Predation on Lake Whitefish Eggs by Longnose Suckers

In November 1981, we observed intense predation on lake whitefish (Coregonus clupeaformis) eggs by longnose suckers (Catostomus catostomus) on lake whitefish spawning grounds in northwestern Lake Huron. Since longnose suckers commonly frequent the same habitat used by spawning lake whitefish, there exists the potential for high losses of eggs due to sucker predation.     

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.     

Maternal Transfer of Organochlorines to Eggs of Walleye (Stizostedion vitreum) in Lake Manitoba and Western Lake Superior

Gravid walleye were sampled from Lake Manitoba and western Lake Superior (St. Louis River) to measure the concentrations of organochlorine contaminants (OCs) in eggs and muscle and to assess the influence of maternal age and size on the transfer of OCs from mother to egg. Concentrations of most OCs in Lake Superior walleye eggs were 1 to 3 orders of magnitude greater than in Lake Manitoba eggs. Toxaphene (mean concentration (wet weight) ± 1 SE, 1580 ± 462 ng/g) and polychlorinated biphenyls (PCBs) (240 ± 24 ng/g) were the predominant OCs in Lake Superior walleye eggs, whereas DDT and metabolites (eggs 16 ± 1.5 ng/g, muscle 2.1 ± 0.36 ng/g) and PCBs (eggs 9.2 ± 0.83 ng/g, muscle 2.0 ± 2.4 ng/g) were the most common OCs in Lake Manitoba walleye eggs and female muscle. Egg size (dry mass) and the concentration of most OCs in Lake Manitoba walleye eggs were positively correlated with female length and age. This relationship was strongest for more hydrophobic OCs (e.g., PCBs) but was not significant for less hydrophobic OCs (e.g., hexachlorocyclohexanes (HCHs)). Neither egg size nor egg OC concentration of Lake Superior walleye were significantly correlated with female length or age. There was no relationship between OC concentrations in muscle tissue and female length or age of Lake Manitoba walleye. OC concentrations in Lake Manitoba walleye eggs were not correlated with concentrations in the muscle tissue of the mothers, suggesting that OCs in walleye eggs are derived from various tissues. A positive relationship between the egg:muscle ratio of PCB concentrations and the egg:muscle ratio oflipid in freshwater fish suggests that the maternal transfer of PCBs in freshwater fish is related to the relative amounts of lipid in the eggs and mother. The transfer of hydrophobic OCs from mother to eggs in freshwater fish appears to vary within and among fish species and with the hydrophobicity of the OC.     

Molecular Evidence for Divergent Breeding Groups of Walleye (Stizostedion vitreum) in Tributaries to Western Lake Erie

Molecular evidence from mitochondrial DNA (mtDNA) restriction fragment length polymorphisms (RFLPs) supports the existence of genetically different spawning groups of walleye (Stizostedion vitreum) among the Maumee, Sandusky, and Grand rivers that flow into Lake Erie. Three separate regions of the mtDNA molecule (the D-loop region, the NADH dehydrogenase 3, 4, and 4L genes, and the 12S and 16S rRNA genes) from female walleye eggs were amplified using the polymerase chain reaction technique. Amplifications were digested with nine different four base cutting restriction endonucleases and were resolved on 9% polyacrylamide gels. The D-loop and the NADH genes produced RFLPs, revealing a total of eight different haplotypes. The frequencies of haplotypes within the Maumee River spawning walleye were significantly different from the haplotypes within the Sandusky River. Frequencies of the haplotypes within the Grand River spawning walleye were not statistically different from those of the Maumee or Sandusky rivers. These results support the hypothesis that the Maumee and Sandusky River spawning walleye are members of two different breeding groups. The molecular identification of these walleye breeding groups may help in future fisheries management decisions.     

Spatial Patterns Emphasize the Importance of Coastal Zones as Nursery Areas for Larval Walleye in Western Lake Erie

Lake Erie walleye Sander vitreus exhibits significant interannual variability in year-class strength. Recent research revealed the importance of larval growth and survival rates in determining walleye year-class strength in western Lake Erie, indicating that spatial and temporal overlap of larvae with good habitat conditions (e.g., abundant prey, warm waters) promoted walleye growth and survival. To assess the spatial overlap between walleye larvae and habitat parameters (water depth, temperature, water clarity, prey density) in western Lake Erie, we evaluated the spatial distribution of walleye larvae and these habitat parameters with intensive sampling at 30 to 36 sites during spring 1994–1999. We analyzed spatial relationships among pelagic walleye larvae and various habitat attributes using a geographic information system and principal components analysis. Larval walleye density was consistently highest at nearshore sites during all years and showed a high degree of spatial overlap with high ichthyoplankton density, and warm water temperatures. Larval walleye density was negatively associated with water depth and water clarity. Two principal components represented 79.6% of the total variability in site attributes. Principle components analysis supported our spatial analysis by graphically separating sites into distinct groups based on larval walleye density and habitat attributes. These analyses indicated that similar relationships between larval distribution and habitat attributes occur each year, emphasizing the importance of nearshore coastal zones as nursery areas for walleye.     

