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USGS2025

Dead giveaway: Rising mortality rates suggest effectiveness of Lake Erie grass carp (Ctenopharyngodon idella) response

Grass carp ( Ctenopharyngodon idella ) are large, invasive fish that threaten Lake Erie’s economy and ecosystem. Incidental catches of grass carp have occurred since the 1980s in Lake Erie, while multi-day removal events were carried out in 2014 and 2017. To mitigate ecosystem impacts, a large-scale, multi-agency response to remove as many grass carp as possible from the Lake Erie basin (“strike teams”) began in 2018 and has increased every year. To date, total annual removals of fish has been the primary measure of progress; however, total annual removals do not indicate how efforts are affecting the grass carp population. Population vital rates, such as mortality rate, can indicate population demographic changes and may provide an alternative approach to measure how removals have impacted the grass carp population. We estimated annual mortality rates using 553 grass carp, representing 82.9 % of all grass carp removed in the Lake Erie basin, using a hierarchical catch-curve model and catch-at-age data from 2014 to 2022. Annual average mortality rates were initially low (4.3 %) and increased between 2017 and 2022 with the highest mortality (13.6 %) observed in 2021. Positive correlations between mortality and the number of fish harvested per year suggest that removals may be driving increases in the grass carp mortality rate. This increase in mortality rate shows promise for controlling the spread of grass carp within the Lake Erie ecosystem. This research supports the needs of fishery managers to better understand grass carp population dynamics and the adaptive management framework identified in the Lake Erie Grass Carp Adaptive Response Strategy.

Lake Erie↗

USGS2009

Determining the efficacy of microsatellite DNA-based mixed-stock analysis of Lake Michigan’s lake whitefish commercial fishery

Management of commercially exploited fish should be conducted at the stock level. If a mixed stock fishery exists, a comprehensive mixed stock analysis is required for stock-based management. The lake whitefish Coregonus clupeaformis comprises the primary commercial fishery across the Great Lakes. Recent research resolved that six genetic stocks of lake whitefish were present in Lake Michigan, and long-term tagging data indicate that Lake Michigan's lake whitefish commercial fishery is a mixed stock fishery. The objective of this research was to determine the usefulness of microsatellite data for conducting comprehensive mixed stock analyses of the Lake Michigan lake whitefish commercial fishery. We used the individual assignment method as implemented in the program ONCOR to determine the accuracy level at which microsatellite data can reliably identify component populations or stocks. Self-assignment of lake whitefish to their population and stock of origin ranged from > 96% to 100%. Evaluation of genetic stock discreteness indicated a moderately high degree of correct assignment (average = 75%); simulations indicated supplementing baseline data by &sim; 50 to 100 individuals could increase accuracy by up to 4.5%. Simulated mixed stock commercial harvests with known stock composition showed a high degree of correct proportional assignment between observed and predicted harvest values. These data suggest that a comprehensive mixed stock analysis of Lake Michigan's lake whitefish commercial fishery is viable and would provide valuable information for improving management.

Michigan, Wisconsin↗

USGS2003

Boll weevil eradication: a model for sea lamprey control?

