Geology topics

Brian F. Lantry

Publications and source records attributed to Brian F. Lantry.

At least 37 records · Page 2Linked to original sources

USGS2021

Diversity in spawning habitat use among Great Lakes Cisco populations

Cisco ( Coregonus artedi ) once dominated fish communities in the Laurentian Great Lakes. Restoring the abundance and distribution of this species has emerged as a management priority, yet our understanding of Cisco spawning habitat use is insufficient to characterise habitat needs for these populations and assess whether availability of suitable spawning habitat could be a constraint to recovery. We characterised the distribution of incubating Cisco eggs in situ across gradients of depth and substrate types to describe the spawning habitat used by three Great Lakes populations. In Chaumont Bay, Lake Ontario, eggs were concentrated on shallow bedrock shoals and not found on deeper silt or sand substrate. In contrast, eggs in Thunder Bay, Lake Superior, and Elk Rapids, Lake Michigan, were found on deeper fine grain sediments with low utilisation of shallow rocky and cobble habitats. These patterns of egg incubation habitat use suggest a broad spawning habitat niche at the species level but distinct spawning habitat preferences at the population level. While our results indicate some historical diversity in spawning habitat use has been maintained across the species’ range in the Great Lakes, comparisons of contemporary spawning habitat utilisation against historical accounts raise questions as to whether some spawning habitat use behaviours may no longer be prevalent within specific lakes. Thus, characterising the portfolio of spawning strategies remaining within lakes may improve our understanding of habitat needs and identify opportunities to maintain population diversity while supporting Cisco rehabilitation.

Michigan, New York↗

USGS2021

Dynamics of the seasonal migration of Round Goby (Neogobius melanostomus, Pallas 1814) and implications for the Lake Ontario food web

Seasonal migrations of fish populations can have large effects on lake nutrient budgets and food web dynamics, but the addition of a migrating non‐native species may alter these dynamics. The Round Goby ( Neogobius melanostomus ) arrived in Lake Ontario (USA/Canada) about 20 years ago with a documented history of annual offshore–inshore migrations in its native range. Here we combined nearshore, fixed‐plot video with offshore trawl data to document the annual migration of this population over multiple years. This behaviour was correlated with seasonal, nearshore temperature changes. The population size structure and mean fish length of returning fish were smaller than those of out‐migrating fish. The out‐migrating population contained an estimated 37.7 metric tonnes of phosphorous; and we estimated roughly 20 metric tonnes were translocated to and remained in offshore waters over the winter months, representing an important nutrient subsidy to a variety of offshore piscivorous fish. Lake Sturgeon ( Acipenser fulvescens ) have incorporated Round Goby extensively into their diet and consume a size range of fish matching the size range of missing Round Goby that fail to return to the nearshore. We conclude Round Goby are an important prey within the food web of Lake Ontario and translocate roughly 6.5% of the monthly total phosphorous load entering from surface waters. Further investigations of the nutrient content, population size structure and fate of migrating Round Goby in Lake Ontario are warranted to clarify the extent of this prey and nutrient subsidy in ongoing assessments of lake condition.

Lake Ontario↗

USGS2021

Comparisons among three diet analyses demonstrate multiple patterns in the estimated adult diet of a freshwater piscivore, Salvelinus namaycush

Understanding trophic interactions is critical for successful resource management. However, studying diet patterns (e.g., spatial and seasonal changes) can require extensive effort. Using individual analyses to interpret patterns may be further complicated by assumptions and limitations of the analytical approach. We investigated and compared predicted adult lake trout (Salvelinus namaycush) diet composition and patterns using stomach content analysis (SCA), fatty acid analysis (FAS), and stable isotope analysis (SIA) individually and simultaneously. The three analyses were conducted for fall-captured fish in Lake Ontario and provided different diet composition estimates; SCA suggested alewife (Alosa pseudoharengus) was dominant by frequency and mass, while FAA and SIA suggested rainbow smelt (Osmerus mordax) contributed the most based on similarity among fatty acid signatures and two-stable isotope (carbon and nitrogen) mixing models, respectively. We hypothesize the disagreement among diet estimates is a result of a seasonal shift in diet variably expressed due to differing extent of time reflected by the diet metric: hours to days for SCA, weeks to months for FAA and several months for SIA. Despite variability in diet composition estimates among methods, similar patterns in lake trout diet were observed among the three diet analyses; the contribution of alewife in lake trout diet was greater for larger individuals and for males compared to females, particularly in the east and northeast regions of the lake where alewife density was relatively low. Thus, the complementary results from the three analyses suggest that length, location, sex, and season all influence lake trout diet. Individually, analyses often failed to identify these patterns in lake trout diet with significance, and some of the patterns have not been observed in previous studies of lake trout diet in Lake Ontario. The thorough description of lake trout diet obtained from a single sampling season demonstrates how simultaneous use of multiple diet analyses may allow investigation of spatial and seasonal diet composition and with reduced sampling effort.

