Geology topics

Scott T. Koenigbauer

Publications and source records attributed to Scott T. Koenigbauer.

6 recordsLinked to original sources

USGS2026

Genetic bottleneck and panmixia following the collapse of a Great Lakes lake whitefish fishery

Lake whitefish Coregonus clupeaformis abundance has declined throughout most of the Laurentian Great Lakes in North America for two decades. Current management strategies in Lake Erie assume that there is a single stock of lake whitefish that spawns in the West Basin. There is documented lake whitefish spawning activity throughout the lake, leading to questions about locally adapted genetic stocks. Past research on lake whitefish genetic structure in Lake Erie has supported the single-stock hypothesis, but these studies used only neutral genetic markers or contained a limited number of samples that were collected during the spawning season when stocks would be spatially isolated. Using a GT-seq panel, we evaluate the genetic structure of lake whitefish collected from spawning shoals in the West, Central, and East basins of Lake Erie and compare these populations to lake whitefish from Lake Huron. We then investigate evidence of local adaptation and conduct demographic reconstruction using whole-genome sequencing. Our goals were to conclusively quantify intra-lake genetic structure in Lake Erie and determine whether spawning aggregations possess putatively adaptive variants that could be used for genetic stock identification at a sub-lake level. Our analysis supported the single-stock hypothesis in Lake Erie. However, Lake Erie stocks were distinct from neighboring Lake Huron. Whole-genome analysis did not identify any strong evidence of adaptive loci differentiating stocks. Inference of historic effective population size suggests that declines in lake whitefish populations may have caused a genetic bottleneck. Combined, these results indicate that lake whitefish in Lake Erie may have experienced an Allee Effect after population declines, resulting in a loss of population structure and genetic diversity as spawning shoals were recolonized from a common source.

Michigan, Ohio, Ontario↗

USGS2026

Adaptive capacity of freshwater organisms in North America: Current understanding and future applications

Freshwater species are increasingly threatened by climate change, yet our ability to assess their vulnerability remains incomplete. Typically, climate change vulnerability assessments (CCVAs) evaluate three components: exposure, sensitivity, and adaptive capacity. Adaptive capacity, defined as the ability of a species to adjust to changing conditions, provides critical insight into how species may persist under future scenarios and can strengthen conservation planning by highlighting opportunities for resilience and targeted management strategies. Trait-based approaches offer a promising path for managers to operationalize adaptive capacity by identifying measurable biological and ecological traits that influence climate change response strategies. However, these insights are rarely integrated into broader vulnerability frameworks that support conservation decision making. We build on previous research to synthesize current understanding of adaptive capacity for three freshwater taxa in North America: fishes, mussels, and crayfishes. Our objectives were to: (1) assess the relevance of adaptive capacity factors for fishes, mussels, and crayfishes; (2) identify key opportunities and gaps in linking trait-based information into adaptive capacity assessments; and (3) illustrate how incorporating adaptive capacity can enhance management decisions for freshwater species under climate change. We used an expert workshop, literature review, and case studies to identify relevant adaptive capacity factors, assess available information, and evaluate inclusion in management contexts. We found that all three taxa had sufficient information to inform adaptive capacity assessments. In addition to existing adaptive capacity factors, we identified Morphology as an important yet underutilized cross-cutting diagnostic category when information was limited. By explicitly linking trait-based approaches with adaptive capacity frameworks, we offer practical guidance for improving climate adaptation strategies and prioritizing management actions for freshwater biodiversity under accelerating global change.

Global Change Biology Communications↗

USGS2026

Lake Trout population dynamics on Six Fathom Bank and Yankee Reef in Lake Huron, 1992–2023

Objective Under the auspices of the Great Lakes Fishery Commission, the Lake Huron Committee and its technical committee initiated offshore stocking of Lake Trout Salvelinus namaycush beginning in 1985 as an additional step toward restoring a self-sustaining Lake Trout population to the lake, with stocking occurring first at Six Fathom Bank and then later at Yankee Reef. The goal of this study was to assess progress toward Lake Trout rehabilitation on Six Fathom Bank and Yankee Reef in Lake Huron through 2023. Methods We conducted annual (1992–2023) gill-net surveys in the spring–summer and the fall to assess juvenile and adult populations, as well as beam trawl surveys in the spring–summer to detect naturally reproduced age-0 Lake Trout. Result During 2000–2015, relative abundance of unclipped (wild) Lake Trout surged from levels of <2 fish · 305 m of gill net −1 · d −1 to levels exceeding 50 fish · 305 m of gill net −1 · d −1 on both Six Fathom Bank and on Yankee Reef, based on fall gill-net surveys, and has remained at a relatively high level through 2023. The proportion of wild fish in both the spring gill-net surveys and the fall gill-net surveys averaged well over 50% in the Six Fathom Bank–Yankee Reef (SFBYR) complex during 2014–2023. Sea Lamprey Petromyzon marinus wounding rate in the SFBYR complex decreased from 20 wounds/100 fish during 1994–2002 to just 7 wounds/100 fish during 2004–2023, based on the fall gill netting. Annual mortality rate estimates for SFBYR adult Lake Trout during the 2004–2023 period averaged 21%. Wild age-0 Lake Trout were captured in beam trawls in the SFBYR complex during the 1994–2022 period, providing further evidence that Lake Trout were actively spawning within this offshore reef complex. Conclusion Based on several metrics, the SFBYR Lake Trout population appeared to be self-sustaining. Lake Trout stocking, Sea Lamprey control, and restrictions on fishing for Lake Trout played important roles in the population recovery. The lessening of the negative effect of Alewives Alosa pseudoharengus on Lake Trout natural recruitment was likely a key factor in the restoration process.