Invasions of boll weevil ( Anthonomus grandis ) into the United States and sea lamprey ( Petromyzon marinus ) into the Great Lakes were similar in many ways. Important species (American cotton, Gossypium hirsutum , and lake trout, Salvelinus namaycush ) and the industries they supported were negatively affected. Initial control efforts were unsuccessful until pesticides and application technologies were developed. For boll weevils, controls relying on pesticides evolved into an integrated program that included recommended farming practices and poisoned baits. However, the discovery of a boll weevil sex pheromone in 1964 allowed adoption of an ongoing program of eradication. Despite opposition over concept and cost, insecticides, pheromone traps, poisoned baits, and approved farming practices were used to eradicate boll weevils from Virginia, North Carolina, South Carolina, Georgia, Florida, and Alabama by 1999. Using the working back approach along the path of the original invasion, eradication was nearly completed by 2002 in Mississippi and eradication programs were underway in Arkansas, Tennessee, Oklahoma, Louisiana, and parts of Texas. Insecticide use for cotton production decreased 50 to 90%, and cotton yields and farm income increased an average of 78 kg/ha and $190 U.S./ha in areas where boll weevils were eradicated. For sea lampreys, integrated management uses lampricides, barriers to migration, trapping, and release of sterilized males. Although sea lamprey eradication is not currently feasible, recent research on larval and sex pheromones might provide the tools to make it possible. A successful eradication program for sea lampreys starting in Lake Superior and expanding to the lower Great Lakes would ultimately provide huge ecological and economic benefits by eliminating lampricide applications, removing barriers that block teleost fishes, and facilitating the recovery of lake trout. Should the opportunity arise, the concept of sea lamprey eradication should not be rejected out of hand. The successful boll weevil eradication program shows that sea lamprey eradication might be achievable.

Journal of Great Lakes Research↗

USGS2024

Larval coregonine density and diet composition along beaches of northern Lake Michigan

Recent oligotrophication in Lake Michigan has contributed to reduced biomass of spring zooplankton and a shift in the zooplankton assemblage toward more calanoid copepods. These changes have likely altered prey availability for first feeding native fish species that hatch in early spring, including coregonines. While spring zooplankton density and community composition are routinely monitored in offshore areas of Lake Michigan, descriptions of zooplankton in nearshore areas such as shallow beach environments and associated diet characteristics among larval coregonine species are limited. In this study, we describe the nearshore (<1 m depth, beach environment) zooplankton community in northeastern Lake Michigan during early spring 2015-2019 and compare the diets and diet selectivity of larval Lake Whitefish ( Coregonus clupeaformis ) and Cisco ( C. artedi ). Zooplankton density and composition varied among years, but calanoid copepods and copepod nauplii consistently dominated the zooplankton assemblage. Cisco and Lake Whitefish larvae were captured regularly, with Elk Rapids containing the highest proportion of Ciscoes each year. Calanoid and cyclopoid copepods were common in diets and estimated to have a positive selection. Although previous research has indicated high consumption of cyclopoid copepods by larval coregonines in Lake Michigan, our results provide new evidence that larval Lake Whitefish and Cisco of northeastern Lake Michigan will also consume and positively select for calanoid copepods when they are abundant. As such, should calanoid zooplankton continue to dominate the copepod community in Lake Michigan, larval coregonines appear capable of exploiting this abundant prey to improve their likelihood of survival to later life stages.

Michigan↗

USGS2026

Lake trout colonization of artificial reefs: Who’s interested, and how long does it take?

Restoring self-sustaining lake trout ( Salvelinus namaycush ) populations has been a major management objective for decades across the species’ native range. Reproduction has been observed but recruitment has been limited in many areas of the Laurentian Great Lakes. Reef restoration and construction have been proposed to increase recruitment, leading to the construction of experimental spawning reefs in Thunder Bay, Lake Huron, during 2009–2010. Research shortly after reef construction demonstrated lake trout quickly colonized those reefs during spawning. We revisited this site after 10 years to evaluate lake trout encounter rate and residency on each reef over time and relative to an adjacent historical, anthropogenic reef complex using fine-scale acoustic telemetry. Encounter frequency increased at most experimental reefs since reef construction, but changes in residency were dependent on lake trout origin (hatchery or wild). Hatchery-produced fish increased their residency on the experimental reefs and spent more time on these reefs collectively than the historical reef; wild lake trout continued to primarily use the historical reef. We expected younger wild fish to have increased residency on the experimental reefs assuming these individuals could have originated from those reefs and were therefore more likely to return to them; however, residency on experimental reefs remained low (< 50%) for these fish. These results indicate that reef construction provided additional habitat used by spawning lake trout, but wild individuals continue to prefer older habitat including naive wild fish born after reef construction.

