Evidence of lake trout (Salvelinus namaycush) spawning and spawning habitat use in the Dog River,Lake Superior

Lake trout spawn primarily in lakes, and the few river-spawning populations that were known in Lake Superior were believed to be extirpated. We confirmed spawning by lake trout in the Dog River, Ontario, during 2013–2016 by the collection of and genetic identification of eggs, and we describe spawning meso- and microhabitat use by spawning fish. Between 2013 and 2016, a total of 277 lake trout eggs were collected from 39 of 137 sampling locations in the river. The majority of eggs (220) were collected at the transition between the estuary and the river channel crossing the beach. Lake trout eggs were most often located near the downstream end of pools in areas characterized by rapid changes in depth or slope, coarse substrates, and increased water velocities, where interstitial flows may occur. Depths in wadeable areas where eggs were found averaged 0.9?m (range: 0.4 to 1.3?m) and substrate sizes consisted of large gravel, cobble, and boulder; comparable to spawning characteristics noted in lakes. Water velocities averaged 0.66?m·s^?1 (range: 0.33 to 1.7?m³·s^?1) at mid-depth. This information on spawning habitat could be used to help locate other remnant river-spawning populations and to restore river-spawning lake trout and their habitat in rivers that previously supported lake trout in Lake Superior. The Dog River population offers a unique opportunity to understand the ecology of a river spawning lake trout population.     

Recruitment of lake trout in Lake Champlain

Lake trout were extirpated from Lake Champlain by 1900, and are currently the focus of intensive efforts to restore a self-sustaining population. Stocking of yearling lake trout since 1972 has re-established adult populations, spawning occurs at multiple sites lake-wide, and fry production at several sites is very high. However, little to no recruitment past age-0 has occurred, as evidenced by the absence of adults without hatchery fin clips in fall assessments; no regular sampling for juveniles is conducted. We began focused sampling for juvenile lake trout in fall, 2015, in the Main Lake using bottom trawling, and expanded sampling to sites in the north and south of the lake in 2016. In 2015 we collected 303 lake trout < 350 mm total length, of which 23.8% were unclipped. Based on non-overlapping length modes, these wild fish comprised at least three age classes (young-of-year, age-1, and age-2). In 2016, we collected 1215 lake trout < 350 mm, including a fourth wild year class (2016 young-of-year). Forty-nine percent of juvenile lake trout from the Main Lake were unclipped; however, only 20% from the north lake and 9% from the south lake were unclipped. The absence of older unclipped fish indicates that recruitment of wild fish began recently. We discuss several hypotheses to explain this sudden, substantial recruitment success, and factors that may be affecting lake trout restoration in Lake Champlain and the Great Lakes.     

Spatial and seasonal comparisons of growth of wild and stocked juvenile lake trout in Lake Champlain

After 42 years of stocking in Lake Champlain, recruitment of wild juvenile lake trout (Salvelinus namaycush) was first observed in 2015. Abundance of wild lake trout juveniles was spatially heterogeneous. Recruitment of wild fish to age-1 and subsequent survival are likely related to growth including overwinter growth. We hypothesized that growth potential or growth-related mortality of wild and stocked fish may explain spatial differences in abundance. We collected juvenile (age-0 to 3) lake trout by bottom trawling in the central, north, and south Main Lake every 2–4 weeks during the ice-free season, 2015–2018. The percentage of wild juveniles increased from 27.8% of the total catch in 2015 to 65.7% in 2018. Rates of growth in length and change in condition were compared in wild versus stocked lake trout, among sampling areas, and between seasons (sampling season relative to winter). Wild juveniles grew equally or faster in length than stocked juveniles at the same age, but changed more slowly in condition. There was a higher percentage of wild juveniles in the central sampling area than the north and south, but no differences in growth among sampling areas. Wild and stocked fish grew in length over winter, but most cohorts (6 of 7) maintained or increased condition. Results indicate high growth potential of wild juvenile lake trout and progress toward population restoration.     

