Major shift in the phenology of crustacean biomass in western Lake Superior associated with temperature anomaly

Variable weather patterns during the early months of 2014 and 2015 resulted in differences between years in spring and summer surface water temperatures in the offshore areas of western Lake Superior. Zooplankton were collected in western Lake Superior during several cruises from late spring to early fall in 2014 and 2015 to test the hypotheses that colder summer water temperatures in 2014 were correlated with reduced zooplankton biomass, later peaks in zooplankton biomass, and a smaller contribution of warm-water taxa to the zooplankton assemblage. The total amount of zooplankton biomass from early June through early October did not differ greatly between years. Of the taxonomic subcategories (large-bodied calanoids, small-bodied calanoids, cyclopoids, nauplii, and herbivorous cladocerans) however, cyclopoid and cladoceran biomass was somewhat smaller in 2014 compared to 2015, providing some support for the hypothesis that warm-water taxa contribute less to offshore zooplankton biomass in colder years. The timing of peak biomass for cladocerans, small-bodied calanoids, and cyclopoids did not differ between years, but peaks in the biomass of copepod nauplii and large-bodied calanoids (primarily Limnocalanus macrurus) occurred several weeks later in 2014 than 2015 which was evidence for phenological delay during a year with unusually cold spring and summer surface water temperatures. Though this study only evaluates the role of temperature in driving zooplankton biomass and phenology in Lake Superior, it does provide insight into the potential effects of climate variability on the Lake Superior food web.     

Spatial and vertical bias in down-looking ship-based acoustic estimates of fish density in Lake Superior: Lessons learned from multi-directional acoustics

Hydroacoustic surveys using hull-mounted down-looking transducers are useful for estimating pelagic fish densities; however, this method may miss shallow fish owing to the acoustic surface dead zone and vessel avoidance. Our objective was to compare pelagic fish density estimates acquired by a traditional down-looking acoustic survey to estimates obtained by a new multi-directional-towed sled capable of sampling the entire water column using upward-, sideways-, and downward-aimed transducers simultaneously. We deployed both systems concurrently in the western arm of Lake Superior during a period of stable stratification. We found the two survey approaches provided significantly different estimates of fish density in the upper water column layer (~4–9 m below the lake surface) with the sled up-looking transducer providing 56 times higher densities compared to the traditional ship down-looking method. Densities also varied significantly in the 9–14 m layer where densities were 6.2 times higher in the sled survey. Midwater trawl sampling indicated that cisco (Coregonus artedi) and rainbow smelt (Osmerus mordax) were the predominant species occupying the uppermost 14 m of the water column. The two acoustic approaches provided similar results at water column depths >14 m where rainbow smelt and kiyi (Coregonus kiyi) were predominant. Overall, the sled-based method estimates were, on average, 2.5 times higher for the whole water column. Our findings show that the new sled can reduce bias by better sampling the surface dead zone leading to more accurate estimation of pelagic fish densities for both management and research.     

Evaporation from Lake Superior: 1. Physical controls and processes

The surface energy balance of Lake Superior was measured using the eddy covariance method at a remote, offshore site at 0.5-h intervals from June 2008 through November 2010. Pronounced seasonal patterns in the surface energy balance were observed, with a five-month delay between maximum summer net radiation and maximum winter latent and sensible heat fluxes. Late season (winter) evaporation and sensible heat losses from the lake typically occurred in two- to three-day-long events, and were associated with significant release of stored heat from the lake. The majority of the evaporative heat loss (70-88%) and sensible heat loss (97-99%) occurred between October and March, with 464 mm (2008-2009) and 645 mm (2009-2010) of evaporative water loss occurring over the water year starting October 1. Evaporation was proportional to the horizontal wind speed, inversely proportional to the ambient vapor pressure, and was well described by the ratio of wind speed to vapor pressure. This ratio remained relatively constant between the two water years, so the differences in evaporative water loss between years were largely associated with differences in lake surface conditions (e.g. water temperature, ice cover, and ice duration). Since late-season water temperature decline is driven by evaporative and sensible heat loss, the potential for a negative feedback mechanism between evaporation and ice cover is discussed.     

