sander vitreus, and Smallmouth Bass Micropterus dolomieu, are important sportfish in the four main stem Missouri River reservoirs in South Dakota: Lakes Oahe, Sharpe, Francis Case, and Lewis and Clark. However, native Sauger populations, once assumed to be stable, may be in decline. To identify temporal trends and potential interspecific mechanisms affecting Sauger populations, we examined their long-term abundance trends in standard gillnet surveys and angler catch and harvest trends in long-term creel surveys. We also used a robust design occupancy model to examine changes in within-lake distribution of this species. There are concerns regarding the effects of Walleye and Smallmouth Bass on Sauger, so we also described the population trends of these potential competitors. Standard gillnet surveys indicated declining abundance of both Sauger and Walleye in Lakes Oahe and Sharpe. Sauger abundance has trended down in Lewis and Clark, but upward in Francis Case. Conversely, Walleye abundance trends declined in Francis Case and increased in Lewis and Clark. Occupancy (ψ̂) of Sauger declined in all four reservoirs, indicating a contracting distribution throughout the reservoirs. Walleye occupancy remained ∼1.0. Smallmouth Bass occupancy increased in the three reservoirs with sufficient data for analysis, excluding Lewis and Clark Lake. Smallmouth Bass exhibited steady increases in angler catch and harvest, as well as abundance in long-term gillnet surveys, suggesting expanding and increasing populations. Habitat alteration is hypothesized to be a major driver of the Sauger occupancy and abundance declines. However, Walleye and Smallmouth Bass interactions could also be contributing to observed declines of native Sauger.

Mid-late Holocene anthropogenic and natural variations in geochemistry and sedimentation in the Yazoo Basin: Clark Lake, Sharkey County, Mississippi

ABSTRACTA 4000-yr history at Clark Lake reveals natural variations in sediment geochemistry and nutrient levels and anthropogenic influence on twentieth century sedimentation rates. Sediment texture and ridge and swale topography indicate that the channel system creating Clark Lake is now occupied by the Yazoo River. Between 1.24 and 0.60 m (2522–865 cal yr BP), total carbon percentages and the C/N ratio average 42% and 17, respectively. The base of the 1650-yr interval and onset of high organic activity in the lake coincides with the abandonment of the Yazoo Meander Belt. The top of the interval is marked by a drop in C/N ratio to 11 and a geochemical transition zone. No change in the rate of sediment accumulation or clay mineralogy was observed despite increased cumulative percentages of Al, Fe, K, Mg, Mn, Ca, and Na. The decrease in organic activity at 865 cal yr BP is attributed to unfavorable growth conditions related to the entrenchment of the Yazoo River and changes in the hydroperiod of the area. Significant floodplain alteration was completed in 1978, but the only major effect was increased sedimentation in the late twentieth century due to the completion of the Whittington Auxiliary Channel.

Otolith Microchemistry Reveals Natal Origins of Walleyes in Missouri River Reservoirs

AbstractReproductive habitats are vital for sustaining fish populations, but their location and relative natal contributions are often unknown or poorly understood. We used otolith microchemistry to examine natal origins of Walleyes Sander vitreus in Missouri River reservoirs (i.e., Lake Oahe, Lake Sharpe, Lake Francis Case, and Lewis and Clark Lake) in North Dakota and South Dakota. Water Sr:Ca and Ba:Ca were spatially heterogeneous and temporally consistent in all impoundments. Otolith Sr:Ca and Ba:Ca from age‐0 Walleyes permitted the reclassification of fish to known natal habitats (i.e., tributary, embayment, main stem) and individual sites with 87% and 75% accuracy, respectively. Natal contributions were highest in tributaries, particularly those in Lake Oahe, where 32% of all adults and 77% of Lake Oahe adults hatched. Embayments and main‐stem environments had high natal contributions (67–78%) in Lakes Sharpe and Francis Case and Lewis and Clark Lake, where tributaries are less abundant. Our research demonstrates the utility of otolith microchemistry for measuring habitat‐ and site‐specific natal contributions and provides further information that can be used in managing Walleyes in Missouri River reservoirs, particularly for broodstock collection, habitat protection and restoration, and harvest regulations.Received April 17, 2015; accepted December 11, 2015 Published online March 30, 2016

Demographic responses of piping plovers to habitat creation on the Missouri river

