We examined the stomach contents of 1,045 lake trout (Salvelinus namaycush) caught on Six Fathom Bank and Yankee Reef, two offshore reef complexes in Lake Huron, during late spring and early summer 1998–2003. Lake trout ranged in total length from 213 to 858 mm, and in age from 2 to 14 years. In total, 742 stomachs contained food. On a wet-weight basis, alewife (Alosa pseudoharengus) dominated the spring-summer diet of lake trout on both of these offshore reef complexes. Alewives accounted for 75 to 90% of lake trout diet, depending on the lake trout size category. Size of alewives found in lake trout stomachs increased with increasing lake trout size. Faster growth of juvenile lake trout on Six Fathom Bank and Yankee Reef than on Sheboygan Reef in Lake Michigan was attributed to greater availability of small alewives on the offshore reefs in Lake Huron. Our findings indicated that alewives inhabited Six Fathom Bank and Yankee Reef during spring and summer months. Thus, our study provided support for the contention that alewives may have interfered with natural reproduction by lake trout on these offshore reef complexes in Lake Huron.

The spatial distribution of hydrophobic organic contaminants, including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and octachlorostyrene (OCS) in sediments of the Detroit River was established using data from a 1999 river-wide survey. The survey employed a stratified random sampling design that divided the river into six geostatistical zones consisting of upper, middle, and lower U.S. and equivalent Canadian river reaches. Organic carbon normalized OCS sediment concentrations demonstrated no significant differences between U.S. or Canadian sediments or upstream/downstream gradients suggesting that OCS is derived primarily from sources upstream of the Detroit River. In contrast, sum PCBs and sum PAHs were significantly elevated at U.S. as compared to Canadian stations and demonstrated significant increasing upstream/downstream gradients in organic carbon normalized sediment contamination. The upper and middle U.S. river reaches contained a number of near-shore stations with high localized PCB and PAH sediment concentrations suggesting multiple inputs along the upper U.S. portion of the river. Consistent with past surveys, wide-spread sediment contamination of PCBs and PAHs continues to be observed in the highly industrialized Trenton Channel and downstream of Grosse Isle. Threshold effect level (TEL) sediment quality guidelines for PAHs and PCBs were exceeded in 92.6 and 77.8%, respectively, of stations in Trenton Channel and downstream of Grosse Isle. This large reservoir of degraded sediments in the lower U.S. river reach has the potential to enter Lake Erie during sediment disturbance events and likely contributes to gentoxic stress and increased bioaccumulation of PCBs in resident benthos, fish, and wildlife.

The continued lack of natural reproduction by lake trout (Salvelinus namaycush) in the Great Lakes has prompted development of models focused on the potential negative effects of interstitial predators. To aid in parameterization of such models we investigated the effect of temperature (1–2°C, 4–5°C, 7–8°C, and 10–11°C), predator group size, interspecific competition, egg density (60–6000 eggs m⁻²), and an alternate food source on egg consumption by slimy (Cottus cognatus) and mottled (Cottus bairdii) sculpins, round gobies (Neogobius melanostomus), and the native crayfish (Orconectes propinquus) in the laboratory. Egg consumption by the sculpins and round goby all increased over the range of temperatures investigated (ca 0.5 eggs·day⁻¹ at 1–2°C to 1.5 eggs·day⁻¹ at 10–11°C). Predator group size affected consumption; fewer eggs were eaten per individual slimy sculpin and round goby at densities of 5 or 10 per tank than 1 individual per tank. There was no effect of interspecific competition on egg consumption by slimy sculpins or round gobies at a density of 10 individuals per tank for various species combinations (10:0, 9:1, 5:5, 1:9, 0:10). A type II functional response to egg density was observed for sculpins, gobies, and crayfish although at extreme densities per capita consumption by crayfish and gobies declined. The presence of zebra mussels (Dreissena polymorpha) did not affect the number of rainbow trout (Oncorhynchus mykiss) eggs eaten by round gobies whose mussel consumption averaged 75% BW·day⁻¹. Of the four species examined, round gobies appeared to be the most effective egg predator while crayfish were the least.

