Sauger Research Articles

Environmental DNA assays for the sister taxa sauger (Sander canadensis) and walleye (Sander vitreus).

Sauger (Sander canadensis) and walleye (S. vitreus) are percid fishes that naturally co-occur throughout much of the eastern United States. The native range of sauger extends into the upper Missouri River drainage where walleye did not historically occur, but have been stocked as a sport fish. Sauger populations have been declining due to habitat loss, fragmentation, and competition with non-native species, such as walleye. To effectively manage sauger populations, it is necessary to identify areas where sauger occur, and particularly where they co-occur with walleye. We developed quantitative PCR assays that can detect sauger and walleye DNA in filtered water samples. Each assay efficiently detected low quantities of target DNA and failed to detect DNA of non-target species with which they commonly co-occur.

Historical and Contemporary Patterns of Mercury in a Hydroelectric Reservoir and Downstream Fishery: Concentration Decline in Water and Fishes.

Mercury (Hg) contamination can pose risks to human and animal health as well as commercial fisheries. Reservoir construction in riverine systems produces flooded conditions amenable to Hg(II)-methylating bacteria, which can transform this relatively benign environmental contaminant into the bioaccumulative, environmentally relevant, and neurotoxic methyl-Hg (MeHg). Hg concentrations ([Hg]) in fishes from reservoirs can take decades to decrease to pre-dam levels, but less is known about Hg exported downstream and its dynamics within downstream fish populations. We examined and compared the multidecadal rates of biotic [Hg] decrease and contemporary factors affecting [Hg] in fish collected from a hydroelectric reservoir (Tobin Lake) and a related downstream fishery (Cumberland Lake) along the Saskatchewan River, Canada. Rates of [Hg] decrease were considered in four species-northern pike (Esox lucius), sauger (Sander canadensis), goldeye (Hiodon alosoides), and walleye (S. vitreus)-all of which showed a significant decrease over time (p<0.001) and are now lower than Health Canada consumption guidelines (0.5μg/g). Rates of decrease ranged from 0.5 to 3.9 %/year and were similar between sites in the cases of northern pike and sauger. Contemporary factors affecting [Hg] in walleye collected downstream include fish length (p<0.001), fish age (p<0.001), and trophic magnification through the food web (p<0.001), and relationships between [Hg] and trophic level in predatory and prey fish are now similar to those found in non-Hg-inundated systems at a similar latitude. Together, these results suggest connected contamination between the two sites and delineate the timeline during which [Hg] in a variety of fish species decreased to nontoxic levels in both locations.

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 &amp; Sons, Ltd.

Diet of walleye and sauger and morphological characteristics of their prey in Lake Winnipeg

Abstract Lake Winnipeg has the second largest commercial walleye ( Sander vitreus ) fishery in North America. The lake has experienced and will continue to undergo comprehensive changes such as eutrophication, invasion of non-indigenous aquatic species, and climate change. The North and South Basins of the lake differ in many ways, e.g. mean water depth and temperature, turbidity, and fish community. The study objectives were to establish a baseline for diet of walleye and sauger ( Sander canadensis ) in Lake Winnipeg, to determine whether the diets currently differ between basins and among seasons, and to investigate whether the non-indigenous rainbow smelt ( Osmerus mordax ) contributes substantially to their diet. Walleye and sauger diets in the South Basin had more diverse species composition, whereas in the North Basin, the diet consisted almost entirely of the introduced rainbow smelt (as well as troutperch ( Percopsis omiscomaycus ) for sauger). Some seasonal variation was also documented and found to be attributable to the emergence of young-of-year fish and mayfly larvae. The predominant incorporation of the abundant and large rainbow smelt in the diets of walleye and sauger in the North Basin may lead to increased growth and condition of fish in this basin. These data provide a baseline for comparison in future investigations of walleye and sauger diets as changes occur in the food web of the lake with invasion of zebra mussels ( Dreissena polymorpha ) and spiny water fleas ( Bythotrephes longimanus ).

