Geology topics

Research about Lake Ontario

Source-linked reports with geographic coverage including Lake Ontario.

At least 19 recordsLinked to original sources

USGS2026

A targeted approach for mapping groundwater discharge to surface water and fish thermal refuge in four Lake Ontario tributaries

The duration, magnitude, and frequency of heatwaves are predicted to increase in the coming decades, a combination that can reduce the survival of many fish species. Across the world, there is broad interest in identifying thermal refuge for heat-intolerant fish species and exploring opportunities to enhance or protect these areas. Because deeper groundwater maintains a relatively constant temperature, groundwater-influenced areas along streams can provide cool-water refuge for fish during periods of extreme heat. A targeted approach was developed for identifying existing cold-water zones and areas of substantial groundwater discharge in four high priority Lake Ontario tributaries. Our approach included: (1) predicting where groundwater discharge is most likely with a simple geospatial model and (2) using model predictions to select field sites for intensive high-resolution study, including ground-based mapping of groundwater features (springs, seeps, tributaries) as well as drone-based optical and thermal infrared surveys. Results from field sites were used to both verify model performance and map different types and aerial extents of thermal anomalies. Geospatial modelling successfully predicted regions of widespread groundwater upwelling, later verified and mapped by field and drone surveys. Comparison of model and field survey results further highlighted specific geospatial layers, such as soil/bedrock types and topographic wetness index, as being particularly useful for predicting groundwater influence on streams in the study area. In addition, a comparison of geospatial model results with a model of fish abundances along the studied streams showed significant positive correlations for many heat-intolerant fish species over a wide geographic area. The approach developed in this study can be applied to other watersheds to highlight areas of probable groundwater discharge and could be used by fishery and water resource managers to support cold-water fish habitat management decision-making and resource conservation.

New York↗

USGS2026

Bottom trawl assessment of Lake Ontario’s benthic prey fish community, 2025

Since 1978, bottom trawl surveys in Lake Ontario have provided information on the status and trends of the benthic prey fish community related to Fish Community Objectives that include understanding prey fish population dynamics and community diversity. Beginning in 2015, the benthic prey fish survey expanded from only U.S. sites to incorporate Canadian sites, increasing the survey’s spatial coverage to a lake-wide scale. Additionally, sampling in the eastern U.S. embayments (Black River, Chaumont, Guffin, and Henderson Bays), that were historically sampled during a September bottom trawl survey to index Yellow Perch ( Perca flavescens ; 1978-2007), resumed in 2015. The current survey provides abundance indices for sculpins, Round Goby ( Neogobius melanostomus ) and Bloater ( Coregonus hoy i) using techniques, gear, and timing comparable to surveys on Lake Michigan. This alignment provides a necessary biological reference point for evaluating Lake Ontario Bloater reintroduction. In 2025, the benthic prey fish survey completed 100 bottom trawl sites across main lake and embayment habitats at depths from 6 to 168 m. Sampling in US waters was limited in 2025 compared to previous years. In total, the 2025 survey sampled 59,870 fish from 23 species. No Bloater were detected in the 2025 survey. Round Goby was the most common species comprising 46% of the total catch by number, followed by Deepwater Sculpin ( Myoxocephalus thompsonii ), White Perch ( Morone americana ), and Alewife ( Alosa pseudoharengus ) at 23%, 9%, and 9% respectively. Slimy Sculpin ( Cottus cognatus ) lake-wide biomass density continues to be lower than when lakewide sampling began in 2015; zero Slimy Sculpin were detected in US waters, however sampling in the main lake within US waters was limited to the southeastern area of Lake Ontario. Deepwater Sculpin biomass has remained high since population recovery began in 2010. Embayment sampling in 2025 was limited to only Chaumont Bay.

