Great Plains Reservoir Research Articles

Seasonal and Spatial Distribution of Walleye Sex Ratios in a Large Nebraska Reservoir

Abstract The ratio of female to male Walleye Sander vitreus across the spatial scale of large reservoirs and during nonspawning times receives little attention, even though standardized sampling occurs during this time. This study evaluated whether the proportion of female Walleye collected from seasonal sampling at different spatial areas within a large reservoir fell within the 0.450–0.550 range, which would closely reflect a 1:1 female-to-male sex ratio. We used a Bayesian generalized linear mixed-effects model with a binomial probability distribution to assess the proportion of female Walleye, using season (spring and fall) and reservoir zone (riverine, transitional, and lacustrine) as fixed effects and year (2015 and 2016) as a random effect. We collected a total of 2,163 Walleye using standardized Nebraska Game and Parks Commission gill-netting methodology and determined sex on a random subsample of fish (n = 989) collected throughout each reservoir zone. There was no meaningful deviation from the 0.450–0.550 range in the mean posterior estimate of the proportion of female Walleye caught in the riverine and transitional zones during either spring or fall. The mean (SD) posterior estimate of the proportion of female Walleye in the lacustrine zone was 0.182 (0.024) in the spring and 0.621 (0.032) in the fall. These results are consistent with previous observations of increased male presence near spawning locations in the spring and demonstrate that increased fall female catch in the lacustrine zone could potentially bias sampling results. This study provides further insight into the distribution of sexes across the spatial gradient of a large Great Plains reservoir and demonstrates a need to sex Walleye during standardized fall surveys.

Seasonal Sampling Influence on Population Dynamics and Yield of Channel Catfish and Walleye in a Large Great Plains Reservoir

AbstractFish samples collected during different times of the year can be subject to various biases, but the influence of sampling during different seasons on population dynamics and yield metrics in large reservoirs is not well reported. This study compared the age structure, growth, mortality, and yield estimates of Channel Catfish Ictalurus punctatus and Walleye Sander vitreus collected during spring and fall with standardized gill netting in a large Nebraska, USA, reservoir. We sampled fish by using the Nebraska Game and Parks Commission standardized gill net survey methodology. We estimated ages from pectoral spines of Channel Catfish and from sagittal otoliths of Walleye, derived age-length keys, and compared mean spring and fall ages with t-tests. We compared spring and fall von Bertalanffy growth curves with likelihood-ratio tests and mortality estimates from weighted catch curves with an analysis of variance. We visually compared spring and fall yield estimates derived from yield-per-recruit models to assess the impact of variable population dynamics estimates. Estimates of mean age, growth coefficient, mean asymptotic length, total annual mortality, and yield of Channel Catfish did not differ between spring and fall. Conversely, older age structure of Walleye in spring resulted in lower estimates of total annual mortality and higher yield than in fall. Estimates of mean asymptotic length and growth coefficient differed between spring and fall for female Walleye, and mean asymptotic length, growth coefficient, and theoretical time at age 0 estimates varied between spring and fall for male Walleye. Fall yield estimates were substantially lower than spring estimates for both male and female Walleye. These results demonstrate that the sample collection season can impact population dynamics estimates for certain species, whereas others remain relatively unaffected.

Gear‐ and Season‐Specific Catch Rates of Age‐0 Walleyes and White Bass: Standard Sampling Recommendations for Great Plains Reservoirs

AbstractWalleye Sander vitreus and White Bass Morone chrysops are two of the most popular sport fish species sought by anglers in the Great Plains. However, not all sampling approaches effectively capture age‐0 Walleyes and White Bass, and therefore it may be difficult for fisheries managers to index age‐0 year‐class strength. We evaluated the differences among three gears for sampling age‐0 Walleyes and White Bass: bag seining, boat electrofishing, and small‐mesh gill netting. Boat electrofishing had the highest average catch, lowest minimum sample size needed to obtain a relative standard error of 25%, low operational effort, and the lowest mortality. The average catches of age‐0 Walleyes and White Bass were positively correlated, suggesting that the two species can be sampled simultaneously. Considering all of the metrics evaluated, we recommend boat electrofishing in September as the most appropriate way to sample age‐0 Walleyes and White Bass in reservoirs.