Lake Ontario↗

USGS2021

The path toward consistent achievement of sea lamprey abundance and lake trout marking targets in Lake Ontario, 2000–2019

Lake Ontario boasts a diverse fish community comprised of native and introduced species that support vibrant recreational, commercial and Indigenous fisheries. The effective delivery of a program to assess and control the sea lamprey ( Petromyzon marinus ) is crucial to achievement of Lake Ontario Fish Community Objectives of rehabilitating native fish stocks while protecting and maintaining the abundance of introduced salmonines. During 2000–2019, the Great Lakes Fishery Commission (GLFC) and its control agents, Fisheries and Oceans Canada (DFO) and the U. S. Fish and Wildlife Service (USFWS), delivered a consistent program of sea lamprey assessment and control. Beginning in 2004, rising sea lamprey abundance and marking rates on lake trout ( Salvelinus namaycush ) in Lake Ontario coincided with a decline of large lake trout in gillnet surveys. Efforts were undertaken to identify and control important sources of juvenile sea lampreys, including larvae that survived treatment, inhabited deepwater areas, or colonised previously uninhabited stream reaches and tributaries. A renewed reliance on proven conventional controls, including lampricide treatments and barriers, has resulted in consistent suppression of sea lamprey abundance and lake trout marking to prescribed targets in Lake Ontario during 2014–2019. This achievement is unprecedented in the 49-year history of Sea Lamprey Control Program delivery in Lake Ontario, and is attributable to the collaborative efforts of the GLFC, the control agents, and federal, provincial, state, and Indigenous partners.

Lake Ontario↗

USGS2021

Lake trout rehabilitation in Lake Ontario, 2020

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout (Salvelinus namaycush) population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from standard surveys performed by USGS and NYSDEC. Response to the COVID-19 pandemic limited survey effort such that spring and summer bottom trawl surveys and the creel survey were not completed in 2020, and sites sampled during the fall gillnet survey were limited to those east of Rochester, NY. The catch per unit effort of adult lake trout in gill nets increased each year from 2008-2014, recovering from historic lows recorded during 2005-2007. Adult abundances declined each year from 2015 to 2017; and in 2017 were about 35% below the 2014 peak and 17% below the 1999-2004 mean. Adult abundance increased in 2018 by 51% over the 2017 value and remained nearly stable between 2018 and 2020. The 2020 rate of wounding by sea lamprey (Petromyzon marinus) on lake trout caught in gill nets was 2.27 A1 wounds (fresh wound) per 100 lake trout and was near target (2 wounds per 100 lake trout). Condition values for adult lake trout, indexed in September from the predicted weight for a 700 mm lake trout from annual length-weight regressions and Fulton’s K for age-6 males, were among the highest levels observed for the 1983-2020 time series. Reproductive potential for the adult stock indexed from the CPUE of mature females ≥ 4000 g was again above the target in 2020 continuing a trend observed in nine of the last ten years. The 2020 catch of young wild lake trout marked the 26th observation in the last 27 years, however the low numbers of native adults observed during that time period continues to indicate substantial restoration impediments still exist.

