Southeastern Lake Ontario Research Articles

Round goby predation on Hemimysis anomala

The invasive Ponto-Caspian mysid Hemimysis anomala (hereafter Hemimysis) was first observed in south-eastern Lake Ontario in May 2006. In Lake Ontario, Hemimysis is most abundant at nearshore habitats characterised by cobble–rubble substrate, which it shares with the round goby Neogobius melanostomus (hereafter goby). To better understand the interaction if any between gobies and Hemimysis, gobies were collected throughout the summer and fall periods at three shallow (<3m) nearshore locations representing eastern, central, and western Lake Ontario where Hemimysis are relatively abundant. Goby stomach contents were examined for evidence of Hemimysis and other prey. In addition, gobies were collected at two locations in southwestern Lake Ontario in shallow- (3m) and deep- (11m) water nearshore habitat where stomach contents were also used to characterise diet. Despite higher Hemimysis abundance nearshore, Hemimysis were not consumed by any gobies collected from shallow nearshore locations, and only found in three of 23 gobies collected at the deep site. Goby abundance and consumption of Hemimysis by gobies at the deep site were unrelated to Hemimysis abundance in traps. At all locations, gobies fed on soft-bodied invertebrates and dreissenids although dreissenids were the dominant prey among large (>74mm) gobies. We suspect that the ability of Hemimysis to avoid predation by gobies is the result of a combination of anti-predator behaviours such as an evasive startle response, reduced activity and depth dependent segregation in interstitial spaces during the day, and a feeding mode used by gobies that is poorly suited for an evasive species like Hemimysis.

Seasonal consumption of Hemimysis anomala by fish in Southeastern Lake Ontario, 2009–2010

We investigated the seasonal occurrence of Hemimysis anomala in the diets of fish that prey on macroinvertebrates at two sites with established Hemimysis populations east of Oswego, NY, during 2009–2010. In 2009, we examined 320 stomachs from 10 species and found Hemimysis only in alewife (Alosa pseudoharengus), rockbass (Ambloplites rupestris), and yellow perch (Perca flavescens). Of those species, alewife consumed Hemimysis most frequently and it represented a greater proportion of their diets. During 2009, the dry weight composition of Hemimysis in alewife diets varied seasonally between <1% in June, 5% in July, 98.5% in August, and 18.8% in September. In contrast, we examined 667 stomachs from 15 species in 2010 and observed Hemimysis in only one alewife and two rockbass stomachs. For alewife from September 2009, we found no relationship between predator size and the number of Hemimysis consumed, or between the presence of Hemimysis in fish diets and the presence of other diet taxa or diet diversity. Fish diets collected as bycatch from other assessments revealed large numbers of Hemimysis in fishes that had not previously been observed consuming Hemimysis in Lake Ontario, including cisco (Coregonus artedi) and white perch (Morone americana). Our results indicate Hemimysis consumption by nearshore fish can be high, but that it is variable across seasons and years, and may be most prevalent in fish that feed up in the water column, at or near dark, and have the ability to consume swift moving prey like Mysis diluviana or small fish.

Occurrence of the Great Lake's most recent invader, Hemimysis anomala, in the diet of fishes in southeastern Lake Ontario

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.

Importance of light, temperature, zooplankton and fish in predicting the nighttime vertical distribution of Mysis diluviana

The opossum shrimp Mysis diluviana (formerly M. relicta) performs large amplitude diel vertical migrations in Lake Ontario and its nighttime distribution is influenced by temperature, light and the distribution of its predators and prey. At one location in southeastern Lake Ontario, we measured the vertical distribution of mysids, mysid predators (i.e. planktivorous fishes) and mysid prey (i.e. zooplank- ton), in addition to light and temperature, on 8 occasions from May to September, 2004 and 2005. We use these data to test 3 different predictive models of mysid habitat selection, based on: (1) laboratory- derived responses of mysids to different light and temperature gradients in the absence of predator or prey cues; (2) growth rate of mysids, as estimated with a mysid bioenergetics model, given known prey densities and temperatures at different depths in the water column; (3) ratio of growth rates (g) and mor- tality risk (μ) associated with the distribution of predatory fishes. The model based on light and temper- ature preferences was a better predictor of mysid vertical distribution than the models based on growth rate and g:μ on all 8 occasions. Although mysid temperature and light preferences probably evolved as mechanisms to reduce predation while increasing foraging intake, the response to temperature and light alone predicts mysid vertical distribution across seasons in Lake Ontario.