Combining High-Throughput Sequencing of sedaDNA and Traditional Paleolimnological Techniques To Infer Historical Trends in Cyanobacterial Communities.

Freshwaters worldwide are under increasing pressure from anthropogenic activities and changing climate. Unfortunately, many inland waters lack sufficient long-term monitoring to assess environmental trends. Analysis of sedimentary ancient DNA ( sedaDNA) is emerging as a means to reconstruct the past occurrence of microbial communities of inland waters. The purpose of this study was to assess a combination of high-throughput sequencing (16S rRNA) of sedaDNA and traditional paleolimnological analyses to explore multidecadal relationships among cyanobacterial community composition, the potential for cyanotoxin production, and paleoenvironmental proxies. DNA was extracted from two sediment cores collected from a northern Canadian Great Plains reservoir. Diversity indices illustrated significant community-level changes since reservoir formation. Furthermore, higher relative abundances in more recent years were observed for potentially toxic cyanobacterial genera including Dolichospermum. Correlation-based network analysis revealed this trend significantly and positively correlated to abundances of the microcystin synthetase gene ( mcyA) and other paleoproxies (nutrients, pigments, stanols, sterols, and certain diatom species), demonstrating synchrony between molecular and more standard proxies. These findings demonstrate a novel approach to infer long-term dynamics of cyanobacterial diversity in inland waters and highlight the power of high-throughput sequencing to reconstruct trends in environmental quality and inform lake and reservoir management and monitoring program design.

Energy acquisition and retention by age-0 and age-1 paddlefishPolyodon spathula(Walbaum, 1792) in relation to size, growth, and rearing conditions in two Great Plains reservoirs and hatchery ponds

The objective of this study was to investigate lipid accumulation and storage in age-0 and age-1 paddlefish Polyodon spathula (Walbaum, 1792) in relation to age, stock, year, and growth. Juvenile paddlefish were collected from three locations in North Dakota and Montana, USA, during July and August of 2011 and 2012 and proximate analysis was used to determine lipid content. RNA/DNA ratios were used as an index of growth rates. Differences in age-based lipid accumulation and storage in juvenile paddlefish suggest a split allocation between growth and lipid storage, with growth being the highest initial priority and emphasis on energy storage occurring at a larger size, later in life. Differences in lipid allocation between stocks indicate that allocation is influenced by hatchery/wild rearing conditions. Differences within and between year-classes are consistent with field evidence observed in 2012 of a strong 2011 year-class, and indicate that during productive times, paddlefish may allocate energy to both body growth and lipid reserves, and that allocation differs among years. The lack of a relationship between RNA/DNA ratio and lipid does not support a physiologically exclusive allocation strategy between growth and lipid. Evidence from this and other studies suggests rather that an emphasis on growth, some energy storage, and a large rostrum size in relation to overall fish length in age-0 and age-1 fish, may be adaptive in avoiding predation while accruing necessary energy reserves for overwintering. Although this study also provides reference information regarding proximate composition of wild and hatchery origin juvenile paddlefish, much more study is needed into the relationships among growth, low and high lipid groups, lipid allocation in juvenile paddlefish as well as the existence and timing of allocation changes between growth and storage. To aid in understanding paddlefish survival and year-class strengths, these relationships also need to be linked to inter-annual differences in early rearing environments for age-0 and age-1 fish.

