Louis River Estuary Research Articles

Predicting submerged aquatic vegetation cover and occurrence in a Lake Superior estuary

Submerged aquatic vegetation (SAV) provides the biophysical basis for multiple ecosystem services in Great Lakes estuaries. Understanding sources of variation in SAV is necessary for sustainable management of SAV habitat. From data collected using hydroacoustic survey methods, we created predictive models for SAV in the St. Louis River Estuary (SLRE) of western Lake Superior. The dominant SAV species in most areas of the estuary was American wild celery (Vallisneria americana Michx.). Maximum depth of SAV in 2011 was approximately 2.1m. In regression tree models, most of the variation in SAV cover was explained by an autoregression (lag) term, depth, and a measure of exposure based on fetch. Logistic SAV occurrence models including water depth, exposure, bed slope, substrate fractal dimension, lag term, and interactions predicted the occurrence of SAV in three areas of the St. Louis River with 78–86% accuracy based on cross validation of a holdout dataset. Reduced models, excluding fractal dimension and the lag term, predicted SAV occurrence with 75–82% accuracy based on cross validation and with 68–85% accuracy for an independent SAV dataset collected using a different sampling method. In one area of the estuary, the probability of SAV occurrence was related to the interaction of depth and exposure. At more exposed sites, SAV was more likely to occur in shallow areas than at less exposed sites. Our predictive models show the range of depth, exposure, and bed slope favorable for SAV in the SLRE; information useful for planning shallow-water habitat restoration projects.

Genetic assessment of straying rates of wild and hatchery reared lake sturgeon (Acipenser fulvescens) in Lake Superior tributaries

Natal philopatry in lake sturgeon (Acipenser fulvescens) has been hypothesized to be an important factor that has lead to genetically distinct Great Lakes populations. Due to declining abundance, population extirpation, and restricted distribution, hatchery supplementation is being used to augment natural recruitment and to reestablish populations. If hatchery-reared lake sturgeon are more likely to stray than naturally produced individuals, as documented in other well-studied species, outbreeding could potentially jeopardize beneficial site-specific phenotypic and genotypic adaptations. From 1983 to 1994, lake sturgeon propagated using eggs taken from Lake Winnebago adults (Lake Michigan basin) were released in the St. Louis River estuary in western Lake Superior. Our objective was to determine whether these introduced individuals have strayed into annual spawning runs in the Sturgeon River, Michigan. Additionally, we estimated a natural migration rate between the Sturgeon River and Bad River, Wisconsin populations. Presumed primiparous lake sturgeon sampled during Sturgeon River spawning runs from 2003 to 2008 were genotyped at 12 microsatellite loci. Genotypic baselines established for the Sturgeon River (n=101), Bad River (n=40), and Lake Winnebago river system (n=73) revealed a relatively high level of genetic divergence among populations (mean FST=0.103; mean RST=0.124). Likelihood-based assignment tests indicated no straying of stocked Lake Winnebago strain lake sturgeon from the St. Louis River into the Sturgeon River spawning population. One presumed primiparous Sturgeon River individual likely originated from the Bad River population. Four first-generation migrants were detected in the Sturgeon River baseline, indicating an estimated 3.5% natural migration rate for the system.

Distribution, Abundance, and Range of the Round Goby, Apollina melanostoma, in the Duluth-Superior Harbor and St. Louis River Estuary, 1998–2004

