Spatial Structure and the Estimation of Zooplankton Biomass in Lake Erie

Data collected by an optical plankton counter were analyzed to quantify the horizontal spatial patterns of zooplankton biomass in Lake Erie during 1994. During spring and late summer, an optical plankton counter was towed along a total of 11 transects, ranging from 26 to 67 km in length, distributed among the three major basins of the lake. A general model of spatial variation was used to identify large-scale trends, cyclic components at intermediate scales, and small-scale autocorrelation. Significant trends in biomass were found along all transects, while significant spatial autocorrelation underlying these trends was present in all but one case. The observed spatial autocorrelation was then removed, and standard statistical methods were used to estimate mean biomass and confidence limits. In most cases, the larger-scale spatial trends remained after removing autocorrelation. Regression methods were therefore used to estimate mean biomass in the presence of these trends. Relatively little overlap in confidence bands of the regression estimates were found from different regions of the lake. Mean biomass estimates for the entire lake from two seasons, when spatial trends and autocorrelation were ignored, fell outside the 95% confidence limits of estimates that did account for these spatial structures more than 50% of time. The relatively large change in biomass within and among many transects show that spatial variability of zooplankton biomass should be incorporated in future zooplankton studies in Lake Erie and the other Great Lakes.     

Sampling Larval Fish in the Littoral Zone of Western Lake Erie

Sampling techniques for larval fish were evaluated in the littoral zone (1- to 6-m deep) of western Lake Erie in 1975 and 1976. Catch rates were compared using slow-speed, 1-m-diameter plankton nets in daytime and nighttime oblique and stratified tows above bottom and in daytime epibenthic tows with an aluminum sled. Sampling efficiency also was compared using nets of 363-, 571-, 760-, and 1,000-μm mesh towed from 1 to 5 min. The most abundant larvae captured were clupeids (Alosa pseudoharengus and Dorosoma cepedianum), yellow perch (Perca flavescens), rainbow smelt (Osmerus mordax), and white bass (Morone chrysops) Larvae did not consistently occur in one stratum over another in water above bottom, but concentrated near bottom during the day. Oblique, nighttime tows above bottom caught at least 20 times the larvae caught in daylight tows above bottom. Post-yolk-sac larvae were most efficiently captured in nighttime oblique or stratified tows, while yolk-sac larvae were more efficiently captured by epibenthic, daytime tows. The 363-μm-mesh net retained more yolk-sac larvae than nets of larger mesh sizes and was at least as effective as the larger nets at capturing post-yolk-sac larvae. Nets with 571-μm mesh towed for 1, 2, 3, 4, and 5 min had similar catch rates so mesh plugging was not a problem under conditions sampled. Filtering rates of 363- and 760-μm mesh were similar to the filtering rate of 571-μm mesh when towed for 3 min. Precision (number of larvae caught per minute) and number of species caught were similar in tows more than 1-min long up to 5 min.     

Fish Assemblages and Environmental Conditions in the Lower Reaches of Northeastern Lake Erie Tributaries

Lake Erie and its tributaries have experienced extensive changes in environmental conditions and community structure during recent decades. To assess the relative importance of environmental conditions in determining fish community composition, fish communities and their associated environmental conditions were sampled from the lower reaches and mouths of the tributaries flowing into the northeastern basin of Lake Erie. These data were used to assess relationships between habitat and fish community composition on spatial and temporal scales using correspondence analysis and canonical correspondence analysis. Multivariate analyses revealed that the fish assemblage was size structured and related to water chemistry but also showed influences due to temperature, sampling date and aquatic macrophytes. The community composition showed the effects of biotic interactions, predominantly negative predator-prey associations, but there were also assemblage differences specific to particular tributaries and sampling methodologies.     