Nitrogen dry deposition to Lake Superior and Lake Michigan

Nitrate (NO₃^?) levels in Lake Superior have increased from historic levels of about 5?μM to its current concentration of about 25?μM. The atmosphere makes a substantial contribution to the nitrogen budgets for Lake Superior and Lake Michigan. This study provides a more well-defined estimate of nitrogen dry deposition rates derived from the measurement of over-water concentrations, and in situ meteorological measurements, which were input into the Resistance Model. We obtained a nitrogen dry deposition rate of [(3.41?±?2.26)?×?10⁷?kg?N/yr; (5.90?±?3.91)?kg?N/ha/yr] over Lake Michigan, and [(1.54?±?1.06)?×?10⁷?kg?N/yr; (1.87?±?1.27)?kg?N/ha/yr] over Lake Superior. Nitric acid (HNO₃), which originates from the combustion of fossil fuels, contributes 84% of the total nitrogen dry deposition to Lake Michigan; and 66% to Lake Superior. Ammonia (NH₃), which originates from agricultural activities and gasoline combustion, is the second highest contributor of nitrogen dry deposition to both lakes: contributing 13% to Lake Michigan and 32% to Lake Superior. The nitrogen dry deposition is approximately 68% of the nitrogen wet deposition over Lake Superior, and approximately 80% of wet deposition over Lake Michigan. The over-water dry deposition velocity of HNO₃ and NH₃ were also evaluated. We obtained morning deposition velocities of 0.099?cm/s for NH₃ and 0.095?cm/s for HNO₃; and afternoon values of 0.137?cm/s for NH₃ and 0.132?cm/s for HNO₃. Another key finding is that the atmospheric concentrations of nitrogen compounds near Lake Michigan and Lake Superior have decreased since 2003.     

Evaporation from Lake Superior: 2: Spatial distribution and variability

Evaporation is a critical component of the water balance of each of the Laurentian Great Lakes, and it is expected that because of their shear size, evaporation cannot be spatially or temporally uniform. Despite this, examples of spatially distributed estimates of evaporation in the scientific literature are rare for most of the lakes and non-existent for Lake Superior. Direct measurements of evaporation taken at an offshore site on Lake Superior from June 2008 to October 2010 were used with concurrent satellite and climate model data to extrapolate evaporation measurements across the entire lake. Evaporation rates, large scale forcing mechanisms, and spatial patterns and variability are presented. Spatial patterns of evaporation tend to follow synoptic-scale air masses traveling over the lake. While most evaporation occurs during relatively short term events, these episodes tend not to occur in isolated locations on the lake, but are spatially widespread. The exceptions to this rule are during periods of a stable atmosphere and low evaporation, and when a transient ice cover can limit evaporation from some areas.     

Perfluoroalkyl acids in Lake Superior water: Trends and sources

Perfluoroalkyl acids (PFAs) are a family of highly persistent compounds which are present in the environment as a result of degradation of polyfluorinated precursors, from use as processing aids for production of fluoropolymers, and use in fire fighting foams. The purpose of this study was to investigate prevailing concentrations and possible sources of PFAs in Lake Superior, as well as in Siskiwit Lake on Isle Royale. Between 2001 and 2005, replicate water samples were taken from lake surface waters, and from depth profiles, as well as from major tributaries including municipal waste water treatment plants (WWTPs) at three major population centers. Perfluorooctanoate (PFOA) was the predominant PFA in Lake Superior, with concentrations ranging from 0.07 to 1.2 ng/L in surface waters. PFOA concentrations were generally 1.5 to 2-fold greater than perfluorooctanesulfonate (PFOS) levels. WWTPs were found to contribute up to 20 fold higher concentrations of PFOA (22 ng/L) relative to the intake water from Lake Superior, while most tributaries contained lower concentrations of perfluorocarboxylates (PFCA) and perfluoroalkylsulfonates (PFSs) (< 0.1 ng/L). Overall tributaries and precipitation were estimated to be the major sources of PFCAs and PFSs to Lake Superior. Tributaries were estimated to be the largest source contributing 59% of PFOA and 57% of PFOS inputs to the lake. Profiles conducted over the deepest points in the lake showed that PFAs were found throughout the water column, however, there was no distinctive trend with depth.     