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.     

Predation on Pacific Salmon Eggs by Salmonids in a Tributary of Lake Ontario

Diets of salmonids in a tributary of Lake Ontario were examined during the fall of 1977. Pacific salmon eggs accounted for at least 90% of the October diet of juvenile steelhead and coho salmon, and adult brook trout and brown trout. In November, salmon eggs comprised 38-95% of the diet. Egg consumption appeared to be responsible for large increases in the condition factor of all groups studied. Increased condition may enhance survival during the severe winters characteristic of the Tug Hill region.     

Food of Freshwater Drum in Western Lake Erie

The abundance of freshwater drum (Aplodinotus grunniens) suggests they play an important role in the Lake Erie ecosystem. Our analysis of freshwater drum digestive tracts and macrobenthic samples collected from western Lake Erie indicates that drum were selective feeders. Planktonic cladocerans and larval midges (Chironomidae) were the primary prey organisms eaten by drum. Young-of-the-year fed mostly on cladocerans, while yearling and older drum ate both cladocerans and midge larvae. Decapods, pelecypods, and fish were found only in the digestive tracts of drum longer than 250 mm. While the most abundant organisms in benthic samples were cladocerans (ephippial) and oligochaetes (89.5% by number), they constituted less than 1% of the diet. An evaluation of food selectivity, using Ivlev's index of electivity for benthic organisms, indicated that adult drum preferred midges to any other benthic food.     

Predation on Lake Trout Eggs and Fry: a Modeling Approach

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush, associated with spawning reefs. Three kinds of predation were simulated: epibenthic egg predators consuming eggs on the substrate surface during spawning, interstitial egg predators that can move in rocky substrate and consume incubating eggs, and fry predators. Also simulated was the effect of water temperature on predation rates. The model predicted that interstitial predation on eggs accounted for most (76 to 81%) of the predation on early life history stages of lake trout; epibenthic egg predation (12 to 19%) and fry predation (0 to 12%) had less effect on lake trout survival. Initial predation conditions chosen for the model were: epibenthic egg predation peaked at 2 eggs/m²/d over 30 d, interstitial egg predation at 2 eggs/m²/d over 180 d, and fry predation at 1 fry/m²/d over 60 d. With a starting egg density of 100 eggs/m² and initial predation conditions, no lake trout were estimated to survive to swim-up. At egg densities of 250 eggs/m², 36% of the lake trout survived. At the highest egg densities examined, 500 to 1,000 eggs/m², estimated survival increased to about 70 to 80%. Simulated survival rates of lake trout decreased dramatically as predation rate increased but were not as sensitive to increases in the duration of predation.     

Seasonal Variation of Nutrient Limitation in Western Lake Erie

Monthly nutrient enrichment experiments were performed from April through October, 1983, to identify growth limiting nutrients of natural phytoplankton assemblages collected from a station in the Pigeon Bay waters off the north shore of Lake Erie's western basin. Data from these experiments suggest that silica was the major limiting nutrient in April, phosphorus was the major limiting nutrient in May-September, and trace metals were limiting in October. These results show that nutrient enrichment experiments should be performed often enough to account for seasonal changes in the physicochemical environment as well as seasonal succession in phytoplankton. The conclusion that phosphorus was the major limiting nutrient in summer is different from the conclusions of the late 1960s and early 1970s that nitrogen was the major limiting nutrient in the summer in the western basin and suggests a possible shift from nitrogen to phosphorus limitation. Pigeon Bay nutrient trend data show that summer nitrate:soluble reactive phosphorus ratios have increased from approximately 4 in the late 1960s to over 40 in the late 1970s and early 1980s, corroborating that a shift has probably occurred. This shift in nutrient limitation is probably due to reduced bioavailable phosphorus loadings and increased nitrate loadings to the western basin. The southern portion of the western basin is physicochemically different from the northern portion and may not have responded in the same manner.     

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.     