Characteristics and Spatial Segregation of Sympatric Saugers and Walleyes in the Ottawa River, Canada

AbstractFew comparative studies exist on the sympatric populations of Saugers Sander canadensis and Walleyes S. vitreus, especially in northern rivers. Depth‐stratified, standardized index netting surveys were conducted in the Ottawa River, Canada—a large, fragmented northern river. The objectives of this study were to (1) determine whether Saugers and Walleyes were spatially segregated within river reaches; (2) assess whether relative abundances of the two species were correlated within river reaches and ascertain factors affecting their relative abundances; (3) determine whether life history characteristics in this northern river were within the variation reported for each species; and (4) evaluate whether there was synchrony in year‐class strength between the two species and identify the factors affecting year‐class strength. Saugers and Walleyes were spatially segregated, specifically by depth. Probability of capture was greatest in the 20–35‐m depth stratum for Saugers and in the 6–12‐m depth stratum for Walleyes. Relative abundances of Saugers and Walleyes were correlated and were positively related to reach characteristics (i.e., mean and maximum depth, reach length, and river kilometers upstream from the confluence) but negatively related to thermal conditions (i.e., growing degree‐days, water temperature at preferred depths, and human population in proximity to the river). Life history characteristics were within the literature‐reported ranges except for Saugers, which were older with a smaller length at 50% maturity. Year‐class strengths of Saugers and Walleyes were synchronous at the reach and river levels and were positively correlated with mean annual temperature but negatively correlated with mean annual river flow. Saugers and Walleyes can coexist within large water bodies. Recruitment synchrony suggests that spawning management efforts could benefit both species, which could be advantageous when managing the Sauger, a lesser studied species. However, life history differences advocate that harvest regulations (e.g., size limits) must be species specific in order to be effective.Received June 13, 2013; accepted January 27, 2015

Prey consumption and trace element concentrations in double-crested cormorants ( Phalacrocorax auritus ) from Lake Winnipeg, Canada

Abstract Double-crested cormorants ( Phalacrocorax auritus ) have generally increased throughout their range in North America over the last 40 years, leading to increased conflict with commercial and recreational fisheries that often view cormorants as competitors. Lake Winnipeg, Manitoba, Canada and adjacent large lakes support a significant portion of the continent's breeding population, and have high economic value for recreational and commercial fisheries; no recent assessment of cormorant diet has been conducted in this region. We measured stable isotopes ( δ 13 C, δ 15 N, and δ 34 S) in cormorant muscle and used a Bayesian mixing model approach to estimate cormorant diet composition throughout the Lake Winnipeg system, including the contribution of commercially and recreationally harvested walleye ( Sander vitreus ) and sauger ( Sander canadensis ). We estimated that cormorants occupied a trophic position around 4.0, which corresponds to a generalist diet, and consumed a small proportion of walleye (range of mean estimates: 6–12%) and sauger (range of mean estimates: 7–12%). We also examined the concentrations of 15 trace elements in cormorant muscle to evaluate the potential role that these birds played in contaminant flow and how these elements behaved trophically. Cd, Fe, Mn, Hg, and Se showed evidence of biomagnification in Lake Winnipeg's north basin, but only Hg biomagnified in the south basin; nutrient source (benthic vs. pelagic) had little effect on elemental concentrations. Our results add to the growing evidence that the two main basins of Lake Winnipeg are biologically distinct from each other, and that cormorants likely have little effect on the populations of harvested fishes.