Michigan↗

USGS1993

Evidence of spring spawning lake trout in Lake Superior

In 1992, the U. S. Fish and Wildlife Service began research on the life history, population dynamics, and stock delineation of siscowet lake trout Salvelinus namaycush siscowet in Lake Superior. Siscowet were captured with gill nets in 80-150 m of water on 23-26 April 1992 north of the Apostle Islands in western Lake Superior. Of 91 captured siscowets, one male had fully developed testes in nearly ripe condition and one female had eggs running from the vent. This observation represents the earliest dates that lake trout of any morphotype have been found in spawning or near-spawning condition.

Journal of Great Lakes Research↗

USGS2021

Validation of the model-predicted spawning area of grass carp Ctenopharyngodon idella in the Sandusky River

Spawning of grass carp, Ctenopharyngodon idella, in the Great Lakes basin was verified when eight fertilized eggs were collected in the Sandusky River, a tributary to Lake Erie, in 2015. Using a fluvial drift model (FluEgg) and simulation modeling, researchers predicted the fertilization location for those eggs was 3.8 ± 1 km (95% credible interval, CI) downstream of Ballville Dam. In June 2018, simultaneous collection of fertilized eggs and adults within the model-predicted spawning area provided the opportunity to verify the fertilization location. We used estimated developmental time (Dt) of eggs calculated from developmental stages, water temperature, and an equation that predicts Dt from cumulative thermal units experienced by developing eggs, in two analyses. First, we regressed Dt versus location of capture and solved that equation for developmental time of 0 hrs (Dt 0 ) to estimate fertilization location. Second, we used Dt in the Fluvial Drift Simulator (FluEgg) to simulate 23 scenarios representative of drift conditions throughout the spawning event using the model-predicted spawning area and the site of Ballville Dam as potential spawning locations. Regression analysis placed the mean fertilization location 3.36 km (95% CI 2.27, 4.24) downstream of the site of Ballville Dam, within the model-predicted spawning area. Drift models demonstrated the model-predicted spawning area was best supported. Histograms of fertilization times overlapped with capture times by boat electrofishing of diploid adult grass carp in the model-predicted spawning area. This suite of analyses confirms the model-predicted spawning area and validates the methodology used to locate it.

Ohio↗

USGS2021

A renewed philosophy about supplemental sea lamprey controls

Invasive sea lamprey ( Petromyzon marinus ) populations in the Laurentian Great Lakes have been reduced by up to 90% through the use of selective pesticides (lampricides) and physical sea lamprey barriers that block spawning migrations. Nevertheless, other control methods are needed to achieve integrated pest management objectives, delay biological resistance, and address societal pressure to reduce pesticide use and restore lotic connectivity through dam removals. Despite decades of research and scientific advances, new control tools that focus on controlling adult and juvenile life stages have been rare because tactics have not been cost-effective alternatives to lampricides and sea lamprey barriers. Here, we propose a renewed philosophy highlighting that new control methods need not be true alternatives to lampricides and sea lamprey barriers (i.e., have similar effectiveness), but instead can be useful as supplemental controls integrated with current methods, especially in places where current methods are less effective due to environmental or societal conditions. Current case studies pairing multiple supplemental controls together on two Lake Huron tributaries, the Black Mallard and Cheboygan Rivers, have shown promise in reducing sea lamprey reproductive success, the scope of lampricide treatments, and ultimately the number of juvenile sea lampreys produced. Additional case studies are planned and will be evaluated within a decade-long adaptive assessment plan.