Lake Ontario↗

USGS2026

Lake Ontario August gillnet survey and lake trout assessment, 2025

Lake Ontario Lake Trout ( Salvelinus namaycush ) rehabilitation has been assessed with fishery dependent and independent surveys to evaluate program benchmarks and compare observations with management objectives since 1983. These surveys provide information on the abundance, strain composition, and performance of stocked Lake Trout, as well as information on levels of natural recruitment, and Sea Lamprey ( Petromyzon marinus ) wounding rates. Lake Trout catch per unit effort (CPUE) in the August gillnet survey was notably lower in 2025. Percentage of naturally produced Lake Trout in US waters continued to be relatively low for mature and immature fish. Sea Lamprey wounding rates on Lake Trout > 432 mm in 2025 were below management target in US waters with zero A1 wounds observed. Overall, the 2025 survey results suggest that Lake Trout indicators continue to meet some of the management objectives but are not showing signs of meaningful recruitment to the adult stock.

Lake Ontario↗

USGS2025

Quantifying benthic flux of Mysis biomass through diel vertical migration at the ecosystem scale

Mysis diluviana is a macroinvertebrate that couples benthic and pelagic habitats on a daily timescale through diel vertical migration (DVM). However, quantifying how much Mysis biomass is exchanged between benthic and pelagic habitats at an ecosystem scale is difficult because of sampling limitations and variability in Mysis DVM behavior related to light and depth. Although Mysis are benthic-pelagic migrators, a portion remains pelagic during the day offshore in Lake Ontario, partially contradicting the assumption of population-level DVM over deep areas. To estimate the amount of biomass transferred from benthic to pelagic habitat via DVM in Lake Ontario, we estimated the portion of pelagic biomass at night originating from benthic habitat as the difference between night and day pelagic estimates from net tows along a bathymetric depth gradient. We then modeled the portion as a function of depth, extrapolated these depth-dependent estimates to an existing lake wide night-pelagic dataset, and summed amounts across depth strata. We estimated more biomass was transferred from benthic to pelagic habitat at intermediate lake depths (100–160 m) despite greater offshore (> 180 m) night-pelagic biomass. Our results suggest ways to improve estimates of Mysis habitat coupling and how to account for important factors such as depth and light for modeling Mysis DVM behavior at the population- and ecosystem-levels.

Lake Ontario↗

USGS2025

Unique thermal mixing patterns in Lake Ontario revealed by novel year-round observations of thermal stratification

Year-round records of thermal stratification in the Great Lakes are rare, and there are few observations of thermal stratification during winter. In this paper, we analyze temperature data from 13 temperature logger chains and from over 130 benthic acoustic receivers that were deployed across Lake Ontario for 2 yr. The timing and duration of the fall overturn correlate with the local average water depth, and shallow sites (< 50 m depth) overturn up to a month before deep sites (> 100 m depths). Likewise, in spring, the shallow sites warm faster. Lake Ontario has partial ice cover, so wind-driven mixing stirs the water column throughout winter, and inverse thermal stratification is largely absent. The depth-averaged winter water temperatures vary between 0°C and 4°C, with the coldest temperatures (near 0.1°C) found in the shallow Kingston basin and warmest temperatures (near 4°C) at sites near the 244 m deep Rochester Basin. Lake Ontario appears to be a warm monomictic lake, rather than having a dimictic mixing pattern as previously described—there is no sustained ice cover or inverse stratification that inhibits vertical mixing in winter. Winter is a poorly understood season for many aquatic processes, including fish bioenergetics, fish distribution, biochemical processes, invertebrate distribution, and production. Moreover, the lack of knowledge of winter has hampered the use of correct initial conditions for running large lake hydrodynamic models.