Evidence of lake trout (Salvelinus namaycush) natural reproduction in Lake Erie

Native lake trout were extirpated from Lake Erie around 1965 and committed restoration efforts began in 1982. In 2021 and 2022, a total of six lake trout (Salvelinus namaycush) in the free embryo or post-embryo life stage were captured in lake trout embryo traps in Lake Erie offshore of Shorehaven Reef, NY. This represents the first conclusive evidence of successful natural reproduction since extirpation. Trapping locations were identified using the results of a fine-scale positioning acoustic telemetry array, visual observations of adult lake trout exhibiting spawning behavior, and underwater cameras to visually identify possible spawning locations. Lake trout utilized a very specific spawning habitat type—the eastern side of shallow offshore humps in 5–8 m of water. These sites were comprised of habitat typically associated with lake trout spawning with slopes of 5–14° and clean rubble-cobble sized rock with visible interstitial spaces. Genetic barcoding was used to identify the post-embryo stage salmonids to species, and microsatellite genotypes assigned strongly to the Seneca strain which comprises the majority of the adult population. These findings represent a significant milestone for lake trout rehabilitation efforts in Lake Erie, confirming that successful reproduction to the post-embryo stage is possible and supporting continued rehabilitation efforts by Lake Erie management agencies.     

Evaluation of post-stocking dispersal and mortality of juvenile lake trout Salvelinus namaycush in Lake Ontario using acoustic telemetry

Wild reproduction by stocked lake trout Salvelinus namaycush in Lake Ontario has yet to produce a self-sustaining population, requiring a reliance on stocking. Once released, age-1 juvenile lake trout are not typically surveyed until age-2, creating a gap in knowledge of fine-scale post-release behaviors. A method to track fine-scale movements and estimate mortality of juvenile lake trout could complement standard survey methods and benefit management decisions regarding stocking locations. We used acoustic telemetry to estimate post-stocking mortality and observe fine-scale spatial and temporal movements of 38 hatchery-reared, age-1 lake trout from an offshore stocking site in the eastern basin of Lake Ontario from 2017 to 2018. Cumulative post-stocking mortality was estimated at 5.3%, 10.5%, and 26.3% after one week, one month and one year, respectively. The majority of lake trout (68.4%) emigrated from the stocking location within two months and entered deep water (～50 m) once warm-water incursions at the stocking site exceeded lake trout thermal preferences (15 °C). Lake trout made large movements (i.e., median 1.9 km, maximum 12.4 km straight-line distance) within the first hour post-release and had an average swimming speed of 1.64 km?hr^?1over the first day. There was no statistically significant relationship between total distance traveled and time of day, although distance traveled tended to be greater during crepuscular and dark periods compared to daylight. Our results provide a conservative estimate of post-release mortality and reveal behaviors of hatchery-reared juvenile lake trout that may be helpful when selecting stocking locations beneficial to restoration program goals.     

Lake trout in northern Lake Huron spawn on submerged drumlins

Recent observations of spawning lake trout Salvelinus namaycush near Drummond Island in northern Lake Huron indicate that lake trout use drumlins, landforms created in subglacial environments by the action of ice sheets, as a primary spawning habitat. From these observations, we generated a hypothesis that may in part explain locations chosen by lake trout for spawning. Most salmonines spawn in streams where they rely on streamflows to sort and clean sediments to create good spawning habitat. Flows sufficient to sort larger sediment sizes are generally lacking in lakes, but some glacial bedforms contain large pockets of sorted sediments that can provide the interstitial spaces necessary for lake trout egg incubation, particularly if these bedforms are situated such that lake currents can penetrate these sediments. We hypothesize that sediment inclusions from glacial scavenging and sediment sorting that occurred during the creation of bedforms such as drumlins, end moraines, and eskers create suitable conditions for lake trout egg incubation, particularly where these bedforms interact with lake currents to remove fine sediments. Further, these bedforms may provide high-quality lake trout spawning habitat at many locations in the Great Lakes and may be especially important along the southern edge of the range of the species. A better understanding of the role of glacially-derived bedforms in the creation of lake trout spawning habitat may help develop powerful predictors of lake trout spawning locations, provide insight into the evolution of unique spawning behaviors by lake trout, and aid in lake trout restoration in the Great Lakes.     