Journal of Great Lakes Research↗

USGS1992

Lake trout spawning habitat in the Six Fathom Bank-Yankee Reef lake trout sanctuary, Lake Huron

Attempts to reestablish self-sustaining stocks of lake trout ( Salvelinus namaycush ) in the lower four Great Lakes, where the species was extinguished in the 1950s and 1960s, have been largely unsuccessful. To avoid many of the problems believed to be contributing to this failure, the fishery management community recently established several sanctuaries in the offshore waters of the Great Lakes where the development and protection of self-sustaining stocks of lake trout would be a primary management objective. One of these, the Six Fathom Bank-Yankee Reef sanctuary, was created in the south-central portion of Lake Huron. This sanctuary covers 168,000 ha and includes the shallower portions of the Six Fathom and Ipperwash scarps, which are major bathymetric features in the southern half of the lake. Historical accounts describe Six Fathom Bank as the most important lake trout spawning ground in the lake. Here we present the results of lake bed surveys conducted in the sanctuary with side-scan sonar, underwater videocamera systems, and a small research submarine. Our observations of the lake bed are consistent with what is known of the bedrock stratigraphy, glacial history, and karst geomorphology of the Lake Huron basin. Most of the loose rock we found seemed to be derived from local carbonate bedrock formations, although non-carbonate rock probably from Precambrian sources to the north was also present in some areas. Much of the bedrock and loose rock displayed karst solution features described for the Bruce Peninsula on the Ontario shoreline. Our surveys revealed substantial areas of lake bed at water depths of 20–36 m that resembled suitable spawning and fry production habitat for the shallow-water strains of lake trout that are the focus of the rehabilitation effort. Low mid-lake nutrient levels documented recently by others and the extremely high abundance of Mysis relicta (an important item in the diet of young lake trout) that we documented on Yankee Reef also contributed to our evaluation of the sanctuary as a site with high potential to support a self-sustaining population of lake trout.

Journal of Great Lakes Research↗

USGS2006

Storm-induced redistribution of deepwater sediments in Lake Ontario

High-resolution seismic reflection profiles, side-scan sonar profiles, and surface sediment analyses for grain size (% sand, silt & clay), total organic carbon content, and carbonate content along shore-perpendicular transects offshore of Olcott and Rochester in Lake Ontario were utilized to investigate cm-thick sands or absence of deep-water postglacial sediments in water depths of 130 to 165 m. These deepwater sands were observed as each transect approached and occupied the "sills," identified by earlier researchers, between the three deepest basins of the lake. The results reveal thin (0 to 5-cm) postglacial sediments, lake floor lineations, and sand-rich, organic, and carbonate poor sediments at the deepwater sites (> 130 m) along both transects at depths significantly below wave base, epilimnetic currents, and internal wave activity. These sediments are anomalous compared to shallower sediments observed in this study and deeper sediments reported by earlier research, and are interpreted to indicate winnowing and resuspension of the postglacial muds. We hypothesize that the mid-lake confluence of the two-gyre surface current system set up by strong storm events extends down to the lake floor when the lake is isothermal, and resuspends and winnows lake floor sediment at these locations. Furthermore, we believe that sedimentation is more likely to be influenced by bottom currents at these at these sites than in the deeper basins because these sites are located on bathymetric highs between deeper depositional basins of the lake, and the bathymetric constriction may intensify any bottom current activity at these sites.

Journal of Great Lakes Research↗

USGS2021

Advances in the use of lampricides to control sea lampreys in the Laurentian Great Lakes, 2000–2019