Foraging Locations of Double-crested Cormorants on Western Lake Erie: Site Characteristics and Spatial Associations with Prey Fish Densities

Radio-tagged double-crested cormorants (Phalacrocorax auritus) nesting on Middle Island, Ontario and unmarked cormorants in the western basin of Lake Erie were monitored in 1999. Radio-tagged cormorants were located by aircraft and by boat along regular survey routes. In addition, foraging flocks of radio-tagged and unmarked cormorants were located during the boat surveys. Approximately 79% of foraging radio-tagged individuals, and approximately 65% of all foraging flocks were observed within 2.5 km of shore. These percentages were greater than expected, based on the percentage of the area of water within 2.5 km of shore. All size classes of flocks examined were found more frequently than expected on water ≤10 m deep. Trawling data collected annually from 1988 to 1999 during the month of August were used to determine the historical distributions of the four fish species found to comprise the majority of the diet of cormorants in the area. August corresponded to a period when there is maximal overlap in the diets of cormorants and walleye (Stizostedion vitreum) in the area and when the number of foraging cormorants in the area is large. Flocks of cormorants of all size classes examined were not found proportionately more in regions that contained higher than the historical median annual catches of any of the four prey species. These results, coupled with previous bioenergetics studies, suggest that the impact of cormorants on the fishery of the western basin of Lake Erie is localized with respect to depth and distance from shore.     

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.     

Occurrence of Zebra Mussels in Near-shore Areas of Western Lake Erie

We measured biomass, percent coverage, and length-frequency of zebra mussels in near-shore areas of western Lake Erie between 16 September and 10 November 1993 as part of a larger study on the ecological relationship between diving ducks and zebra mussels. Wet weight biomass of zebra mussels, determined by SCUBA diving, ranged from 0 to 3,611 g/m² and averaged ( ± 1 SE) 1,270 ± 380 g/m² (n = 11). Percent coverage of lake bottom by zebra mussels ranged from 0 to 70% and averaged 17 ± 4.0% (n = 27). Percent coverage of zebra mussels was relatively high in the northern portion (28–70% coverage) and in the southwestern portion (18–40%), but relatively low ( < 5%) in the southeastern portion of the study area. Percent coverage by zebra mussels, determined from underwater videography, was highly correlated (r² = 0.96) with zebra mussel biomass. Analysis of length-frequency data indicated that there was prominent recruitment of juvenile zebra mussels at only three of eight sites. Average shell length ranged from 11 mm to 15 mm at the other five sites. The non-uniform distribution of zebra mussels, as determined from biomass and videography, may have important ramifications when assessing zebra mussel impacts on waterfowl. These data may also be used when assessing impact of zebra mussels on other aquatic organisms in the near-shore areas of western Lake Erie.     

Sculpins and Crayfish in Lake Trout Spawning Areas in Lake Ontario: Estimates of Abundance and Egg Predation on Lake Trout Eggs

Crayfish (Orconectes spp.) and sculpins (Cottus spp.) were collected at eight lake trout spawning reefs in Lake Ontario to assess abundance and potential to consume lake trout eggs. Abundance of crayfish ranged from a high of 9.5/m² in eastern Lake Ontario to 0/m² in western Lake Ontario where the absence or near absence at four reefs sampled was attributed to cold water upwelling. Sculpin abundance ranged from 4.2 to 50.1/m². Mean daily egg consumption (eggs/stomach) for sculpins 50 to 75 mm in length, ranged from 0 to 0.9 but differences among reefs were not significant. At one reef, significantly more eggs (2.5 eggs/stomach) were consumed by large sculpins (> 75 mm) than by small (44–49 mm) sculpins (0.2 eggs/stomach). Estimated egg consumption (eggs/stomach/m²) for sculpins > 43 mm for the eight reefs for the period between estimated date of peak lake trout spawning and a standardized 30-d period post spawning, ranged from 0 to 496 eggs/m² consumed or from 0 to 54% of estimated egg abundance. No lake trout eggs were found in crayfish stomachs, because of their mode of feeding. Estimated egg consumption by crayfish was indirectly estimated from a relationship developed between carapace length and egg consumption using published literature and experimental work. Using this procedure, estimated egg consumption by crayfish for a standardized 30-d period after the date of peak spawning ranged from 0 to 65 eggs/m² consumed, or from 0 to 82% of potential egg abundance for the eight reefs. At low egg abundance (< 100/m²), the density of crayfish and sculpin observed in Lake Ontario could result in sufficient egg consumption to cause almost 100% mortality of lake trout eggs. At higher egg abundance, however, mortality due to crayfish and sculpins appears to be relatively low. Deposition was sufficiently low at 5 of 8 sites to suggest the possible importance of sculpin and crayfish predation on lake trout recruitment failure in Lake Ontario.     