Recent Deformation in the Bottom Sediments of Western and Southeastern Lake Ontario and its Association with Major Structures and Seismicity

Geophysical surveys, undertaken in the Toronto-Burlington corridor of western Lake Ontario and in the Rochester Basin of southeastern Lake Ontario, revealed the presence of features affecting the young lake-bottom sediments. In the western part of the lake, they include inferred pop-ups in bedrock, and plumose structures, dark linear patterns, and linear belts of circular to elliptical signatures in the modern mud. In southeastern Lake Ontario the glacial and post-glacial sediments display vertical separations of on the order of 10-15 m. Pop-ups are tectonically-induced structures. The features in the modern mud commonly parallel the orientation of P-stresses measured in Paleozoic rocks nearby and, along with the pop-ups, are spatially related to an aeromagnetic lineament. Furthermore, all of these features occur within a seismically active belt. The vertical displacements of the layered glacial and post-glacial sediments, within the Rochester Basin, are located along the southern margin of the postulated WSW extension of the seismically active St. Lawrence rift system and are interpreted to be due to faulting. The geologically young age of the sediments affected by the various deformational features, along with the characteristics of the features themselves, suggest that the lake-bottom sediments surveyed in this study may have recorded the effects of neotectonic processes.

Integrated Measures of Anthropogenic Stress in the U.S. Great Lakes Basin

Integrated, quantitative expressions of anthropogenic stress over large geographic regions can be valuable tools in environmental research and management. Despite the fundamental appeal of a regional approach, development of regional stress measures remains one of the most important current challenges in environmental science. Using publicly available, pre-existing spatial datasets, we developed a geographic information system database of 86 variables related to five classes of anthropogenic stress in the U.S. Great Lakes basin: agriculture, atmospheric deposition, human population, land cover, and point source pollution. The original variables were quantified by a variety of data types over a broad range of spatial and classification resolutions. We summarized the original data for 762 watershed-based units that comprise the U.S. portion of the basin and then used principal components analysis to develop overall stress measures within each stress category. We developed a cumulative stress index by combining the first principal component from each of the five stress categories. Maps of the stress measures illustrate strong spatial patterns across the basin, with the greatest amount of stress occurring on the western shore of Lake Michigan, southwest Lake Erie, and southeastern Lake Ontario. We found strong relationships between the stress measures and characteristics of bird communities, fish communities, and water chemistry measurements from the coastal region. The stress measures are taken to represent the major threats to coastal ecosystems in the U.S. Great Lakes. Such regional-scale efforts are critical for understanding relationships between human disturbance and ecosystem response, and can be used to guide environmental decision-making at both regional and local scales.

Shifts in the diets of slimy sculpin (Cottus cognatus) and lake whitefish (Coregonus clupeaformis) in Lake Ontario following the collapse of the burrowing amphipod Diporeia