The periodic application of chemical lampricides that selectively kill larval sea lampreys ( Petromyzon marinus ) in their nursery habitats remains a primary component of the Great Lakes Fishery Commission’s (GLFC) Sea Lamprey Control Program in the Laurentian Great Lakes. Lampricides include 3-trifluoromethyl-4-nitrophenol (TFM) and niclosamide, the 2-aminoethanol salt of 2′, 5-dichloro-4′-nitrosalicylanilide, which may be used as an additive to TFM during stream treatments, or alone in a granular, bottom-release formulation to target sea lamprey larvae in deepwater environments where dilution would render TFM ineffective. During the early 1990s, the GLFC identified lampricide reduction targets in response to societal concerns with pesticide use, rising lampricide costs, and promising research into alternative controls. By 1999, the GLFC’s control agents, Fisheries and Oceans Canada (DFO) and the U.S. Fish and Wildlife Service (USFWS), had reduced TFM use by 36%. However, without effective alternative methods to compensate for increasing larval and juvenile production, sea lamprey abundance and lake trout ( Salvelinus namaycush ) marking rates rose throughout the Great Lakes. Beginning in the early 2000s, the GLFC and its control agents responded to burgeoning sea lamprey populations by implementing measures to advance the use of lampricides, which included: 1) assessing and controlling sea lamprey larvae that survived treatment; 2) enhancing treatment efficacy; 3) developing new technology to effectively treat larval populations that inhabit deepwater environments; 4) increasing operational capacity to treat more tributaries and lentic areas at shorter intervals; and, 5) conducting large-scale and targeted treatment strategies. When comparing lampricide use between the decades of 1990–1999 and 2010–2019, significant increases occurred in the mean number of treatments and amounts of TFM and niclosamide applied annually. Concurrent with these actions, researchers undertook studies to identify factors that erode lampricide treatment efficiency, elucidate physiological mode of action, and investigate lethal and sub-lethal impacts of lampricide exposure on aquatic organisms. By integrating new operational tactics and strategies with advances in science and technology, the GLFC, DFO, and USFWS, with support from the U.S. Geological Survey and the U.S. Army Corps of Engineers, have achieved unprecedented suppression of sea lampreys and reduction in lake trout marking in the Great Lakes. However, emerging challenges potentially threaten the future use of lampricides.

Journal of Great Lakes Research↗

USGS2024

Controls on in-stream nitrogen loss in western Lake Erie tributaries

Management efforts to reduce cyanobacterial harmful algal blooms (cHABs) in the Great Lakes have focused on decreasing tributary inputs of phosphorus (P). Recent research has indicated that reduction of both P and nitrogen (N) can lessen cHABs severity. Microbially mediated N cycling in streambed sediment may reduce N riverine loads, yet little is known about in-stream N processing rates in the Maumee River Basin, a major source of nutrients to Lake Erie. During summer of 2019 and 2021, we sampled streambed sediment to measure potential nitrification and denitrification rates using the acetylene block method at 78 sites throughout the Maumee River network. We used structural equation models to identify indirect and direct drivers of denitrification. Precipitation was greater in 2019, resulting in a 67 % increase in mean discharge, 41 % of farm fields to be fallow, and a 50 % reduction in fertilizer use. During summer field surveys, median stream-water nitrate concentrations were not different between 2019 and 2021. Median denitrification rates were 13.3 mg N/m2/h and 31.2 mg N/m2/h, respectively, indicating high potential to remove N. Nitrate concentrations and nitrification rates were strong direct drivers of denitrification, especially in 2019 when coupled nitrification–denitrification sustained denitrification. Nitrate concentrations varied with land use. Notably, nitrate concentrations increased with the area of fallow land, which may indicate the presence of a legacy N source. These findings indicate that promoting streambed denitrification could reduce N loads to Lake Erie, but legacy N currently stored in the system may mask N reduction efforts.

Indiana, Michigan, Ohio↗

USGS2013

Great Lakes rivermouth ecosystems: scientific synthesis and management implications

At the interface of the Great Lakes and their tributary rivers lies the rivermouths, a class of aquatic ecosystem where lake and lotic processes mix and distinct features emerge. Many rivermouths are the focal point of both human interaction with the Great Lakes and human impacts to the lakes; many cities, ports, and beaches are located in rivermouth ecosystems, and these human pressures often degrade key ecological functions that rivermouths provide. Despite their ecological uniqueness and apparent economic importance, there has been relatively little research on these ecosystems as a class relative to studies on upstream rivers or the open-lake waters. Here we present a synthesis of current knowledge about ecosystem structure and function in Great Lakes rivermouths based on studies in both Laurentian rivermouths, coastal wetlands, and marine estuarine systems. A conceptual model is presented that establishes a common semantic framework for discussing the characteristic spatial features of rivermouths. This model then is used to conceptually link ecosystem structure and function to ecological services provided by rivermouths. This synthesis helps identify the critical gaps in understanding rivermouth ecology. Specifically, additional information is needed on how rivermouths collectively influence the Great Lakes ecosystem, how human alterations influence rivermouth functions, and how ecosystem services provided by rivermouths can be managed to benefit the surrounding socioeconomic networks.