A three-dimensional model of Lake Superior with ice and biogeochemistry

The formation of winter ice on Lake Superior has been shown to be important in determining the annual thermal cycle of the lake and long-term trends of surface water temperature increase. However, modeling studies of Lake Superior to date have not included dynamic and thermodynamic ice cover. These physical characteristics of the lake in turn can have significant impacts on biogeochemical cycling within the lake. We present a new three-dimensional model of Lake Superior that includes a dynamic and thermodynamic ice model and a biogeochemical model. Results from the model forced by observed meteorological conditions for the period 1985 to 2008 are discussed and compared with available observations. Modeled long-term interannual trends in increasing water temperature and decreasing ice cover are compared with observed rates. In the model, total annual gross primary productivity is found to correlate positively with mean annual temperature and negatively with mean winter ice-cover magnitude.     

Lake Superior water level fluctuation and climatic factors: A dynamic linear model analysis

We use Dynamic Linear Models (DLM) to analyze the time series of annual average Lake Superior water levels from 1860 to 2007, as well as annual averages of climate drivers including precipitation (1900–2007), evaporation and net precipitation (1951–2007). Our results indicate strong evidence favoring the presence of a systematic trend over a random walk for Lake Superior water levels, and this trend has been negative in recent decades. We then show decisive evidence, in terms of improved predictive performance, favoring a model in which the trend component is replaced with regression components consisting of climatic drivers as predictor variables. Because these models use lagged values of precipitation or net precipitation as predictors, the models can be used to forecast water levels, with the associated uncertainty, several years into the future. We use several of the best fit models and compare one (2008) and two step-ahead (2009) forecasts. The 2008 forecasts compare very well with the observed 2008 water level; the two step-ahead 2009 forecasts are offered as testable hypotheses. The Bayesian context in which these models are developed provides a rigorous framework for data assimilation and regular model updating.     

Lake Sturgeon (Acipenser fulvescens) in Goulais Bay,Lake Superior: Cohort strength determinants and population viability

Lake Sturgeon (Acipenser fulvescens) is a species of conservation concern throughout North America, and healthy populations are rare. Earlier sampling efforts identified the Goulais Bay population in Lake Superior as a potentially healthy population after three years of sampling. With seven additional years of sampling, we updated the earlier analysis and developed a matrix population model to conduct a population viability analysis (PVA). We identified a non-linear relationship between cohort strength and May river discharge rate which was incorporated into the population model to evaluate the influence of future discharge scenarios on population persistence. Population size was estimated, with an open-population mark-recapture model, at approximately 5,200 juvenile Lake Sturgeon. This estimate equates to approximately 440 mature females and 625 mature males in the population. A population of this size has a probability of extinction of 4 % and 18 % over 250 and 1000 years under status quo conditions. If the May river discharge were to decrease in the future, which may represent the most likely scenario under future climate conditions, our model predicts an increased risk of population extirpation. This indicates that increased management actions may be required to ensure this population remains resilient.     