Lake Ontario↗

USGS2021

2020 Status of the Lake Ontario lower trophic levels

Significant Findings for Year 2020: Note that due to covid-19 restrictions, offshore sampling was limited in 2020. 1) May – Oct total phosphorus (TP) in 2020 was 10.6 µg/L (offshore) and 7.7 µg/L (nearshore), higher than the long-term (1995-2019) average in the offshore (6.2 µg/L) and close to average in the nearshore (7.8 µg/L); mean TP values for the past decade (2010-2019) were 6.0 µg/L and 7.9 µg/L in the offshore and nearshore, respectively. In 2020, TP concentrations were significantly higher (p=0.03) in the offshore compared to the nearshore. Note that offshore duplicate samples had high relative percent difference (average 54%. 6-117%) making inferences for the offshore in 2020 uncertain. 2) May – Oct epilimnetic chlorophyll-a was similar at nearshore (1.9 µg/L) and offshore (2.1 µg/L) sites. These values were slightly higher than the average for 1995 – 2019 (1.7 µg/L, offshore; 1.5 µg/L, nearshore) and higher than for the last decade (1.4 µg/L, both offshore and nearshore). 3) May – Oct Secchi depth ranged from 3.5 m to 10.4 m (11 ft to 34 ft) at individual sites and was not significantly different between nearshore (6.3 m; 20.7 ft) and offshore (6.5 m; 21.3 ft) locations. Long-term (1995-2019) average was 7.2 m in the offshore and 6.4 m in the nearshore; means for the last decade were 7.8 m in the offshore and 6.2 m in the nearshore. 4) Despite higher TP values in 2020 than in recent years, TP, chlorophyll-a and Secchi depth are indicative of oligotrophic conditions in the offshore of Lake Ontario. 5) Nearshore summer zooplankton biomass was 10.5 µg/L, near the all-time low (9.4 µg/L, 2017) since monitoring began in 1995. Offshore epilimnetic summer zooplankton biomass was 11.7 µg/L. These values are similar to biomass in the last decade (2010-2019). 6) Peak (July) epilimnetic biomass of Cercopagis was 3.0 µg/L in the nearshore and represented 25% of the zooplankton community at that time; Cercopagis was absent from the July offshore epilimnetic samples in 2020 but was present in whole water column samples taken in August by other agencies. Epilimnetic biomass of Bythotrephes peaked in late-September in both the nearshore (1.0 µg/L) and offshore (1.8 µg/L) and represented 10% and 18% of the zooplankton community at those times, respectively. 7) Summer nearshore and offshore epilimnetic zooplankton density and biomass declined significantly 1995 – 2020. The declines were due mainly to reductions in cyclopoid copepods in both habitats.

Lake Ontario↗

USGS2020

Differentiation between lake whitefish and cisco eggs based on diameter

Cisco ( Coregonus artedi ) and lake whitefish ( Coregonus clupeaformis ) are native fish species of management concern in the Laurentian Great Lakes that often overlap in spawning locations and timing. Thus, species-level inference from in situ sampling requires methods to differentiate their eggs. Genetic barcoding and hatching eggs to visually identify larvae are used but can be time and cost intensive. Observations in published literature indicate that lake whitefish eggs may be larger than cisco eggs in the Great Lakes, but this has not yet been substantiated. Samples from shared spawning grounds are unlikely to contain similarly sized or colored eggs from other species. Thus, we assessed whether lake whitefish and cisco eggs could be separated based on size alone. Fertilized, hardened eggs were collected in situ during spawning at Elk Rapids, Lake Michigan and Chaumont Bay, Lake Ontario and preserved in ethanol. Individual eggs were measured and genetically identified. Mean diameter for cisco (2.45 mm, SD = 0.22, n = 444) was smaller than for lake whitefish (3.21 mm, SD = 0.20, n = 99). We used classification trees to identify a species-separating size threshold of 2.88 mm (95% bootstrap CI = [2.877, 2.976]), which classified eggs with an accuracy rate of 96%. Differences between species across other samples from the same locations were mostly consistent with the threshold size, but we suggest validation if applying this method to other populations. Separation of cisco and lake whitefish eggs by diameter can be accurate, efficient, and especially suitable for large sample sizes.

