Origins of Rainbow Smelt in Lake Ontario

The first rainbow smelt (Osmerus mordax) to enter Lake Ontario were probably migrants from an anadromous strain introduced into New York's Finger Lakes. Since the upper Great Lakes were originally stocked with a landlocked strain from Green Lake, Maine, subsequent migration to Lake Ontario from Lake Erie makes Lake Ontario unique among the Great Lakes in probably having received introductions from two distinct populations.     

Lake Trout (Salvelinus Namaycush) Spawning Habitat in Seneca Lake,New York

Lake trout from Seneca Lake provide an important source of stock for Great Lakes rehabilitation but the lake trout in Seneca Lake have been hatchery supported, themselves, for many years. Hatchery catch data show a continued decline in lake trout population and this is assumed to reflect changes in hatchery stocking, fishing pressure, and lamprey predation. A commensurate increase in the smelt population, since 1973, may have also contributed to the decrease of natural recruitment by lake trout. No indication of reduced egg survival was found in the hatchery which might be related to lake contamination effects. Our survey observations (1980–81) indicate that the lower parts of deep water cobble gravels have become much degraded by fine particulates, making such sites unsuitable for spawning lake trout. It is thought that natural replacement in Seneca Lake is strongly dependent on successful hatch of eggs laid at depths of 25 to 35 m, but the observed relationship between egg deposition and optimal thermal conditions seems to be anomalous. Since no controlling relationship was found between long-term decline of the lake trout population and climatic variation, it is believed that degradation of lake spawning sites has strongly influenced natural recruitment.     

Seasonal Food of Juvenile Lake Trout in U.S. Waters of Lake Ontario

Stomach contents of 3,554 lake trout (Salvelinus namaycush), 100 to 449 mm in total length, captured with bottom trawls during April through October 1978–81 along the south shore of Lake Ontario were examined. Invertebrates appeared to be an important food of lake trout less than 200 mm long but were only occasionally eaten by larger fish. For all seasons and size groups of juvenile lake trout combined, the slimy sculpin (Cottus cognatus) was the principal forage fish, making up 42% (by weight) of identifiable fish remains. Young-of-the-year slimy sculpins were a major food of recently stocked yearling lake trout during July through October. Alewives (Alosa pseudoharengus) were the principal forage during April and May, and made up 28% (by weight) of the identifiable fish remains. They were rarely eaten during July and August, however, when lake trout remained in the hypolimnion and alewives were above it. Over 99% of the alewives eaten from April through August were yearlings and over 99% eaten during October were young-of-the-year. Rainbow smelt (Osmerus mordax) were the primary forage during July and August, but contributed only a small part of the diet during other seasons; overall, they made up 25% of identifiable fish remains. Johnny darters (Etheostoma nigrum) made up 4% of identifiable fish remains and were most common in stomachs of small lake trout during October.     

Finite Element Analysis of a Radioactive Tritium Patch and a Waste Heat Plume Observed Near the Pickering Nuclear Power Generating Station,Lake Ontario

Effluents from industrial outfalls often form a moving patch or a steady plume in the receiving water, depending on the duration of the release. Empirical studies of coastal diffusion have shown that the eddy diffusivity obeys a power law of the length scale of the patch or plume. By analyzing a moving patch of radioactive tritium concentration and a steady plume of waste heat, the one superimposing over the other as indicated by the observed data, it is found that the cross-flow eddy diffusivity for a given length scale of the patch is about twice as large as that of the plume. The analysis is based on a variable-grid finite element method, which is used to derive the flow field and also to simulate the transport and diffusion processes. The proposed method is found particularly suitable for domains with irregular coastal structures, such as water intakes and outfalls.     

Determinants of temperature in small coastal embayments of Lake Ontario

Along 25 km of the Lake Ontario shoreline near Toronto, Ontario, small coastal embayments (0.4–32 ha) have been constructed or modified by lake-infilling to restore warmwater fish habitat. The variation in thermal habitat quality for warmwater fishes among these embayments is very high; temperatures range from those found within a small pond to those of much cooler Lake Ontario. Since meteorological conditions and surface heat fluxes are almost identical, the temperature variation among embayments must be caused by differences in bathymetry or exchange with Lake Ontario. However, a previous study on these embayments found paradoxically that temperatures were not strongly associated with channel size or embayment bathymetry. This paper resolves the paradox by showing that flushing times for almost all of the constructed embayments were less than 1 day, and often less than 12 h. With so little time to warm within the embayments, water temperatures of almost all embayments remained very close to the temperatures of the adjacent lake waters. The coldest embayments connected directly to open Lake Ontario and warmer embayments connected to Lake Ontario through other embayments or protected harbors, where the inflowing water from Lake Ontario had already substantially warmed. To allow embayments along the exposed shoreline of Toronto to reach acceptable temperatures for warmwater fish, we use heat budgets to calculate that average summer flushing times must be increased from their current length of 1.5 to 5.5 h to approximately 30 h. Such changes could be achieved through large reductions in the channel cross section.     