The population genetic structure of smallmouth bass, Micropterus dolomieu, in Lake Erie was investigated using two mitochondrial DNA sequences (control region and cytochrome b) and eight nuclear DNA microsatellite loci. The objective was to evaluate relative resolution of fine-scale versus broad-scale spawning population genetic structure across Lake Erie. Results showed that only cytochrome b sequences supported the divergence of populations grouped by basins, suggesting little correspondence to bathymetric features of Lake Erie. The majority of sampling sites were characterized by large within site variances, particularly with the microsatellite data, reducing the efficiency to delimit populations with the given sample sizes. Although conclusions from mtDNA and microsatellites were not corroborative, all data sets revealed some divergent sites across and within basins. The apparently weak genetic structuring of populations does not reflect the strong behavioral patterns of male nest-site fidelity and adult migration. Finer-scale structure among geographically proximate sites was detected primarily with microsatellite data. Several locations were consistently identified as most genetically divergent suggesting that they may serve as long-term attractor areas for spawning populations. Mitochondrial DNA data indicated a broader-scale pattern reflecting either colonization from at least two glacial refugia or different dispersal routes from a common refugium with subsequent genetic divergence through drift. Genetic variation of smallmouth bass in Lake Erie is likely a product of glacial history with behavioral and stochastic factors interacting at different spatial and temporal scales. A precautionary management approach would weigh both genetic and behavioral patterns and develop appropriate conservation strategies for a non-panmictic smallmouth bass population in Lake Erie.

In this paper we utilize 7 years of SeaWiFS satellite data to obtain seasonal and inter-annual time histories of the major water color-producing agents (CPAs), phytoplankton chlorophyll (chl), dissolved organic carbon (doc), and suspended minerals (sm) for Lake Michigan. We first present validation of the Great Lakes specific algorithm followed by correlations of the CPAs with coincident environmental observations. Special attention is paid to the satellite observations of the extensive episodic event of sediment resuspension and calcium carbonate precipitation out of the water. We then compare the obtained time history of the CPA's spatial and temporal distributions throughout the lake to environmental observations such as air and water temperature, wind speed and direction, significant wave height, atmospheric precipitation, river runoff, and cloud and lake ice cover. Variability of the onset, duration, and spatial extent of both episodic events and seasonal phenomena are documented from the SeaWiFS time series data, and high correlations with relevant environmental driving factors are established. The relationships between the CPAs retrieved from satellite data and environmental observations are then used to speculate on the future of Lake Michigan under a set of climate change scenarios.

We compared density estimates from day bottom trawl tows against night midwater trawl tows and acoustic gear to test the hypothesis that adult lake herring (≥250 mm) are underestimated by day bottom trawl tows during the annual USGS spring fish community survey in Lake Superior. We found average density at nine nearshore stations was significantly higher at night (21.3 adult fish/ha) compared to day (1.0 adult fish/ha; p = 0.0119). At nine offshore stations, no lake herring were captured during the day but density averaged 39.6 adult fish/ha at night. At a lakewide scale (n = 18 stations), precision (relative standard error) was much better using night midwater trawls and acoustic gear (37%) compared to day bottom trawls (100%). Moderate sample size increases using the former methodology would likely bring precision within recommended levels (≤30%) for stock-recruit data sets. Our results suggest that 1) population abundances of adult lake herring in Lake Superior are much higher than previously considered, 2) the annual spring fish community survey may not provide a relative index of abundance of adult lake herring, 3) night midwater trawls and acoustic gear are necessary for assessing adult lake herring abundance, and 4) previous studies using lake herring data from the annual spring fish community survey need to be re-evaluated in light of these results. Lake herring appear to become progressively more pelagic and less susceptible to bottom trawling as they mature. Day bottom trawls appear to be an adequate tool for estimating relative density of age-1 recruits, although this method still suffers from relatively poor precision.

