Stable isotope ratios of organic carbon and nitrogen (δ¹³C and δ¹⁵N) were measured in suspended particulate matter (SPM) and sediment in the near-shore areas of Tanzanian waters of Lake Victoria (LV) to identify the various sources of organic matter in different areas of the lake. Spatial variations in δ¹³C, δ¹⁵N, and C/N ratios in SPM and sediments in inshore areas were due to differences in the proportions and sources of autochthonous or allochthonous matter. Watershed characteristics, such as urbanization, and lake characteristics, such as algal blooms, also immensely influenced the stable isotope signal of the organic matter in sediments. Stable C and N ratios showed that inshore areas in bays without pronounced fluvial input were dominated by autochthonous planktonic organic matter; conversely, for bays receiving significant fluvial inflows, the composition of organic matter depended on the extent of preservation of shoreline vegetation. Signals resulting from input of anthropogenic organic waste as a result of urbanization were distinguishable from natural sources. This work demonstrates the potential to discriminate between input sources of organic material into lakes using stable isotope signals in sediment and suspended particulate matter.

Infections with motile Aeromonas species were detected in lake whitefish collected over a one-year period from four stocks within lakes Michigan and Huron, USA. Sixty-nine isolates were recovered from the kidneys and swim-bladders of sixty-four infected fish. Representative isolates were Gram-negative bacilli that produced cytochrome oxidase, grew in the absence of salt, were facultative anaerobes, and were resistant to the vibriostatic agent 2,4-diamino,6,7-di-isopropylpteridine. Phenotypic characterization placed twenty-two isolates into the A. hydrophila complex, twelve into the A. sobria complex, and one into the A. caviae complex, while six isolates were characterized as A. allosaccharophila, two as A. veronii bv. veronii, and one as A. popoffi. The prevalence of infection by motile aeromonads varied by site and season, with lake whitefish sampled in the summer having a significantly higher prevalence. Clinical signs in lake whitefish infected only with Aeromonas spp. included congestion and hemorrhaging in the fins and musculature; generalized pallor; congestion, hemorrhaging, and multifocal necrotic foci within the liver; moderate to severe splenomegaly; congestion and swelling of the kidneys; ascites within the peritoneal cavity; and hemorrhagic enteritis. This study provides evidence on the wide spread prevalence of motile aeromonad infections in lake whitefish stocks inhabiting northern lakes Michigan and Huron.

The colonization of the zebra mussel (Dreissena polymorpha) in Saginaw Bay dramatically altered the phytoplankton community composition resulting in exclusion of light sensitive species and dominance of species with oligotrophic preferences and light resistance. In 1990, the NOAA Great Lakes Environmental Research Laboratory initiated a 7-year survey program to monitor changes in the lower food web of Saginaw Bay, where zebra mussels became established in the fall of 1991. To investigate shifts in the phytoplankton community composition over the 7-year period from 1990 to 1996 we searched for clusters of similar composition using multivariate principal component analysis (PCA) on proportions of 22 taxonomic groupings of the total phytoplankton density (cells per milliliter). We then used an agglomerative hierarchical clustering analysis of the PCA scores. We identified five characteristic phytoplankton communities in configurations that allowed recognizing four distinct periods in Saginaw Bay linked to the zebra mussel invasion. Significant changes were indicative of increased water clarity and eutrophic conditions being replaced by more oligotrophic conditions as clusters dominated by light sensitive species, such as the cyanobacteria Oscillatoria redekii, became immediately rare and clusters dominated by diatoms such as Cyclotella spp. became common. Microcystis spp., a light tolerant cyanobacteria not grazed by zebra mussel, dominated assemblages after 1994. The shifts in phytoplankton composition confirm that zebra mussels effects on phytoplankton communities are mediated by both direct (filtration) and indirect (nutrient cycling) mechanisms and also suggests that increased light penetration is an important mechanism behind some changes.

Herein we describe the first report of Aeromonas salmonicida subspecies salmonicida infections in lake whitefish (Coregonus clupeaformis) collected from four sites in lakes Michigan and Huron, Michigan, USA. The bacterium was isolated from the kidneys of four out of 1286 lake whitefish that were tested over a three-year period. The four isolates were phenotypically similar to one another and exhibited the morphological, colonial, and biochemical traits typical of A. salmonicida subspecies salmonicida. Amplification of 16S rRNA genes specific to A. salmonicida subspecies salmonicida via polymerase chain reaction and subsequent gel electrophoresis analyses confirmed the identity of the four lake whitefish isolates. Clinical signs associated with infection included extensive external hemorrhaging, exophthalmia, splenomegaly, splenic and renal congestion, fibrinous adhesions of the spleen and liver, and hemorrhagic enteritis. Histopathological examination of infected fish revealed multi-focal hemorrhage and infiltration of lymphocytes and histiocytes in subdermal adipose tissues and musculature. A low infection incidence of A. salmonicida salmonicida in Great Lakes lake whitefish does not preclude the fact that overt signs of disease were observed in infected individuals and that lake whitefish may act as a reservoir for this bacterium that is highly pathogenic to numerous fish species.