Lake Ontario↗

USGS2025

Factors affecting short-term post-release survival probability of Lake Trout implanted with acoustic telemetry transmitters

The use of acoustic telemetry is steadily expanding to help answer questions related to habitat use, movement, and behavior of fishes. Significant time and resources are invested to start acoustic telemetry studies; therefore, careful planning is needed to limit post-release mortality of tagged individuals. Deep, cold-water species present additional challenges to acoustic tagging because of changes in temperature and pressure experienced during capture. The objective of our study was to determine if capture method, surface water temperature, water depth, or fish size influenced short-term post-release survival of a deep, cold-water species, Lake Trout Salvelinus namaycush . In 2023, 299 Lake Trout were captured with angling or gillnets across Lake Ontario (Laurentian Great Lake – U.S. & CAN) and surgically implanted with acoustic transmitters. We estimated 30-day post-release mortality and 24-h post-release distance traveled for tagged Lake Trout. We used Cox proportional hazards models to identify factors affecting survival probability and multiple linear regression to identify factors affecting post-release distance traveled. Thirty-day post-release mortality was minimal (9.03 %, 27/299 Lake Trout); however, mortality was 6.37 times more likely for Lake Trout captured in gillnets compare to angling ( p = 0.003). Lake Trout length had a marginally significant effect on mortality ( p = 0.052) but capture depth and temperature did not ( p > 0.05). Lake Trout post-release distance traveled was not significantly influenced by capture gear, depth, temperature, or Lake Trout length ( p = 0.61). Our results indicate that tagging-induced post-release mortality is minimal for Lake Trout tagged in the spring, but survival can be increased by avoiding use of gillnets.

Lake Ontario↗

USGS2025

Lake Ontario August gillnet survey and Lake Trout assessment, 2024

Lake Ontario Lake Trout ( Salvelinus namaycush ) rehabilitation has been assessed with fishery independent surveys to evaluate program benchmarks and compare observations with management objectives since 1983. These surveys provide information on the abundance, strain composition, and performance of stocked Lake Trout, as well as information on levels of natural recruitment, and Sea Lamprey ( Petromyzon marinus ) wounding rates. In 2024, the gillnet survey occurred in United States (US) and Canadian waters marking the first lake-wide Lake Trout assessment since 2008. Lake Trout catch per unit effort (CPUE) was higher in US than Canadian waters. Recaptures of stocked fish with coded wire tags occurred mostly in US waters, and were composed of the following strains: Lake Champlain, Seneca Lake, Superior Klondike Reef, and Huron Parry Sound. Percentage of naturally produced Lake Trout in US waters continued to be relatively low for mature and immature fish. Interestingly, the percentage of naturally produced Lake Trout was higher in Canadian waters, despite lower total numbers of Lake Trout caught. Sea Lamprey wounding rates on Lake Trout > 432 mm in 2024 were above management targets in US and Canadian waters. Overall, the 2024 survey results suggest that Lake Trout indicators continue to meet some of the management objectives and show spatial differences in overall abundance and the proportion of stocked vs wild fish between the US and Canadian stocks.