Spatial and temporal trends in reservoir physicochemistry and phosphorus speciation within Lake Diefenbaker, a Great Plains reservoir, as inferred from depositional sediments

Previous research and observations by area residents suggested that the frequency of algal blooms in the Qu'Appelle arm of Lake Diefenbaker, Saskatchewan, Canada, has been increasing over time. However, limited historical data were available to assess long-term trends in the overall reservoir. Narrow river-valley reservoirs, such as Lake Diefenbaker, are known to display marked longitudinal physicochemical and biological gradients. To assess both spatial and temporal geochemical trends, sediment cores were collected from eight sites along the longitudinal axis of this reservoir and sectioned vertically for analysis of various parameters. Surficial sediments showed an increasing trend in organic carbon, total phosphorus concentrations, and δ15N values, and decreasing trends in δ13C values and in the carbon to nitrogen ratio, with distance down-reservoir. This was attributed to reduced deposition of allochthonous detritus and increased entrainment of nutrients as settled autochthonous materials, as the reservoir transitioned to less dynamic lacustrine conditions. A strong correlation was determined in the Qu'Appelle arm between chlorophyll a concentrations and the more biologically available forms of P (non-apatite inorganic P + organic P) in the sediment profile (r = 0.955, p < 0.001), suggesting an increase in autochthonous production in this region of the reservoir in the mid-1990s, which subsequently plateaued. The spatial and temporal trends illustrated in the sediment core profiles of this study demonstrate that paleolimnological investigations of narrow river-valley reservoirs need to consider geochemical and biological spatial gradients associated with reservoir zonation.

Thermal alteration and macroinvertebrate response below a large Northern Great Plains reservoir

Abstract Large hydroelectric dams directly alter the abiotic condition of rivers by releasing water with large differences in temperature relative to natural conditions. These alterations in the thermal regime along with alterations in flow often result in altered ecosystems downstream. For sustainable management of this aquatic resource, there is a need to balance services a reservoir provides with ecosystem protection. Here we conduct a high-resolution study on the thermal regime and associated aquatic macroinvertebrate community downstream of a hydroelectric dam on a large-order Northern Great Plains River and analyze these findings with a non-central hypothesis test model, Test Site Analysis. Specifically, we monitor the temperature regime of this tailwater environment, and compare the annual change in temperature downstream to reference sites unaffected by the dam. We find that reaches downstream of the dam are significantly cooler than reference through the summer into August and do not reach the temperature optima of reference reaches. Cold-water release, or some other change in flow characteristics, changes abundance, diversity, % Orthocladiinae, and community composition. We used these metrics to compare test sites to reference sites and to quantify the impact of the Lake Diefenbaker reservoir on community metrics characteristic of temperature stress. Our results have implications primarily for understanding and quantifying the ecosystem impacts of hydroelectric energy production, but also range expansion of cold-water tolerant taxa, the life-history of select groups of invertebrates, and ultimately the forage resources available to the fish assemblages of this river system.

The Zooplankton Community of a Turbid Great Plains (USA) Reservoir in Response to a Biomanipulation with Common Carp (Cyprinus carpio)

The effects of a biomanipulation with adult carp (Cyprinus carpio) removals on water quality and the abundance, composition, and body size of zooplankton were investigated in Bowman-Haley Reservoir, North Dakota in a two-year study. In both years, decreases in zooplankton abundance, Daphnia body size, and Daphnia clutch size in carpuneradicated areas coincided with the appearance and subsequent domination of the blue-green algae Aphanizomenon. Concurrently, in areas where carp were eradicated, water clarity increased, total suspended solids decreased, and prevalence of blue-green algae blooms decreased. As a result of these improved feeding conditions, zooplankton abundance, Daphnia size, and Daphnia clutch size increased. Because adult carp, which fed to a very limited extent on zooplankton in spring, represented over 95% of the fish removed, changes in the zooplankton community were not attributable to decreased predation by fish. Furthermore, it is unlikely that predation by fish significantly affected...