ABSTRACTThe piping plover (Charadrius melodus) was listed under the United States Endangered Species Act (ESA) because of habitat loss and excessive predation. The Missouri River provides important habitat for the Great Plains population of the species, some of which nest and forage on river sandbars deposited naturally during high river flows. The United States Army Corps of Engineers (USACE) operates a series of dams on the river that affect water level and the size, number, distribution, and vegetative cover of these sandbars. As a federal agency, USACE is required by the ESA to have a program to conserve the piping plover, and is prohibited from engaging in activities that jeopardize the plover's continued existence. Pursuant to these obligations, the USACE implemented a habitat creation program on the Gavins Point Reach (GVP) and Lewis and Clark Lake (LCL) on the Missouri River from 2004 to 2011. This habitat creation provided an opportunity to study the piping plover's demographic response to several habitat types, and in particular to habitat creation. The goal of this study was to assess the effects of management on plovers using the Missouri River. We studied the changes in engineered and natural habitats, and compared the effects of newly engineered habitat versus naturally created habitat on plover demography during 2005–2011. To this end, we estimated changes in nesting habitat (open or sparsely vegetated dry sand) and examined the factors affecting nest success, chick survival from hatching to fledging, survival, and movement (between and among engineered and natural sandbars) of hatch‐year and adult birds, fidelity of plovers to the study area, and immigration of plovers into engineered habitat. We used demographic estimates to determine overall and habitat‐specific reproductive output and overall population growth rate. Under the assumption that plovers are habitat limited on the Missouri River, we predicted that they would respond positively to the creation of engineered habitat, that their demographic rates would be higher at those sites than on older, natural sandbars, and that over time, the rates would resemble those on older, natural habitats. Engineered sandbars had proportionally more plover nesting habitat than natural sandbars, but the proportion of nesting habitat decreased through vegetation encroachment and erosion as the sandbars aged. Adult and hatch‐year plovers immigrated to engineered sandbars, but immigration slowed as nesting density increased. Nesting density on engineered sandbars increased soon after sandbar construction, peaked 2–3 years later, and then declined to levels similar to those on older, natural sandbars. Birds that nested on engineered sandbars had higher nest success, and those nesting on LCL had higher chick survival than those that nested on GVP sandbars. Adult survival did not differ between engineered or natural habitat, but apparent survival was lower for birds that were not known to nest, indicating higher emigration or mortality rates for non‐nesters. Adult and hatch‐year plovers had high fidelity to the study area (>60% for hatch‐year birds, >90% for adults), and hatch‐year fidelity was highest (>80%) when habitat availability increased. We estimated that given observed survival rates, the reproductive output needed for a stationary population was 1.25 chicks fledged per pair, a rate which was equaled or exceeded in 3 of 4 years on LCL, in 2 of 5 years on engineered sandbars on GVP, and in 1 of 5 years on natural sandbars on GVP. Our results support the hypothesis that piping plovers were habitat‐limited before and during the study. Although nest exclosure and predator control sometimes can improve reproductive output, we predict that these interventions will do little to increase population size unless there is additional habitat to capture enhanced productivity. Based on high fidelity rates and short distances between subsequent nesting attempts (median = 12 km for adults), we suggest that habitat construction be widely distributed within approximately 12 km of a source population to maximize the efficiency of the population‐building process. © 2015 The Wildlife Society.

Diet Breadth and Variability in Sander spp. Inferred from Stable Isotopes

AbstractWe used stable isotopes of carbon and nitrogen to evaluate trophic similarity between sauger Sander canadensis and walleye S. vitreus in three Missouri River impoundments characterized by unique differences in riverine habitat. Mean δ15N was similar for sauger and walleye in each reservoir ranging from 15.7 to 17.8‰ for sauger and 15.2 to 17.7‰ for walleye. However, mean δ13C was greater for sauger (−24‰) than for walleye (−25‰) in Lake Oahe (lacustrine habitat), where rainbow smelt Osmerus mordax is an important prey species for walleye. Variation in δ15N and δ13C values was similar between walleye and sauger in Lewis and Clark Lake (riverine habitat), but was greater for sauger than for walleye in Lake Oahe, implying that in pelagic environments, sauger exhibit a larger diet breadth and lower diet consistency compared with walleyes. Isotope analyses support observations from traditional gut content studies that diet overlap between sauger and walleye varies with environmental conditions and is more similar in riverine food webs than in large lakes and impoundments. Copyright © 2015 John Wiley & Sons, Ltd.