The complete mitochondrial genome sequence of pike perch (Sander canadensis)

Pike perch (Sander canadensis) is a member of the largest order of Osteichthyes, Perciformes, and is an important ecological and economic freshwater species, which distributes in Ili River and Ergis River of Xinjiang Province, China. In this study, we sequenced the whole mitochondrial genome of pike perch, and analyzed the similarity with its related species. The mitochondrial genome of S. canadensis is 16,542 bp in length with 55.05% AT content, contained 13 protein coding genes, 22 tRNA genes, 2 ribosomal genes and an 892 bp non-coding region. In control region, 6 CSBs (CSB-1, CSB-2, CSB-3, CSB-D, CSB-E and CSB-F), one potential TAS and one poly-T region were identified. Comparing all protein-coding genes and whole genome sequence with 4 species of Perciformes (three species of Percidae, Perca flavescens. Percina macrolepida. Etheostoma radiosum and one outgroup Oreochromis sp. red tilapia), ND3 gene has the highest mutation rate, and S. canadensis has higher similarity with Perca flavescens than others. The mitochondrial genomic sequence will help us to study the conservation genetic and evolution of Percidae.

The Use of Fluorescent Randomly Amplified Polymorphic DNA Markers to Identify Hybrids: A Case Study Evaluating the Origins of Saugeye following the Cessation of Stocking in an Ohio Reservoir

AbstractHybridization and introgression continue to gain recognition as important issues in the management and conservation of native fishes. It is often necessary to identify hybrids in natural populations and to distinguish among individuals of various hybrid categories. Molecular methods are important for these purposes, and it is valuable if researchers have a range of molecular methods to apply, since each method has unique advantages and disadvantages. The determination of the best class of marker for a particular study depends on various factors, including the goals of the study, the resolution required, and the genomic and marker information already available for the taxa of interest. We modified a protocol to generate fluorescent randomly amplified polymorphic DNA (FRAPD) markers for hybridization studies. To our knowledge, this type of marker has not previously been used for hybrid identification. To demonstrate the utility of the modified methods, FRAPD markers were used to evaluate potential reproduction by saugeye (female walleye Sander vitreus × male sauger Sander canadensis) in a central Ohio reservoir. Our approach successfully generated a battery of diagnostic genetic markers that were used to test the hypothesis that young‐of‐year saugeye were later‐generation offspring of saugeye cohorts previously stocked into the reservoir. Alternatively, the fish may have been immigrant first‐generation saugeye from other sources. Data obtained from the FRAPD markers provided strong support favoring the alternative hypothesis. These methods provide a very useful tool for distinguishing between pure parentals and various classes of hybrid individuals, both in Sander spp. and in other taxa, offering a powerful and easily developed alternative to other molecular methods of generating informative genetic markers for hybridization studies.Received September 20, 2011; accepted April 5, 2012

Heterogeneous detection probabilities for imperiled Missouri River fishes: implications for large-river monitoring programs

Occupancy modeling was used to determine (1) if detection probabilities (p) for 7 regionally imperiled Missouri River fishes (Scaphirhynchus albus, Scaphirhynchus platorynchus, Cycleptus elongatus, Sander canadensis, Macrhybopsis aestivalis, Macrhybopsis gelida, and Macrhybopsis meeki) differed among gear types (i.e. stationary gill nets, drifted trammel nets, and otter trawls), and (2) how detection probabilities were affected by habitat (i.e. pool, bar, and open water), longitudinal position (five 189 to 367 rkm long segments), sampling year (2003 to 2006), and season (July 1 to October 30 and October 31 to June 30). Adult, large-bodied fishes were best detected with gill nets (p: 0.02-0.74), but most juvenile large-bodied and all small-bodied species were best detected with otter trawls (p: 0.02-0.58). Trammel nets may be a redundant sampling gear for imperiled fishes in the lower Missouri River because most species had greater detection probabilities with gill nets or otter trawls. Detection probabilities varied with river segment for S. platorynchus, C. elongatus, and all small-bodied fishes, suggesting that changes in habitat influ- enced gear efficiency or abundance changes among river segments. Detection probabilities var- ied by habitat for adult S. albus and S. canadensis, year for juvenile S. albus, C. elongatus, and S. canadensis, and season for adult S. albus. Concentrating sampling effort on gears with the great- est detection probabilities may increase species detections to better monitor a population's response to environmental change and the effects of management actions on large-river fishes.