Estimation of phosphorus loads from septic systems to tributaries in the Canadian Lake Erie Basin

The contribution of septic systems to watershed nutrient loads is poorly quantified although they are often cited as potentially important nutrient sources. The study used a geospatial model to estimate P loads from septic systems to the tributaries of the Canadian Lake Erie Basin to inform Lake Erie nutrient management initiatives. There is currently no inventory of septic systems in the Lake Erie Basin (e.g., numbers and locations of septic systems). Therefore a geospatial model was developed to automatically locate individual septic systems and to use these locations to estimate P load contributions to tributaries. The model was first tested on three subwatersheds in the Canadian Lake Erie Basin before being applied across the Basin. Present-day basin-wide P load estimates reveal that: (i) only a fraction of septic effluent is currently reaching the tributaries due to slow transport and other delays, as well as (ii) P attenuation in the subsurface, range from 23 ± 11 to 68 ± 32 MT/yr. Based on these estimates, septic systems may currently contribute 1.7 ± 0.8–5 ± 2.3% of the P loads to Lake Erie from Canada. However, maximum P load estimates and transient model results show that the contribution of septic systems to P loads will increase over time as slow moving septic-derived groundwater P plumes reach tributaries if aging septic systems are not maintained. This study provides widely applicable new knowledge and methodology; as well as specific findings needed to inform nutrient and septic system management in the Lake Erie Basin.     

Limnetic Larval Fish in the Nearshore Zone of the Western Basin of Lake Erie

Gizzard shad/alewife, Dorosoma cepedianum/Alosa pseudoharengus, emerald shiners, Notropis atherinoides, white bass/white perch, Morone chrysops/Morone americana, and yellow perch, Perca flavescens, constituted over 97% of the larval fish collected in Ohio and Michigan waters of the western basin of Lake Erie during 1977. Significantly greater numbers of gizzard shad/alewife and spottail shiner, Notropis hudsonius, larvae were captured immediately adjacent to the shore than at a depth of 5 m offshore while greater numbers of smelt, Osmerus mordax, larvae were captured at points further offshore at a depth of 5 m than at points immediately adjacent to the shore. Significantly greater numbers of walleye, Stizostedion vitreum, larvae were collected along the Ohio shoreline portion of the study area than in Maumee Bay or along the Michigan shoreline. Significantly greater numbers of freshwater drum, Aplodinotus grunniens, larvae were collected in Maumee Bay.     

Combined Effects of Cadmium and Zinc on a Lake Mighican Zooplankton Community

Two 3-week experiments with small enclosures were conducted in situ in northeastern Green Bay, Lake Michigan, to compare the effects of separate and combined additions of cadmium and zinc on the zooplankton community. The radioisotopes ¹⁰⁹Cd and ⁶⁵Zn were used as tracers to determine the sorption of cadmium and zinc by different particle size fractions. Separate additions of 2 μg Cd/L or 100 μg Zn/L, as well as combined additions of 2 μg Cd/L + 100 μg Zn/Lor 1 μg Cd/L + 50 μg Zn/L, caused significant reductions of total crustacean density, species diversity, two community similarity indices, and final dissolved oxygen concentration. The effects of separate additions of 100 μg Zn/L were generally more pronounced than those of 2 μg Cd/L, but were similar to those of ～5 μg Cd/L. The effects of combined additions of 2 μg Cd/L + 100 μg Zn/L were not significantly different from those of 100 μg Zn/Lalone and were primarily due to zinc because it reduced cadmium uptake by the plankton (10–85 μm and >85 μm fractions). The effects of combined additions of l μg Cd/L + 50 μg Zn/L probably were also mainly due to zinc. The overall results of this study suggest that less than a ten-fold increase in the concentration of zinc in Lake Michigan (presently ～5 μg/L) could have pronounced effects on the plankton community.     