Lake Erie in Mid-Winter

The results of four surveys of Lake Erie during mid-winter are presented here. The most recent survey, from February 15 to 17, 1977, was conducted during an exceptionally cold winter to determine whether six weeks of complete ice-cover had led to low levels of oxygen concentration in the lake. The results showed that all parts of the lake, even the shallow, normally highly productive areas, contained acceptable levels of oxygen. Apparently, production of oxygen by a small phytoplankton population counterbalanced a fairly low uptake of oxygen and maintained the level of oxygen concentration in most of the water above 90% saturation. The 1976-77 winter phytoplankton biomass was low (0.1 to 1.0 gm biomass per m³) and consisted mostly of diatoms. It appears that some of the phytoplankton were photo-synthetically active under 70 cm of ice and 23 m of water. All surveys of the lake showed the water to be virtually isothermal at a temperature just above the freezing point of water. The maximum temperature differences observed were about 0.2° in magnitude and were found in the East Basin. Nevertheless, the slight temperature differences apparently caused density currents under the ice, which resulted in lowered oxygen concentrations in the deepest part of the East Basin.     

Aromatic Hydrocarbons in Biota from the Detroit River and Western Lake Erie

Polynuclear aromatic hydrocarbons (PAHs) and PCBs in zebra mussels were elevated to concentrations greater than 5,000 ng/g lipid and 15,000 ng/g lipid, respectively, at the Ambassador Bridge in the Detroit River and concentrations gradually declined at downstream locations, which included three stations in the western basin of Lake Erie (Middle Sister Island, East Sister Island, Pelee Island). PCB concentrations in zebra mussels collected at the stations in western Lake Erie were elevated relative to the concentrations in mussels at the upstream end of the Detroit River (Stoney Point). There is no evidence that PAH contamination in the Detroit River elevated PAH concentrations in zebra mussels in western Lake Erie relative to mussels at Stoney Point. Fluorescent aromatic compounds (FACs) representing metabolites of PAHs were analyzed in the bile of gizzard shad (Dorosoma cepedianum) and freshwater drum (Aplodinotus grunniens) collected from several sites in the Detroit River and western Lake Erie. Mean FAC concentrations were >l,000 ng BaP equivalents per mL of bile in fish from the Trenton Channel and Boblo Island in the Detroit River, but FAC data provided no evidence that fish captured at two sites in western Lake Erie (East Sister Island, Pelee Island) were exposed to elevated concentrations of PAHs through ingestion of contaminated biota or exposure to contaminated sediments.     

Macroinvertebrate Communities on Hard Substrates in Western Lake Erie: Structuring Effects of Dreissena

Of the approximately 140 non-indigenous species that have invaded the Great Lakes since the early 1800s, few have had greater effects on this ecosystem than the zebra and quagga mussel (Dreissena polymorpha and D. bugensis, respectively). In this study the effects of these bivalves on macroinver-tebrates inhabiting hard substrates in western Lake Erie were quantified. Biomass, densities, diversity of macroinvertebrates, and paniculate organic matter mass were measured on bricks with high and low Dreissena densities that were held at a depth of 3.5 mfor 49 days in 1996. Total macroinvertebrate densi ties and biomass (excluding Dreissena) were two and five times greater on substrates with high Dreissena densities than when Dreissena were rare. These differences were largely attributed to the amphipod Echinogammarus ischnus, itself an invading species, which constituted 29 and 31% of total macroinvertebrate densities and biomass, respectively, on Dreissena-dominated substrates. Dreissena also stimulated increased macroinvertebrate diversity, causing a shift from a community dominated by the chironomid Dicrotendipes neomodestus to an assemblage characterized by increased densities and equitability of hydroids (Hydridae), the flatworm Dugesia tigrina, tubificid oligochaetes, leeches (Alboglossiphonia het-eroclita and immature Erpobdellidae), limpets (Ancylidae), snails (Physella integra and Amnicola limosa), Echinogammarus, the microcaddisfly Hydroptila ?waubesiana, and the chironomid Micro-tendipes pedellus. No taxon responded negatively to Dreissena in this study. In addition, particulate organic matter mass, an important food and habitat resource for benthic invertebrates, was two times greater on Dreissena-dominated substrates than on bricks with few Dreissena. Our results support hypotheses that Dreissena have strong effects on community dynamics and energy flow pathways in the Great Lakes.     

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.     

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.