Lake sturgeon (Acipenser fulvescens) spawn in the St. Marys River Rapids,Michigan

The St. Marys River connects Lake Superior to Lake Huron, comprising the international border between Michigan, United States, and Ontario, Canada. This Great Lakes connecting channel naturally encompasses various habitats including lakes, wetlands, islands, tributaries, side channels, and main channels. The St. Marys River Rapids are shallow rock areas with high flow velocities (>1 m/s) in the upper river adjacent to the navigation locks and electric power generating stations, while the Little Rapids are shallow, recently restored rocky areas with lower velocities located about 7 km downstream. The St. Marys River Rapids provide important spawning habitat for several native and introduced fishes, but spawning by lake sturgeon (Acipenser fulvescens) was not previously documented. We sampled for lake sturgeon eggs and larvae in both locations during June and July 2018–2019 using weekly benthic egg mat lifts and overnight D-frame larval fish drift nets. Viable lake sturgeon eggs (11 in 2018, 45 in 2019) were collected in the tailrace of a hydroelectric power facility adjacent to the St. Marys River Rapids. Larval lake sturgeon (21 in 2018, 1 in 2019) were collected in the same area as the eggs. Neither lake sturgeon eggs nor larvae were collected at Little Rapids in either year. Our results are the first documentation of successful lake sturgeon spawning and larval drift in the upper St. Marys River. While our observations showed spawning in a human-made tailrace area, the fate of larvae produced here is unknown and warrants further research.     

A modeling study to determine the contribution of interbasin versus intrabasin phosphorus loads on the southwestern nearshore of Lake Ontario

Elevated phosphorus and nuisance algae such as Cladophora have been persistent environmental concerns in the coastal areas of Lake Ontario. Phosphorus is regarded as one of the drivers of nearshore Cladophora and the most likely mitigation that can be used to control levels of this nuisance algae in the lakes. The Niagara River, carrying the Lake Erie interbasin load, is the major contributor of the overall phosphorus load to Lake Ontario. Due to circulation patterns in the lake, this contribution is especially significant in the southwestern nearshore areas. Here we apply a mathematical model to provide insight into the relative contribution of the Niagara River versus loadings from local rivers (intrabasin loads) on the nearshore phosphorus concentrations in this region. We performed numerical experiments to determine to what extent the Niagara, Genesee and smaller local rivers impact the nearshore (<20 m depth) phosphorus concentrations. Our model results show that the Niagara River dominates the nearshore region between its discharge location and the Genesee River’s mouth, but the Genesee River strongly impacts the nearby Ontario Beach region in the very nearshore (<5 m depth). Smaller rivers have some impact close to their discharge locations. However, uncertainty with the Niagara River phosphorus load is the limiting factor in making any credible nearshore phosphorus predictions. Model accuracy is also impacted by insufficient short time scale phosphorus loads for all of the rivers, the dynamic nature of the lake circulation in shallow nearshore areas, and the simplified assumptions of the model.     

Genetic origins and diversity of lake sturgeon in the St. Louis River Estuary

Lake sturgeon Acipenser fulvescens were extirpated from the St. Louis River Estuary (SLRE) by the early 1900’s due to overfishing and habitat degradation. A restoration stocking program began in 1983, and continued almost annually until 2000. Lake sturgeon stocked into the SLRE were primarily obtained from the Wolf River (Lake Winnebago) genetic stock (n = 861,000) but some sturgeon were obtained from the Sturgeon River (Lake Superior) genetic stock (n = 61,380). Recently, spawning and natural recruitment has been documented near the Fond du Lac Dam, the upstream limit for lake sturgeon migrating from Lake Superior. However, the genetic origin of lake sturgeon spawning in the SLRE was unknown. Our objectives were to determine (1) the genetic origins and (2) genetic diversity of lake sturgeon spawning in the SLRE. Using both GENECLASS2 and ONCOR, a majority (79–81%) of lake sturgeon captured in the SLRE during spawning (2016–2018) assigned to the Wolf River genetic stock (Lake Winnebago) with greater than 80% probability using established microsatellites and a standardized genetic baseline. Other genetic stocks present (≥1%) included the Pic and Goulais rivers and possibly the Black Sturgeon River (identified using GENECLASS2, but not ONCOR); no fish assigned to the Sturgeon River using either method. Genetic diversity metrics showed that the SLRE lake sturgeon population was similar to other Lake Superior lake sturgeon populations. Overall, the SLRE Sturgeon population appears headed towards recovery. Adaptive management practices currently being employed should be continued to help guide further recovery of this population.     