Potential Strategies for Recovery of Lake Whitefish and Lake Herring Stocks in Eastern Lake Erie

Lake Erie sustained large populations of ciscoes (Salmonidae: Coregoninae) 120 years ago. By the end of the 19^th century, abundance of lake whitefish (Coregonus clupeaformis) had declined drastically. By 1925, the lake herring (a cisco) population (Coregonus artedii) had collapsed, although a limited lake herring fishery persisted in the eastern basin until the 1950s. In the latter part of the 20^th century, the composition of the fish community changed as oligotrophication proceeded. Since 1984, a limited recovery of lake whitefish has occurred, however no recovery was evident for lake herring. Current ecological conditions in Lake Erie probably will not inhibit recovery of the coregonine species. Recovery of walleye (Sander vitreus) and efforts to rehabilitate the native lake trout (Salvelinus namaycush) in Lake Erie will probably assist recovery because these piscivores reduce populations of alewife (Alosa psuedoharengus) and rainbow smelt (Osmerus mordax), which inhibit reproductive success of coregonines. Although there are considerable spawning substrates available to coregonine species in eastern Lake Erie, eggs and fry would probably be displaced by storm surge from most shoals. Site selection for stocking or seeding of eggs should consider the reproductive life cycle of the stocked fish and suitable protection from storm events. Two potential sites in the eastern basin have been identified. Recommended management rocedures, including commercial fisheries, are suggested to assist in recovery. Stocking in the eastern basin of Lake Erie is recommended for both species, as conditions are adequate and the native spawning population in the eastern basin is low. For lake herring, consideration should be given to match ecophenotypes as much as possible. Egg seeding is recommended. Egg seeding of lake whitefish should be considered initially, with fingerling or yearling stocking suggested if unsuccessful. Spawning stocks of whitefish in the western basin of Lake Erie could be utilized.     

Overlap in Offshore Habitat Use by Double-crested Cormorants and Boaters in Western Lake Erie

Double-crested cormorants (Phalacrocorax auritus) and boats of 2 length classes (≤ 8 m and > 8 m) were counted from a boat along 31 established strip transects in western Lake Erie from 24 April to 1 September 2000. Each transect included only one of the following habitats: (1) offshore of a breeding island or roosting/loafing area for cormorants (“refuge”), (2) reefs or shoals, (3) open water, or (4) offshore of an island shoreline that had evidence of development by humans. Foraging cormorants were recorded most often offshore of refuges and least often on open water. There was no difference between the numbers of foraging cormorants/km² recorded offshore of developed shorelines and on reefs and shoals. More than half of all boats recorded were on transects that were within 1 km of developed shorelines. Among those transects > 1 km from developed shorelines, there were no differences among the habitats for the number of boats of either length class. The respective ranks of the 31 transect means of the numbers of cormorants/km² and the numbers of boats/km² in either length class were uncorrelated. The results suggest that (1) cormorants select foraging habitats based mainly on shoreline type, distance from shoreline, and depth, and (2) the amount of boat traffic is influenced by proximity to port and trip objectives, including sport angling and recreational boating. Although there is overlap in habitat use by cormorants and humans, this overlap is not complete. The perception of cormorants as a threat to fish populations may in part be due to this overlap.     

Application of distance sampling techniques for diving ducks on Lake St. Clair and western Lake Erie

Lake St. Clair and western Lake Erie are important migration staging areas for diving ducks including canvasbacks (Aythya valisineria), redheads (Aythya americana), and lesser and greater scaup (Aythya affinis and Aythya marila). Starting in 1983, the Michigan Department of Natural Resources (MDNR) attempted to census diving ducks on the United States portion of Lake St. Clair throughout autumn migration; however, in 2010 the MDNR expanded the traditionally surveyed area to include all of Lake St. Clair and a portion of western Lake Erie. The idea of achieving a census over the expanded study area was unrealistic, and instead distance sampling techniques were adopted in an effort to generate statistically valid estimates of detection probabilities and abundances for diving ducks during spring and autumn migration. We found distance sampling techniques to be a viable option for estimating diving duck abundance as long as flock size is accounted for as a covariate affecting the detection function. Diving ducks were generally more abundant on our study area during autumn migration with a mean of 306,327 ducks/survey (SE = 40,729) compared to an average spring abundance of 91,053 ducks/survey (SE = 19,175). Peak abundance occurred on 20 November 2012 with an estimated 596,335 diving ducks on Lake St. Clair and western Lake Erie. Ultimately, our methodology could be used to establish long-term, standardized data collection techniques and applied to conservation planning for waterfowl in the Great Lakes region.     