We estimated the prevalence, intensity, and abundance of swimbladder nematode infection in 1281 lake whitefish (Coregonus clupeaformis) collected from four sites in northern lakes Huron (Cheboygan and DeTour Village) and Michigan (Big Bay de Noc and Naubinway) from fall 2003 through summer 2006. Morphological examination of nematode egg, larval, and mature stages through light and scanning electron microscopy revealed characteristics consistent with that of Cystidicola farionis Fischer 1798. Total C. farionis prevalence was 26.94%, while the mean intensity and abundance of infection was 26.72 and 7.21 nematodes/fish, respectively. Although we detected C. farionis in all four stocks that were examined, Lake Huron stocks generally had higher prevalence, intensity, and abundance of infection than Lake Michigan stocks. A distinct seasonal fluctuation in prevalence, abundance, and intensity of C. farionis was observed, which does not coincide with reported C. farionis development in other fish species. Lake whitefish that were heavily infected with C. farionis were found to have thickened swimbladder walls with deteriorated mucosa lining, which could affect swimbladder function. Whether C. farionis infection may be negatively impacting lake whitefish stocks in the Great Lakes is unclear; continued monitoring of C. farionis infection should be conducted to measure responses of lake whitefish stocks to infection levels.

Sediment samples were collected in 1987–1990 from Green Bay and in 1994–1996 from Lake Michigan. Surficial sediments (0–1 cm) from both locations were analyzed for lead for the purpose of describing the horizontal variation of lead in 1994–1996 Lake Michigan and 1987–1990 Green Bay sediments, estimating lead fluxes to surficial sediments, and comparing results to earlier studies. With Lake Michigan concentrations ranging from below the method detection limit to 180 µg/g, the surficial sediments had mean and median lead concentrations of 70 µg/g and 64 µg/g, respectively. Lead concentrations in Green Bay surficial sediments were similar to those in Lake Michigan and ranged between the method detection limit and 160 µg/g. For the bay, mean and median concentrations were 58 and 59 µg/g, respectively. Surficial lead concentrations were highest in the Southern, Waukegan, and Grand Haven basins of Lake Michigan and in the central region of Green Bay in the vicinity of Chambers Island. For Lake Michigan and Green Bay, dated sediment cores illustrate the decline in lead concentrations during the last 30 and 10 years, respectively. Lead fluxes ranged between <0.049 and 7.2 µg/cm²/yr for Green Bay and between 0.47 and 20 µg/cm²/yr for Lake Michigan. Lead fluxes to Lake Michigan were lower than those reported for 1972. These are the most comprehensive fluxes of lead to Lake Michigan and Green Bay surficial sediments reported to date.

Historically, the Niagara River received the discharge of persistent bioaccumulative and toxic chemicals from municipal and industrial outfalls and hazardous waste landfills. American and Canadian governments have coordinated investigations of chemicals entering the river and initiated remedial measures and monitoring programs with a goal to reduce loadings of toxic chemicals to the river. This study, a component of the Ontario Ministry of Environment Mussel Biomonitoring Program, compares contaminant concentrations in quagga mussels (Dreissena bugensis) collected from nine locations in the Niagara River in 1995 and 2003 to assess anticipated changes in tissue concentrations of contaminants in response to ongoing remedial efforts by government agencies and local industries. The concentrations of persistent organic compounds (e.g., PCBs, hexachlorobenzene, hexachlorobutadiene, octachlorostyrene) in quagga mussels in 2003 were lower than concentrations measured in 1995, consistent with a decrease in reported mean annual concentrations of these compounds in water. Significant differences in total PCB concentrations in mussels between stations (F = 4.6; P < 0.001) suggested sources of PCBs on the American side of the upper Niagara River. In general, highest concentrations of persistent organic compounds were found downstream of the Occidental Chemical Corporation Buffalo Avenue facility suggesting local sources of these contaminants notwithstanding remedial efforts. In contrast, metal concentrations in quagga mussels in 2003 were similar to concentrations found in 1995 and to values reported in the literature for mussels collected from industrialized areas in the Great Lakes. Overall, our results suggest that remedial efforts to improve water quality in the Niagara River have been successful.

Lake whitefish (Coregonus clupeaformis) from four stocks in northern Lakes Michigan and Huron were collected seasonally from fall 2003 through summer 2006 and examined for the presence of Renibacterium salmoninarum, the causative agent of bacterial kidney disease (BKD), using culture techniques on modified kidney disease medium (MKDM) and the quantitative enzyme-linked immunosorbent assay (Q-ELISA). R. salmoninarum was detected in 62.31% (according to Q-ELISA) of the 1284 examined lake whitefish, with some fish displaying the typical signs of BKD, such as renal congestion, swelling, and whitish nodules. Kidney cultures on MKDM yielded bacteria with morphological and biochemical characteristics identical to those of R. salmoninarum recovered from other Great Lakes fish species, as well as those from other parts of the world. Isolate identification was confirmed via nested polymerase chain reaction. Antibiograms demonstrated high sensitivity to enrofloxacin and ciprofloxacin, sensitivity to oxytetracycline, erythromycin, azithromycin, chloramphenicol, novobiocin, and carbenicillin, and resistance to polymyxin B, clindamycin, and kanamycin. Statistical analysis of R. salmoninarum prevalence and intensities revealed significant interactions among stocks, years and sampling seasons, with highest prevalence generally in fall and frequent wide variation in prevalence and intensity from one season to the next for a particular stock. It was surprising to find that the prevalence of R. salmoninarum exceeded 50% in the four stocks, much higher than originally thought. Moreover, a positive association between R. salmoninarum intensity and the abundance of the swimbladder nematode, Cystidicola farionis, was identified. Our findings suggest that Great Lakes lake whitefish are vulnerable to serious fish pathogens.