Rapid recovery of a fish assemblage following an ecosystem disruptive algal bloom

Disturbance of freshwater ecosystems through cultural eutrophication has resulted in an increased global occurrence of harmful algal blooms (HABs). Ecosystem disrupting algal blooms (EDABs) are a subset of HABs that produce extensive disturbances across entire ecosystems. Prymnesium parvum is an EDAB species that has invaded freshwater systems worldwide, causing massive fish kills and other negative effects. Fish kills frequently occur during HABs and EDABs, but few studies exist of the long-term implications of these fish kills and the resilience and recovery of fish assemblages following kills. We sampled fish near- and offshore over an annual cycle encompassing a P. parvum EDAB in 2 coves (i.e., a bloom site and a reference site) of a southern Great Plains reservoir, Lake Texoma, Oklahoma–Texas (USA). Our objective was to document the extirpation and recovery of a fish assemblage in response to the disturbance of an EDAB event. Prymnesium parvum bloomed in 1 cove from mid-December 2008 until May 2009 and eliminated all fish during this period. Fish toxicity bioassays indicated no substantial differences in susceptibility among fish species to P. parvum toxins. Fish recolonized the bloom site rapidly in May 2009 after the bloom diminished. Fish assemblages were resilient to the P. parvum EDAB, and recovered to previous abundance, richness, and composition within 6 mo. Our results suggest that the reservoir-wide fish meta-assemblage enabled a rapid recovery of local fish assemblages after a spatially heterogeneous EDAB.

Effects of Sedimentation on the Profundal Benthic Macroinvertebrates of a Great Plains Reservoir

Reservoir sedimentation has become a large and pervasive problem throughout the entire United States. Sedimentation gradually destroys and eliminates the services for which reservoirs were constructed (flood protection, water storage, and recreation), yet sedimentation is also an ecological problem. Organisms that depend on the deep parts of lakes cannot survive if their habitats are being buried by sediments. Perry Lake, in northeastern Kansas, has lost 23% of its original volume. Sediment thicknesses (depth of sediment accrued since lake formation) in the main lake range from 2–140cm, and upper portions of the lake have become unnavigable. To measure the effect of sedimentation the diversity and density of profundal invertebrate macrofauna were sampled. Thirteen taxa were collected and assemblages were dominated by oligochaetes, midges (chironomidae), and the Phantom Midge Chaoborus. No significant associations between sediment thickness and invertebrate metrics were found, however sediment size was cor...

Trends in nutrient and sediment retention in Great Plains reservoirs (USA)

Reservoirs are artificial ecosystems with physical, chemical, and biological transitional characteristics between rivers and lakes. Greater water retention time in reservoirs provides conditions for cycling materials inputs from upstream waters through sedimentation, biological assimilation and other biogeochemical processes. We investigated the effects of reservoirs on the water quantity and quality in the Great Plains (Kansas, USA), an area where little is known about these dominant hydrologic features. We analyzed a 30-year time-series of discharge, total phosphorus (TP), nitrate (NO3(-)), and total suspended solids (TSS) from six reservoirs and estimated overall removal efficiencies from upstream to downstream, testing correlations among retention, discharge, and time. In general, mean removal of TP (42-74%), TSS (0-93%), and NO3(-) (11-56%) from upstream to downstream did not change over 30 years. TP retention was associated with TSS removal, suggesting that nutrient substantial portion of P was adsorbed to solids. Our results indicated that reservoirs had the effect of lowering variance in the water quality parameters and that these reservoirs are not getting more or less nutrient-rich over time. We found no evidence of temporal changes in the yearly mean upstream and downstream discharges. The ratio upstream/downstream discharge was analyzed because it allowed us to assess how much contribution of additional unsampled tributaries may have biased our ability to calculate retention. Nutrient and sediment removal was less affected by hydraulic residence time than expected. Our study demonstrates that reservoirs can play a role in the removal and processing of nutrient and sediments, which has repercussions when valuing their ecological services and designing watershed management plans.

Exploitation of walleye in a Great Plains reservoir: harvest patterns and management scenarios

Abstract This study assessed exploitation and evaluated management options for walleye, Sander vitreus (Mitchill), in Glen Elder Reservoir, Kansas. A total of 2429 walleye varying from 240 to 687 mm was tagged with Carlin dangler tags during 2000–2003. After correcting for tag loss and non‐reporting, exploitation of walleye was estimated as 68.3%. More than 85% of the tagged walleye were harvested during April to June and 75% were harvested within 6 months after tagging. A Beverton‐Holt yield‐per‐recruit model was used to evaluate six minimum length limits varying from 250 to 610 mm. Given current exploitation rates, population demographics and harvest regulations (381‐mm minimum length limit), the walleye population is probably experiencing recruitment overfishing. Model results suggested that a 610‐mm minimum length limit would be required to prevent growth overfishing and a 533‐mm or longer minimum length limit would prevent recruitment overfishing.