In Lake Ontario, the diets of slimy sculpin Cottus cognatus and lake whitefish Coregonus clupeaformis shifted from a diet dominated by the burrowing amphipod, Diporeia, and to a lesser extent, Mysis, to a more diverse diet, after Diporeia collapsed, to one dominated by Mysis and prey that were formerly less important or uncommon such as Chironomidae, Oligochaeta, and Ostracoda. Additionally, lake whitefish still preyed on native mollusks like Sphaeriidae and Gastropoda, but also preyed on exotic mollusks, Dreissena spp., which are swallowed intact and subsequently crushed in its muscular stomach. Whether Diporeia was abundant (1992) or scarce (1999), selection indices for Diporeia by slimy sculpins was positive, suggesting that Diporeia was a preferred prey. Unlike lake whitefish, slimy sculpins avoided Dreissena; therefore, energy diverted to Dreissena production was a real loss for slimy sculpins. The shifts in the diet of these benthic fishes corresponded with drastic changes in the benthic community between 1992 and 1999. The collapse of Diporeia, formerly the most abundant macroinvertebrate in the benthic community, along with sharp declines in the abundance of Oligochaeta and Sphaeriidae, coincided with the establishment and rapid expansion of Dreissena bugensis, the quagga mussel, and to a lesser degree Dreissena polymorpha, the zebra mussel. It appears that the Diporeia population first collapsed at depths &amp;gt;70 m in southeastern Lake Ontario by autumn 1992, at shallower depths in the eastern Lake Ontario by 1995, and along the entire south shore line at depths &amp;lt;100 m, and perhaps in some areas &amp;gt;100 m by 1999. In response to the disappearance of Diporeia, populations of two native benthivores, slimy sculpin and lake whitefish, collapsed in eastern Lake Ontario, perhaps due in part to starvation, because Diporeia was their principal prey. Presently, alternative food resources do not appear sufficient to sustain these two benthivores at their former levels of abundance. We do not expect slimy sculpin and lake whitefish to recover unless Diporeia returns to earlier levels of abundance.

The disjunct coastal plain flora in the Great Lakes region

Three areas in the Great Lakes region are known to harbor species whose primary range is the coastal plain: (1) the southeastern Georgian Bay region of Ontario, (2) the sandplains near Lake Michigan in southwestern Michigan and northern Indiana, and (3) the lacustrine sand deposits in central and northern Wisconsin. Secondary areas with smaller concentrations are found in the southeastern Lake Ontario region of New York, the Lake Erie region, small areas of north-central Illinois, and local areas of northern Michigan. These areas are all sand deposits associated with postglacial lakes and drainage channels. A review of the flora of the Great Lakes region disclosed a list of 62 primarily coastal plain species that are disjunct to the Great Lakes region. The species are largely herbs, nearly half are graminoids, and many are annuals. Their habitats are primarily sandy, gravelly, or peaty emergent shores of shallow, soft-water ponds and small lakes with fluctuating water levels, or sometimes sandy, periodically flooded swales. A few species are aquatic, and fewer still are bog or wet forest species. Most are evident only during years of low water levels, and sometimes their appearance is quite sporadic, making survey and monitoring work difficult. However, the consequences of loss of populations can be severe since, with disjuncts, there may be no seed source nearby to facilitate recolonization of sites. The sandy lakeshore habitats are frequently prime recreational lands, thus creating additional pressures. Previous hypotheses for the occurrence of these disjuncts suggested gradual migration along the shores of postglacial lakes and drainages. However, these species do not typically inhabit shores of rivers and large lakes. As well, habitats along these shores undoubtedly were not continuous. Nevertheless, the localized occurrence of the species at the termini of major postglacial drainages in spite of the more widespread availability of apparently suitable habitats argues against random long distance dispersal. Here proposed is that these species migrated into the Great Lakes region through dispersal jumps of varying distances between substantial areas of suitable habitat created along major postglacial drainage channels. Once in the Great Lakes area, they were most successful in areas with extensive drying shorelines.

Food and habitat partitioning between young-of-year alewives and rainbow smelt in southeastern Lake Ontario

Thermal and depth distributions, diets and time of feeding of young-of-year (YOY) alewives and YOY rainbow smelt were compared for evidence of resource partitioning in southeastern Lake Ontario. YOY alewives were largely epilimnial during August and September, but moved toward the bottom during fall turnover. Alewives were most abundant in the warmest available water. YOY rainbow smelt were concentrated at depths between 10 and 30 m in August and September, but moved into deeper water at fall turnover. Depth distribution of YOY smelt was correlated with temperatures of 8–12°C Both species fed predominantly during day on zooplankton during August and September. Cyclopoid copepods were the most common prey, but bosminids, eubosminids, and occasionally calanoid copepods were frequently eaten. As YOY rainbow smelt grew (> 60 mm), they consumed more Mysis relicta and amphipods, which became the major prey of rainbow smelt by November. YOY alewives consumed mostly zooplankton in all months. Diet overlap of the two species was greatest in warm water (> 12.0° during October (94.3% similarity) and August (80.0% similarity) and lowest in November (16.9% similarity). Positive size-selection on zooplankton was found in all months for YOY rainbow smelt, but only in late September through November for YOY alewives. Thus, during thermal stratification, the species were spatially segregated by water temperature but had a high degree of overlap in time of feeding and types of prey eaten. In contrast, after fall turnover there was a greater separation in diet but a higher overlap in habitat use.

