Author ORCID Identifier

https://orcid.org/0009-0001-9194-639X

Semester

Summer

Date of Graduation

2026

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Division of Forestry and Natural Resources

Committee Chair

Kyle Hartman

Committee Member

David Thorne

Committee Member

John Sweka

Committee Member

Caroline Arantes

Committee Member

Brent Murry

Abstract

The persistence of fish populations depends on the repeated production and survival of new year classes, also referred to as recruitment. Recruitment is broadly defined as the number of individuals in a fish population or stock that survive to a specific stage. However, the broader recruitment process reflects the cumulative outcome of many earlier life stages, including egg survival, fry emergence, and survival through the recruitment period. As a result, recruitment can vary substantially among years and populations, producing strong or weak year classes that influence population abundance and persistence. Understanding why recruitment varies is therefore central to fisheries ecology and is especially important for freshwater fishes facing climate change and other anthropogenic stressors.

Eastern Brook Trout (Salvelinus fontinalis) are a native salmonid found throughout much of the eastern United States. Central Appalachian headwater streams represent an important stronghold for wild Brook Trout within the region. However, populations within the Appalachian region have declined due to legacy impacts from mining and widespread timber harvest, and they remain vulnerable to continued stressors such as climate change. The long-term persistence of these populations depends on successful recruitment. Therefore, understanding the factors that influence recruitment in this system may be critical for effectively managing Brook Trout populations into the future.

The overall goal of this dissertation was to identify how population dynamics and environmental conditions shape Brook Trout recruitment in Central Appalachian streams. In this dissertation, recruitment was defined as the number of age-0 Brook Trout entering the population each year following emergence and surviving to the fall season (October-December). Building on more than two decades of long-term habitat and fish monitoring in West Virginia streams, I evaluated the influence of three factors on Brook Trout recruitment: stream temperatures, spawning sediment, and fecundity.

In my first chapter, I reviewed the ecological importance of recruitment and established the conceptual framework for evaluating Brook Trout recruitment in headwater streams. I also described the long-term Brook Trout monitoring project in West Virginia. Previous research from this project has improved understanding of Brook Trout diet, growth, condition, habitat use, density dependence, stock-recruitment relationships, and responses to disturbance. However, the environmental and maternal factors driving recruitment variability remain less understood.

In my second chapter, I characterized stream thermal regimes and evaluated how air-water temperature relationships, groundwater influence, and seasonal thermal conditions were related to Brook Trout population dynamics. I placed three water temperature sensors and two air temperature sensors at each of the 25 study streams, for a total of 125 loggers, and collected temperature data from 2021 to 2024. Thermal regimes were quantified using air-water linear regressions and sine-wave models to estimate slope, intercept, R², phase lag, amplitude ratio, and mean ratio. Results indicated thermal heterogeneity among streams. Most streams demonstrated moderate groundwater influence, while a subset showed evidence of strong groundwater influence. Mean summer water temperature influenced all Brook Trout population responses, thermal stability was an important predictor of abundance, and degree days greater than 20°C were negatively associated with adult condition and abundance. These findings suggest that groundwater and stream thermal regimes structure Brook Trout populations across life stages.

In my third chapter, I examined long-term patterns in spawning sediment composition and evaluated how spawning substrate influenced Brook Trout young-of-the-year abundance. Using a 17-year dataset from 25 headwater streams, I evaluated relationships among fine sediment, coarse sediment, and Brook Trout young-of-the-year abundance, as well as the influence of climate on YOY-sediment relationships. Clay-sized sediments < 0.06 mm had the strongest negative effects on young-of-the-year abundance when they comprised approximately 2% of total substrate composition. Generalized additive model results indicated that the effects of clay sediment depended on the availability of coarse sediment > 32 mm and on winter and summer climate conditions. These findings suggest that sediment effects on Brook Trout recruitment are not driven by fine sediment alone, but by coarse sediment composition and interactions among sediment and climate.

In my fourth chapter, I evaluated maternal and environmental drivers of fecundity across a subset of long-term headwater streams. Brook Trout were collected during the 2022 and 2023 spawning seasons, and fecundity was evaluated using total egg number, eggs per gram of female body weight, total gonad dry mass, and individual egg dry mass. I used generalized linear models to identify how maternal traits, thermal characteristics, and spawning substrate influenced reproductive allocation. Female total length was the strongest predictor of fecundity across streams. However, larger females produced fewer eggs per gram of body mass, indicating that egg production did not increase proportionally with body size. Additionally, females with greater total egg numbers tended to produce smaller individual eggs, suggesting a potential egg size-number tradeoff. This tradeoff was associated with summer thermal sensitivity and spawning substrate composition.

Collectively, this dissertation highlights the importance of evaluating recruitment as a multi-stage process rather than a single population response. By linking long-term monitoring with stream temperature, sediment composition, and reproductive ecology, this research provided insight into why Brook Trout recruitment varies among streams and identified mechanisms that may influence population persistence under future climate and land-use change. This work can help guide conservation strategies that protect cold-water habitat, maintain suitable spawning substrate, and support the reproduction of wild Brook Trout populations in the region.

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