Round gobies were first discovered in the Duluth-Superior Harbor, Lake Superior, in 1995. Anecdotal sightings by anglers and others suggested that the infestation was growing and expanding; however, direct evidence of the distribution and expansion rate in the harbor was largely unknown. Distribution and range of the round goby, Apollonia melanostoma, (formerly Neogobius melanostomus) was assessed using bottom trawl sampling throughout the Duluth-Superior Harbor, and portions of the lower St. Louis River from 1998 to 2004. Previous to 1998, round gobies only were reported to occupy the harbor between the two shipping entries (river kilometer 1 to 7). By 2004, they expanded throughout the harbor and upstream to river kilometer 13, but remained absent in western Lake Superior. The number of round gobies captured per 5 minutes of trawling (catch per unit effort, CPUE) increased from less than 1 fish in 1998 to an average 5.4 ± 1.2 SE fish in 2004, indicating a large increase in the population. The median yearly fish total length varied from 56.0 to 81.5 mm and wet weight varied from 2.3 to 7.0 g. As nest guarding male round gobies were located in rocky habitats inaccessible to trawling, the initial years were dominated by female round gobies with a 16:1 female to male ratio, but by 2002 the maximum ratio was 2:1. The ratio change may be indicative of the increasing population forcing males from their preferred rocky habitat onto open substrates that were more accessible to trawling.

Burrowing mayflies as indicators of ecosystem health: Status of populations in two western Lake Superior embayments

The U.S. Environmental Protection Agency and Environment Canada are supporting the development of indicators of ecosystem health that can be used to report on progress in restoring and maintaining the Great Lakes ecosystem, as called for in the Great Lakes Water Quality Agreement between the United States and Canada. One indicator under development for Great Lakes mesotrophic environments is based on burrowing mayflies (Hexagenia: Ephemeroptera: Ephemeridae). In this paper, we report the results of a benthic survey in spring 2002 to determine the status of nymphal populations of Hexagenia in two western Lake Superior embayments, the St. Louis River estuary, an area with significant water-use impairments, and Chequamegon Bay, an area with no known water-use impairments. Ponar grab samples collected throughout these embayments showed nymphs were generally abundant in finely particulate, cohesive substrate (clay or mixtures of clay and sand) in both embayments. However, in the St. Louis River estuary nymphs were absent in those preferred substrates at 11 stations in the eastern portion of St. Louis Bay and the adjoining northwestern portion of the Duluth-Superior Harbor, where the sediments were variously contaminated with visible amounts of taconite pellets, paint chips, oil, or combusted coal waste (clinkers). Our results suggest that human activities have rendered those portions of the St. Louis River estuary unsuitable for habitation by Hexagenia nymphs and we recommend that trend monitoring of the nymphal population there be conducted to permit reporting on progress in restoring and maintaining the health and integrity of this Great Lakes ecosystem embayment, consistent with the intent of the Great Lakes Water Quality Agreement.

Analyses of Lake Superior Seiche Activity for Estimating Effects on Pollution Transport in the St. Louis River Estuary under Extreme Conditions

Cleanup of toxic residues within the Great Lakes basin requires the assessment of various cleanup options. An important tool for such evaluations is water quality modeling where impacts under hypothetical hydrodynamic conditions can be simulated. In assessing various options for a contaminated site in the St. Louis River estuary at the western end of Lake Superior, it was found that inclusion of the lake seiche is vital to accurate predictions of mass transport. Seiche amplitudes are analyzed and are used to develop simulated seiche activity relevant to simulating potential erosion and/or pollution transport under extreme conditions. Methods and results for calibration of the hydrodynamic/water quality model are also presented.

Environmental Influences on Benthic Community Structure in a Great Lakes Embayment

Biological and chemical measurements of sediment are useful parameters when establishing long-term assessment and monitoring tools for designated areas of concern (AOCs) in the Great Lakes. An intensified Environmental Monitoring and Assessment Program (EMAP) sampling grid in the St. Louis River estuary of western Lake Superior was used to assess the relationship between surficial sediment characteristics and benthic community structure. Ninety sites within two habitat classes (< 5.5 m and > 5.5 m depth) were randomly sampled. Sediment for chemical analysis was collected with a cylindrical drop core while benthic macroinvertebrate abundance and composition were determined from petite Ponar grab samples. Taxa richness was variable (1 to 25 taxa) among sites in the St. Louis River AOC. Oligochaeta were the most abundant taxa while Chironomidae larvae provided a majority of the taxa richness with 43 genera. Results from multivariate redundancy analysis (RDA) on 13 environmental parameters revealed that the majority of variation in benthic community structure was attributed to water depth and site distance from the headwaters. Although physical habitat alterations occur over large spatial scales and are more subtle than those conditions associated with chemically impacted sites, only a small portion of the variability in benthic community structure was explained by sediment chemistry variables. Variability in benthic community structure during this survey was best explained by physical habitat features and must first be quantified prior to understanding benthic response to contaminated sediments.