Contemporary diets of Lake Superior lake whitefish off the Keweenaw Peninsula and changes in condition from the 1980s to 2010s

Over the last two decades, declines in lake whitefish (Coregonus clupeaformis) recruitment and growth in many areas of the Laurentian Great Lakes have raised concerns about the status of this important species. Although Lake Superior populations have been less affected than those in other Great Lakes, these populations still face multiple threats. We characterized lake whitefish diets collected off the Keweenaw Peninsula between 2015 and 2017 and compared results to previous Lake Superior studies. We additionally estimated length-weight relationships to determine whether lake whitefish body condition (i.e., expected weight-at-length) had changed since the 1980s. Diet diversity was low, although individual specialization was moderate to high. Fish transitioned from consuming Diporeia in the spring to Mysis and fish eggs during fall and winter; sphaeriids composed 20–30% of diets across all seasons. Compared to findings for other Lake Superior regions, lake whitefish diets comprised lower percentages of high energy items (e.g., Diporeia, Mysis) and higher percentages of low energy items (e.g., sphaeriids). Expected weights in the 2000s and 2010s were lower in the 400- and 500-mm length groups but similar in larger lengths groups compared to the 1980s; condition was highest across all lengths in the 1990s. The observed decline in condition since the 1990s in the 400- and 500-mm length groups, in combination with possibly greater consumption of less energetically profitable items, suggests that lake whitefish <600 mm or preferred prey resources in this lake region may be experiencing stressors leading to condition declines, although what these stressors are remain unknown.     

Microplastic contamination of sediments across and within three beaches in western Lake Superior

Microplastic pollution of the environment is ubiquitous, but the processes by which microplastics accumulate within beach sediments are not yet well understood. We isolate microplastic pollution from the sediments at three western Lake Superior beaches. Samples of both surface and subsurface sediments are considered. We find that the average microplastic contamination is 65 microplastic particles kg^?1 sediment across our sites with significant variability across beaches, but the microplastic composition is always dominated by polyester fibers. The variation across beaches does not seem to relate to the distance from suspected sources of microplastics to the lake. Within each beach, we find no significant variation of the mean microplastic concentration in the cross-shore direction or in the surface vs. subsurface sediments at the wrack line. We interpret this mean microplastic concentration in the sediment as a measure of the bulk microplastic concentration in the nearshore water at each beach. In subsurface sediments, we observe a significant difference in the variance of microplastic concentrations, and we attribute this variation to the intermittency of the extreme hydrodynamic conditions that deposit microplastics deeper into the sediment.     

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 F_ST = 0.103; mean R_ST = 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.     

Small eddies observed in Lake Superior using SAR and sea surface temperature imagery

Making use of the fine resolution of satellite SAR imagery, we observe small eddies during the spring and summer months in several locations in Lake Superior. During these months there is a thermal gradient between warmer nearshore waters and colder offshore waters which enhances cyclonic coastal currents. Using spaceborne SAR imagery from the European Space Agency's ERS-1 and ERS-2 missions from 1992 to 1998, we observe small eddies, identifying and mapping basic eddy characteristics including diameter, location, and rotational sense. In total, 45 eddies were located, of which 41 were cyclonic and 4 anticyclonic. Average diameter was 9.8 km and average distance to shore was 8.1 km. Based on sea surface temperature data from AVHRR, the eddies are located within the region of sharp thermal gradients of order 3–5 °C per 3 km. Spatial and temporal coverage was uneven, however, more eddies were seen in SAR images taken in late summer along the southern and eastern shores as well as areas where the boundary current interacts with topographic features including islands and promontories.     

Patterns in the crustacean zooplankton community in Lake Winnipeg,Manitoba: Response to long-term environmental change

Changes in the crustacean zooplankton community composition and abundance in Lake Winnipeg (1969–2006) provide a rare opportunity to examine their response to environmental changes in the largest naturally eutrophic lake on the Canadian prairies. Since 1929, zooplankton species composition in Lake Winnipeg has changed little except for the addition of the invasive cladoceran, Eubosmina coregoni in 1994. The dominant taxa in the lake in summer include: Leptodiaptomus ashlandi, Acanthocyclops vernalis, Diacyclops thomasi, Daphnia retrocurva, Daphnia mendotae, Diaphanosoma birgei, Eubosmina coregoni, and Bosmina longirostris. Climate-accelerated nutrient loading to southern Lake Winnipeg over the last two decades has led to increased phytoplankton abundance and higher frequency of cyanobacterial blooms especially in its northern basin. Crustacean zooplankton have likewise increased especially in the North Basin, but less so in the more nutrient rich South Basin, possibly as a consequence of higher densities of pelagic planktivorous fish and light-limited primary production compared with the more transparent North basin (Brunskill et al., 1979, 1980). Calanoid copepods play a larger role in the South basin food web in contrast to cyclopoid copepods and Cladocera in the North basin. The study begins to fill the recognized gap in understanding of Lake Winnipeg's food web structure and provides a baseline for evaluating ongoing changes in the zooplankton community with the arrival of new non-indigenous taxa, e.g. Bythotrephes longimanus and Dreissena polymorpha. It reinforces previous work demonstrating that zooplankton provide valuable indices toward evaluating the health of an ecosystem.     