Fish Community Support in Wetlands within Protected Embayments of Lake Ontario

Fish community data were collected to investigate the role of wetlands in supporting fish communities of protected embayments in Lake Ontario. Wetland and deeper, more open, littoral sites were sampled in five protected embayments using gill nets, fyke nets, minnow traps, and electrofishing gear during the summers of 2001 and 2002. Pooled gear data were used to analyze community composition, size frequency, and species richness. We found that even within protected embayments where community composition of both habitats is similar, wetlands support a community of fish different in species dominance and size structure than littoral embayment habitats. The abundance of young-of-year fish suggests that wetlands support fish populations by providing important nursery habitat. The similarity in fish community composition between wetland and littoral habitats indicates that wetlands remain important in supporting a subset of the embayment fish community. These results demonstrate that both wetlands and littoral areas in embayments are valuable and intensively utilized fish habitats that should receive special consideration in ecosystem management plans for the Great Lakes.     

Thermal and hydrologic suitability of Lake Erie and its major tributaries for spawning of Asian carps

Bighead carp Hypophthalmichthys nobilis, silver carp H. molitrix, and grass carp Ctenopharyngodon idella (hereafter Asian carps) have expanded throughout the Mississippi River basin and threaten to invade Lakes Michigan and Erie. Adult bighead carp and grass carp have been captured in Lake Erie, but self-sustaining populations probably do not exist. We examined thermal conditions within Lake Erie to determine if Asian carps would mature, and to estimate time of year when fish would reach spawning condition. We also examined whether thermal and hydrologic conditions in the largest tributaries to western and central Lake Erie were suitable for spawning of Asian carps. We used length of undammed river, predicted summer temperatures, and predicted water velocity during flood events to determine whether sufficient lengths of river are available for spawning of Asian carps. Most rivers we examined have at least 100 km of passable river and summer temperatures suitable (> 21 C) for rapid incubation of eggs of Asian carps. Predicted water velocity and temperature were sufficient to ensure that incubating eggs, which drift in the water column, would hatch before reaching Lake Erie for most flood events in most rivers if spawned far enough upstream. The Maumee, Sandusky, and Grand Rivers were predicted to be the most likely to support spawning of Asian carps. The Black, Huron, Portage, and Vermilion Rivers were predicted to be less suitable. The weight of the evidence suggests that the largest western and central Lake Erie tributaries are thermally and hydrologically suitable to support spawning of Asian carps.     

Diatoms abound in ice-covered Lake Erie: An investigation of offshore winter limnology in Lake Erie over the period 2007 to 2010

The limnology of offshore Lake Erie during periods of extensive (> 70%) ice cover was examined from ship borne sampling efforts in 2007 to 2010, inclusive. Dense and discrete accumulations of the centric filamentous diatom Aulacoseria islandica (> 10 μg Chl-a/L) were located in the isothermal (< 1 °C) water column directly below the ice and only detectable in the ship wake; viable phytoplankton were also observed within ice. Evidence from these surveys supports the notions that winter blooms of diatoms occur annually prior to the onset of ice cover and that the phytoplankton from these blooms are maintained in the surface waters of Lake Erie and reduce silicate concentrations in the lake prior to spring. The mechanisms by which high phytoplankton biomass rise at this time of year requires further investigation, but these winter blooms probably have consequences for summer hypoxia and how the lake responds to climate change.     

Young-of-the-Year Coregonus Hoyi in Lake Michigan: Prey Selection and Influence on the Zooplankton Community

Young-of-the-year bloater, Coregonus hoyi, 16 to 71 mm standard length, were collected from an offshore reference station 100 m deep in southern Lake Michigan during July-August, 1985 and 1986. Gut contents of the fish were examined for prey taxa and prey size. Small bloaters (<20 mm) ate Cyclops copepodids almost exclusively. Bloaters between 20 and 35 mm had increasing proportions of Daphnia in their diets as a function of increased body length. Daphnia, especially D. pulicaria, was the most important component in the diets of the largest fish (<35 mm). Larger YOY bloaters preyed selectively on large individuals of D. pulicaria. Abundance of Coregonus increased during 1985 and 1986 subsequent to a decrease in the population of alewife (Alosa pseudoharengus) in Lake Michigan. Planktivory by bloaters may have been an important selective influence on the summer plankton community in offshore regions of the lake, contributing to a decrease in D. pulicaria.     