Catch and effort variation in the commercial gillnet fishery of Lake Winnipeg, Canada, in relation to environmental factors

The impact of environmental factors on the fishing effort and catch rate of sauger (Sander canadensis) and walleye (Sander vitreus) was examined for the commercial fishery of Lake Winnipeg's south basin. Time was represented biologically as degree days. The influences of light intensity, wave height, barometric pressure, and the discharge rate of the Red River were examined using generalized linear models with the quasi-family of distributions. The percentage of the null deviance was found to be an appropriate selection criterion for choosing variables to include in the models. Effort declined throughout the early fishery and declined with increasing winds later in the year. Walleye catch rate declined through the early season. Sauger catch rates increased and then declined as the early season progressed and were associated with indicators of decreased light intensity. The relationship between catch rate and each statistically significant environmental variable was consistent with the habitat preferences of the species under examination.

Longitudinal variation and habitat associations of small fishes in the Bighorn River, Wyoming: influences of river regulation and introduced fishes

We assessed variation in longitudinal distributions of native and introduced fishes and their occurrences in different habitat types downstream from Boysen Dam in the Bighorn River, Wyoming. The closure of Boysen Dam in 1952 and construction of three downstream water diversion dams have led to channel changes in the Bighorn River causing reductions in the numbers and areas of side channels, backwaters, and riffles. Eleven native and five introduced fish species were collected by seining during 2005. Fish samples were dominated by sand shiner (Notropis stramineus), flathead chub (Platygobio gracilis), and longnose sucker (Catostomus catostomus). Introduced fish species included common carp (Cyprinus carpio), emerald shiner (Notropis atherinoides), plains killifish (Fundulus flavis), yellow perch (Perca flavescens), and sand shiner. Differences in relative abundances of fishes among habitat types were observed. Fathead minnow (Pimephales promelas), longnose sucker, white sucker (Catostomus commersoni), plains killifish, and sauger (Sander canadensis) were found almost exclusively in backwaters, and channel catfish (Ictalurus punctatus) was collected almost exclusively in side channels. Changes from the pre-European fish community are occurring in association with invasions of introduced fish species and losses of side channels, backwaters, and riffles.

Survival of Angled Saugers in the Lower Tennessee River

AbstractAn intense winter fishery for sauger Sander canadensis exists in the lower Tennessee River, and the objective of this study was to estimate the survival of angled saugers. In February 2008 and January–March 2009, 81 angled saugers (72 live plus 9 euthanized) were affixed with ultrasonic tags. The movements (or lack thereof) by saugers released alive were compared with those of euthanized fish to assess survival. Sixty‐eight percent of the tagged saugers that were released alive exhibited maximum daily movements exceeding the greatest movement of any euthanized fish (0.5 km/d), and those fish were subsequently classified as survivors. The upstream movements of several euthanized fish indicated that their carcasses were ingested by piscivorous scavengers. In logistic models, the probability of mortality was significantly and inversely related to total length but not to capture depth, water temperature, handling time, or ascent rate. In 2 × 2 contingency tables, the fate of released saugers was not found to be associated with either the presence or absence of bleeding from the hooking wound or whether or not the fish displayed gastric distension. Most released fish survived despite the fact that gastric distension was observed in 72% of the angled saugers.Received August 11, 2010; accepted April 21, 2011

Winter Catch‐and‐Release Hooking Mortality of Saugers below Lock and Dam 3 of the Mississippi River