Numerical modeling of sediment flushing from Lewis and Clark Lake

Lewis and Clark Lake is located on the main stream of the Missouri River. The reservoir is formed behind Gavins Point dam near Yankton, South Dakota, U.S.A. The Lewis and Clark Lake reach extends about 40 km from the Gavins Point dam. The reservoir delta has been growing since the closure of Gavins Point dam in 1955 and has resulted in a 21% reduction of storage within the maximum pool of the reservoir. Among several sediment management methods, drawdown flushing has been recommended as a possible management technique. The engineering viability of removing sediments deposited in the lake should be examined by numerical modeling before implementing a drawdown flushing. GSTARS4 was used for this study and calibrated by using measured data from 1975 to 1995. Channel cross-section changes and amount of flushed sediment were predicted with four hypothetical flow scenarios. The flushing efficiencies of all scenarios were estimated by comparing the ratios between water consumption and flushed sediment during flushing.

Piping plover habitat selection and nest success on natural, managed, and engineered sandbars

AbstractLoss of breeding habitat and nest predation have contributed to the decline of many shorebird species. The United States Army Corps of Engineers (USACE) initiated a piping plover (Charadrius melodus) habitat creation and augmentation program on the Missouri River in the summer of 2004. The USACE increased unvegetated sandbar habitat by depositing dredged material (engineered sandbars) and by clearing vegetation from existing sandbars (managed sandbars). We evaluated the effects of this increase in nesting and foraging habitat on habitat selection and nest daily survival rate (DSR) of piping plovers on Lewis and Clark Lake and the Gavins Point Reach of the Missouri River from 2005 to 2007 (n = 623 nests). Piping plovers selected engineered sandbars more often than expected based on area and selected natural and managed habitats less than expected based on area. Daily survival rate on engineered sandbars was significantly higher than on natural or managed sandbars (log odds: 2.50, 95% CI: 1.05–5.94). Thus, plovers' habitat selection may have increased their nesting success. Our results suggest that habitat augmentation may stave off declines in piping plover populations limited by insufficient habitat and low nesting success. © 2011 The Wildlife Society.

Age‐Structured Assessment of Walleyes, Saugers, and Naturally Produced Hybrids in Three Missouri River Reservoirs

AbstractWalleye Sander vitreus and sauger Sander canadensis naturally hybridize in many populations, but the factors influencing the recruitment of hybrids are unknown. We determined relative year‐class strength for 1,454 saugers, walleyes, and naturally produced hybrids from three Missouri River reservoirs. Hybridization rates varied from 4% in Lakes Sharpe and Francis Case to 21% in Lewis and Clark Lake. Hybrids comprised multiple year‐classes in each system, indicating that hybridization does not occur in erratic pulses but at a consistent low‐level recruitment rate. The year‐class strength of hybrids was not correlated with that of either walleyes or saugers. Our models suggest that higher than average recruitment of walleyes, saugers, and hybrids can be expected during years with warmer spring and early summer water temperatures in Lake Sharpe and Lewis and Clark Lake and during years when inflow (from main‐stem discharge for hybrids and tributary inputs for saugers and walleyes) is reduced in Lewis and Clark Lake.

Distribution of Selenium, Mercury, and Methylmercury in Surficial Missouri River Sediments

Sediment deposition into Lewis and Clark Lake, an impoundment of the Missouri River, has caused substantial storage capacity reductions. Current proposals to hydrologically flush sediment would disturb river and reservoir sediment that may contain heavy metals. We quantified existing concentrations of selenium (Se), mercury (Hg), and methylmercury (MeHg) in surficial sediments upstream of and in Lewis and Clark Lake. We found elevated levels of Se (range 0.12-9.62 microg/g) and Hg (range 0.021.55 microg/g) at several sites throughout the study area; however, few sites contained levels of MeHg above detection limits. Sites with highest MeHg concentrations were found in Lewis and Clark Lake and ranged from below detection limit to 0.79 ng/g. We conclude that further investigation of sediment-sequestered contaminants in Lewis and Clark Lake should be conducted.