Lake Michigan, Lake Ontario↗

USGS2020

Lake Ontario deepwater sculpin recovery: An unexpected outcome of ecosystem change

Fish population recoveries can result from ecosystem change in the absence of targeted restoration actions. In Lake Ontario, native Deepwater Sculpin Myoxecephalus thompsonii, were common in the late-1800s, but by the mid-1900s the species was possibly extirpated. During this period mineral nutrient inputs increased and piscivore abundance declined, which increased the abundance of the nonnative planktivores Alewife Alosa pseudoharengus and Rainbow Smelt Osmerus mordax. Deepwater Sculpin larvae are pelagic and vulnerable to predation by planktivores. Annual bottom trawl surveys did not capture Deepwater Sculpin from 1978 – 1995 (n = 6,666 tows) despite sampling appropriate habitat (trawl depths: 7 – 170 m). The absence of observations during this time resulted in an elevated conservation status for the species, but no restoration actions were initiated. In 1996, three individuals were caught in bottom trawls, the first observed since 1972. Since then, their abundance has increased and in 2017 they were the second most abundant Lake Ontario prey fish. The food-web changes that occurred from 1970 through the 1990s contributed to this recovery. Alewife and Rainbow Smelt abundance declined during this period due to predation by stocked salmonids and legislation that reduced nutrient inputs and food web productivity. In the 1990s, the proliferation of nonnative, filter-feeding dreissenid mussels dramatically increased water clarity. As light penetration increased, the early-spring depth distribution of Alewife and Rainbow Smelt shifted deeper, away from larval Deepwater Sculpin habitat. The intentional and unintentional changes that occurred in Lake Ontario were not targeted at Deepwater Sculpin restoration but resulted in conditions that favored the species’ recovery. While standard surveys documented the recovery, more diverse information (e.g. observations in deep habitats and early-life stages) would have improved our understanding of why the species recovered when it did. Annual Lake Ontario trawl surveys have collaboratively expanded their spatial extent and diversified habitat sampled, based on lessons learned from the Deepwater Sculpin recovery.

Lake Ontario↗

USGS2020

2019 Status of the Lake Ontario Lower Trophic Levels

Spring total phosphorus (TP) in 2019 was 3.2 µg/L (offshore) and 4.7 µg/L (nearshore), both all-time lows; however, there is no significant time trend in our data series (1995-2019 for nearshore; 2002-2019 for offshore). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.7 – 6.5 µg/L). TP and SRP concentrations were not significantly different between nearshore and offshore habitats. Chlorophyll- a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a declined significantly 1995 – 2019. Nearshore chlorophyll- a increased 1995 – 2004 and then stabilized 2005 – 2019. In 2019, epilimnetic chlorophyll-a averaged between 1.3 and 2.9 μg/L across sites, and Apr/May – Oct concentrations were not significantly different between nearshore and offshore sites. Summer Secchi depth increased significantly in the offshore 1995 – 2019 from ~6 m to ~8 m. In the nearshore Secchi depth increased 1995 – 2004 but has remained around 6 m since 1999. Apr/May – Oct Secchi depth ranged from 3.8 m to 9.1 m (12 ft to 30 ft) at individual sites and was significantly higher offshore (7.6 m; 25 ft) than nearshore (5.7 m; 19 ft). In 2019, nearshore summer zooplankton biomass increased to 16.7 mg/m 3 after an all-time low (10.3 mg/m 3 ) in 2017. Offshore biomass (12.0 mg/m 3 ) was near the all-time low (8.1 mg/m 3 , 2006). Apr/May – Oct epilimnetic zooplankton density and biomass were not different between nearshore and offshore sites. However, zooplankton average size was significantly higher in the offshore (0.72 mm) than the nearshore (0.61 mm). Peak (July) epilimnetic biomass of Cercopagis was 2.4 mg/m 3 in the nearshore and 1.4 mg/m 3 in the offshore. Peak (September) epilimnetic biomass of Bythotrephes was 2.0 mg/m 3 in the nearshore and 2.9 mg/m 3 in the offshore. Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2019. The decline was due mainly to reductions in cyclopoids copepods. Summer epilimnetic daytime offshore zooplankton density decreased significantly 1995 – 2004, but biomass did not. Density and biomass declined significantly 1995 – 2019. Density was 3885/m 3 in 2019, about one-fourth the level observed the previous year. Offshore summer epilimnetic zooplankton biomass in 2019 was 12 mg/m 3 —well below the mean from 2005 – 2018 (20 mg/m 3 ). Most offshore zooplankton biomass was found in the metalimnion in July and early-October, and in the hypolimnion in September. Limnocalanus dominated the metalimnion in July while daphnids comprised most of the biomass in October. In September, Limnocalanus dominated the hypolimnion.