Lake Huron, Six Fathom Bank, Yankee Reef↗

USGS2026

A post-restoration evaluation of fish spawning on Coreyon Reef in Saginaw Bay, Lake Huron

Habitat diversity is important to fisheries for promoting resiliency to interannual environmental variation. Historical land use change resulting in increased sedimentation has impaired fish rock reef habitats in Saginaw Bay, Lake Huron. Pursuant to the recovery of Saginaw Bay’s walleye population, and to benefit other species, came the decision to restore the offshore habitat Coreyon Reef, a 0.8 ha rock reef complex. Following a pre-restoration assessment in 2014–2016 and construction in 2019, we conducted a comprehensive assessment from fall 2020 to spring 2022 to document the restored habitat’s viability for fish spawning. This assessment featured two objectives: (1) to evaluate reproductive usage by lake whitefish and walleye, and (2) to evaluate their corresponding egg incubation environment. We sampled directly on Coreyon Reef and at nearby unrestored control sites for comparison, with gears standardized to the pre-restoration assessment. We confirmed spawning of lake whitefish and walleye on the restored reef less than 2 years post-construction. Relative to the pre-restoration assessment, peak egg deposition increased substantially for walleye and marginally for lake whitefish. However, concurrent reproductive utilization at nearby unrestored sites was consistent or even greater than directly on the restored site. Dissolved oxygen concentration was sufficient for embryo development, but invasive round goby were abundant and consumed eggs. The fish assemblage at our sampling sites was consistent before and after restoration. We predict eggs deposited on the restored site have improved survival relative to unrestored sites, as the new reef structure may protect incubating embryos from predation and sedimentation.

Michigan↗

USGS2024

Egg size scales negatively with system size in a periodic fish species

Optimal egg size theory implies that female organisms balance between fecundity and individual offspring investment according to their environment. Past interspecific studies suggest that fishes in large marine systems generally produce smaller eggs than those in small freshwater systems. We tested whether intraspecific egg size variation reflected a similar pattern by comparing egg size among yellow perch ( Perca flavescens ) populations inhabiting a range of system sizes. In 2018, 2019, and 2023, we collected yellow perch egg samples from 12 locations in systems ranging in surface area from 37 to 5,390,492 ha. First, we found that egg diameter significantly increased with maternal total length in five of eight individually tested populations. After accounting for these maternal effects, we found a significant interaction, where females inhabiting larger lakes, such as the main basins of Lakes Erie and Michigan, produced smaller eggs than those in smaller inland lakes, and the greatest differences were demonstrated among females of greater total length. This egg size variation in the largest females is consistent with interspecific egg size comparisons between marine and freshwater fishes. However, by examining a single species across vastly different environments, we were able to support theoretical expectations that maternal investment in offspring should vary with environmental conditions controlling early-life resource acquisition and competition.

Ecology and Evolution↗

USGS2022

Variation of cisco egg size among Laurentian Great Lakes populations

Many fish species display inter-population and inter-individual egg size variation. Intra-specific differences in egg size seemingly reflect both energetic experiences of individual spawning fish and long-term population responses to differing ecosystems. Optimal egg size theory implies that selection influences a population’s mean egg size in response to its early-life environment, given the well-established trade-off between egg size and fecundity. Currently, there is strong interest in rehabilitation of Laurentian Great Lakes cisco, Coregonus artedi, which is characterized by inter-population variation of morphological and behavioral traits. However, the extent of cisco egg size variation is under-described. In fall 2018 and 2019, we collected egg samples by stripping ripe females at seven total locations in four Great Lakes. We measured unfertilized egg diameters using imaging software and compared mean egg diameters among locations with and without including maternal total length as a covariate. Lake Michigan females produced the largest eggs overall but were excluded from analyses using the total length covariate because of their significantly larger body sizes. Maternal length had a positive effect on egg size, and when accounting for this effect, females in Lake Huron produced the largest eggs followed by Lake Ontario and Lake Superior. We also found that egg size varied among locations within Lake Superior. These findings aligned with observations of morphological and behavioral differences among populations and suggest that cisco phenotypic variation at a fine spatial scale extends to reproductive biology. Consideration of cisco reproductive traits, such as egg size, may inform restoration strategies, including supplemental stocking.

Journal of Great Lakes Research↗