Lake Ontario↗

USGS2025

Lake Ontario spring prey fish bottom trawl survey and Alewife assessment, 2025

The multi-agency Lake Ontario spring prey fish survey quantifies changes in pelagic prey fish populations, in particular Alewife Alosa pseudoharengus , which are the primary prey supporting the lake’s sport fishes. The 2025 survey included 230 trawls in the main lake and embayments and sampled depths from 5.5 to 245 m (15 – 810 ft). The survey captured 504,541 fish from 33 species with a total weight of 7,301 kg (16,095 lbs). Alewife were 85% of the total catch numerically, while Yellow Perch Perca flavescens , Round Goby Neogobius melanostomus , Deepwater Sculpin Myoxocephalus thompsonii , and Rainbow Smelt Osmerus mordax , comprised 5%, 4%, 3%, and 1% of the catch, respectively. The Alewife biomass index decreased from 2024 to 2025 (83 to 78 kg·ha -1 ) however due to an abundant 2024 Alewife year class the density index increased from 3,727 to 9,182 fish per ha -1 . The Age-1 biomass (2024 year class) was 27.5 kg·ha -1 , which was the greatest value estimated in the modern time series (since 1997). The abundance estimate for the 2024 Alewife year class (13.8 billion) was more than three times the number of all other Alewife combined (3.6 billion). Adult Alewife abundance decreased in 2025 which was consistent with predictions from 2024. Those predictive models suggested that adult Alewife biomass is likely to increase in 2026 and 2027, as the 2024 year class matures. Alewife condition declined in 2025, which was expected given the relatively high Alewife density. Acoustic-based prey fish densities were greater than previous years acoustic estimates especially at depths from 180 – 220 m (591 – 722 ft), however acoustic based densities continue to be substantially lower than trawl-based densities. The 2025 biomass index was similar to 2024 for Emerald Shiner Notropis atherinoides and Threespine Stickleback Gasterosteus aculeatus , but was lower for Rainbow Smelt, and higher for Cisco Coregonus artedi . Three purported Bloater Coregonus hoyi were caught in the 2025 survey. Analysis of archived tissue identified five Bloater captured in previous surveys which increased the total number caught in Lake Ontario bottom trawl surveys to n = 24, since restoration stocking began in 2012. Whole lake density estimates of Lake Whitefish Coregonus clupeaformis increased in 2025 relative to 2024. Those density increases were due to increased catches in Canadian waters, as density in U.S. waters has remained low. The density index for wild or naturally reproduced juvenile Lake Trout Salvelinus namaycush increased in 2025 relative to 2024, with the most frequent catches occurring in waters around the Niagara River.

Lake Ontario↗

USGS2024

U.S. Geological Survey Tunison Laboratory of Aquatic Science research to rehabilitate native prey fish of the Lake Ontario fish community—Coregonine fishes

Restoration of native coregonines to Lake Ontario of the Laurentian Great Lakes will improve the diversity of forage for salmonid predators and ecological function in the lake, but efficacy of experimental releases for native species restoration must be evaluated. The Coregonine Research Program at the U.S. Geological Survey Tunison Laboratory of Aquatic Science encompassed a diverse array of research, with an emphasis on improved culture methods and field assessments of experimentally released juvenile coregonines. This research was carried out to support the Fish Community Objectives of the Lake Ontario Committee, is funded largely by the Great Lakes Restoration Initiative, and was done in collaboration with other laboratories and agencies, particularly, the U.S. Fish and Wildlife Service; New York State Department of Environmental Conservation; Ontario Ministry of Natural Resources and Forestry; and other U.S. Geological Survey laboratories. The Tunison Laboratory of Aquatic Science and partners have developed new and innovative hatchery techniques to raise cisco and bloater to life stages suitable for survival in Lake Ontario; assessed adult bloater survival in Lake Ontario; and evaluated survival, return rate, and reproduction of adult cisco in historic spawning locations in Lake Ontario embayments. Successes, challenges, and research needs are discussed.

Lake Ontario↗

USGS2024

A comparison of stable isotopes and polychlorinated biphenyls 1 among genetic strains of Lake Ontario lake trout (Salvelinus namaycush)

This study quantified stable carbon (δ 13 C) and nitrogen (δ 15 N) isotopes, polychlorinated biphenyl (PCB) concentrations and growth rates among multiple genetic strains of Lake Ontario lake trout ( Salvelinus namaycush ) to evaluate the potential role of genetics in these parameters. Fish ranging in age from 1 to 31 years ( n = 72) and representing nine genetic strains including wild-recruits to hatchery fish derived from Lakes Ontario, Superior and Champlain watersheds, and individuals of unknown hatchery origin. Carbon (δ 13 C) and nitrogen (δ 15 N) stable isotope values averaged −22.2 ‰ and 17.4 ‰, respectively, but did not differ significantly among genetic strains. ΣPCB concentrations ranged from 42 to 1820 ng/g and varied significantly among individuals including those of similar age and genetic strain. For example, Sum PCB (ΣPCB) concentrations among 7-year-old fish ( n = 16) ranged from 159 to 607 ng/g, which compares to growth rates of 3.5 – 32.9 %/yr for these same fish. Multivariate analysis of stable isotope and PCB profiles, however, provided considerable resolution among the strains. For example, fish of unknown hatchery origin ordinated most similar to Seneca Lake fish, the predominant strain stocked in Lake Ontario. Wild fish had a unique ordination with only Lake Superior Klondike strain fish overlapping into their ordination space. Lakes Champlain and Superior strain individuals had similar ordinations but did not overlap substantially with wild or Klondike strain fish. Combined, these differences agree with the ecologies described for these strains in their native ecosystems suggesting that insight can be gained from strain specific evaluations of ecological tracers and these pollutants among Great Lakes lake trout.