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 2.1 m. 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.     

Dolichospermum blooms in Lake Superior: DNA-based approach provides insight to the past,present and future of blooms

Cyanobacterial blooms are increasing in frequency, duration, and severity globally in freshwater ecosystems. The Laurentian Great Lakes are prone to toxin-producing cyanobacterial blooms and have experienced annually recurring blooms. Because of its oligotrophic nature, Lake Superior has been relatively free of bloom occurrences. However, in recent years, Dolichospermum blooms have occurred with increasing frequency, especially in the western arm. During a Dolichospermum bloom in 2018, opportunistic samples were collected from the offshore bloom and investigated with shotgun metagenomics. We identified a near-complete Dolichospermum genome that is highly similar to genomes from cultures recovered in Lakes Erie and Ontario. The genomes from the Laurentian Great Lakes are typified by their putative ability to produce a suite of secondary metabolites like anabaenopeptin, but not toxins like microcystin. Additionally, we recovered a Dolichospermum lemmermannii 16S rRNA gene from the bloom and using datasets collected from the epilimnion and sediments in Lake Superior show this organism is ubiquitous and that several strains may exist. While there is much to learn about Lake Superior cyanobacterial bloom development and triggers, understanding this organism is endemic to the region, what its genome is capable of and that specific strains may have provenance within the lake provides a distinct ecological basis for understanding and working towards a predictive framework for future blooms.     

Heterogeneity in zooplankton distributions and vertical migrations: Application of a laser optical plankton counter in offshore Lake Michigan

Zooplankton distributions are patchy due to multiple physical, chemical, and biological processes, including diel vertical migration (DVM) behavior. Heterogeneity in the offshore environment is difficult to study with net tows, but newer technologies measure finer-scale distributions. Here, we use laser optical plankton counter (LOPC) data, informed by net tows, to study distributions and DVM of zooplankton in offshore Lake Michigan during July and September 2015. Water column (5–60 m) zooplankton biomass varied by an order of magnitude among transects and a factor of two within individual transects (6–19 km distances); transect coefficients of variation (SD/mean) ranged from 7 to 22% (~0.5 km scale). Horizontal patterns in zooplankton biomass varied among size groups but were consistent from day to night, suggesting that processes driving heterogeneity persist for hours to days. Fine-scale LOPC data show that zooplankton often aggregate in thin layers (1–3 m) within the metalimnion, a feature undetectable by coarser net sampling. Although DVM was not consistently observed, some patterns emerged. Small zooplankton including copepodites, diaptomids (Leptodiaptomus ashlandi, L. minutus), and Diacyclops thomasi often migrated to surface waters at night, and large zooplankton (Limnocalanus macrurus) migrated upward at night in most cases. Beam attenuation coefficient (proxy for phytoplankton biomass) was a significant predictor for zooplankton mean depth (p < 0.001) although it explained more of the variation for night data (R² = 0.72) than day data (R² = 0.53). The heterogeneity observed in zooplankton distributions has implications for planktivorous fish feeding in the offshore zone, as prey density varies greatly with depth.     