Estimating Larval Fish Abundances from Plankton Net Catches in Long Point Bay,Lake Erie,in 1971–78

Larval fish were sampled in Long Point Bay each summer in 1971–78 by towing ½– and 1-m diameter plankton nets at about 1 m/s. We report on the analysis of 2,576 tows, giving detailed consideration to sampling problems and statistical methods. The most common larvae were rainbow smelt (Osmerus mordax), caught in about 50% of the tows, and yellow perch (perca flavescens), clupeids, and cyprinids, caught in about 10 to 20% of the tows. Most of the data contained too high proportions of zero catches to be transformed to approximately normal distribution, and were therefore analyzed using the log-linear model rather than by analysis of variance. Except for cyprinids, larval fish seemed to be scarce in surface waters during the day. Small (4 to 10 mm long) smelt and perch larvae were caught more frequently in 526– than in 782–μm mesh nets. Very few perch and cyprinid larvae longer than 10 mm were ever caught. This, and a more rapid decline of daytime than nighttime catches of larval smelt through the mid-summer, suggests that the nets were avoided by at least the larger larvae. If avoidance of sampling gear is substantial, larval fish abundances may be overestimated in years of slow growth when the larvae remain catchable longer. We saw no evidence that the recent industrial development at Nanticoke, Ontario, has affected larval fish abundances so far. As the annual mean densities of larval fish varied 15-fold or more, it would require several years of observation to detect any but drastic future change from the current levels of abundance.     

The Significance of Seasonal Changes on a Modern Cobble-Gravel Beach used by Spawning Lake Trout,Lake Ontario

In 1979, lake trout (Salvelinus namaycush) spawning was observed and confirmed by divers over a modern cobble-gravel beach in eastern Lake Ontario. Seasonal beach surveys determined that areas where egg deposition took place coincided closely with areas of coarse cobble-gravel where sediment accumulation rates were highest. Egg deposition occurred at depths below subsequent winter ice contact. The seasonal transport of cobble-gravel seems to have largely preceded the spawning episode but addition of some finer gravels, in the area of egg deposition, did occur before freeze-over. There was no survival to hatch.     

Growth,Reproduction, Mortality,Distribution, and Biomass of Freshwater Drum in Lake Erie

Predominant age-groups in the Lake Erie freshwater drum Aplodinotus grunniens population were 3, 4, and 5 as determined from gill net, trap net, bottom trawl, and midwater trawl samples. Age and growth calculations indicated that females grew faster than males. However, the length-weight relation did not differ between sexes and was described by the equation: log W = ?5.4383 + 3.1987 log L. Some males became sexually mature at age 2 and all were mature by age 6. Females matured 1 year later than males. Three sizes of eggs were present in ovaries; the average total number was 127,000 per female for 20 females over a length range of 270 to 478 mm. Seasonal analysis of the ovary-body weight ratio indicated that spawning extended from June to August. A total annual mortality rate of 49% for drum aged 4 through 11 was derived from catch-curve analysis. Freshwater drum were widely distributed throughout Lake Erie in 1977–1979, the greatest concentration being in the western basin. They moved into warm, shallow water (less than 10 m deep) during summer, and returned to deeper water in late fall. Summer biomass estimates for the western basin, based on systematic surveys with bottom trawls, were 9,545 t in 1977 and 2,333 t in 1978.     

Distribution of Larval Yellow Perch (Perca Flavescens) in Nearshore Waters of Southeastern Lake Michigan

Spatial and temporal distribution of larval yellow perch (Perca flavescens) in southeastern Lake Michigan was described from samples collected during 1973–1981 with plankton nets and benthic sleds in water 0.5 to 21 m deep. Yellow perch larvae ≤ 7.5 mm total length were numerous from mid-May to early or mid-July. Larvae taken before mid-June hatched from eggs spawned in inland waters, rather than in Lake Michigan. Those larvae appearing early occurred chiefly in shallow water (≤1.5 m), whereas larvae caught later were chiefly distributed in deeper water (≥ 6 m). Larval perch abundance was similar at all bottom depths ≥ 6 m, was low in surface water during the day, and low near bottom at night. At 0.5- and 1.5-m stations, significantly more larvae were caught at night than during the day.     

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.     