Early mortality syndrome (EMS) is the term used to describe the mortality of juvenile salmonids due to thiamine deficiency within the Great Lakes basin. EMS appears to be related to the presence of thiaminase found in prey fish such as alewives Alosa pseudoharengus, rainbow smelt Osmerus mordax, and gizzard shad Dorosoma cepedianum. Since 1985, the Michigan Department of Natural Resources, in conjunction with Lake Superior State University's Aquatic Research Laboratory, has raised Atlantic salmon Salmo salar for stocking in the St. Marys River region near Sault Ste. Marie, Michigan. The current study correlates egg-thiamine concentrations from 45 individual family groups with egg and larval mortality as well as length, weight, and condition data obtained from spawning females. Thiamine concentrations were measured at three stages of egg-development using a newly developed rapid reversed-phase solid-phase extraction (RP-SPE) method of thiamine analysis. Results suggest a threshold average total egg-thiamine concentration of approximately 1.0 (nmol/g egg) for normal larval survival. Thiamine analysis indicated no significant change in egg-thiamine concentrations from pre-fertilization to the eyed stage of development. Female parent weight showed an inverse relationship with egg-thiamine levels. Thiamine immersion of larval sac-fry eliminated the occurrence of EMS for this study population. Due to low cost and ease of use, the RP-SPE method for large scale egg-thiamine analysis has the potential to impact basin wide management decisions with respect to salmonid stocking programs.

After near extirpation earlier this century in the Great Lakes, double-crested cormorant (Phalacrocorax auritus) populations reached all-time highs, raising concerns among sport anglers and fisheries managers, who see cormorants as a significant source of mortality for yellow perch (Perca flavescens), whose populations are perceived to have declined in concert with cormorant increases. We partitioned age-specific perch mortality for 1995 into that caused by (1) cormorant predation, (2) angler harvest, and (3) other sources. Cormorant consumption of perch was calculated by simultaneously estimating diet composition (using stomach analysis and number of foraging cormorants from aerial and ground surveys), and daily consumption (using energetic values from the literature). Consumption of perch by cormorants was heaviest during April and May (48% of the diet by weight) when perch spawn, but yellow perch was not an important prey species overall (11%). Primary prey groups were alewife (47%) and sticklebacks (15%). Cormorants consumed 11,400 kg of perch, mostly young fish (ages 1–3), but mortality caused by cormorant predation was estimated at ≤6.3% of mortality for all ages of perch. Neither cormorants nor anglers contributed more than one-fourth of the total annual mortality of any age class of perch. Although cormorants were highly visible predators of perch in Les Cheneaux Islands area, they did not represent a major source of mortality in 1995. Impact of cormorants on perch may vary from year to year, and may relate to fluctuations in timing of the birds' migration relative to perch spawning. However, we conclude that overall impact is not significant, and control measures to limit their populations were not warranted at the time of this study.

In an effort to develop indicators for Great Lakes near-shore conditions, diatom-based transfer functions to infer water quality variables were developed from 155 samples collected from coastal Great Lakes wetlands, embayments and high-energy shoreline sites. Over 2,000 diatom taxa were identified, and 352 taxa were sufficiently abundant to include in transfer function development. Multivariate data exploration revealed strong responses of the diatom assemblages to stressor variables, including total phosphorus (TP). Spatial variables such as lake, latitude and longitude also had notable relationships with assemblage characteristics. A diatom inference transfer function for TP provided a robust reconstructive relationship (r² = 0.67; RMSE = 0.28 log(μg/L); r²_jackknife = 0.55; RMSEP = 0.33 log (μg/L)) that improved following the removal of 13 samples that had poor observed-inferred TP relationships (r² = 0.75; RMSE = 0.22 log(μg/L); r²_jackknife = 0.65; RMSEP = 0.26 log (μg/L)). Diatom-based transfer functions for other water quality variables, such as total nitrogen, chloride, and chlorophyll α also performed well. Measured and diatom-inferred water quality data were regressed against watershed characteristics (including gradients of agriculture, atmospheric deposition, and industrial facilities) to determine the relative strength of measured and diatom-inferred data to identify watershed stressor influences. With the exception of pH, diatom-inferred water quality variables were better predicted by watershed characteristics than were measured water quality variables. Because diatom communities are subject to the prevailing water quality in the Great Lakes coastal environment, it appears they can better integrate water quality information than snapshot measurements. These results strongly support the use of diatoms in Great Lakes coastal monitoring programs.