Interactions between Walleyes and Smallmouth Bass in a Missouri River Reservoir with Consideration of the Influence of Temperature and Prey

AbstractWalleyes Sander vitreus are the most popular fish among South Dakota anglers, but smallmouth bass Micropterus dolomieu were introduced to provide new angling opportunities. Some walleye anglers have reported reductions in the quality of walleye fisheries since the introduction of smallmouth bass and attribute this to the consumption of young walleyes by smallmouth bass and competition for shared prey resources. We quantified the diets of walleyes and smallmouth bass in the lower reaches of Lake Sharpe (a Missouri River reservoir), calculated the diet overlap between the two predators, and determined whether they partitioned shared prey based on size. We also quantified walleye diets in the upper reach of the reservoir, which has a different prey base and allowed us to compare the growth rates of walleyes within Lake Sharpe. Age‐0 gizzard shad Dorosoma cepedianum composed a substantial proportion of the diets of both predators, regardless of location, for most of the growing season; the patterns in shad vulnerability appeared to drive the observed patterns in diet overlap. Smallmouth bass appeared to consume a smaller size range of gizzard shad than did walleyes, which consumed a wide range. Smallmouth bass consumed Sander spp. in some months, but in very low quantities. Given that global climate change is expected to alter the population and community dynamics in Great Plains reservoirs, we also used a bioenergetics approach to predict the potential effects of limiting prey availability (specifically, the absence of gizzard shad and rainbow smelt Osmerus mordax) and increased water temperatures (as projected from global climate change models) on walleye and smallmouth bass growth. The models indicated that the absence of rainbow smelt from the diets of walleyes in upper Lake Sharpe would reduce growth but that the absence of gizzard shad would have a more marked negative effect on both predators at both locations. The models also indicated that higher water temperatures would have an even greater negative influence on walleye growth; however, smallmouth bass growth was predicted to increase with higher temperatures. Fisheries managers should consider strategies to enhance the prey base or mitigate the effects of increased water temperatures that may occur in the future as a result of global climate change. Such proactive actions may alleviate potential future competition between walleyes and smallmouth bass resulting from changes in the fish community.

Interactions among Three Top‐Level Predators in a Polymictic Great Plains Reservoir

AbstractAfter the introduction of hybrid striped bass (white bass Morone chrysops × striped bass M. saxatilis) into Harlan County Reservoir, Nebraska, gill‐net catch per unit effort (CPUE) of walleyes Sander vitreus appeared to decline while that of white bass remained stable. This result prompted the question of whether these three species can be managed collectively in reservoir ecosystems. However, despite the frequency with which these three popular sport fishes coexist in Great Plains reservoirs, we are unaware of any studies that evaluate resource overlap among them. Therefore, we compared their diets, diet overlap, isotopic composition, vertical distribution, and vertical overlap in Harlan County Reservoir from June to September 2002 and 2003. All three species consumed similar prey (i.e., gizzard shad Dorosoma cepedianum and Chironomidae), and diet overlap was high (i.e., Pianka's index &gt; 40) during all months. On no occasion did all three predators consume the same sizes of gizzard shad. Hybrid striped bass consumed larger gizzard shad than white bass did in September 2002 and 2003, whereas white bass consumed smaller gizzard shad than walleyes and hybrid striped bass did in August 2002 and 2003. Stable isotope analysis corroborated the diet analysis and indicated that all three species occupied the same trophic level and that each predator derived carbon from a similar prey source. White bass were consistently located within the upper 3 m of water, whereas the vertical distribution of hybrid striped bass and walleyes varied from the surface to 10 m deep. Spatial overlap was therefore not as high as dietary overlap and was variable among species and months. Although diet overlap was high, resource partitioning (i.e., different feeding locations and different sizes of gizzard shad eaten) reduced the negative interactions among the three predators. Therefore, we conclude that concurrent management of these three sport fishes is feasible in highly productive reservoirs similar to the one in this study.