Ontogenetic patterns in prey use by pallid sturgeon in the Missouri River, South Dakota and Nebraska

The pallid sturgeon (Scaphirhynchus albus) is an endangered species native to the Missouri and Mississippi rivers. To date, recovery efforts have focused on stocking juvenile fish, but little is known about ontogenetic changes in diet composition. Although diet composition for pallid sturgeon is believed to change from macroinvertebrates to fish, it is unclear at what size and/or age these ontogenetic diet shifts occur. To evaluate diet composition, 29 hatchery-stocked pallid sturgeon (range 356–720 mm fork length [FL]; mean = 549; SE = 23) were collected from the Missouri River downstream of Fort Randall Dam, South Dakota and Nebraska during summer 2006. The majority of pallid sturgeon (72%) were captured within a large delta region formed by the Niobrara River in the headwaters of Lewis and Clark Lake. Predominant prey of pallid sturgeon based on percent occurrence was Ceratopogonidae (81%), Isonychiidae (67%), Chironomidae (52%), and fishes (24%). Percent composition by wet weight showed that diets were composed of fishes (68%), Ephemeroptera (23%), Decapoda (6%), and Diptera (3%). Graphical analysis of combined data showed that mayflies, particularly Isonychiidae, were an important component of pallid sturgeon diets. Nonetheless, the percent composition of fishes in the diet increased with pallid sturgeon body size; for fish > 600 mm FL (5–7 years of age) diets were composed primarily of fish prey (66%, mostly johnny darters Etheostoma nigrum). These findings highlight the importance of ontogenetic changes in diet composition for pallid sturgeon. Moreover, the unique habitat formed in the delta region is characterized by higher fish and invertebrate densities that may enhance foraging opportunities and thus improve recovery efforts for stocked pallid sturgeon.

Conversion of a Missouri River Dam and Reservoir to a Sustainable System: Sediment Management1

Abstract: A present and future challenge for water resources engineers is to extend the useful life of our dams and reservoirs. Ongoing reservoir sedimentation in impoundments must be addressed; sedimentation in many reservoirs already limits project benefits and effective project life. Sustainability requires that incoming sediment be moved downstream past the impounding dam. We use Lewis and Clark Lake, the most downstream of the six Missouri River main stem reservoirs, to demonstrate how a reservoir in advanced stages of its project life could be converted to a sustainable system with local benefits exceeding costs by a factor of 1.5. Full consideration of benefits would further enhance project justification. The proposed strategy involves four phases that will take about 50 years to complete. Cost estimates for this potential project range from the quantitative to the plausible, but it is clear that the results justify a full engineering, environmental, and economic study of this model project. If implemented, the project will create scientific knowledge and develop technologies useful for achieving sustainability at many other reservoirs in the Mississippi River basin and beyond.

Metazoan Parasites of Young-of-the-Year Paddlefish from Lewis and Clark Lake, Nebraska, U.S.A

Young-of-the-year paddlefish, Polyodon spa- thula (Polyodontidae), from Lewis and Clark Lake, an impoundment of the Missouri River in Nebraska, U.S.A., were surveyed for parasites. In 2001 and 2002, 28 and 48 fish were examinedfor parasites, respectively. Only the nematode Rhabdochona decaturensis infected fish collected in 2001, but 8 parasite taxa (R. decaturensis, Spinitectus sp., Camallanus sp., Contracaecum sp., Marsipometra sp., Diclybothrium hamulatum, Ergasilus elongatus, and 1 unidentified leech) infected fish collected in 2002. Rhabdo- chonadecaturensiswasthe mostcommonparasite,occurring in21.4%offishin2001and79.2%offishin2002.Prevalence of other parasite species infecting fish from 2002 was 33% or less. The helminth community of young-of-the-year paddle- fish in both years was dominated by nematodes. This study is the first report on parasites of young-of-the-year paddlefish and documents a new host record for R. decaturensis.

Flexible diet and trophic position of dreissenid mussels as inferred from stable isotopes of carbon and nitrogen

In this study, the trophic position and food-web impacts of invading zebra mussels (Dreissena polymorpha) were investigated by sampling mussels, seston (= phytoplankton), macrophytes, zooplankton, and surficial sediment in two small inland lakes (1999–2002) and similarly in western Lake Erie (1999 only). Tissues from quagga mussels (Dreissena bugensis) from Lake Erie were also analyzed. Stable-isotope ratios (15N/14N and 13C/12C) were used to identify likely food sources and estimate relative trophic position. For Lake Erie, stable-isotope ratios indicated no diet differences between the two mussel species. For all lakes, zooplankton δ13C was indicative of phytoplanktivory. The 13C stable isotope ratios indicated that seston comprised ~50% of food sources for mussels in Lake Erie, but 73%–97% and 52%–100% of the diet of mussel populations in Lake Wawasee and Clark Lake, respectively. Stable nitrogen isotope ratios placed zooplankton at trophic levels equal to or higher than those of mussels in seven of eight comparisons. Dreissena polymorpha and D. bugensis are able to exploit suspended detritus as a significant energy source, as well as compete directly with zooplankton for seston as a food source and with each other in areas of sympatry.