High-resolution seismic reflection profiles, side-scan sonar profiles, and surface sediment analyses for grain size (% sand, silt & clay), total organic carbon content, and carbonate content along shore-perpendicular transects offshore of Olcott and Rochester in Lake Ontario were utilized to investigate cm-thick sands or absence of deepwater postglacial sediments in water depths of 130 to 165 m. These deepwater sands were observed as each transect approached and occupied the “sills,” identified by earlier researchers, between the three deepest basins of the lake. The results reveal thin (0 to 5-cm) postglacial sediments, lake floor lineations, and sand-rich, organic, and carbonate poor sediments at the deepwater sites (> 130 m) along both transects at depths significantly below wave base, epilimnetic currents, and internal wave activity. These sediments are anomalous compared to shallower sediments observed in this study and deeper sediments reported by earlier research, and are interpreted to indicate winnowing and resuspension of the postglacial muds. We hypothesize that the mid-lake confluence of the two-gyre surface current system set up by strong storm events extends down to the lake floor when the lake is isothermal, and resuspends and winnows lake floor sediment at these locations. Furthermore, we believe that sedimentation is more likely to be influenced by bottom currents at these at these sites than in the deeper basins because these sites are located on bathymetric highs between deeper depositional basins of the lake, and the bathymetric constriction may intensify any bottom current activity at these sites.

The concentrations of polycyclic and nitro musks were determined in freshwater fish from two urbanized areas in the lower Great Lakes: Hamilton Harbour in western Lake Ontario, and the Detroit River and nearby western Lake Erie. Fish collected included brown bullhead (Ameiurus nebulosus), gizzard shad (Dorosoma cepedianum), white perch (Morone americana), yellow perch (Perca fluviatilus), and a single walleye (Stizostedion vitreum). No residues of nitro musks were detected in any of the fish, but since no attempt was made to analyze for the amino-metabolites of these compounds, it cannot be ruled out that these metabolites were present in the fish tissues. Fish from Hamilton Harbour had higher concentrations of polycyclic musks in their tissues than fish from the Detroit River, with a single yellow perch from Hamilton Harbour having the highest concentration of total polycyclic musks of 945 ng/g wet weight. The three polycyclic musk compounds present in the highest concentrations in fish were, in order of relative concentration, Galaxolide® (i.e, HHCB) > Tonalide® (i.e., AHTN) > Traseolide® (i.e., ATII). Lower concentrations of Celestolide® (i.e., ADBI) and Phantolide® (i.e., AHMI) were also detected. There appeared to be species-dependent variability in the accumulation of musks that may be related to differences in the capacity of fish to metabolize these compounds.

An analysis of composite samples of 820 lake trout, walleye, steelhead, Chinook, and coho from the Laurentian Great Lakes reveals differences in contaminant processing among and between lakes which results in differing concentrations of bioaccumulative contaminants. Generally, contaminants are most concentrated in fish from Lake Michigan and least concentrated in fish from Lake Superior, with the notable exceptions of toxaphene and alpha-HCH. Differences in contamination patterns, however, are apparent not only among the lakes but between sites within a lake or even fish within a site. Lake trout composites from Lake Superior show an increase in the degree of chlorination of PCBs with increasing total PCBs. The PCB congener profile of lake trout from the Sturgeon Bay site of Lake Michigan is substantially different from that of the Saugatuck site of Lake Michigan, possibly due to the influence of contamination from nearby Green Bay. Finally, the ratios of selected PBDE and PCB congeners are much different in Lake Superior fish compared to fishes from all the other lakes. We hypothesize that this is a result of the colder temperatures and associated lower plankton growth rates in Lake Superior allowing PCB and PBDE uptake by phytoplankton to reach near equilibrium, thus enhancing the relative concentrations, in phytoplankton and the food web in general, of congeners that may be kinetically limited in other lakes.