Analysis of Environmental Variation in a Great Plains Reservoir Using Principal Components Analysis and Geographic Information Systems

We present a method for spatial interpretation of environmental variation in a reservoir that integrates principal components analysis (PCA) of environmental data with geographic information systems (GIS). To illustrate our method, we used data from a Great Plains reservoir (Skiatook Lake, Oklahoma) with longitudinal variation in physicochemical conditions. We measured 18 physicochemical features, mapped them using GIS, and then calculated and interpreted four principal components. Principal component 1 (PC1) was readily interpreted as longitudinal variation in water chemistry, but the other principal components (PC2-4) were difficult to interpret. Site scores for PC1-4 were calculated in GIS by summing weighted overlays of the 18 measured environmental variables, with the factor loadings from the PCA as the weights. PC1-4 were then ordered into a landscape hierarchy, an emergent property of this technique, which enabled their interpretation. PC1 was interpreted as a reservoir scale change in water chemistry, PC2 was a microhabitat variable of rip-rap substrate, PC3 identified coves/embayments and PC4 consisted of shoreline microhabitats related to slope. The use of GIS improved our ability to interpret the more obscure principal components (PC2-4), which made the spatial variability of the reservoir environment more apparent. This method is applicable to a variety of aquatic systems, can be accomplished using commercially available software programs, and allows for improved interpretation of the geographic environmental variability of a system compared to using typical PCA plots.

Spatial and Temporal Variability of Zooplankton in a Great Plains Reservoir

Seasonal and daily patterns of zooplankton populations are often predictable in natural lakes. Distinct zonation and geomorphic differences in reservoirs, however, make ecological extrapolations from lakes to reservoirs uncertain. We describe the spatial and temporal distribution of zooplankton, algae, and water clarity across reservoir zones and along a depth gradient in Glen Elder Reservoir, Kansas. Daphnia species were most abundant in the lacustrine zone, with D. pulicaria numerically dominant in early spring and D. mendotae dominant later in 1999 and 2000. Rotifers (Keratella quadrata, Asplanchna spp.) were dominant in the riverine zone in 1999, 2000, and 2001. Algal biomass was not significantly different between zones through most of the sampling periods, except late April in 1999 and mid-April in 2000. Chlorophyll a exceeded 81 l gl )1 in the lacustrine zone in mid- to late-April in 1999 and 2000, and exceeded 90 l gl )1 in the riverine zone in mid-April. Water clarity was significantly lower in the riverine zone in 1999 and 2000. Most zooplankton taxa had similar depth distributions at night and day, indicating a lack of diel vertical migration behavior on a large scale. However, in small scale (30 cm vertical enclosures) laboratory experiments, both D. pulicaria and D. mendotae occupied significantly deeper depths (>25 cm) under lighted conditions in the presence of fish chemical cues compared to shallow water (7–17 cm) under dark conditions and in the absence of fish cues. These contrasting results suggest that, as in other studies, Daphnia sense cues from predators and alter their depth in the water column on small scales without natural constraints on movement and choices. However, other factors in the reservoir such as wind-generated water movements and cues from other predators may prevent depth choices similar to those seen under controlled conditions. These results illustrate biotic and abiotic differences between riverine and lacustrine zones in a large reservoir, and contrast with Daphnia depth segregation and migration patterns in natural lakes.