Development and application of a real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands,Lake Superior

Assessing all pertinent environmental variables to categorize a skill level to safely navigate the water environment can be difficult for inexperienced kayakers, especially at a remote site where internet access is limited. A real-time kayaker safety assessment of water environmental conditions at the Mainland Sea Caves of the Apostle Islands National Lakeshore, Lake Superior is achieved. We present a new cyberinfrastructure that provides kayakers with real-time data access and a Safety Index (SI) with consideration of multiple environmental factors to characterize the degree of navigational difficulty for classifying kayaker skill levels. Specifically, radar reflectivity is added to improve forecasts of dangerous conditions caused by convective storms using state-of-the-art weather and wave modeling. Spectral characteristics of surface waves are employed to correlate the occurrences of extreme and freak waves. In addition, unexpectedly dangerous conditions like coastal upwelling and freak wave occurrence due to changing wind directions are considered. A contingency plan is implemented to handle the issue of possibly missing required environmental data. Display of the SI and visualization of other real-time environmental data are communicated by a power-efficient kiosk. Web analytics demonstrates a public interest in real-time water conditions and the need for the on-site kiosk to provide the latest information before kayakers enter the water. The new real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands, Lake Superior has been successfully operated since 2014.     

Coastal wetland plant community responses to record-high Lake Superior water levels: An Allouez Bay case study

Here we present findings from a natural experiment to better understand coastal wetland plant community responses to rising water levels. Plant communities were monitored in three vegetation zones (submergent, emergent, and wet meadow) at Allouez Bay, a lacustrine coastal marsh, six times over years 2011–2020. Lake Superior water levels reached record-highs in 2017, and again in 2019. During our six sampling campaigns, we encountered eighty-four vascular plant species, seven of which were non-native. Except for reductions in total plant cover in the wet meadow zone, emergent and wet meadow plant communities were only marginally affected by rising water. Percent cover of non-native species did not increase in a clear pattern. Temporal changes in floristic quality were non-significant at the whole site level, and mean coefficient of conservatism values ranged from 5.3 to 6.0. Aquatic vegetation in the submergent zone was most affected by rising water. Submergent zone richness declined from sixteen plant species in 2011 to zero in 2020. Multivariate PERMANOVA analysis showed significant effects of year on site-wide plant composition. Temporal composition changes were predominately driven by species turnover in the submergent vegetation zone, whereby floating aquatic species were replaced by non-floating species from 2011 to 2017, and an absence of aquatic vegetation along research transects in 2020. Tracking regeneration of aquatic vegetation is a focus of future research as unknown effects from prolonged exposure to record-high water levels may affect natural regenerative processes at Allouez Bay, and potentially at other lacustrine Great Lakes wetlands throughout the basin.     

Trophic connections in Lake Superior Part II: The nearshore fish community

We use detailed diet analyses of the predominant planktivorous, benthivorous and piscivorous fish species from Lake Superior to create a nearshore (bathymetric depths < 80 m) fish community food web. The food web was based on analysis of 5125 fish stomachs collected seasonally (spring, summer, fall) from 9 nearshore sites in 2005. Based on mass of prey items, nearshore diets across all sites and seasons were similarly structured with a dominance of macroinvertebrates (Mysis diluviana and Diporeia spp). Although the piscivorous fishes like lean lake trout (Salvelinus namaycush) fed to a lesser extent on Diporeia and Mysis, they were still strongly connected to these macroinvertebrates, which were consumed by their primary prey species (sculpin spp., rainbow smelt Osmerus mordax, and coregonines). The addition of Bythotrephes to summer/fall cisco and lake whitefish diets, and the decrease in rainbow smelt in lean lake trout diets (replaced by coregonines) were the largest observed differences relative to historic Lake Superior diet studies. Although the offshore food web of Lake Superior was simpler than nearshore in terms of number of fish species present, the two areas had remarkably similar food web structures, and both fish communities were primarily supported by Mysis and Diporeia. We conclude that declines in Mysis or Diporeia populations would have a significant impact on energy flow in Lake Superior. The food web information we generated can be used to better identify management strategies for Lake Superior.