Effects of abiotic and biotic factors on population dynamics of brook trout (<i>Salvelinus fontinalis</i>) within Shenandoah National Park, Virginia

Abstract

Aquatic ecosystems are facing numerous threats that are products of anthropogenic activity, including habitat destruction and climate change. Monitoring aquatic ecosystems is important so that we can better understand and remedy the consequences of these threats. Native fish species found within these aquatic ecosystems are often used as quality indicators to determine overall ecosystem health. Brook trout (Salvelinus fontinalis) are cold-water specialists that have a large distribution across the eastern United States and are highly sensitive to habitat disturbance, which makes them important quality indicators for cold-water ecosystems. Brook trout have also faced significant declines throughout their range in recent decades. In this work, I explore the relationships between environmental correlates (e.g., streamflow, temperature) and brook trout abundance and recruitment in Shenandoah National Park, VA for the first time. In Chapter 1, I use generalized linear mixed-models and long-term fish collections data from the National Park Service (1996-2021) to investigate the relationship between brook trout abundance and environmental variables in four categories: (1) Natural (time-invariant) variables, (2) Hydrological/Temperature variables, (3) Anthropogenically-influenced variables, and (4) Biotic variables. I found that all variable categories were important in predicting variation in brook trout abundance across space and over time. Biotic variables had high importance compared to other categories. For example, American eel (Anguilla rostrata) abundance consistently had a negative relationship with brook trout abundance. In Chapter 2, I use linear models and long-term fish survey data from the U.S. Forest Service (1994-2022) to investigate the relationship between temperature, streamflow, and stock size during important life-stages (i.e., (1) Spawning, (2) Incubation, (3) Yolk-sac, (4) Juvenile). In this chapter, I focused on brook trout recruitment in two Appalachian streams, which had contrasting results, limiting the generality and applicability of this work outside of the study streams. I found that streamflow variables were most important in predicting recruitment, but stock size was a poor predictor in Paine Run. For Staunton River, temperature variables and stock size were most important for predicting recruitment. The stock-recruitment relationship for Staunton River followed a hump-shaped curve where recruitment increased with stock size up to a threshold before declining. This work was the first to characterize the stock-recruitment relationship in Staunton River. These findings will be useful to entities involved with managing and conserving brook trout populations, like the National Park Service and U.S. Forest Service, and help them better understand the effects that environmental factors have on brook trout populations.