Beginning in 1995, the size of yearling lake trout (Salvelinus namaycush) stocked into the upper Great Lakes was increased based on the assumption that these fish would be healthier and survive better since natural mortality is thought to be inversely proportional to body size. We compared the post-release, relative survival of paired stockings of lake trout reared to 44 fish/kg (standard size) with larger fish reared to 22–26 fish/kg (enhanced size) in Lake Michigan. About 60,000 lake trout each of the standard and enhanced sizes for the 1994–1997 year classes were released as yearlings in spring near Clay Banks Reef, Wisconsin, and identified with coded-wire tags and an adipose fin-clip. Recaptures were made from 1997 to 2003 in four gill net surveys conducted in spring and fall near the release location. Comparisons of catch-per-unit of effort corrected for numbers stocked generally indicated no significant differences in relative survival of standard and enhanced lake trout. An autopsy-based assessment of overall fish health and condition indicated few measures where significantly different between standard and enhanced lake trout prior to stocking. Size differences between standard and enhanced fish remained statistically significant at all observed ages at recapture; however growth rates were the same for the two groups. Stocking numbers at certain sites on Lake Michigan were reduced concurrent with the change to larger yearlings with the expectation of increased survival, which did not occur; hence recruitment was essentially reduced in these areas for the restoration program.

Round goby (Neogobius melanostomus) range expansion and their possible inclusion in the diet of lake trout (Salvelinus namaycush) were investigated. Fish community index bottom trawls in eastern Lake Ontario (Kingston basin) during summer 2003 and 2004 indicated the presence of the round goby at relatively low densities (3.72 × 10⁻² ± 5.24 × 10⁻³ fish/m²) in depths up to 30 m. Lake trout (mean fork length = 585 ± 78 mm and mean weight = 2,770 ± 1,134 g) stomach contents showed round goby to be the second most abundant diet item at almost 20% by number (36% by mass). Round goby ingested by lake trout ranged in total length from 50 to 110 mm. The most important prey species in terms of abundance (68%) and mass (56%) was alewife (Alosa pseudoharengus). Alewives were the most important diet item for all sizes of lake trout sampled, except those in the 550 - 650 mm size class, which ingested more round goby by mass than alewife. Round goby range expansion to deep water and prominence in the diet of lake trout signal significant change in the eastern Lake Ontario food web.

Recent investigations found high abundances of the fecal indicator Escherichia coli in shoreline sand at freshwater beaches, but it is not known whether these high numbers are due to passive filtration/trapping of the bacteria, or to colonization and growth. This study was initiated to test the hypothesis that high abundance can be explained, at least in part, by the ability of E. coli to persist and grow in beach sand. A combination of laboratory and field studies was used to monitor the densities of environmental isolates of E. coli in beach sand. In controlled laboratory microcosm studies using autoclaved beach sand inoculated with E. coli strains previously isolated from ambient beach sand, E. coli densities increased from 2 CFU/g to more than 2 × 10⁵ CFU/g sand after 2 days of incubation at 19°C, and remained above 2 × 10⁵ CFU/g for at least 35 days. In field studies utilizing similarly inoculated beach sand in diffusion chambers incubated at a Lake Huron beach, E. coli also grew rapidly, reaching high densities (approximately 7.5 × 10⁵ CFU/g), and persisting in a cultivable state at high density for at least 48 days. In comparison, E. coli levels in ambient beach sand adjacent to the chambers always had densities <100 CFU/g. Lake Huron beach sand clearly provides nutrients, temperatures, and other conditions needed to support growth of E. coli. The growth of E. coli in sterile sand diffusion chambers to higher levels than occurs in ambient beach sand may indicate the presence in ambient sand of biological controls on bacterial growth, such as predation or competition.