New York, Ontario↗

USGS2020

Lake trout rehabilitation in Lake Ontario, 2019

Each year we report on the progress toward rehabilitation of the Lake Ontario lake trout ( Salvelinus namaycush ) population, including the results of stocking, annual assessment surveys, creel surveys, and evidence of natural reproduction observed from all standard surveys performed by USGS and NYSDEC. The catch per unit effort of adult lake trout in gill nets increased each year from 2008-2014, recovering from historic lows recorded during 2005-2007. Adult abundances declined each year from 2015 to 2017; and in 2017 were about 35% below the 2014 peak and 17% below the 1999-2004 mean. Adult abundance increased in 2018 by 51% over the 2017 value and increased and addition 16% in 2019. The 2019 rate of wounding by sea lamprey (Petromyzon marinus) on lake trout caught in gill nets (0.53 A1 wounds (fresh wound) per 100 lake trout) was below target (2 wounds per 100 lake trout). Estimates from the NYSDEC fishing boat survey indicated angler catch rate of lake trout was low in 2019 and among the lowest recorded for the time series. Condition values for an adult lake trout, indexed in September from the predicted weight for a 700mm lake trout from annual length-weight regressions and Fulton’s K for age-6 males, were among the highest levels observed for the 1983-2019 time series. Predicted weight for a 400mm lake trout from July 2019 bottom trawl catches was near the long-term average while age-2 K was among the lowest for the time series. Reproductive potential for the adult stock indexed from the CPUE of mature females ≥ 4000g was again above the target in 2019 continuing a trend observed in nine of the last ten years. The 2019 catch of young native lake trout marked the 25th observation in the last 26 years, however the low numbers of native adults observed during that time period continues to indicate substantial restoration impediments still exist.

Lake Ontario↗

USGS2020

Lake trout spawning studies: Updates, new survey, and comparison to standard September gillnet survey

In Lake Ontario, lake trout restoration efforts have not established a self-sustaining population. Herein we describe efforts to evaluate standard and new surveys, and to estimate dispersal from stocking locations, to better understand impediments to natural reproduction. In 2019, lake trout egg deposition was sampled at two locations, Stony Island Reef, and Ford Shoals. No eggs were collected at either site. Egg deposition rates at Stony Island Reef, expressed in eggs/net/day, were lower in 2019 (0) and 2017 (0.0004) than in 1987 and 1989 (1.27 and 0.27, respectively). Spawning lake trout were indexed using standard gillnets set at six locations along the southern shore. Sites were fished overnight with two nets, except Youngstown where only one net was set. When comparing the standard September gillnet survey to the spawning survey, the spawning survey caught more and older fish, but had a similar representation of strains. Both gillnet surveys revealed that, during the early to late fall, most lake trout (>72%) are caught as adults near where they were stocked as juveniles. This spawning survey demonstrated that lake trout in spawning condition are aggregating near possible spawning habitat, but the presence of adults alone cannot identify the specific spawning habitat. Egg deposition results suggest lake trout may be depositing eggs in different habitats then they have in the past. Alternatively, our egg collection methods may not be effective when egg abundance is low. Lake Ontario lake trout restoration would benefit from survey approaches that identify specific spawning habitat.