Differences in seasonal distribution of wild and stocked juvenile lake trout by depth and temperature in Lake Champlain

Lake trout (Salvelinus namaycush) reared in hatcheries are exposed to an environment and feeding regime that is different from wild lake trout, and are stocked at substantially larger sizes with higher lipid reserves. In addition to differences in diet and growth, this early experience may alter habitat use compared to the wild cohort. We used seasonal data on the depth and temperature distribution of wild and stocked juvenile lake trout to test for differences in habitat use and inform sampling strategies to evaluate annual recruitment. Bottom trawling was conducted from 2015 to 2019 in the central basin of Lake Champlain every two to four weeks during the ice-free season. Differences in distribution of wild and stocked lake trout were most pronounced during thermal stratification, when wild juveniles were more abundant than stocked juveniles at shallower depths and warmer temperatures and stocked juveniles were more abundant at deeper depths and colder temperatures. Temperature preferences may be a consequence of different early rearing environments; wild lake trout are acclimated to lake temperatures and forage, whereas stocked fish entered the lake with high lipid content and little foraging experience. Unbiased assessment of the proportion of wild lake trout and growth and survival of the entire juvenile lake trout population using bottom trawl sampling should either take place in the pre- and post-stratification seasons when wild and stocked fish are at the same depths, or include the full range of depths and temperatures that wild and stocked fish occupy during the stratified period.     

Population Characteristics and Movements of Lake Sturgeon in the Sturgeon River and Lake Superior

A 2.6-km reach of the Sturgeon River, containing two sets of rapids, is an important spawning site to a native population of lake sturgeon, Acipenser fulvescens, which ranges widely into southern Lake Superior. Similar spawning areas in other Great Lake tributaries may also be important to the protection and rehabilitation of lake sturgeon throughout this region. Information on range and habitat needs of this species, which is considered “threatened” in the State of Michigan, was obtained from the Sturgeon River spawning population from 1987 to 1995. Radio-tracking was employed to determine movements and habitat use by post-spawning lake sturgeon. Telemetry data from 25 fish were supplemented with data obtained through identification tag returns. During the study 925 lake sturgeon were handled; 86 returned to spawn 1 time and 12 returned 2 times. Spawning intervals for male lake sturgeon were commonly 2, 3, or 4 years; yearly spawning by males was never observed. Females returned to spawn after 3 to 7 years. From 1991 to 1995 the male:female sex ratio at the spawning site was 1.25 to 2.7. In 1990 13 of 18 adults fitted with transmitters moved out of the river within 9 days. Upon reaching Portage Lake nine individuals spent time in shallow (maximum depth, 6 m) Pike Bay. After 3 to 53 days (mean, 22) tagged fish moved into the deeper water of Portage Lake (maximum depth, 17 m) and ranged more widely. Three fish were located in Keweenaw Bay, Lake Superior by late August. Identification tag returns reveal that lake sturgeon traveled 70 to 280 km from the spawning site throughout southern Lake Superior.     