Lake Ontario↗

USGS2024

Spatial and seasonal variability in trophic relationships and carbon sources of two key invertebrate species in Lake Ontario

Mysids ( Mysis diluviana) and dreissenids ( Dreissena polymorpha and mostly D. bugensis ) are important invertebrate taxa in the food webs of the Laurentian Great Lakes but there are uncertainties about the seasonal and spatial variability in their stable isotope signatures. We quantified δ 13 C and δ 15 N in 304 mysid and 366 dreissenid samples across five spatial ecoregions, varying site depth, and three seasons (spring, summer, and fall) in Lake Ontario in 2012 and 2013. Particulate organic matter (POM) was also collected across site depth and season from the Deep Hole ecoregion for use as an isotopic baseline. Lipid normalization models for δ 13 C were generated for both taxa to reduce lipid bias in our statistical analysis. Season was a significant predictor of POM stable isotopes, with δ 13 C lower in the summer and δ 15 N decreasing from spring to summer before increasing into fall. Mysid lipid normalized δ 13 C varied by site depth and ecoregion while δ 15 N decreased across season and did not vary by site depth or ecoregion. Dreissenid stable isotopes varied significantly across season, depth, and ecoregion, with site depth having positive relationship with δ 15 N. Mysids and dreissenids were two trophic positions higher than POM based on δ 15 N; this comparison was restricted to the one region where POM was collected. Isotopic variability suggested selective feeding within POM and differing trophic pathways between mysids and dreissenids. Collecting an appropriate taxon across all observed variables to serve as an isotopic baseline, particularly in spatial and temporal studies, is critical to the correct interpretation of trophic relationships.

Lake Ontario↗

USGS2024

Lake Ontario August gillnet survey and Lake Trout assessment, 2023

Lake Ontario lake trout ( Salvelinus namaycush ) rehabilitation has been annually assessed with fishery independent surveys since 1983, to evaluate program benchmarks and compare observations with management objectives. These surveys provide information on the abundance, strain composition, and condition of the adult lake trout stock, as well as information on levels of natural recruitment, sea lamprey ( Petromyzon marinus ) wounding rates, and abundance indices of other coldwater fish species (burbot Lota lota , cisco C oregonus artedi , and lake whitefish C. clupeaformis ). In 2023, the catch per unit effort (CPUE) of total lake trout in gillnets was notably lower (12.1 fish/net) compared to recent survey years 2018–2022 (average = 17.3 ± 1.0 SD fish/net). CPUE of mature females fell below target levels. Wildproduced mature lake trout remain rare in the adult population (1.0% of adult catch). Strain composition of stocked fish indicated approximately half (51%) of all coded wire tagged lake trout captured in 2023 were from the Superior Klondike strain. Sea lamprey wounding rates decreased in 2023 and were near the target level (2.09 A1 wounds per 100 lake trout). Lake trout condition (predicted weight at length) remains high. Overall, the 2023 survey results suggest that lake trout indicators continue to meet some of the management objectives, however, recruitment of wild-produced offspring to the adult stock continues to be limited, and abundance of stocked fish may be decreasing relative to recent years in response to reduced stocking levels.