Lake Ontario↗

USGS2019

Assessing the spawning ecology of fish in situ using a benthic pump sampler

In situ observations of incubating fish eggs can identify spawning sites and spawning habitat preferences, informing the ecology of fishes with benthic eggs. Suction pumps have been used to sample benthic-incubating, non-adhesive fish eggs, yet their sampling efficiency is not well known. Imperfect or systematically variable egg detection could bias resulting ecological inference if left unaddressed. Here we present results from replicate field trials and examine the effects of varying substrate type, intake design, sampling effort, and egg density on the ability of a gasoline-powered diaphragm pump, rated for 66 gal/min (approx. 250 L/min), to detect egg presence and estimate relative or absolute abundance. A wider box-shaped intake was effective at detecting the presence of eggs on fine, silty substrates, but had limited effectiveness on larger-grained substrates. A narrower cone-shaped intake consistently detected the presence of eggs on silt, gravel, and shallow cobble, and demonstrated potential to measure relative and absolute egg abundance. Neither intake design was able to collect eggs from deep interstitial spaces (e.g. several layers of cobble), indicating that there are limitations to the types of substrates on which benthic sampling pumps can operate. Both intake designs often collected eggs from outside the edge of the intake opening. Most eggs were collected within a two minute period, but increasing pumping time to four minutes produced better egg detection outcomes. Our results suggest that stationary benthic sampling pumps are viable tools for directly sampling incubating eggs on most substrates, but have imperfect and varying sampling efficiency resulting from intake design and substrate type.

Fisheries Research↗

USGS2019

2018 Status of the Lake Ontario lower trophic levels

Significant Findings for Year 2018: 1) Offshore spring total phosphorus (TP) in 2018 was 7.0 µg/L; values have remained stable since 2001. Offshore soluble reactive phosphorus (SRP) remained low (1.3 µg/L) in 2018; Apr/May – Oct mean values have been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 µg/L). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.9 – 7.8 µg/L). TP and SRP concentrations were not significantly different between nearshore and offshore habitats. 2) Chlorophyll-a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a was stable 2000 – 2018. Nearshore chlorophyll-a increased 1995 - 2004 and then stabilized 2005 – 2018; values were below the long-term mean in 2018. In 2018, epilimnetic chlorophyll-a averaged between 0.9 and 1.8 μg/L across sites, and offshore and nearshore Apr/May – Oct concentrations were not significantly different. Summer Secchi depth increased significantly in the offshore 2000 – 2018 and in the nearshore 1995 – 2004. Apr/May – Oct Secchi depth ranged from 4.7 m to 13.5 m (15 ft to 44 ft) at individual sites and was not significantly different between offshore (8.6 m; 28 ft) and nearshore (6.3 m; 21 ft) locations. 3) In 2018, nearshore summer zooplankton biomass increased slightly to 10.7 mg/m3 after an all-time low (10.3 mg/m 3 ) in 2017. Apr/May – Oct epilimnetic zooplankton density was significantly higher in the offshore than the nearshore, but zooplankton size and biomass were not different. Cyclopoid copepods were primarily responsible for the higher density in the offshore. 4) Peak (July) epilimnetic biomass of Cercopagis was 1.3 mg/m 3 in the nearshore and 1.9 mg/m 3 in the offshore. Peak (September-October) epilimnetic biomass of Bythotrephes was 0.4 mg/m 3 in the nearshore and 0.6 mg/m3 in the offshore. Bythotrephes biomass has increased significantly in the nearshore, 1995 – 2018. 5) Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2018. The decline was due mainly to reductions in cyclopoids copepods. 6) Summer epilimnetic daytime offshore zooplankton density and biomass decreased significantly 2000 – 2018, but density increased marginally since 2005. Density was 16000/m 3 in 2018, three times the levels seen 2015 – 2017. Offshore summer epilimnetic zooplankton biomass in 2018 was 11 mg/m 3 — well below the mean from 2005 – 2017 (20 mg/m 3 ). 7) Most offshore zooplankton biomass was found in the metalimnion in July and early-September, and in the hypolimnion in late-September and October. Cyclopoids dominated the metalimnion in July while daphnids and cyclopoids comprised most of the biomass in September. Daphnids dominated the October hypolimnion.