Viral hemorrhagic septicemia virus (VHSV) infects wild and hatchery fish in Europe, Japan, and the Great Lakes and Pacific regions of North America. The virus was associated with a large die-off of yellow perch, Perca flavescens, in Lake Erie in 2006. To determine the infection pattern of VHSV, we sampled yellow perch during the spring, summer, and fall of 2007 and 2008 in the central basin of Lake Erie during routine sampling by the Ohio Division of Wildlife with bottom trawls in nearshore, mid-depth, and offshore locations near the Chagrin River. The Ohio Department of Agriculture's Diagnostic Laboratories and the U.S. Fish and Wildlife Service's La Crosse Fish Health Center tested for VHSV from homogenized samples obtained from yellow perch kidney, spleen, and brain. At each lake sample location, we also measured temperature, dissolved oxygen, and conductivity. In both years, we found yellow perch infected with VHSV during a threeweek period starting in the last week of spawning to early June. A high proportion of adult male and female yellow perch tested positive for VHSV during the infection period in our sample population. Infection appeared to be associated with temperatures between 12 and 18 °C and with significantly higher yellow perch densities during spawning. No large mortalities of yellow perch were observed during the VHSV infection period in 2007 and 2008.

Adult lake whitefish were tagged and released from the Big Bay de Noc (BBN) and Naubinway (NAB) stocks in northern Lake Michigan, and the Detour (DET) and Cheboygan (CHB) stocks in northern Lake Huron during 2003–2006 to describe their spatial and temporal distributions. The contemporary spatial distributions were compared with past distributions of the BBN and NAB stocks. Sixty-two percent of BBN tag recoveries occurred in Wisconsin waters during winter, spring and summer, but 83% of fall tag recoveries were made near the tagging site. Eighty-eight percent of the NAB tag recoveries were made in the management unit of tagging and 7% occurred into northern Lake Huron. Over 90% of the DET stock remained in the vicinity of the tagging sites regardless of the season, while 75% of the CHB tag recoveries were made in northwestern Lake Huron and 17% were made in Ontario. Based on regression tree analysis, there were strong stock, season, and year effects on movement distances, with weaker effects due to sex and length at tagging. Spatial distribution of the BBN stock changed from 1978–1982 to 2003–2008, but spatial distribution of the NAB stock did not. Substantial differences in movement and distribution existed among the four stocks, large seasonal differences in spatial distribution were found within some stocks, and lake whitefish exhibited strong spawning site fidelity. Present management unit boundaries are inappropriate for managing three of our four stocks, and agencies should consider developing single harvest limits for both northern Lake Huron and western Lake Michigan.

Canadian and US federal wildlife agencies completed three surveys (1976–1980, 1989–1991, and 1997–2000) to census colonial waterbirds breeding on the Great Lakes. We here summarize and comment on nest numbers and colony site distribution of common terns (Sterna hirundo) and Caspian terns (Hydroprogne caspia). Common terns are in serious trouble on the Great Lakes. Numbers declined with substantial losses in nests (-19.1%) and colony sites (-23.2%) between the first and third censuses. An increase in numbers at US sites ( 26.6%) did not compensate for losses (-33.1%) at Canadian sites. Caspian terns increased in nest numbers ( 65.9%) and colony sites ( 50.0%) over the same period. The increase at US sites (136.5%) was greater than at Canadian sites (11.5%). Most (70.7%, n = 186) common tern sites had nests during only one census; 17 sites (6.5%) had nests during all censuses. In contrast, 9 of 33 (27.2%) Caspian tern sites had nests during all censuses and contained a majority of nests (50–82%) in each census. Pairs of both species nested on natural substrates across the Great Lakes. Common terns nested mostly on artificial (human-constructed) substrates on the lower Great Lakes. We identify site characteristics that may have contributed to long-term (three census) occupancy by common terns (small size, artificial substrates, absence of ring-billed gulls) and Caspian terns (natural substrates on large, remote islands). We suggest an urgent need for protection and conservation of common tern colonies and identify specific priority sites for implementation of management protocols.

Management of commercially exploited fish should be conducted at the stock level. If a mixed stock fishery exists, a comprehensive mixed stock analysis is required for stock-based management. The lake whitefish Coregonus clupeaformis comprises the primary commercial fishery across the Great Lakes. Recent research resolved that six genetic stocks of lake whitefish were present in Lake Michigan, and long-term tagging data indicate that Lake Michigan's lake whitefish commercial fishery is a mixed stock fishery. The objective of this research was to determine the usefulness of microsatellite data for conducting comprehensive mixed stock analyses of the Lake Michigan lake whitefish commercial fishery. We used the individual assignment method as implemented in the program ONCOR to determine the accuracy level at which microsatellite data can reliably identify component populations or stocks. Self-assignment of lake whitefish to their population and stock of origin ranged from >96% to 100%. Evaluation of genetic stock discreteness indicated a moderately high degree of correct assignment (average = 75%); simulations indicated supplementing baseline data by ∼50 to 100 individuals could increase accuracy by up to 4.5%. Simulated mixed stock commercial harvests with known stock composition showed a high degree of correct proportional assignment between observed and predicted harvest values. These data suggest that a comprehensive mixed stock analysis of Lake Michigan' whitefish commercial fishery is viable and would provide valuable information for improving management.

Traditional lake eutrophication models predict lower phosphorus concentrations with decreased external loads. However, in lakes where decreased external phosphorus loads are accompanied by increasing phosphorus concentrations, a seeming “trophic paradox” exists. Western Lake Erie is an example of such a paradox. Internal phosphorus loads may help explain this paradox. We examined bioturbation and bioirrigation created from burrowing mayfly, Hexagenia spp., as a possible source of internal phosphorus loading. Phosphorus concentrations of experimental microcosms containing lake sediments, filtered lake water, and nymphs (417/m²) collected from western Lake Erie were compared to control microcosms containing sediments and lake water over a 7-day period. Phosphorus concentrations in microcosms containing Hexagenia were significantly greater than microcosms without nymphs. Further, we estimate the soluble reactive phosphorus flux from the sediments due to Hexagenia is 1.03 mg/m²/day. Thus, Hexagenia are a source of internal phosphorus loading. High densities of Hexagenia nymphs in western Lake Erie may help explain the “trophic paradox.” Furthermore, Hexagenia may be a neglected source of internal phosphorus loading in any lake in which they are abundant. Future studies of phosphorus dynamics in lakes with Hexagenia must account for the ability of these organisms to increase lake internal phosphorus loading.