Reintroduction of Lake Sturgeon in the St. Louis River, Western Lake Superior

Lake sturgeon Acipenser fulvescens declined in abundance in Lake Superior's St. Louis River during the late 1800s and were eliminated from the river during the early 1900s because of the combined effects of exploitation, pollution, and habitat alteration. Since then, exploitation in the river and in Lake Superior has been reduced. Furthermore, water quality in the St. Louis River has improved, and its upper-estuary spawning habitat has remained relatively unchanged and adequate. Lake sturgeon have been stocked annually in the St. Louis River since 1983; from 1983 to 1994 stockings included 736,000 fry, 128,000 fingerlings, and 500 yearlings of the Lake Winnebago strain. Relative abundance, distribution, and growth were determined by sampling marked fish in the St. Louis River estuary and western Lake Superior with graded-mesh gill nets and bottom trawls. During 1983–1998, 644 lake sturgeon were caught in 15,486 m of gill net, and 196 were caught in 1,200 trawl tows. Lake sturgeon were sampled most frequently near channelized portions of the St. Louis River and stayed in the estuary up to 5 years before entering Lake Superior. Lake sturgeon were not captured in western Lake Superior prior to stocking, but abundance increased dramatically after 1985. Of 582 lake sturgeon sampled along the Wisconsin shore of Lake Superior from 1985 through 1998 (347,000 m of gill nets), 93% were captured in less than 30 m of water. A total of 93 lake sturgeon were reported from assessment netting conducted along the Minnesota shore of Lake Superior from 1992 through 1997. The current range of stocked lake sturgeon extends from the St. Louis River 145 km east to the apostle Islands in Wisconsin and 110 km northeast to Little Marais in Minnesota. Increases in lake sturgeon abundance were directly attributed to the stocking program. We recommend stocking a minimum of 20 year-classes and the use of a Lake Superior egg source, if possible. Final evaluation of the project will be detection of tagged lake sturgeon successfully spawning at historical spawning areas.

A Collapsible Trap for Capturing Ruffe

Abstract A modified version of the Windermere trap was designed, constructed, and tested for its effectiveness in capturing ruffe Gymnocephalus cernuus. The inexpensive, lightweight, collapsible trap was easily deployed and retrieved from a small boat. Field tests conducted at the St. Louis River estuary in western Lake Superior in spring 1995 and 1996 indicated that the trap was effective in capturing ruffe. Proportions of ruffe in trap and bottom trawl catches were similar in 1995 and 1996. This trap could be a useful tool in surveillance, monitoring, or control programs for ruffe or similar species, either to augment existing sampling programs or especially in situations where gillnetting or bottom trawling are not feasible.

Fish Community Changes in the St. Louis River Estuary, Lake Superior, 1989–1996: Is It Ruffe or Population Dynamics?

Ruffe ( Gymnocephalus cernuus) have been implicated in density declines of native species through egg predation and competition for food in some European waters where they were introduced. Density estimates for ruffe and principal native fishes in the St. Louis River estuary (western Lake Superior) were developed for 1989 to 1996 to measure changes in the fish community in response to an unintentional introduction of ruffe. During the study, ruffe density increased and the densities of several native species decreased. The reductions of native stocks to the natural population dynamics of the same species from Chequamegon Bay, Lake Superior (an area with very few ruffe) were developed, where there was a 24-year record of density. Using these data, short- and long-term variations in catch and correlations among species within years were compared, and species-specific distributions were developed of observed trends in abundance of native fishes in Chequamegon Bay indexed by the slopes of densities across years. From these distributions and our observed trend-line slopes from the St. Louis River, probabilities of measuring negative change at the magnitude observed in the St. Louis River were estimated. Compared with trends in Chequamegon Bay, there was a high probability of obtaining the negative slopes measured for most species, which suggests natural population dynamics could explain, the declines rather than interactions with ruffe. Variable recruitment, which was not related to ruffe density, and associated density-dependent changes in mortality likely were responsible for density declines of native species.