AbstractWe evaluated the effect of length and depth of capture of saugers Sander canadensis on winter hooking mortality below Lock and Dam 3 of the Mississippi River (i.e., Pool 4) by catching saugers using the most common recreational fishing gear in these fisheries (jig and plastic, jig and minnow, and jigging spoons) and holding the fish for 72 h in a net‐pen. Sauger winter hooking mortality was 26.4% and increased with depth of capture. Thirty‐three percent (56 of 172) of the saugers caught at depths of 9 to 24 m died, compared with only 2% (1 of 41) of those caught at depths of 9 m or less. There was no relationship between fish length and mortality; however, fish caught at depths of 12 m or less were significantly larger. We applied our hooking mortality estimates (26.4%) to a concurrent creel census and estimated that 2,500–2,900 kg of saugers were lost each year to winter hooking mortality. The percentage of total angling mortality (harvest and hooking) resulting from catch and release each winter was 30.5% (2,515 kg/8,256 kg) in 2005–2006 and 33.0% (2,812 kg/8,529 kg) in 2006–2007. Based on the historical abundance and annual mortality estimates available for Pool 4 saugers, winter hooking mortality did not substantially reduce the population. However, anglers may reduce winter catch‐and‐release hooking mortality by fishing in shallower water (&lt;9 m).Received May 12, 2010; accepted December 30, 2010

Do native predators feed on non-native prey? The case of round goby in a fluvial piscivorous fish assemblage

We evaluated whether or not the invasive round goby (Neogobius melanostomus) represents an important prey source for seven native fish predators in Lake St. Pierre (St. Lawrence River, Canada). The frequency of occurrence of round goby in the stomach contents of brown bullhead (Ameiurus nebulosus) and channel catfish (Ictalurus punctatus) was very low (<5%), while for the five other predators, it varied between 22% (yellow perch; Perca flavescens) and 65% (sauger; Sander canadensis). Several competing models linking the probability of occurrence of round goby in stomach contents to variables related to space, physical habitat, biotic interactions and predator size were tested for the five species feeding on round goby. Results indicated that space variables influenced round goby occurrence in stomachs for all species. In addition, physical habitat variables had an influence for sauger and walleye (Sander vitreus); biotic variables had an influence for yellow perch, walleye and sauger; and size had an influence for northern pike (Esox lucius), smallmouth bass (Micropterus dolomieu) and walleye. These results are discussed in light of known biological features of the round goby and native predators studied here and have important implications in terms of understanding round goby invasion success in the Great Lakes–St. Lawrence system.

A Comparison of Techniques Using Dorsal Spines to Estimate Sauger Age

AbstractFish age is useful to fishery managers when evaluating growth rates, mortality rates, and reproduction. Our objective was to determine whether two methods for estimating the age of saugers Sander canadensis using dorsal spines—side illumination and spine sectioning—resulted in similar age estimates at the same efficiency and cost. To do this, we determined whether the coefficients of variation (CV = 100 · SD/mean) differed between age estimates of fish using the two techniques in the Missouri River and a portion of the Kansas River. We found that the CVs did not differ significantly between techniques. While reader agreement did not differ significantly, side illumination took one‐half as much time as sectioning. In addition, side illumination displayed outer annuli on older fish better than sectioning and did not require an expensive low‐speed saw, microscope slides, or a mounting medium for processing. We conclude that side illumination is the most time‐ and cost‐efficient method for estimating sauger ages from spines.

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.

Abundance, growth, and life history characteristics of sympatric walleye (Sander vitreus) and sauger (Sander canadensis) in Lake Winnipeg, Manitoba

Walleye (Sander vitreus) and sauger (Sander canadensis) are the two most economically valuable and sought-after species in the Lake Winnipeg fishery, the second largest freshwater commercial fishery in Canada. We compared recent temporal trends (1979–2003) in population and life history characteristics of these species across the three main management zones of the lake (north basin, channel region, and south basin). Walleye abundance (gill net catch-per-unit-effort) increased relative to sauger abundance, particularly in the north and south basins, and the ages and sizes of the sampled fish exhibited greater spatial and temporal variabilities in sauger than in walleye. Walleye of the south basin and channel region exhibit a bimodal growth pattern, previously unreported for walleye populations. Growth rates of both walleye and sauger increased, and ages and sizes of maturity generally decreased from 1979 to 2003. However, walleye showed much greater flexibility in these traits, both spatially and temporally, than sauger. Sauger utilize a reproductive strategy of younger age and smaller size at maturity and higher fecundity with smaller, more lipid-rich eggs relative to walleye. Recent environmental and/or harvesting conditions on the lake appear to favour walleye over sauger, and differences in their life histories could make the sauger population more vulnerable to the impacts of commercial harvest than the walleye population.