Lake Ontario↗

USGS2019

2017 Status of the Lake Ontario Lower Trophic Levels

Significant Findings for Year 2017: 1) Offshore spring total phosphorus (TP) in 2017 was 4.4 µg/L; values remained stable since 2001. Offshore soluble reactive phosphorus (SRP) remained low (1.1 µg/L) in 2017; Apr/May – Oct mean values have been stable in nearshore and offshore habitats since 1998 (range, 0.4 – 3.3 µg/L). Apr/May – Oct mean TP concentrations were low at both nearshore and offshore locations (range, 3.7 – 9.0 µg/L). TP and SRP concentrations were significantly higher in nearshore compared to offshore habitats (7.9 µg/L vs 5.3 µg/L, TP; 1.7 µg/L vs 1.0 µg/L, SRP). 2) Chlorophyll-a and Secchi depth values are indicative of oligotrophic conditions in nearshore and offshore habitats. Offshore summer chlorophyll-a was stable 2000 – 2017. Nearshore chlorophyll-a increased 1995 - 2004 but then declined 2005 – 2015; values were above the long-term mean for 2016 and 2017. In 2017, epilimnetic chlorophyll-a averaged between 1.2 and 2.6 μg/L across sites, and offshore and nearshore Apr/May – Oct concentrations were not significantly different. Summer Secchi depth increased significantly in the offshore 2005 – 2017 and in the nearshore 1995 – 2004. There was no trend in either habitat 1995 – 2017. Apr/May – Oct Secchi depth ranged from 4.4 m to 12.5 m at individual sites and was not significantly different between offshore (8.9 m) and nearshore (5.7 m) locations. 3) In 2017, nearshore summer zooplankton biomass was at an all-time low (10.3 mg/m3). Apr/May – Oct epilimnetic zooplankton density was not different between the offshore and the nearshore, but zooplankton size and biomass were significantly higher in the offshore. (0.7 mm vs 0.52 mm and 14.2 mg/m3 vs 7.7 mg/m3). Daphnid, calanoid copepod, and cyclopoid biomass were all higher in the offshore. 4) Peak (July) epilimnetic biomass of Cercopagis was 2.5 mg/m3 in the nearshore and 1.6 mg/m3 in the offshore. Peak (September/October) epilimnetic biomass of Bythotrephes was 0.9 mg/m3 in the nearshore and 0.5 mg/m3 in the offshore. Bythotrephes biomass has increased significantly in the nearshore, 1995 – 2017. 5) Summer nearshore zooplankton density and biomass declined significantly 1995 – 2004 and then remained stable 2005 – 2017. The decline was due mainly to reductions cyclopoids. 6) Summer epilimnetic offshore zooplankton density and biomass increased significantly 2005 – 2017, due mainly to increases in cyclopoids and daphnids. In 2017, offshore summer epilimnetic zooplankton biomass was 14 mg/m3—well below the mean from 2005 – 2016 (21 mg/m3). 7) Most offshore zooplankton biomass was found in the metalimnion in July and September, and in the hypolimnion in October. Limnocalanus and cyclopoids dominated the metalimnion in July while daphnids and cyclopoids comprised most of the biomass in September. Daphnids dominated the October hypolimnion. Whole water column samples show a declining zooplankton biomass 2015 – 2017. Bythotrephes biomass in whole water column tows is the highest it has been, 2010 – 2017.

Lake Ontario↗

USGS2018

Stomach contents and stable isotopes analysis indicate Hemimysis anomala in Lake Ontario are broadly omnivorous

Hemimysis anomala is a recent invader to North American aquatic ecosystems and is spreading rapidly throughout the Great Lakes region. This is the first littoral mysid in the North American Great Lakes; and, as such, the ecosystem effects are unknown and could be substantial. These effects depend on the role of Hemimysis in the food web and, therefore, on its diet. We examined the stomach contents of two life stages of Hemimysis from two sites in Lake Ontario during the growing season (May–November 2010). We also report the relationship between zooplankton hard parts and size for a number of potential prey species to allow the back-calculation of prey lengths from stomach contents. Both juvenile (2–5 mm) and adult Hemimysis (5–11 mm) were omnivorous, consuming phytoplankton, zooplankton, and benthos when available. However, adults appeared slightly more carnivorous and incorporated larger prey in their diets. Hemimysis were able to consume zooplankton prey up to 30% of their own length, including Bythotrephes longimanus and Cercopagis pengoi . Daphnia and Bosmina were selected over other prey by both juvenile and adult Hemimysis and were most common in stomachs during July and September when their abundances in the zooplankton were highest. Measurements of δ 13 C and δ 15 N corroborated stomach content materials, indicating an omnivorous diet which included benthic and pelagic sources. Omnivory by Hemimysis is typical of mysids in general and makes them less sensitive to seasonal dynamics of preferred prey items.