Heat Balance and Heat Storage Estimates for Lake Erie, 1967 to 1982

Lakewide surface heat flux and components are computed for Lake Erie from detailed measurements conducted during the stratified season from 1967 to 1982. These results are formed into monthly means and compared to other long-term estimates for the period 1952 to 1968, thus providing a review of the climatological estimate of the range and variability of these parameters. Details of the lakewide monthly means of pertinent hydrometeorological and limnological observations are briefly outlined. Lake Erie heat storage is derived from intensive lakewide temperature surveys from 1967 to 1982. A verification of the computed surface heat flux estimates is accomplished by comparison between measured heat storage and computed heat storage which is based on the summation of daily heat flux calculations. A positive residual of 2,557 cal/cm² is estimated for the long-term heat budget. Comparisons of the measured and computed heat storage for individual years over the 15-year period shows good agreement for most years.     

Application of a Depletion-Based Stock Reduction Analysis (DB-SRA) to lake sturgeon in Lake Erie

Lake Erie supported the greatest yield of lake sturgeon within the Laurentian Great Lakes near the end of the 19th century with >2000 metric tons caught at the peak of the fishery. The fishery collapsed by the 1920s when <1% of the previous peak catch was removed. Despite closures of the fishery, lake sturgeon remain rare in Lake Erie. We applied a depletion-based stock reduction analysis (DB-SRA) to the catch of lake sturgeon from 1879 to 1929 to gain estimates of sustainable fishery reference points and the historic carrying capacity of Lake Erie for lake sturgeon. We also simulated population growth of lake sturgeon from 1929 to the present with varying assumptions of the current carrying capacity of the lake. The estimated historic carrying capacity of lake sturgeon was 22,652 metric tons. During the height of the fishery, exploitation was as high as 37% which was more than an order of magnitude greater than that required for maximum sustainable yield. Projections of the population from 1929 to 2016 suggest sufficient time has passed since the collapse of the fishery that the population should have recovered to levels that would support a fishery at maximum sustainable yield. However, lake sturgeon remain rare in Lake Erie indicating that other factors such as habitat availability may be limiting their recovery. Our estimates of carrying capacity will be informative when setting recovery targets which consider the amount of habitat loss.     

Limnetic Larval Fish in the Ohio Portion of the Western Basin of Lake Erie, 1975–1976

A total of 19 taxa of larval fish was collected with metered plankton nets in Ohio and adjacent Ontario waters of the western basin of Lake Erie. Analysis of yellow perch, Perca flavescens, collection data indicates that shallow inshore areas serve as important nursery areas for this species. Collection of larvae provides evidence of relict breeding populations of lake whitefish, Coregonus clupeaformis, and sculpin (Cottus sp.) in the western basin.     

Microplastic pollutants in the coastal dunes of Lake Erie and Lake Ontario

Microplastic particles, often studied as aquatic pollutants, have been recovered from coastal dunes along the shores of Lake Ontario and Lake Erie in New York and Pennsylvania. Surface and shallow sub-surface sand samples were collected from coastal dunes in 1 m² areas from 5 locations along Lake Erie: Sunset Bay, Dunkirk Harbor, Point Gratiot, and Canadaway Creek in New York and Presque Isle State Park Beach #11 in Pennsylvania. Samples were also collected from coastal dunes on Lake Ontario at Sandy Island Beach State Park, NY. Abundances, shapes, sizes, textures, and degradation of microplastics were characterized. Twenty-one of 26 samples yielded a variety of microplastics: pellets, fragments, and fibers. Larger microplastics (5.0–1.0 mm) were dominated by spheroidal and disk-shaped pellets with fewer fragments. Smaller microplastics (≤1.0 mm) were predominantly fibers and small fragments. Some microplastic particles exhibited evidence of degradation and weathering as a consequence of transport and exposure to the elements. The presence of microplastics in coastal dunes is attributable to aeolian transport from the adjacent beach.     