Distribution of Alewives in Southeastern Lake Ontario in Autumn and Winter: A Clue to Winter Mortalities

Alewives Alosa pseudoharengus in the Great Lakes are thought to avoid extreme cold in winter by moving to deep water where the temperature is usually highest because of inverse thermal stratification. Information collected in Lake Ontario during autumn and winter 1981–1984 with an echo sounder and bottom and midwater trawls indicated that many alewives remained at depths above 110 m, regardless of water temperature. Alewives in the Great Lakes that did not descend to greater depths would be exposed to potentially lethal temperatures during cold winters.

Ontogenetic Shifts in Habitat, Diet, and Diel-Feeding Periodicity of Slimy Sculpin in Lake Ontario

Abundance, size, and diet of slimy sculpin Cottus cognatus in southeastern Lake Ontario were determined from 239 bottom trawls at depths of 35 m and 75 m in June and August, and at depths of 8–75 m in October 1984. Slimy sculpin less than 50 mm total length generally inhabited water shallower than 60 m; larger fish dominated catches at 75 m. The fish at 35 m fed mainly at night; those feeding at 75 m showed no diel-feeding periodicity. More slimy sculpin were caught at night than during day at depths of 60 m or less but day and night catches at 75 m did not differ significantly. Amphipods Pontoporeia hoyi formed the main prey of all slimy sculpin; opossum shrimp Mysis relicta were eaten more often by the larger fish in deeper water than by small fish in shallower water. Data suggest that young slimy sculpin shift from a shallow water habitat and nocturnal feeding to continuous activity in deeper water as they mature. The behavior of slimy sculpin in shallower water may reflect an attempt to avoid predators during day.

Rainbow Smelt (Osmerus Mordax) Predation on Slimy Sculpin (Cottus Cognatus) in Lake Ontario

Slimy sculpin (Cottus cognatus) and opposum shrimp (Mysis relicta) formed the primary prey of 319 adult (96–201 mm total length) rainbow smelt (Osmerus mordax) collected day and night at depths of 30–50 m in southeastern Lake Ontario during 21–25 August and 23–31 October 1984. Prey were eaten primarily at night. Between 2000–2400 hours, 77% of rainbow smelt during August and 43% of rainbow smelt during October contained slimy sculpin, compared to less than 10% during the day. Mean number of sculpin per smelt stomach was 1.2 and 1.5, respectively. Mean sizes of slimy sculpin eaten (total lengths of 12.7 mm in August and 21.1 mm in October) were significantly less than those of sculpin (30.4 mm in August and 31.6 mm in October) caught in trawls at the same depths. Occurrence of opposum shrimp in smelt stomachs also peaked at night at 80–90% and an average of up to 2.1 and 5.2 opposum shrimp were found per smelt stomach in August and October, respectively. We infer that rainbow smelt may compete with juvenile lake trout (Salvelinus namaycus) for slimy sculpin in the Great Lakes.

Diversity as a Measure of Alewife (Alosa Pseudoharengus) Dominance in Southeastern Lake Ontario

Nearshore fish assemblages at Nine Mile Point, Lake Ontario, were sampled with gill nets twice a month from April to December in 1974 and 1975. Seasonal fluctuations in diversity (H’) were compared with and without the presence of alewife ( Alosa pseudoharengus), which comprised about 75% of the total number of individuals. Because H’ was highly correlated with the proportional contribution (p i log p i) of alewife abundance, fairly large temporal changes in composition of the remainder of the fish community were masked. This effect was explained by certain properties of the H’ index; i.e., once a species has a dominance greater than about 70%, it influences H’, not only through its own contribution, but also by restricting p i values for all other species below 0.30, the region where the index is most sensitive to change.