Overview of the International Symposium on Eurasian Ruffe ( Gymnocephalus cernuus) Biology, Impacts, and Control

This special topic section is dedicated to ruffe (Gymnocephalus cernuus), a small but aggressive fish native to Europe and Asia. Ruffe were introduced into the St. Louis River, the largest U. S. tributary to Lake Superior, in the early 1980s, probably in the freshwater ballast of ocean-going vessels. The port of Duluth-Superior is located in the St. Louis River estuary in western Lake Superior, and is the largest inland port in the United States. At the time of their discovery in 1987, the available literature suggested that ruffe mature quickly, have a high reproductive capacity, spawn over an extended period, and adapt to a wide variety of environments. This potential for rapid population growth, coupled with the threat of competition for food and space with native fishes, and predation on their eggs (Ogle, this volume), was perceived to pose a serious threat to fisheries in the Great Lakes as well as across North America. True to those early predictions, ruffe became the most abundant fish (based on trawl samples) in the 13,000-acre St. Louis River estuary within 5 years (Bronte et al., this volume). They quickly spread on their own nearly 200 miles along the south shore of Lake Superior by 1994. Ruffe were found in Thunder Bay, Ontario in Canadian waters of Lake Superior in 1991 and in Thunder Bay, Lake Huron (near Alpena, Michigan) in 1995, most likely having been transported via ballast water of ships leaving the Port of DuluthSuperior. Populations at both these locations are small but appear to be reproducing. The International Symposium on the Biology and Management of Ruffe was organized to address the potential threats ruffe pose to North American fisheries. Scientists in diverse disciplines from Eurasia and North America were brought together in an attempt to examine all aspects of the North American invasion of ruffe, and to highlight the effects of similar introductions in Europe and Asia.

Relative Abundance and Distribution of Ruffe ( Gymnocephalus cernuus) in a Lake Superior Coastal Wetland Fish Assemblage

Fish assemblages from Allouez Bay Wetland in the St. Louis River estuary were sampled with fyke-nets from May to October, 1995, to characterize typical use patterns in different seasons and microhabitats. The relative abundance and distribution of ruffe ( Gymnocephalus cernuus) in these habitats was of interest because their recent invasion into the Great Lakes has the potential to disrupt native fish assemblages. A total of 15,867 fish comprised of 34 species were captured in 2,300 h of netting. The majority offish over the whole study were caught in the outer marsh (63%, 9,957 individuals), and seasonally during late June (7,384 individuals/4 net-nights) and early May (2,281 individuals). Yellow perch ( Perca flavescens), brown bullhead ( Ameiurus nebulosus), emerald shiner ( Notropis atherinoides), and silver redhorse ( Moxostoma anisurum) were the most abundant species, comprising 85 percent of the total catch. Ruffe was the seventh most abundant species captured (294 individuals), comprising only two percent of the total catch. They were the fifth most abundant species in the outer marsh, but only thirteenth most abundant in the inner marsh. Ninety-one percent of all ruffe (268 individuals) were caught in the outer marsh. Of the 75 species by life-stage combinations derived by classifying all individuals captured into one of 3 life stage categories (YOY, yearling, and adult), yearling ruffe were the twelfth most abundant, adult ruffe were sixteenth, and YOY ruffe were twenty-seventh. While ruffe have been the most abundant fish captured in bottom trawls in St. Louis River estuary during the 1990s, our results indicate the invasion of ruffe in shallow, heavily vegetated areas like those in Allouez Bay has been much less successful. Our results also suggest further degradation of coastal wetlands and other vegetated habitats would eliminate significant refugia from ruffe competition and could lead to increased dominance of ruffe in shallow water habitats in the Great Lakes.