Factors related to growth and survival of larval walleyes: implications for recruitment in a southern Great Plains reservoir

Larval fishes, limnological characteristics, and zooplankton populations were sampled from Glen Elder Reservoir, Kansas, during 1999–2001 to determine factors associated with growth and survival of larval walleyes ( Stizostedion vitreum). Ichthyoplankton populations were sampled weekly from April to June during all years using paired conical nets. Water temperature and zooplankton populations were sampled at each ichthyoplankton sampling site. Approximately, 70% of all larval fishes and 80% of the larval walleyes were sampled in the upper reservoir during all years. Cyprinidae and Centrarchidae were the only taxa that were more abundant in the main reservoir than the upper reservoir. Despite similarities in zooplankton abundance between years, recruitment of walleyes in 1999 was the lowest in nearly 20 years, while moderate year classes were produced in 2000 and 2001. During 1999, low, variable spring temperatures resulted in poor growth of larval walleyes. Poor growth of walleyes, coupled with high densities of larval gizzard shad ( Dorosoma cepedianum), resulted in poor recruitment during 1999. Walleyes grew faster in 2000 and 2001 and were able to consume larval gizzard shad resulting in moderate recruitment. These results suggest that abiotic conditions mediate biotic interactions and that both abiotic and biotic characteristics are important for regulating walleye recruitment dynamics.

Seasonal variation in condition, growth and food habits of walleye in a Great Plains reservoir and simulated effects of an altered thermal regime

Catch rates in gillnets and relative weight (Wr) of walleye Stizostedion vitreum, in Glen Elder Reservoir, Kansas, were lowest during the summer (June–August) and highest during the autumn (September–November). Approximately 80% of their annual growth in length and mass was attained during late summer and autumn. Growth was minimal during winter (January–February) and spring (March–May). The number of walleye with empty stomachs was highest during the summer. Invertebrates (Cladocera, Chironomidae) were common in walleye stomachs during the summer and spring, but contributed little to the ingested biomass. Gizzard shad Dorosoma cepedianum dominated walleye diets (per cent by mass) throughout the year. A bioenergetics model predicted that the proportion of maximum consumption (Pc) was highest during the autumn and was probably due to spatial overlap of walleye and gizzard shad once water temperatures were &lt;22° C. The bioenergetics model predicted that walleye would lose up to 65% of their body mass during the summer if water temperature increased by 10% (as predicted by some global warming models). Growth during the autumn, winter and spring was enhanced up to 150% by increased temperatures. The results of this study indicate that lower condition, reduced consumption and slow growth are a generalized response of walleye to extreme temperatures. Elevated temperatures may have a net positive effect on walleye growth if they can survive the high thermal stress during summer.

Seasonal variation in condition, growth and food habits of walleye in a Great Plains reservoir and simulated effects of an altered thermal regime

Seasonal variation in condition, growth and food habits of walleye in a Great Plains reservoir and simulated effects of an altered thermal regime

Predation on Age-0 Paddlefish by Walleye and Sauger in a Great Plains Reservoir

From July to October 1994 and 1995, the food habits of walleye Stizostedion vitreum, sauger S. canadense, northern pike Esox lucius, and channel catfish Ictalurus punctatus were studied in Lake Sakakawea, a Missouri River main-stem reservoir in North Dakota. In 1994, no paddlefish Polyodon spathula were found in stomachs of these predators. In 1995, 3% of the walleyes, 12% of the saugers, and 1% of the channel catfish with identifiable prey ate wild age-0 paddlefish. Walleyes ate paddlefish from August to October, with the highest proportions in September, whereas saugers ate paddlefish from July to October in equal proportions. Walleye and sauger stomachs contained wild age-0 paddlefish as large as 167 mm body length (BL; 305 mm total length, TL), and one channel catfish stomach contained a 142-mm-BL (269-mm-TL) paddlefish. Predators were also sampled after 8,000 hatchery-reared, age-0 paddlefish (mean BL = 189 mm) were released in White Earth Bay, Lake Sakakawea. Hatchery-reared paddlefish were absent from stomachs of 47 walleyes, 3 saugers, 9 channel catfish, and 3 white bass Morone chrysops with identifiable prey. However, two hatchery-reared paddlefish (175 and 220 mm BL) were found in 2 of 17 northern pike with identifiable prey. Because we found that walleyes and saugers were capable of eating paddlefish of at least 167 mm BL (305 mm TL), many stocked paddlefish may be susceptible to predation. State agencies should consider stocking larger paddlefish where high densities of sauger or large walleyes (>490 mm TL) are present.