Lake Ontario↗

USGS2024

Bottom trawl assessment of Lake Ontario's benthic preyfish community, 2023

Since 1978, surveys of Lake Ontario preyfish communities have provided information on the status and trends of the benthic preyfish community related to Fish Community Objectives that includes understanding preyfish population dynamics and community diversity. Beginning in 2015, the benthic preyfish survey expanded from US-only to incorporate Canadian sites, increasing the survey’s spatial coverage to a lake-wide scale. Additionally, sampling in eastern US embayments (Black River, Chaumont, Guffin, and Henderson Bays), that were historically sampled during a September bottom trawl survey to index Yellow Perch (Perca flavescens; 1978–2007), resumed in 2015. The current survey provides abundance indices for sculpins, Round Goby (Neogobius melanostomus) and Bloater (Coregonus hoyi) with survey techniques, gear and timing comparable to Lake Michigan. This alignment provides a necessary biological reference point for measuring the success of Lake Ontario Bloater reintroduction. In 2023, the collaborative benthic preyfish survey completed 188 bottom trawl tows across main lake and embayment sites at depths from 6 to 249 m. In total, the 2023 survey sampled 85,801 fish from 38 species. Round Goby was the most common species comprising 43% of the total catch, followed by Deepwater Sculpin (Myoxocephalus thompsonii), and Alewife (Alosa pseudoharengus) at 22% and 13%, respectively. Slimy Sculpin (Cottus cognatus) lake-wide biomass density (0.06 kg/ha) remained low relative to historical observations from US waters during the 1980-1990s and was orders of magnitude lower in US than Canadian waters. Lake-wide Deepwater Sculpin biomass density remains high since the population recovery (4.1 kg/ha). Embayment catches continue to have unique species assemblages compared to main lake habitat. Historically common native benthic preyfish species like Trout-perch (Percopsis omiscomaycus), Spottail Shiner (Notropis hudsonius), and darters (Etheostoma spp.), that are now rare at main lake trawl sites, still occur in some embayment trawl sites.

Lake Ontario↗

USGS2024

Lake Ontario April prey fish survey results and Alewife assessment, 2024

The Lake Ontario April bottom trawl survey assesses pelagic prey fish populations, in particular Alewife Alosa pseudoharengus , which are the primary prey supporting the lake’s sport fish populations. The 2024 survey included 234 trawls in the main lake and embayments and sampled depths from 3.9 to 245 m (13 – 809 ft). The survey captured 441,942 fish from 28 species with a total weight of 10,519 kg (23,142 lbs.). Alewife were 89% of the total catch by number while Deepwater Sculpin Myoxocephalus thompsonii , Round Goby Neogobius melanostomus , and Rainbow Smelt Osmerus mordax , comprised 4%, 3%, and 2% of the catch respectively. The estimated Alewife biomass increases slightly from 2023 to 2024 (83.9 to 84.2 kg·ha-1) and was the largest biomass value since whole lake sampling began in 2016. Adult Alewife abundance increased in 2024 as predicted in 2023, and most of the total Alewife biomass was comprised of adult fish (97%), predominantly from the 2020 and 2022 year classes. In contrast, Age-1 Alewife biomass (2.2 kg·ha-1) was the lowest estimated since whole lake sampling began in 2016 (previous range: 2.7 – 26.7 kg·ha-1), indicating reproductive success was poor in 2023. Adult Alewife biomass is predicted to remain relatively high but decline slightly in 2025 and 2026, due to the smaller year classes produced in 2021 and 2023. Alewife condition as measured by the weight of a standard length fish (165 mm; ~6.5 inches), was 32.8 g, which was within of the range of previously observed values (28.0 – 35.9 g, 1997 – 2023). Acoustic-based prey fish densities, in the water above the bottom trawl, were similar to observations from 2021 – 2023 and were orders of magnitude lower than bottom trawl densities. These acoustic results support the seasonal timing of the April survey, when the majority of Alewife and other pelagic prey fishes are near the lake bottom and susceptible to capture with bottom trawls. The trawl survey also provides information on the status of other pelagic prey fishes and native fish restorations. In 2024, biomass indices for Rainbow Smelt, Emerald Shiner Notropis atherinoides , and Threespine Stickleback Gasterosteus aculeatus , were similar to 2023 values while the index for Cisco Coregonus artedi declined. The density index for naturally reproduced, juvenile Lake Trout Salvelinus namaycush declined relative to 2023. Density estimates of Lake Whitefish Coregonus clupeaformis continue to be orders of magnitude lower in U.S. waters relative to Canadian waters. A single purported Bloater Coregonus hoyi (total length = 148 mm, sampling depth = 105 m) was captured near Rochester, NY during the 2024 survey. This is the eighth Bloater recaptured during this survey since restoration stocking began in 2012.