We combined data from two laboratories to increase the spatial extent of a genetic data set for lake whitefish Coregonus clupeaformis from lakes Huron and Michigan and saw that genetic diversity was greatest between lakes, but that there was also structuring within lakes. Low diversity among stocks may be a reflection of relatively recent colonization of the Great Lakes, but other factors such as recent population fluctuation and localized stresses such as lamprey predation or heavy exploitation may also have a homogenizing effect. Our data suggested that there is asymmetrical movement of lake whitefish between Lake Huron and Lake Michigan; more genotypes associated with Lake Michigan were observed in Lake Huron. Adding additional collections to the calibrated set will allow further examination of diversity in other Great Lakes, answer questions regarding movement among lakes, and estimate contributions of stocks to commercial yields. As the picture of genetic diversity and population structure of lake whitefish in the Great Lakes region emerges, we need to develop methods to combine data types to help identify important areas for biodiversity and thus conservation. Adding genetic data to existing models will increase the precision of predictions of the impacts of new stresses and changes in existing pressures on an ecologically and commercially important species.

Fish have been shown to be sensitive indicators of environmental quality in Great Lakes coastal wetlands. Fish composition also reflects aquatic macrophyte communities, which provide them with critical habitat. Although investigators have shown that the relationship between water quality and fish community structure can be used to indicate wetland health, we speculate that this relationship is a result of the stronger, more direct relationship between water quality and macrophytes, together with the ensuing interconnection between macrophyte and fish assemblages. In this study, we use data collected from 115 Great Lakes coastal marshes to test the hypothesis that plants are better predictors of fish species composition than is water quality. First we use canonical correspondence analysis (CCA) to conduct an ordination of the fish community constrained by water quality parameters. We then use co-correspondence analysis (COCA) to conduct a direct ordination of the fish community with the plant community data. By comparing the statistic ‘percent fit,’ which refers to the cumulative percentage variance of the species data, we show that plants are consistently better predictors of the fish community than are water quality variables in three separate trials: all wetlands in the Great Lakes basin (whole: 21.2% vs 14.0%; n = 60), all wetlands in Lakes Huron and Superior (Upper: 20.3% vs 18.8%; n = 32), and all wetlands in Georgian Bay and the North Channel (Georgian Bay: 18% vs 17%; n = 70). This is the largest study to directly examine plant-fish interactions in wetlands of the Great Lakes basin.

We compared diets of juvenile lake whitefish among six sites in Lake Michigan and one in Lake Superior during 2005 and 2006 to assess spatial and temporal patterns in food habits and evaluate if ontogenetic diet shifts occur that may influence growth and survival. A total of 262 and 496 juveniles were captured in 2005 and 2006, the majority of which were captured during June and July. Sites in southern Lake Michigan tended to have larger juveniles, and the smallest juveniles were observed at Naubinway, northern Lake Michigan, and Whitefish Point, Lake Superior. The mean number of prey items per stomach differed among sampling sites and years. Copepods were the most prevalent prey item, and were present in greater than 70% of juvenile stomachs from most sites. However, the percent by number of copepods decreased during July as chironomids and other benthic macroinvertebrates increased in number. There was a significant positive relationship between percent of benthic prey items and mean length of juvenile lake whitefish. A substantial increase in the percent of benthic prey consumed after 40 mm (total length) was observed and likely resulted from juvenile lake whitefish crossing a size threshold for benthic feeding relating to morphological changes (i.e., transition of mouth opening from terminal to sub-terminal) in addition to a potential increase in the availability of emergent macroinvertebrates. Timing of the transition to benthic feeding is likely regulated by the number of prey per juvenile and the overlap with peak emergence of important benthic aquatic invertebrates such as chironomids. A better understanding of these factors will increase our understanding of juvenile lake whitefish growth and survival, which are necessary for improving year-class strength predictions.

Dreissenid mussels have been regarded as a “dead end” in Great Lakes food webs because the degree of predation on dreissenid mussels, on a lakewide basis, is believed to be low. Waterfowl predation on dreissenid mussels in the Great Lakes has primarily been confined to bays, and therefore its effects on the dreissenid mussel population have been localized rather than operating on a lakewide level. Based on results from a previous study, annual consumption of dreissenid mussels by the round goby (Neogobius melanostomus) population in central Lake Erie averaged only 6 kilotonnes (kt; 1 kt = one thousand metric tons) during 1995–2002. In contrast, our coupling of lake whitefish (Coregonus clupeaformis) population models with a lake whitefish bioenergetics model revealed that lake whitefish populations in Lakes Michigan and Huron consumed 109 and 820 kt, respectively, of dreissenid mussels each year. Our results indicated that lake whitefish can be an important predator on dreissenid mussels in the Great Lakes, and that dreissenid mussels do not represent a “dead end” in Great Lakes food webs. The Lake Michigan dreissenid mussel population has been estimated to be growing more than three times faster than the Lake Huron dreissenid mussel population during the 2000s. One plausible explanation for the higher population growth rate in Lake Michigan would be the substantially higher predation rate by lake whitefish on dreissenid mussels in Lake Huron.