Entrainment and Impingement of Fish by Power Plants in the Great Lakes which use the Once-Through Cooling Process

There are 89 thermal electric generating stations, producing 54,118 Megawatts (Mwe) of electricity, which use water directly from the Great Lakes. Electrical production per capita in Canada, 3.34 kw, is about twice that of the United States, 1.32 kw. These power plants require almost 2000 m³ s^?1of cooling water or, conservatively, >30% of the flow of the St. Lawrence River. Cooling water use is directly related to Mwe production and 176 L are required per kilowatt. The majority (76%) of power plants cause temperature increases of 12° C or less. Impingement of fish is directly related to power plant size (log₁₀ number impinged = 0.414 + 1.844 log₁₀ Mwe capacity) and we calculated that more than 100 × 10⁶ fish will be lost at existing and proposed stations. Impingement results in direct losses to the fishery of more than 25%, by weight, of the annual commercial fish harvest. Entrainment is also directly related to power plant size (log₁₀ number entrained = 2.103 + 1.658 log₁₀ Mwe capacity) and we expect more than 1.28 × 10⁹ larval fish will be lost by entrainment. These estimates of entrainment and impingement are conservative since they are based upon rated pumping capacity, not actual usage which was 67% for the few plants that provided this information. Impingement losses, when combined with entrainment losses which will affect recruitment to some unknown degree, likely constitute a significant undersirable impact upon the Great Lakes fishery.     

Rapid response of the nearshore round goby population to temperature declines associated with upwelling events in Lake Ontario

Upwellings occur in all the Great Lakes in response to prolonged wind events. Several studies have modeled or measured changes in abiotic conditions associated with upwellings, but few direct observations of fish responses have been documented. Video-capture techniques were used in conjunction with moored temperature loggers to link the disappearance of benthic round gobies to temperature declines during upwelling events along the southern Lake Ontario nearshore in summer of 2019. Benthic water temperatures declined by as much as 18 °C within 18 h over as many as nine events. Round goby density estimates were as high as 50/m² prior to upwellings, but declined to as low as 0/m² during the events. Using just nine observation dates, ARMA trend analysis suggested a relationship between benthic temperature and round goby abundance (AIC = 78.7, t = 2.21, P = 0.063). Although the actual response of gobies to rapidly declining temperatures was unknown, this population was unobservable in our sample area during upwellings, yet returned to pre-upwelling densities within days. Understanding the magnitude and frequency of fish responses to these events can improve our understanding of the potential for this non-native benthic fish to affect the nearshore environment.     

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.     

The effects of cool and variable temperatures on the hatch date,growth and overwinter mortality of a warmwater fish in small coastal embayments of Lake Ontario

Little is known about the ecology of warmwater fish in small coastal embayments (< 32 ha) where temperatures are lowered by exchange with the adjacent lake. Using pumpkinseed (Lepomis gibbous) as a model warmwater fish, we compare hatch dates and overwinter survival in two embayments with higher and lower amounts of cold-water input from Lake Ontario, in a warmer and cooler year. In 2007, the embayments differed by approximately 2–5 °C until late-July. In that year, temperatures in the cooler embayment delayed hatching times until July 18–August 20, approximately eight weeks later (May 24–August 20) than in the warmer embayment. Almost all offspring in the cooler embayment were likely too small to survive the winter. In 2008 both embayments had similar temperatures. In that year, pumpkinseed started hatching in early-June, and most were likely large enough to survive the winter. The findings from the two intensively sampled embayments were confirmed with a 21-year fish monitoring dataset; adult pumpkinseed were captured in the littoral zone of warm embayments 6–8 weeks earlier than in cooler embayments. Relative to pumpkinseed in the small inland lakes of eastern and central Ontario, spawning is delayed by at least two weeks in coastal embayments. Using water temperatures as a surrogate for growth, we calculated that only 5 of the 17 embayments for which we have temperature records were able to consistently produce successfully overwintering age-0 fish. Nevertheless, we found pumpkinseed age ≥ 1 in embayments too cold to produce age-0 pumpkinseed, suggesting immigration from warmer embayments.     

Distribution of Rainbow Smelt and Alewife Larvae Along the North Shore of Lake Ontario

Distribution and abundance of pelagic larval fish were determined for 12 sites on the north shore of Lake Ontario between Pickering and Wellington. Alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) larvae represented over 99.9% of the total catch in the nearshore zone between the 3- and 13-m depth contours. Yolk-sac alewife and rainbow smelt larvae were widespread, while most post-yolk-sac alewife larvae occurred in sheltered waters east of Colborne; developing alewife larvae moved away from shore in upper water strata. Rainbow smelt larvae were concentrated in surface waters shortly after hatching, with a subsequent rapid decline in abundance as larvae moved away from shore to deeper strata.     