A Bioenergetics Modeling Evaluation of Top-down Control of Ruffe in the St. Louis River, Western Lake Superior

Ruffe ( Gymnocephalus cernuus), were accidentally introduced into the St. Louis River estuary, western Lake Superior, in the mid 1980s and it was feared that they might affect native fish through predation on eggs and competition for forage and habitat. In an effort to control the abundance of ruffe and limit dispersal, a top-down control strategy using predators was implemented in 1989. We used bioenergetics modeling to examine the efficacy of top-down control in the St. Louis Riverfront 1991 to 1994. Five predators––northern pike ( Esox lucius), walleye ( Stizostedion vitreum vitreum), small-mouth bass ( Micropterus dolomieui), brown bullhead ( Ictalurus nebulosus), and yellow perch ( Perca flavescens)––were modeled to determine their consumption of ruffe and four other native prey species––spottail shiner ( Notropis hudsonius), emerald shiner ( Notropis atherinoides), yellow perch ( Perca flavescens), and black crappie ( Pomoxis nigromaculatus). Although predators ate as much as 47% of the ruffe biomass in 1 year, they were not able to halt the increase in ruffe abundance. The St. Louis River is an open system that allows predators to move freely out of the system, and the biomass of managed predators did not increase. A selectivity index showed all five predators selected the native prey and avoided ruffe. The St. Louis River has several predator and prey species creating many complex predator-prey interactions; and top-down control of ruffe by the predators examined in this study did not occur.

Reproductive characteristics of the ruffe, &lt;I&gt;Gymnocephalus cernuus&lt;/I&gt;, in the St. Louis River estuary on western Lake Superior: a histological examination of the ovaries over one annual cycle

Reproductive characteristics of the ruffe, &lt;I&gt;Gymnocephalus cernuus&lt;/I&gt;, in the St. Louis River estuary on western Lake Superior: a histological examination of the ovaries over one annual cycle

Predation on Ruffe by Native Fishes of the St. Louis River Estuary, Lake Superior, 1989–1991

Abstract The ruffe Gymnocephalus cernuus, an exotic Eurasian percid, recently became established in the St. Louis River estuary, Lake Superior, after accidental introduction. Management actions (catch regulations and stockings) were enacted in 1989 to increase the density of top-level predators in the estuary, and thus to increase predation on ruffe. We conducted a field and laboratory study to determine if, and to what extent, native piscivores consume ruffe. Stomachs of 3,669 predators were examined in 1989–1991. Ruffe occurred in 6.7% of burbot Lota lota, 5.8% of bullheads Ictalurus spp., 4.7% of smallmouth bass Micropterus dolomieu, 2.6% of northern pike Esox lucius, 2.6% of black crappies Pomoxis nigromaculatus, and 1.3% of yellow perch Perca flavescens (4.5% after 1989) captured during the 3-year study. No ruffe were found in 967 stomachs of walleyes Stizostedion vitreum examined. Ruffe were 22.7%, of the diet (by weight) of bullheads (during the only year bullheads were captured) and 0.1–17.9% of t...

Diet and Feeding Periodicity of Ruffe in the St. Louis River Estuary, Lake Superior

Abstract Ruffe Gymnocephalus cernuus, a percid native to Europe and Asia, is established in the Lake Superior drainage and could have negative impacts on native fish through competition for forage and predation on fish eggs. We investigated the diet of ruffes in the 4,654-ha St. Louis River estuary in May–October 1989–1990 and the feeding periodicity of ruffes in two adjacent habitats during five 24-h periods in summers 1990–1991. Ruffes were primarily benthophagous. Age-0 ruffes fed mostly on cladocerans and copepods in early summer and midge larvae (Chironomidae) in late summer and fall. Adult ruffes less than 12 cm fed mostly on midges and other macrobenthos but also consumed large numbers of microcrustaceans. Adult ruffes 12 cm and larger fed mostly on midges, burrowing mayflies Hexagenia spp., and caddisflies (Trichoptera). Ruffes consumed few fish eggs. Adult ruffes in deeper waters and all age-0 ruffes fed throughout the day as indicated by weight patterns of stomach contents. However, adult ruffes...