Great Lakes↗

USGS1995

Long-term simulation of PCB export from the Fox River to Green Bay

A mass balance approach was used to model long-term PCB transport in the Fox River (Wisconsin) from Lake Winnebago to Green Bay. The objectives of this research were to (1) extend the modeling approach for the Fox River to permit realistic long-term simulations of contaminant transport and fate, (2) forecast long-term PCB export from the Fox River to Green Bay, and (3) develop a rational approach for evaluating sediment remediation alternatives. Field data collected as part of the Green Bay Mass Balance Study during 1988-90 and additional data collected by the Wisconsin Department of Natural Resources and the U.S. Geological Survey during 1992-93 were used to develop the model. A 10-year hindcast was conducted to confirm long-term model predictions. A series of 25-year forecasts were then conducted to explore the potential effects of hydrograph structure, extremely high flows, and sediment remediation on long-term PCB export from the Fox River to Green Bay. PCB export from the Fox River is forecast to decrease, and most (75%) of the PCB reservoir in Fox River sediment is expected to remain in place. However, extremely high flows in future years are forecast to cause significant PCB resuspension and export. Model forecasts suggest that long-term PCB export is only mildly sensitive to changes in hydrograph structure. Sediment remediation is forecast to reduce but not eliminate PCB export.

Wisconsin↗

USGS2010

Genetic diversity of lake whitefish in lakes Michigan and Huron: sampling, standardization, and research priorities

We combined data from two laboratories to increase the spatial extent of a genetic data set for lake whitefish Coregonus clupeaformis from lakes Huron and Michigan and saw that genetic diversity was greatest between lakes, but that there was also structuring within lakes. Low diversity among stocks may be a reflection of relatively recent colonization of the Great Lakes, but other factors such as recent population fluctuation and localized stresses such as lamprey predation or heavy exploitation may also have a homogenizing effect. Our data suggested that there is asymmetrical movement of lake whitefish between Lake Huron and Lake Michigan; more genotypes associated with Lake Michigan were observed in Lake Huron. Adding additional collections to the calibrated set will allow further examination of diversity in other Great Lakes, answer questions regarding movement among lakes, and estimate contributions of stocks to commercial yields. As the picture of genetic diversity and population structure of lake whitefish in the Great Lakes region emerges, we need to develop methods to combine data types to help identify important areas for biodiversity and thus conservation. Adding genetic data to existing models will increase the precision of predictions of the impacts of new stresses and changes in existing pressures on an ecologically and commercially important species.

Journal of Great Lakes Research↗

USGS2025

First evidence of lake trout Salvelinus namaycush spawning aggregation in Ohio waters of Lake Erie following reintroduction