Changes in Marsh Area Along the Canadian Shore of Lake Ontario

Baseline marsh area is approximated for the Canadian shoreline of Lake Ontario west of the Bay of Quinte using maps dated from 1789 to 1962. The measured difference between that and the area of marsh indicated on topographical maps dated from 1977 to 1979 reveals a net loss of about 4,000 acres or 57% of the baseline area for 38 marshes. Using extrapolation for another 24 marshes, the net loss for 62 marshes is estimated at approximately 4,745 acres or 43% of the baseline area. Losses were particularly high for marshes west of and including Toronto. Estimated net loss was lower in absolute terms, but similar in proportion to that from a previous study which was based on waterfowl production habitat. Relative losses of marsh area along the Canadian shoreline of Lake Ontario are consistently higher than previous estimates for inland wetlands in counties fronting the same shoreline. This and other studies suggest that heavily settled Great Lakes environments have generally lost up to 75% of their baseline wetland area and almost 100% in a few cases. The use of historic maps provides an early baseline estimate of wetland area, in some cases the only estimate possible, but it is less subject to standardization, probably reflects emergent vegetation, and is somewhat cumbersome.     

Neonatal Behavioral Assessment Scale Performance in Humans Influenced by Maternal Consumption of Environmentally Contaminated Lake Ontario Fish

Behavioral effects in neonates of their mothers’ consumption of Lake Ontario fish were examined using the Neonatal Behavioral Assessment Scale (NBAS). Newborns of women who had consumed > 40 equivalent pounds of fish were placed in a high-exposure group (n = 152), those of women who had consumed < 40 equivalent pounds of fish were placed in a low-exposure group (n = 243), and offspring of women who reported having never eaten Lake Ontario fish comprised the control group (n = 164). Assessments were given at 12–24 hours after birth, and again at 25–48 hours after birth. Despite relatively low levels of fish consumption, newborns in the high-exposure group scored more poorly than those in both the low-exposure and control groups on the Reflex, Autonomic, and Habituation clusters of the NBAS. No significant group differences were found on the Orientation, Range of State, Regulation of State, or Motor clusters of the NBAS, nor did birth weight or head circumference differ between groups. These results represent the first replication and extension of the neonatal results of the Lake Michigan Maternal Infant Cohort study (Jacobson et al. 1984).     

Catches of Larval Rainbow Smelt (Osmerus Mordax) and Alewife (Alosa Pseudoharengus) in Plankton Nets of Different Mesh Sizes

Four 0.5-m plankton nets (one each of 0.355-, 0.450-, 0.560-, and 0.750-mm mesh) were used to collect larvae of the alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) in northwestern Lake Huron and the St. Marys River. The number of larvae collected varied inversely with mesh size and the average length of larvae varied directly with mesh size. Numbers of each species caught in 0.355- and 0.450-mm mesh nets were significantly greater (P < 0.01) than the numbers caught in 0.560- and 0.750-mm mesh nets. Numbers of alewives caught were significantly greater (P < 0.01) in the 0.355- than in the 0.450-mm mesh, but numbers of rainbow smelt caught in the two meshes were about equal. Between the two larger-mesh nets, numbers of each species caught did not differ significantly. Nets with mesh larger than 0.355 mm were less effective at catching recently hatched larvae, and this reduced effectiveness accounted wholly for the smaller numbers caught in the 0.450-mm mesh net. Smaller numbers were caught in the 0.560- and 0.750-mm mesh nets not only because they caught fewer recently hatched larvae but also because they failed to retain older, larger larvae. Information on the effect of mesh size and towing speed on catches of larvae is important for making accurate estimates of larval densities.     

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.     

First record of the non-indigenous parasitic copepod Neoergasilus japonicus (Harada, 1930) in the Lake Ontario Watershed: Oneida Lake,New York

Four specimens of the Asiatic parasitic copepod Neoergasilus japonicus (Harada, 1930) were collected from Oneida Lake, New York in September 2018; one specimen was from a white sucker Catostomus commersonii, another from a green sunfish Lepomis cyanellus, and two from a bluegill Lepomis macrochirus. The four adult female specimens were found attached to the base of the gills of their respective hosts along with other ergasilid species. The average total length of the adult female N. japonicus specimens we found was 0.609 mm. These detections represent the first known occurrence of this non-native species in the state of New York, extends the easternmost distribution of this parasite over 400 miles, and now includes the Lake Ontario watershed for the first time. It is commonly believed that the international aquaculture industry and aquarium fish trade are the most likely vectors of dispersal for N. japonicus. Monitoring the spread of non-indigenous aquatic species is an important step towards the development of management plans and mitigation efforts with regards to the anthropogenic causes of dispersal, and fish parasites are no exception.