We used hydroacoustics to characterize temporal dynamics of fish schools in Georgian Bay and the North Channel of Lake Huron from 2000 to 2004. Dramatic changes in fish school numbers and characteristics were observed over the 5-year period. In 2000, fish schools had an average trace length of 18.2 m and an average height of 2.7 m. Between 2000 and 2004, there was then an increase in the distance of schools from bottom and a drop in the number of schools per kilometer of transect, in the number and proportion of benthic schools, and in the depth, length, height, area, and volume of schools. Netting data confirm that there was a reduction in alewife (Alosa pseudoharengus) that could explain the declines in the number of schools and the changes in fish school characteristics. There was also evidence that the alewife schools were replaced, to a degree, by lake herring schools in Georgian Bay and rainbow smelt schools in the North Channel. Our work provides an example of how fisheries acoustics can be used to study the spatial and behavioural dynamics of fish schools in the Great Lakes.

Sexual-selection theory predicts males will increase investment in ejaculates if there is an increase in the level of sperm competition. Production of ejaculates is energetically costly, so males in better condition should be able to produce ejaculates of higher quality than individuals in poorer condition. We examined how ejaculate investment (i.e., relative testes mass) and sperm quality (i.e., sperm swimming speed) in lake whitefish (Coregonus clupeaformis) were related to residual soma mass, fork length, and fish age using data collected from Lake Michigan and Bay of Quinte (Lake Ontario). Populations from both lakes had positive relationships between relative testes mass and residual soma mass. Fork length was the most important predictor of sperm swimming speed with larger males from both lakes tending to have faster swimming sperm than smaller fish. Testis asymmetry, which is a commonly observed phenomenon in other animals but which has only recently been reported in fishes, was found to occur in the majority of examined lake whitefish with the left testes typically larger than the right.

Many lake whitefish stocks in Lake Michigan have experienced substantial declines in growth and condition since the 1990s. Reduced growth and condition could result in reduced quality or quantity of eggs produced by spawning females, which in turn could negatively impact recruitment. We evaluated the potential for reduced recruitment by measuring early life stage density and length, and we discuss the utility of these measures as early indicators of lake whitefish year-class strength. Overall, mean larval density (number per 1000 m³ ± SE) in Lake Michigan was greater in 2006 (373.7 ± 28.3) than in 2005 (16.6±24.8); whereas, mean length (mm±SE) of larval lake whitefish was smaller in 2006 (12.87±0.07) than in 2005 (14.38± 0.13). The ratio of Zooplankton to fish density did not show an expected relationship with larval fish density or length. Rather, variation in larval density was best explained by a multiple-regression model that included larval length, spring wind intensity, and adult stock density as predictor variables. Our results suggest that the density of larval lake whitefish is not directly regulated by temperature or Zooplankton density at the time of emergence, but that a potential for density-dependent regulation exists when larval emergence rates are high. We conclude that the observed declines in growth and condition of adult lake whitefish are not resulting in substantial reductions in recruitment.

Dreissenid (zebra and quagga) mussels are widely recognized as having strong, adverse ecological and economic impacts, e.g., biofouling and loss of water column primary production. We assessed perceptions and values associated with two less often considered ecological outcomes of dreissenid mussel influences on coastal ecosystems along Lake Ontario and the western St. Lawrence River in New York State. One, the generation of water clarity through filtration, we define as an ecosystem service; the other, the production of large amounts of nuisance algae (e.g., Cladophora and Microcystis) is defined as an ecosystem disservice. Surveys of business owners and homeowners quantified their preferences and the formation of values regarding these products of zebra mussel influence. Water clarity increased greatly, particularly in the eastern portion of Lake Ontario, and algal problems increased throughout. Businesses attributed increases and decreases in revenues associated with water clarity and algae; homeowners reported analogous changes in property values. Water clarity was positively associated, and algae negatively associated, with changes in revenues and property values. Threshold responses of costs as functions of filamentous algae were evident. Given the likely continued influx of invasive species due to human activities, further development of the ecosystem service concept should consider potential “goods” and “bads” of invasives and their influence on ecosystem and social system resiliency.

Recent declines in growth and condition of several Great Lakes lake whitefish populations have raised concerns over potential impacts on juvenile physiological condition and ultimately recruitment. To test whether the condition of spawning adults influences juvenile condition via energy allocation dynamics, we partitioned the variation in age 0 juvenile physiological condition (i.e., growth in length and weight, whole-body moisture content, energy density, and protein content) among adult male and female (i.e., body condition, muscle moisture content, energy density, and protein content) and egg (i.e., wet and dry weight, moisture content, energy density, energy content per egg, and protein content) effects using redundancy analysis. Overall, a model that included sampling site, female condition, and egg quality explained 39% of the variation in juvenile physiological condition. After partitioning out the effects of females and eggs, site explained the most variation (23%). When other factors were accounted for, neither females (1.4%) nor eggs (2.7%) explained much variation in juvenile physiological condition. Of the variables studied, female muscle energy density, muscle moisture content, and egg moisture content were most closely associated with juvenile physiological condition. Our results suggest that parental effects, such as size, age, body condition, or body composition, may not be as important as extrinsic site-related effects or density-dependent effects in determining juvenile physiological condition.

Daily energy expenditure (DEE) and daily food intake (DFI) are key parameters in estimating population level consumption by cormorants. A number of different methods are still employed in estimating these parameters along with different estimates for assimilation efficiency (if used) and prey energy density. The pellet/fish size reconstruction and percent adult body weight methods underestimate DFI for a number of reasons including an implied underestimation of DEE. In the absence of study-specific data, an assimilation efficiency of 0.80 and prey energy density of 5.42 kJ·g^-1 are recommended. The bioenergetic model for field metabolic rate from Ellis and Gabrielsen (2002) is recommended for adults during the nesting season and their model for basal metabolic rate (BMR × 2.5) is recommended for adults or sub-adults outside the nesting season. Comparisons between empirical and bioenergetic models for chick DFI are also made with recommendations on estimating DFI.