Electroshock‐induced mortality in freshwater fish embryos increases with embryo diameter: a model based on results from 10 species

The purpose of this study was to develop a model to predict electroshock‐induced mortality in embryos of freshwater fishes. Herein, electroshock‐induced mortality was evaluated for sauger Sander canadensis and rainbow trout Oncorhynchus mykiss, and results were combined with published results obtained for eight other species in studies that used consistent methodology. The model was based on embryo diameter (1·1–4·1 mm among species), the most sensitive stage of embryonic development (near completion of epiboly for all species), and mortality (to hatching or eyed stage) after exposure to a homogeneous electric field [direct current (DC) or 60 Hz pulsed DC (PDC)]. Embryo diameter was positively related to electroshock‐induced mortality for DC (P &lt; 0·001) and 60 Hz PDC (P &lt; 0·05). Results suggested that vulnerability to electroshock‐induced mortality was related to physical characteristics (i.e. size) of embryos rather than species differences, and indicated that prediction of vulnerability in untested species is possible. This is particularly important for protection of endangered species, and those species with larger embryo sizes may be at most risk from electroshock. Conversely, results also suggested that it may be possible to assist in removal of invasive non‐native fish species with large embryo diameters (e.g. O. mykiss) by application of electroshock to target and kill embryos of these species in some freshwater habitats.

The Importance of Phosphorus and Copper Carryover in Pond Sediments for Juvenile Percid Survival, Growth, and Yield

AbstractOver‐fertilization with phosphorus and carryover copper residual in the sediment from copper sulfate treatment in double‐cropped ponds were suspected as the primary causes of low larval percid survival in coolwater aquaculture ponds. Consequently, in this study, we compared saugeye (male sauger Sander canadensis × female walleye S. vitreus) survival, growth, and yield among ponds that were single‐cropped with only saugeyes in the spring during the previous two consecutive years (SS ponds) and ponds that were double‐cropped (with saugeye culture in the spring and channel catfish Ictalurus punctatus culture in the summer) during the previous two consecutive years (DD ponds). We also compared sediment phosphorus (soluble reactive phosphorus [SRP] and total phosphorus [TP]), sediment copper concentrations, phytoplankton biomass, and zooplankton biomass. Fish survival (number harvested) and fish yield (mass harvested) were significantly lower in DD ponds than in SS ponds in 2001 but were similar in 2002 (a year of wide temperature fluctuation early in the production season). Sediment analyses revealed that DD ponds had significantly lower SRP and TP but higher copper concentrations than did SS ponds. A detailed study done in 2002 revealed that individual length and wet weight of percids were significantly higher in the SS ponds than in DD ponds; phytoplankton biomass was similar in both sets of ponds, while zooplankton biomass was significantly lower in DD ponds. These results suggest that residual materials used in double‐cropped channel catfish ponds may negatively affect subsequent years' percid culture.

Competition Potential between Saugers and Walleyes in Nonnative Sympatry

AbstractSauger Sander canadensis populations throughout North America have exhibited declines over the past few decades. Various factors may be contribute to the reduced population abundance of saugers in the middle Missouri River of Montana, including interspecific competition with walleyes Sander vitreus. We compared the seasonal migrations, habitat use, and diets of both species in the middle Missouri River to assess competition potential. Before the presumed spawning period, 96% of saugers and 57% of walleyes migrated as far as 264 kilometers downstream. After spawning, both species returned to previously occupied river reaches and demonstrated site fidelity during the nonmigratory season. Habitat use by saugers and walleyes was similar at three hierarchical spatial scales. Diet overlap was high during the spring and summer and moderate during autumn. Resource overlap of saugers and walleyes in the middle Missouri River of Montana suggests that the competition potential between these species is high, which may preclude the recovery of native sauger populations where resources are limiting.