Contribution of lake trout stocked as fry to an adult population in Lake Superior

Lake trout Salvelinus namaycush fry treated with heated water to create thermal marks in their otoliths were stocked at Sve's Reef in Minnesota waters of Lake Superior in 1994, 1995, and 1996. These fish began to reach maturity in 2000, and were vulnerable to annual assessment gill nets set at several locations along the Minnesota shoreline. Captured fish also included fin-clipped lake trout stocked as yearlings, and naturally reproduced (wild) lake trout. Otoliths from 3106 unclipped lake trout were aged and examined for thermal marks from 2000 to 2007, of which 1152 were from the target year classes (1994–1996). Thermal marks were found in otoliths from 64 fish, or 5.6% of those in the target year classes, demonstrating that stocked fry contributed to the adult lake trout population in Minnesota waters. Although numbers of recaptured fish were too low to demonstrate statistically significant differences, higher recapture rates of marked fish at Sve's Reef in fall and spawning assessments suggest that these fish may have imprinted at the stocking location and homed back to this area to spawn. Wild lake trout populations in Lake Superior may be approaching fully rehabilitated levels, but recovery in the lower Great Lakes has progressed more slowly, and evidence of success with fry stocking could benefit those populations.     

Evidence of Lake Whitefish Spawning in the Detroit River: Implications for Habitat and Population Recovery

Historic reports imply that the lower Detroit River was once a prolific spawning area for lake whitefish (Coregonus clupeaformis) prior to the construction of the Livingstone shipping channel in 1911. Large numbers of lake whitefish migrated into the river in fall where they spawned on expansive limestone bedrock and gravel bars. Lake whitefish were harvested in the river during this time by commercial fisheries and for fish culture operations. The last reported landing of lake whitefish from the Detroit River was in 1925. Loss of suitable spawning habitat during the construction of the shipping channels as well as the effects of over-fishing, sea lamprey (Petromyzon marinus) predation, loss of riparian wetlands, and other perturbations to riverine habitat are associated with the disappearance of lake whitefish spawning runs. Because lake whitefish are recovering in Lake Erie with substantial spawning occurring in the western basin, we suspected they may once again be using the Detroit River to spawn. We sampled in the Detroit River for lake whitefish adults and eggs in late fall of 2005 and for lake whitefish eggs and fish larvae in 2006 to assess the extent of reproduction in the river. A spawning-ready male lake whitefish was collected in gillnets and several dozen viable lake whitefish eggs were collected with a pump in the Detroit River in November and December 2005. No lake whitefish eggs were found at lower river sites in March of 2006, but viable lake whitefish eggs were found at Belle Isle in the upper river in early April. Several hundred lake whitefish larvae were collected in the river during March through early May 2006. Peak larval densities (30 fish/1,000 m³ of water) were observed during the week of 3 April. Because high numbers of lake whitefish larvae were collected from mid-and downstream sample sites in the river, we believe that production of lake whitefish in the Detroit River may be a substantial contribution to the lake whitefish population in Lake Erie.     

Acoustic estimates of abundance and distribution of spawning lake trout on Sheboygan Reef in Lake Michigan

Efforts to restore self-sustaining lake trout (Salvelinus namaycush) populations in the Laurentian Great Lakes have had widespread success in Lake Superior; but in other Great Lakes, populations of lake trout are maintained by stocking. Recruitment bottlenecks may be present at a number of stages of the reproduction process. To study eggs and fry, it is necessary to identify spawning locations, which is difficult in deep water. Acoustic sampling can be used to rapidly locate aggregations of fish (like spawning lake trout), describe their distribution, and estimate their abundance. To assess these capabilities for application to lake trout, we conducted an acoustic survey covering 22 km² at Sheboygan Reef, a deep reef ( < 40 m summit) in southern Lake Michigan during fall 2005. Data collected with remotely operated vehicles (ROV) confirmed that fish were large lake trout, that lake trout were 1–2 m above bottom, and that spawning took place over specific habitat. Lake trout density exhibited a high degree of spatial structure (autocorrelation) up to a range of ∼ 190 m, and highest lake trout and egg densities occurred over rough substrates (rubble and cobble) at the shallowest depths sampled (36–42 m). Mean lake trout density in the area surveyed (∼ 2190 ha) was 5.8 fish/ha and the area surveyed contained an estimated 9500–16,000 large lake trout. Spatial aggregation in lake trout densities, similarity of depths and substrates at which high lake trout and egg densities occurred, and relatively low uncertainty in the lake trout density estimate indicate that acoustic sampling can be a useful complement to other sampling tools used in lake trout restoration research.     