Lake Ontario↗

USGS2023

Larval cisco and lake whitefish exhibit high distributional overlap within nursery areas

Coregonine fishes, including lake whitefish ( Coregonus clupeaformis ) and cisco ( C. artedi ), are socioecologically important in the Laurentian Great Lakes and of conservation concern, but the processes driving recruitment variability are unclear. In Lake Ontario, cisco and lake whitefish exhibit similar spawning behaviours and early life histories, but population trajectories are diverging. One hypothesis is that sympatric cisco and lake whitefish larvae occupy distinct habitats and experience dissimilar local environmental conditions, despite co-occurrence within nursery areas. We described the spatiotemporal distributions of larval cisco and lake whitefish among multiple Lake Ontario embayment nursery areas, characterised physical habitat features associated with their distributions, determined the degree of spatial habitat partitioning between species and evaluated how habitat niche divergence occurred along an ontogenetic progression. Both species were widely distributed across larval nursery areas, though lake whitefish were less abundant and more narrowly distributed than cisco. Within the yolk sac stage, lake whitefish occupied more nearshore, shallower and colder waters than cisco, indicating potential habitat niche partitioning between congeners. However, distributional differences were subtle and likely driven by differential hatch timing and staggered ontogenetic habitat shifts. Combined, our results illustrate similar habitat use between cisco and lake whitefish through the larval stage and demonstrate that ontogeny and species-specific phenology influence habitat use for these species. This study provides additional evidence that the early life histories of cisco and lake whitefish are highly similar and does not support the hypothesis that larval habitat use differences are a major driver of differential recruitment success for these species.

New York↗

USGS2023

Lake Ontario’s nearshore zooplankton: Community composition changes and comparisons to the offshore

In large lake systems the nearshore habitat is an intermediate zone between the shoreline and offshore, is an important nursery for larval fish, and is highlighted as an area in need of research in the Laurentian Great Lakes. In this study, we used two long-term monitoring programs to characterize the nearshore zooplankton community composition using seasonal data (May – October) and to compare the nearshore and offshore zooplankton community composition changes over time (1998 – 2019) to determine if the changes were synchronized. In the nearshore, we found the highest zooplankton biomass during the late summer/early fall (August 27th – Oct 6th), compared to mid-summer (July 1st – Aug 26th) and late spring (May 20th – June 30th). In the summer, the nearshore zooplankton community was dominated by cladocerans while copepods dominated the offshore community. From 1998 to 2019, both nearshore and offshore copepods shifted from a cyclopoid to a calanoid-dominated state, but the details of this change were different. For example, taxon-specific analysis revealed that despite reduced cyclopoids in both habitats, Mesocyclops edax increased in the nearshore. Additionally, taxon-specific analysis suggested the changes occurred an average of three years earlier in the nearshore. Using Analysis of Similarity, the nearshore and offshore summer zooplankton community compositions became increasingly distinct over time. Results from this study highlight the uniqueness of the nearshore in large lake systems, the importance of seasonal and long-term monitoring, and the potential of the nearshore as an early indicator of offshore changes.