The temporal and spatial relationships of a suite of organochlorine contaminants and mercury were examined in various fish species of the St. Clair River/Lake St. Clair corridor, Canada, in order to evaluate the effectiveness of remediation efforts and to assess the risk to human and wildlife fish consumers. In Lake St. Clair, fish tissue concentrations of mercury, polychlorinated biphenyls (PCBs), octachlorostyrene (OCS), hexachlorobenzene (HCB), and dichlorodiphenyltrichloroethane (DDT) decreased consistently from the 1970s until the 1980s and 1990s, after which the rate of contaminant decline slowed or concentrations stabilized. This trend was consistent in up to 13 species (both young-of-the-year and adult fishes) comprising different trophic positions and dietary habits, suggesting that the changes were reflective of ambient conditions rather than food web processes. Elevated concentrations of mercury, PCBs, OCS, HCB, and DDT were detected in St. Clair River young-of-the-year spottail shiner compared with fish from Lake Huron, indicating that non-atmospheric inputs of these chemicals, likely originating from sediment, remain in the St. Clair River. Current concentrations of mercury and PCBs, and mercury, PCBs, and DDT remain of concern to human and wildlife fish consumers, respectively. Given that contaminant decreases have generally stabilized in fish, we suggest that further natural recovery of contaminants in St. Clair corridor fishes will be slow since contaminants will likely continue to be influenced by sediment levels.

We used Monte Carlo simulations to evaluate the sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting. The data-generating model used in the simulations assumed that tagging was conducted annually for 4 years with tag recoveries occurring over a 4-year period. Several different combinations of instantaneous fishing (F) and natural (M) mortality were evaluated in the simulations. The data-generating model additionally assumed that immediate-shedding and handling-mortality rates equaled 2.5% and 0%, respectively, and that chronic shedding was a sigmoidal function of months since tagging. Two spatial patterns of reporting rates were considered-one where reporting was a function of distance from the tagging site and one where reporting was a random generation across the study area. Maximum likelihood estimates of F and M were calculated from the recovery of tags from the data-generating model under different assumed rates of tag shedding, handling mortality, and tag reporting. We found that assumptions about reporting rates resulted in the most variability in mortality estimates regardless of which combination of F and M was evaluated, with assumptions about chronic shedding also contributing substantially to overall variability in mortality estimates for most mortality combinations. Assumptions about immediate tag shedding and handling mortality had relatively minor effects on mortality estimates compared to reporting rate. When planning a tag-recovery study, care should be taken to ensure that chronic shedding and tag-reporting rates are accurately measured, as inaccurate measurements in these factors can result in significant errors in mortality estimates.

We analyzed tag-recovery data to estimate instantaneous fishing (F) and natural mortality (M) rates of four lake whitefish stocks in lakes Michigan and Huron during 2004–2007. We tagged and released 22,452 adult lake whitefish of which 8.7% were subsequently recovered. Annual tag-reporting rates ranged from 17.8% to 56.2%. Tag retention was high for the first 5–6 months after tagging, but tag loss increased substantially thereafter. Nine tag-recovery models were evaluated with respect to whether F and/or M varied among stocks, lakes, or years. There was support for three models based on Akaike information criteria. The best model had yearly and stock-specific estimates of F of 0.03 to 0.79 and lake-specific estimates of M of 0.35 for Lake Michigan and 0.60 for Lake Huron. The second best model had yearly and stock-specific estimates of F of 0.04 to 0.71 and a constant estimate for M of 0.52. The third model had yearly and stock-specific estimates of F of 0.04 to 0.85 and stock-specific estimates of M of 0.32 to 0.67. Model-averaged estimates of F ranged from 0.04 to 0.78 and were substantially different than statistical catch-at-age estimates of F. Model-averaged estimates of M ranged from 0.40 to 0.59 and were greater than estimates obtained from prediction equations, possibly due to sea lamprey-induced mortality. We recommend that tag-recovery estimates of F and M be used as Bayesian priors in future lake whitefish stock assessments to help refine mortality estimates for the stocks.

The invasive round goby, Neogobius melanostomus, consumes eggs and fry of other fishes, competes for resources with native fish species, and hence poses a threat to Great Lakes aquatic communities. We provide the first description of round goby demographic patterns in Hamilton Harbour, in the western tip of Lake Ontario, and the connected Cootes Paradise Marsh, a recently restored wetland. By monitoring round goby populations on a variety of distinct habitats for 7 years (2002–2008), we found that populations have declined at all sample locations and that average fish body size also has decreased. We also related abundance, body size, and reproductive patterns to seasonality, to substrate types (mud, sand, cobble and boulder) and to water quality in all locations. Round gobies were found on all substrates sampled including mud, although they were less abundant on mud than on other substrates, and to date have not extensively colonized Cootes Paradise Marsh. Our work confirms previous studies, which have suggested that habitats lacking hard structures will have fewer round gobies because they lack substrates on which round gobies can breed. However, our results also indicate that muddy and sandy substrates are not resistant to round goby invasion and will not prevent round goby colonization, a potential concern for Cootes Paradise Marsh an important spawning, nursery, and refuge habitat for warmwater native fishes and for other similar wetlands.