Morphometric differentiation and gene flow in emerald shiners (Notropis atherinoides) from the lower Great Lakes and the Niagara River

Differences in habitat (e.g., water velocity, prey, and predator regimes) are a driving force causing adaptive divergence among fish populations. This study used geometric shape analysis to assess morphological differences among emerald shiner (Notropis atherinoides) populations inhabiting the Niagara River, Lake Erie, and Lake Ontario. It was expected that emerald shiners inhabiting the two lakes would have more robust bodies and smaller heads, while river emerald shiners were expected to display more fusiform bodies with larger heads. The results of this study indicate that emerald shiners from Lake Erie and the Niagara River had a more robust form on average than individuals from Lake Ontario. Specifically, emerald shiners collected from Lake Ontario displayed more streamlined bodies and larger heads than emerald shiners collected from Lake Erie and the Niagara River. In addition, this divergence in body shape has apparently occurred despite the lack of distinct genetic differentiation as measured with microsatellite variation. Our results suggest that differences in water velocity alone may not be responsible for phenotypic variation in body shape among these emerald shiner populations, and other factors such as differences in prey or predator regimes are likely involved.     

History of Lake Ontario Contamination from the Niagara River by Sediment Radiodating and Chlorinated Hydrocarbon Analysis

Contamination of Lake Ontario by persistent organic compounds began with the development of the chemical industry along the Niagara River. These compounds are discharged to the river where they are scavenged from the water column by sedimenting particulates which in turn settle out in depositional areas of Lake Ontario. We have determined ²¹⁰Pb, ¹³⁷Cs, and chlorinated hydrocarbon profiles of sediment cores taken about 3 km from the mouth of the Niagara River. Age profiles of the sediments were constructed from the radionuclide measurements and used to determine historic trends of chlorinated hydrocarbon input to Lake Ontario. The historical record found in the sediments for chlorobenzenes, chlorotoluenes, hexachlorobutadiene, octachlorostyrene, mirex, and PCBs is in good agreement with known production and usage patterns of the chemicals. Pollution of Lake Ontario with chlorinated hydrocarbons from the Niagara River is still occurring, but the worst contamination of the lake occurred in the 1960s.     

Historical genetic connectivity of lake sturgeon in a dammed Great Lakes tributary

Lake sturgeon (Acipenser fulvescens) populations are the focus of rehabilitation efforts across the Great Lakes. Although historical fisheries were a major cause of population collapses, habitat fragmentation and/or loss and reduced access to spawning and juvenile habitat impose contemporary challenges for population recovery. The loss of connectivity between habitat types required by different life stages may particularly limit recruitment rates, inhibiting population increase towards recovery targets. We used microsatellite DNA genotyping to assess population structure, diversity, and historical connectivity of lake sturgeon in the Black Sturgeon River watershed, a major tributary of Black Bay, Lake Superior with both historical and contemporary dams. Genotype data from lake sturgeon sampled above and below an existing major barrier, as well as from lakes in the upper watershed, showed evidence of historical connectivity throughout the watershed. Despite the existing barrier fragmenting the river and preventing upstream migration, lake sturgeon from the Black Sturgeon watershed showed clear membership to a single ancestral gene pool. Estimates of genetic effective population size (N_e) for the above- and below-barrier population segments were reduced compared to the larger (watershed level) gene pool. Although the longevity of lake sturgeon has largely enabled the retention of historical genetic diversity for the population in the watershed, the reduced productive capacity of this significant tributary may have implications for recovery rates for the regional Lake Superior metapopulation. Restoring connectivity among habitats would benefit the long-term conservation and management of this species throughout this river system, and potentially the regional metapopulation.     