Lake Ontario↗

USGS2023

Factors influencing egg thiamine concentrations of Lake Ontario lake trout: 2019–2020

In the Great Lakes region, thiamine deficiency is considered a recruitment bottleneck for lake trout Salvelinus namaycush and has been correlated with the consumption of non-native alewife Alosa pseudoharengus . While alewife, the most abundant forage fish in Lake Ontario, are the predominant prey for lake trout, they also consume benthic prey such as round goby Neogobius melanostomus . Because variation in the proportion of alewife in lake trout diets is linked to variation in egg thiamine concentrations, understanding how factors such as region of capture and hatchery-strain of lake trout influence diet, are key to understanding the patterns of variation in egg thiamine concentrations observed in this species. With recent increases in natural recruitment of lake trout being observed in the western region of the lake, understanding if egg thiamine is a potential driver is crucial to the rehabilitation of lake trout. In this study, we evaluated egg thiamine concentrations in lake trout during 2019–2020. We found no significant difference in egg thiamine concentrations among regions. However, a stocked Lake Superior deepwater morphotype (Superior Klondike Wild – SKW) showed significantly higher egg thiamine concentrations compared to the lean morphotype including Seneca (SEN) and Lake Champlain Domestic (LCD) strains. An analysis of fatty acid signatures of each hatchery-strain suggested that the SKW strain consumed a higher proportion of round goby than lean strains. Overall, these results suggest that morphotypic differences in the feeding ecology of lake trout can result in biochemical changes which may influence the effectiveness of restoration efforts.

Lake Ontario↗

USGS2023

Bottom trawl assessment of Lake Ontario's benthic preyfish community, 2022

Since 1978, surveys of Lake Ontario preyfish communities have provided information on the status and trends of the benthic preyfish community related to Fish Community Objectives that includes understanding preyfish population dynamics and community diversity. Beginning in 2015, the benthic preyfish survey expanded from US-only to incorporate Canadian sites, increasing the survey’s spatial coverage to a lake-wide scale. Additionally, sampling in eastern US embayments (Black River, Chaumont, Guffin, and Henderson Bays), that were historically sampled during a September bottom trawl survey to index Yellow Perch ( Perca flavescens ; 1978–2007), resumed in 2015. The current survey provides abundance indices for sculpins, Round Goby ( Neogobius melanostomus ) and Bloater ( Coregonus hoyi ) with survey techniques, gear and timing comparable to Lake Michigan. This alignment provides a necessary biological reference point for measuring the success of Lake Ontario Bloater reintroduction. In 2022, the collaborative benthic preyfish survey completed 171 bottom trawl tows across main lake and embayment sites at depths from 6 to 222 m. In total, the 2022 survey sampled 141,552 fish from 34 species. Round Goby was the most numerically abundant species comprising 36% of the total catch, followed by Alewife ( Alosa pseudoharengus ) and Deepwater Sculpin ( Myoxocephalus thompsonii ), at 20% and 16%, respectively. Alewife accounted for most (623 kg) of the fish biomass sampled during the 2022 survey (total=2,197 kg), followed by Deepwater Sculpin (547 kg), and Round Goby (262 kg). Slimy Sculpin ( Cottus cognatus ) lake-wide biomass density (0.03 kg/ha) remained low relative to historical observations from US waters during the 1980-1990s and was similar to the average from the previous three survey years (2019-2021 average 0.04 ± 0.02 kg/ha). Lake-wide Deepwater Sculpin biomass density reached a new high (4.4 kg/ha) in 2022. Embayment catches continue to have unique species assemblages compared to main lake habitat. Historically common native benthic preyfish species like Trout-perch ( Percopsis omiscomaycus ), Spottail Shiner ( Notropis hudsonius ), and darters ( Etheostoma spp.), that are now rare at main lake trawl sites, still occur in some embayment trawl sites.

Lake Ontario↗