Lake trout Salvelinus namaycush, an important apex predator native to Lake Erie, were extirpated by 1965 due to overexploitation, introduction of invasive species, and habitat degradation. Cooperative lake-wide lake trout stocking has been ongoing since 1982, with stocking strategies adapting as research identifies the age at stocking, locations, and strains that optimize the recovery of lake trout. Despite these efforts, limited evidence of lake trout spawning has been documented in the western half of Lake Erie. On 20 November 2023, n = 99 lake trout were captured via gillnet in Fairport Harbor, Ohio. This sample consisted largely of ripe adults (79.4 %) that were likely spawning within the vicinity of Fairport Harbor. Coded wire tags recovered from these fish revealed that most of these lake trout had been stocked in Fairport Harbor (99.0 %), were of the Seneca Lake strain (92.7 %), and were stocked as age-1 fish (93.7 %). This study demonstrates the survival of fish from Fairport Harbor stockings, suggests evidence of stocking-site fidelity, supports the stocking of the Seneca Lake strain, and suggests that stocking age-1 lake trout may have advantages over younger life stages. Most importantly, this study demonstrates that lake trout are likely spawning near Fairport Harbor. These findings can guide future studies that identify lake trout spawning habitat, recruitment bottlenecks, movement, and stocking-site fidelity in Lake Erie and can be used to inform future recovery strategies.

Ohio↗

USGS2014

Assessing and addressing the re-eutrophication of Lake Erie: central basin hypoxia

Relieving phosphorus loading is a key management tool for controlling Lake Erie eutrophication. During the 1960s and 1970s, increased phosphorus inputs degraded water quality and reduced central basin hypolimnetic oxygen levels which, in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macroinvertebrate prey species for fishes. In response to load reductions initiated in 1972, Lake Erie responded quickly with reduced water-column phosphorus concentrations, phytoplankton biomass, and bottom-water hypoxia (dissolved oxygen < 2 mg/l). Since the mid-1990s, cyanobacteria blooms increased and extensive hypoxia and benthic algae returned. We synthesize recent research leading to guidance for addressing this re-eutrophication, with particular emphasis on central basin hypoxia. We document recent trends in key eutrophication-related properties, assess their likely ecological impacts, and develop load response curves to guide revised hypoxia-based loading targets called for in the 2012 Great Lakes Water Quality Agreement. Reducing central basin hypoxic area to levels observed in the early 1990s (ca. 2000 km 2 ) requires cutting total phosphorus loads by 46% from the 2003–2011 average or reducing dissolved reactive phosphorus loads by 78% from the 2005–2011 average. Reductions to these levels are also protective of fish habitat. We provide potential approaches for achieving those new loading targets, and suggest that recent load reduction recommendations focused on western basin cyanobacteria blooms may not be sufficient to reduce central basin hypoxia to 2000 km 2 .

Great Lakes;Lake Erie↗

USGS2026

Seasonal space use and spatial overlap of lake sturgeon populations inhabiting Lake St. Clair

Multi-jurisdictional management of adult lake sturgeon ( Acipenser fulvescens ) requires characterizing seasonal dynamics of their spatial distributions. Despite decades of research into lake sturgeon movement ecology, system-wide spatiotemporal behavior remains poorly understood in large lakes, particularly those with metapopulations differentiated by spawning river or migratory phenotypes. This study described seasonal space use of lake sturgeon populations in Lake St. Clair, a large, shallow lake divided by the international border between the State of Michigan and Province of Ontario. Our objectives were to characterize spatial behavior of adult lake sturgeon by: 1) assessing U.S. and Canadian residency patterns and cross-boundary movements with relevance for interjurisdictional management; 2) identifying seasonally important habitats where sturgeon regularly congregate; and 3) comparing seasonal spatial distributions and behavioral metrics among spawning populations and migratory phenotypes. A large sample of acoustic-tagged adult lake sturgeon of known spawning river and migratory phenotype were detected with a high-density (∼5 km spacing), lake-wide receiver grid. Home ranges estimated via Brownian Bridge movement models indicated near lake-wide use and seasonal variation in areas occupied, total area used, and residency within and across jurisdictional boundaries. Lake sturgeon seasonally congregated in several distinct areas but were not completely segregated by spawning populations or migratory phenotypes. Instead, space use by the two spawning populations followed a seasonally dependent, north-south gradient associated with the location of spawning inlet and outlet rivers. These results suggest that managers consider internationally coordinated approaches, especially for population assessment, that account for seasonal habitat shifts and cross-population and phenotypic mixing.

Michigan, Ontario↗