Identifying sources and year classes contributing to invasive grass carp in the Laurentian Great Lakes

Relative contributions of aquaculture-origin and naturally-reproduced grass carp (Ctenopharyngodon idella) in the Laurentian Great Lakes have been unknown. We assessed occurrence and distribution of aquaculture-origin and wild grass carp in the Great Lakes using ploidy and otolith stable oxygen isotope (δ¹⁸O) data. We inferred natal river and dispersal from natal location for wild grass carp using otolith microchemistry and estimated ages of wild and aquaculture-origin fish to infer years in which natural reproduction and introductions occurred. Otolith δ¹⁸O indicated that the Great Lakes contain a mixture of wild grass carp and both diploid and triploid, aquaculture-origin grass carp. Eighty-eight percent of wild fish (n = 49 of 56) were caught in the Lake Erie basin. Otolith microchemistry indicated that most wild grass carp likely originated in the Sandusky or Maumee rivers where spawning has previously been confirmed, but results suggested recruitment from at least one other Great Lakes tributary may have occurred. Three fish showed evidence of movement between their inferred natal river in western Lake Erie and capture locations in other lakes in the Great Lakes basin. Age estimates indicated that multiple year classes of wild grass carp are present in the Lake Erie basin, recruitment to adulthood has occurred, and introductions of aquaculture-origin fish have happened over multiple years. Knowledge of sources contributing to grass carp in the Great Lakes basin will be useful for informing efforts to prevent further introductions and spread and to develop strategies to contain and control natural recruitment.     

Predation on emergent lake trout fry in Lake Champlain

The rehabilitation of extirpated lake trout (Salvelinus namaycush) in the Great Lakes and Lake Champlain has been hindered by various biological and physiological impediments. Efforts to restore a lake trout fishery to Lake Champlain include hatchery stocking and sea lamprey control. Despite these management actions, there is little evidence of recruitment of naturally-produced fish in annual fall assessments. Spawning occurs at multiple sites lake-wide in Lake Champlain, with extremely high egg and fry densities, yet sampling for juvenile lake trout has only yielded fin-clipped fish. To investigate this recruitment bottleneck, we assessed predation pressure by epi-benthic fish on emergent fry on two spawning reefs and the subsequent survival and dispersal of fry in potential nursery areas. Epi-benthic predators were sampled with 2-h gillnet sets at two small, shallow sites in Lake Champlain throughout the 24-h cycle, with an emphasis on dusk and dawn hours. In total, we documented seven different species that had consumed fry, with consumption rates from 1 to 17 fry per stomach. Rock bass and yellow perch dominated the near-shore fish community and were the most common fry predators. Predator presence and consumption of fry was highest between 19:00 and 07:00. Predators only consumed fry when fry relative abundance was above a threshold of 1 fry trap^− 1 day^− 1. We used an otter trawl to sample for post-emergent fry adjacent to the reef, but did not capture any age-0 lake trout. Due to the observed predation pressure by multiple littoral, species on shallow spawning reefs, lake trout restoration may be more successful at deep, offshore sites.     

Assessing habitat for lake sturgeon (Acipenser fulvescens) reintroduction to the Maumee River,Ohio using habitat suitability index models

Lake sturgeon (Acipenser fulvescens) were a candidate for reintroduction in the Maumee River, Ohio, where they were historically abundant, but are now functionally extirpated. Our objective was to determine if current habitat quality and quantity could support reintroduction efforts. We developed a spatially explicit habitat suitability index model for two lake sturgeon life stages: spawning adult and age-0 fish. To estimate habitat quality, substrate, water depth, and water velocity were assessed and integrated into suitability index values to delineate good, moderate, and poor areas for each life stage. Each habitat characteristic was mapped and combined to provide an overall assessment of habitat suitability, quantity, and location. Model results indicated 208 ha (10.2% of all habitat) of good adult spawning habitat (e.g., coarse substrates, depths between 0.3 and 8 m, and velocity between 0.5 and 1 m/s) and 529 ha (28.2% of all habitat) of good age-0 habitat (e.g., fine substrates, depths between 0.2 and 6 m, and velocity between 0.1 and 0.7 m/s). Good age-0 habitat was located mostly downstream of good spawning habitat, which will provide nursery areas for age-0 fish after hatch. Our models suggested habitat is not limiting for lake sturgeon and efforts to reintroduce this species into the Maumee River, and for the first time in the Lake Erie basin, were supported. The results of this work supported reintroduction efforts that began in 2018.