Lake Ontario↗

USGS2018

Comparison of genetic and visual identification of cisco and lake whitefish larvae from Chaumont Bay, Lake Ontario

Cisco Coregonus artedi are an important component of native food webs in the Great Lakes, and their restoration is instrumental to the recovery of lake trout Salvelinus namaycush and Atlantic salmon Salmo salar . Difficulties with visual identification of larvae can confound early life history surveys, as cisco are often difficult to distinguish from lake whitefish C. clupeaformis . We compared traditional visual species identification methods to genetic identifications based on barcoding of the mitochondrial cytochrome C oxidase I gene for 726 coregonine larvae caught in Chaumont Bay, Lake Ontario. We found little agreement between the visual characteristics of cisco identified by genetic barcoding and the most widely used dichotomous key, and the considerable overlap in ranges of traditionally utilized metrics suggest that visual identification of coregonine larvae from Chaumont Bay is impractical. Coregonines are highly variable and plastic species, and often display wide variations in morphometric characteristics across their broad range. This study highlights the importance of developing accurate, geographically appropriate larval identification methods in order to best inform cisco restoration and management efforts.

New York↗

USGS2018

Lake trout spawning and habitat assessment at Stony Island Reef

Lake trout stocking began in the 1970s as part of a binational effort to restore a self-sustaining population of lake trout in Lake Ontario. Despite 48 years of restoration stocking, lake trout in Lake Ontario have not reestablished a self-sustaining population. Spawning surveys done at Stony Island Reef (SIR) in eastern Lake Ontario in 1987 and 1989 documented lake trout egg deposition and swim-up fry. Bottom trawls in the early 1990s found naturally-reproduced juvenile lake trout in this region of the lake. More recently, naturally-reproduced juveniles have been found in western Lake Ontario, but few have been found near SIR in the eastern basin. In 2017 and 2018, we examined SIR spawning habitat and lake trout egg deposition rates and compared them to historical values. The average interstitial depth observed in 2018 was less than 4 cm, and the maximum depth observed was 15 cm. These interstitial depths are greatly reduced from depths up to 45 cm reported in the 1980s. Only one egg was captured in 95 egg nets deployed during the spawning period, which resulted in a CPUE of 0.00035 eggs/net/day, markedly lower than the egg densities measured at SIR in 1987 and 1989 of (1.27 eggs/net/day and 0.27 eggs/net/day respectively). Observations of the cobble spawning habitat suggested interstitial spaces were more infilled relative to conditions observed in the 1980s. Infill material was heavily comprised of dreissenid mussels shells and shell fragments. These findings indicate that changes in lake trout spawning habitat may be inhibiting lake trout reproduction at SIR.

Lake Ontario, Stony Island Reef↗

USGS2017

Deepwater sculpin status and recovery in Lake Ontario

Deepwater sculpin are important in oligotrophic lakes as one of the few fishes that use deep profundal habitats and link invertebrates in those habitats to piscivores. In Lake Ontario the species was once abundant, however drastic declines in the mid-1900s led some to suggest the species had been extirpated and ultimately led Canadian and U.S. agencies to elevate the species' conservation status. Following two decades of surveys with no captures, deepwater sculpin were first caught in low numbers in 1996 and by the early 2000s there were indications of population recovery. We updated the status of Lake Ontario deepwater sculpin through 2016 to inform resource management and conservation. Our data set was comprised of 8431 bottom trawls sampled from 1996 to 2016, in U.S. and Canadian waters spanning depths from 5 to 225 m. Annual density estimates generally increased from 1996 through 2016, and an exponential model estimated the rate of population increase was ~ 59% per year. The mean total length and the proportion of fish greater than the estimated length at maturation (~ 116 mm) generally increased until a peak in 2013. In addition, the mean length of all deepwater sculpin captured in a trawl significantly increased with depth. Across all years examined, deepwater sculpin densities generally increased with depth, increasing sharply at depths > 150 m. Bottom trawl observations suggest the Lake Ontario deepwater sculpin population has recovered and current densities and biomass densities may now be similar to the other Great Lakes.

Journal of Great Lakes Research↗