We examined the spatial and temporal dynamics of health indicators in four lake whitefish (Coregonus clupeaformis) stocks located in northern lakes Michigan and Huron from 2003 to 2006. The specific objectives were to (1) quantify spatial and temporal variability in health indicators; (2) examine relationships among nutritional indicators and stock-specific spatial and temporal dynamics of pathogen prevalence and intensity of infection; and (3) examine relationships between indicators measured on individual fish and stock-specific estimates of natural mortality. The percent of the total variation attributed to spatial and temporal sources varied greatly depending on the health indicator examined. The most notable pattern was a downward trend in the concentration of highly unsaturated fatty acids (HUFAs), observed in all stocks, in the polar lipid fraction of lake whitefish dorsal muscle tissue over the three study years. Variation among stocks and years for some indicators were correlated with the prevalence and intensity of the swimbladder nematode Cystidicola farionis, suggesting that our measures of fish health were related, at some level, with disease dynamics. We did not find relationships between spatial patterns in fish health indicators and estimates of natural mortality rates for the stocks. Our research highlights the complexity of the interactions between fish nutritional status, disease dynamics, and natural mortality in wild fish populations. Additional research that identifies thresholds of health indicators, below (or above) which survival may be reduced, will greatly help in understanding the relationship between indicators measured on individual fish and potential population-level effects.

We identified an objective set of 25 commonly available ecosystem metrics applicable across the world's large continental freshwater and brackish aquatic ecosystem. These metrics measure trophic structure, exploited species, habitat alteration, and catchment changes. We used long-term trends in these metrics as indicators of perturbations that represent an ecosystem not in homeostasis. We defined a healthy ecosystem as being in a homeostatic state; therefore, ecosystems with many changing trends were defined as more disturbed than ecosystems with fewer changing trends. Healthy ecosystems (lakes Baikal, Superior, and Tanganyika) were large, deep lakes in relatively unpopulated areas with no signs of eutrophication and no changes to their trophic structure. Disturbed ecosystems (lakes Michigan, Ontario, and Victoria) had shallow to moderately deep basins with high watershed population pressure and intense agricultural and residential land use. Transitioning systems had widely varying trends and faced increasing anthropogenic pressures. Standardized methodologies for capturing data could improve our understanding of the current state of these ecosystems and allow for comparisons of the response of large aquatic ecosystems to local and global stressors thereby providing more reliable insights into future changes in ecosystem health.

Although lake whitefish Coregonus clupeaformis populations in the Laurentian Great Lakes have rebounded remarkably from the low abundance levels of the 1960s and 1970s, recent declines in fish growth rates and body condition have raised concerns about the future sustainability of these populations. Because of the ecological, economic, and cultural importance of lake whitefish, a variety of research projects in the Great Lakes have recently been conducted to better understand how populations may be affected by reductions in growth and condition. Based upon our participation in projects intended to establish linkages between reductions in growth and condition and important population demographic attributes (natural mortality and recruitment potential), we offer the following recommendations for future studies meant to assess the health of Laurentian Great Lakes lake whitefish populations: (1) broaden the spatial coverage of comparative studies of demographic rates and fish health; (2) combine large-scale field studies with direct experimentation; (3) conduct multi-disciplinary evaluation of stocks; (4) conduct analyses at finer spatial and temporal scales; (5) quantify stock intermixing and examine how intermixing affects harvest policy performance on individual stocks; (6) examine the role of movement in explaining seasonal fluctuations of disease and pathogen infection and transmission; (7) evaluate sampling protocols for collecting individuals for pathological and compositional examination; (8) quantify sea lamprey-induced mortality; and (9) enact long-term monitoring programs of stock health.

Water column primary production is a major term in the organic carbon cycle, particularly in large lakes with relatively reduced shoreline and near-shore influence. Presently, there is a large imbalance in the known inputs vs. outputs of organic carbon in Lake Superior. This study examined primary production in offshore Lake Superior using in situ incubations over a range of conditions representing an annual cycle. Primary producers were dominated by small (<20 µm) cells and included a relatively large abundance of small, spherical flagellates. During conditions with a warm surface layer, chlorophyll concentrations were two- to three-fold higher within the deep chlorophyll maximum (DCM) than at the surface. Volumetric production (mass L^-1 d^-1) was maximal at 2–10 m depth, well above the typical DCM depth. On average, 22% of ¹⁴C label appeared in the dissolved pool at the end of the incubation period with the rest appearing in GF/F-strained particles. A statistical model for volumetric production explained 93% of the variance in individual measurements for depths>2 m, using temperature and light as predictors. This model was applied to annual fields of temperature and light, and a new estimate for whole-lake annual primary production, 9.73 Tg y^-1,was derived. This combination of new measurements and modeling results brings the organic carbon cycle of Lake Superior closer to being balanced.

Taihu Lake, the third largest freshwater lake in China, is located in the Chanjiang Delta of the Yangtze River. Its waters are used by agriculture, industry and as major drinking water for several cities including Shanghai and Wuxi. The lake also is important for tourism, aquaculture and flood control. Taihu Lake and its surrounding areas are facing three major water-related threats: deteriorating water quality with inflow and runoff from its watershed; flooding during the rainy seasons; and water shortages during drier months. Noxious algae blooms are occurring with increasing frequency and water quality continues to decline. Remedial actions implemented to date have been ineffective. This paper proposes that the problems could be remedied by constructing a by-pass channel (BPC), which would divert low-quality water from the lake during low precipitation periods and allow better quality water to flow into the lake during high flow periods. This remedial action would simultaneously deal with the deteriorating water quality of Lake Taihu and maintain its water level at a desired level. A preliminary assessment of this strategy shows that, if the BPC were implemented, the water quality of Taihu Lake would be improved significantly in few years, the flood disaster would be greatly mitigated, and the water shortage problem in the basin would be alleviated.