Analysis of Models and Measurements for Sediment Oxygen Demand in Lake Erie

In situ measurements of water column oxygen consumption and sediment oxygen demand (SOD) in the central basin of Lake Erie are historically 50% to 100% larger than observed from decreases in stocks of dissolved oxygen. Recent statistical and modeling analyses of observed oxygen data, and in situ measurements of SOD using a dome with gentle mixing, suggest consistent values for SOD of 0.2 to 0.3 g/m²/d. These values are lower than historical estimates. Three SOD models applicable to Lake Erie are examined. One (Walker) describes SOD as a function of oxygen concentration, and of biological and chemical components. The second (Klapwijk) describes SOD as a function of carbonaceous oxidation, nitrification, denitrification, and ammonia produced by diffusion and in the aerobic, anoxic, and anaerobic zones of the sediments. The third (DiToro) describes SOD as a function of settling fluxes of algae and organics from the water column, and assumes that all anaerobically produced carbon is oxidized in the sediments. It is suggested that aspects of the latter two models are required for future modeling of SOD in Lake Erie. More measurements of sediment profiles of POC are required to resolve certain modeling questions.     

From River to Lake: Phosphorus partitioning and algal community compositional changes in Western Lake Erie

The Maumee River is an important source of phosphorus (P) loading to western Lake Erie and potentially a source of Microcystis seed colonies contributing to the development of harmful algal blooms in the lake. Herein, we quantified P forms and size fractions, and phytoplankton community composition in the river–lake coupled ecosystem before (June), during (August), and after (September) a large Microcystis bloom in 2009. Additionally, we determined the distribution and density of a newly emergent cyanobacterium, Lyngbya wollei, near Maumee Bay to estimate potential P sequestration. In June, dissolved organic phosphorus (DOP) was the most abundant P form whereas particulate P (partP) was most abundant in August and September. Green algae dominated in June (44% and 60% of total chlorophyll in river and lake, respectively) with substantial Microcystis (17%) present only in the river. Conversely, in August, Microcystis declined in the river (3%) but dominated (32%) the lake. Lake phytoplankton sequestered < 6% of water column P even during peak Microcystis blooms; in all lake samples < 112 μm non-algal particles dominated partP. Lyngbya density averaged 19.4 g dry wt/m², with average Lyngbya P content of 15% (to 75% maximum) of water column P. The presence of Microcystis in the river before appearing in the lake indicates that the river is a potential source of Microcystis seed colonies for later lake blooms, that DOP is an important component of early summer total P, and that L. wollei blooms have the potential to increase P retention in nearshore areas.     

A Framework for Defining Fish Habitat Domains in Lake Ontario and its Drainage

Old and new paradigms for freshwater fish habitat science are examined and a framework for classifying habitat domains outlined in the Lake Ontario basin. The old paradigm emphasized static measures of both habitat and fish while the new one emphasizes dynamic process-oriented metrics. Temperature, light, and motion are the primary axes of the new paradigm and individual and population processes like growth, survival, and movement are the preferred fish metrics. The science that is contributing to the formation of the new paradigm is reviewed. Habitat domains with relatively homogeneous features are identified in lake and stream contexts and some of their patterns on Lake Ontario described. Human and other disturbances to those domains are explored. The correspondences between elements of the fish assemblage in Lake Ontario and the habitat domains are examined. Lotic and lentic examples of fish-habitat phenomena related to the new paradigm are presented. The paradigm shift has implications for scientific and management activities in the Great Lakes. The framework of habitat domains provides a basis for increasing our understanding of the role of habitat in fishery productivity as well as a basis for coordinating agency efforts to manage habitats for multiple use. There is a need to establish and maintain broad-based ecosystem monitoring programs to facilitate the use of habitat knowledge in decisionmaking, and to integrate fisheries management and fish habitat management within the responsible jurisdictions as a key step to implementing ecosystem-based management.