The spread of nonindigenous species (NIS) over land and via interconnecting water bodies is threatening aquatic ecosystems worldwide. This study examines the invasion of the first known NIS zooplankter, Eubosmina coregoni, into Lake Winnipeg, Manitoba, Canada. Analyses of cladoceran microfossils from a sediment core collected in the North Basin of the lake indicate this species first appeared in sediments dated to the late 1980s. An increase in total cladoceran accumulation rates coupled with increasing N, C, P, and chlorophyll a over the last 40 years provides evidence of eutrophication. Extant samples from fall 2002–2005 indicate that E. coregoni is mainly restricted to the North Basin while Bosmina longirostris is present throughout the lake. Results from this study provide baseline data regarding the invasion and establishment of E. coregoni, a precursor to future NIS that may have substantial ecological and economic impacts on the Lake Winnipeg ecosystem.

We report on the emergence of the potentially toxic filamentous cyanobacterium, Lyngbya wollei as a nuisance species in western Lake Erie. The first indication of heavy L. wollei growth along the lake bottom occurred in September 2006, when a storm deposited large mats of L. wollei in coves along the south shore of Maumee Bay. These mats remained intact over winter and new growth was observed along the margins in April 2007. Mats ranged in thickness from 0.2 to 1.2 m and we estimated that one 100-m stretch of shoreline along the southern shore of Maumee Bay was covered with approximately 200 metric tons of L. wollei. Nearshore surveys conducted in July 2008 revealed greatest benthic L. wollei biomass (591 g/m² ± 361 g/m² fresh weight) in Maumee Bay at depth contours between 1.5 and 3.5 m corresponding to benthic irradiance of approximately 4.0–0.05% of surface irradiance and sand/crushed dreissenid mussel shell-type substrate. A shoreline survey indicated a generally decreasing prevalence of shoreline L. wollei mats with distance from Maumee Bay. Surveys of nearshore benthic areas outside of Maumee Bay revealed substantial L. wollei beds north along the Michigan shoreline, but very little L wollei growth to the east along the Ohio shoreline.

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.

The Ponto-Caspian mysid, Hemimysis anomala, was first observed in southeastern Lake Ontario in May 2006. During July and August 2007, gill nets were fished in 6 to 8 m of water at two locations of known Hemimysis colonization in southeastern Lake Ontario to determine if fish that consume macroinvertebrates were beginning to include this new invasive mysid in their diets. Of nine fish species captured in August, September, and October 2007, three species had consumed Hemimysis: alewife (Alosa pseudoharengus), rock bass (Ambloplites rupestris), and yellow perch (Perca flavescens); and six species had not: round goby Apollonia melanostoma, smallmouth bass Micropterus dolomieu, spottail shiner Notropis hudsonius, gizzard shad Dorosoma cepedianum, white perch Morone americana and log perch Percina caprodes. Diets of alewives from all samples were composed predominantly of Hemimysis (69.6% – 100% frequency of occurrence, 46.0%– 74.5% dry weight diet composition). Two of 6 rock bass stomachs sampled in August contained ≥98.9% Hemimysis (10 and 40 individuals each) and one of 61 yellow perch stomachs sampled in September contained 10.0% Hemimysis (6 individuals) and 90.0% fish. While Hemimysis were observed only sparsely in the diet of most nearshore fish, their predominance in alewife diets and their omnivorous feeding behavior indicated that they have the potential to alter energy flow in Great Lakes' foodwebs.

The zebra mussel, Dreissena polymorpha, is widespread in the St. Lawrence River while the conspecific quagga mussel, Dreissena bugensis, is found only in the Lake Ontario outflow region of the river. This situation provided an opportunity to evaluate in situ environmental and interspecific heterogeneity in shell and tissue growth. Shell dry weight, carbon content, and shell strength of D. polymorpha from the four spatially discrete water masses differed significantly. For instance, D. polymorpha total and tissue mass increased over the summer in the shallow fluvial Lac Saint-Pierre but decreased in the upstream and downstream water masses. Standardized shell mass and strength of D. polymorpha was lowest where the mussels experienced salinity or low calcium. Although the response pattern of mass and glycogen content for D. polymorpha was spatially complex, mussels from the stressful oligohaline estuary population had the weakest shells and lowest glycogen content, even though their standardized tissue mass was the heaviest. This disparity in shell and tissue response suggests that some aspect of shell physiology alone may be limiting these mussels in estuarine environments. Tissue characteristics of D. polymorpha and D. bugensis were similar at the site where both were present, but the shell strength of D. bugensis was only equivalent to the weakest of D. polymorpha. We also conclude that lighter shells might make D. bugensis more susceptible to predation or mechanical damage but may also offer a bioenergetic advantage that is contributing to its rapid displacement of D. polymorpha where the two species co-occur.

Ballast water regulations implemented in the early 1990s appear not to have slowed the rate of new aquatic invasive species (AIS) establishment in the Great Lakes. With more invasive species on the horizon, we examine the question of whether eradication of AIS is a viable management strategy for the Laurentian Great Lakes, and what a coordinated AIS early detection and eradication program would entail. In-lake monitoring would be conducted to assess the effectiveness of regulations aimed at stopping new AIS, and to maximize the likelihood of early detection of new invaders. Monitoring would be focused on detecting the most probable invaders, the most invasion-prone habitats, and the species most conducive to eradication. When a new non-native species is discovered, an eradication assessment would be conducted and used to guide the management response. In light of high uncertainty, management decisions must be robust to a range of impact and control scenarios. Though prevention should continue to be the cornerstone of management efforts, we believe that a coordinated early detection and eradication program is warranted if the Great Lakes management community and stakeholders are serious about reducing undesired impacts stemming from new AIS in the Great Lakes. Development of such a program is an opportunity for the Laurentian Great Lakes resource management community to demonstrate global leadership in invasive species management.