Decadal changes in stream fish communities and contemporary ecological drivers of species occupancy in two Appalachian U.S. National Parks: A Thesis in Wildlife and Fisheries Science

Stum, Morgan

Freshwater streams and rivers are among the most biodiverse habitats, yet they are also the most threatened by human activities and climate change. Although the conservation of freshwater fish biodiversity remains a challenge, protected areas represent important landscapes that may serve as a refuge from some environmental stressors. In the eastern United States, the National Park Service (NPS) manages several park units with high-value freshwater resources within its Eastern Rivers and Mountains Network (ERMN). The ERMN extends across four Appalachian states and includes two larger river parks - Delaware Water Gap National Recreation Area (DEWA) and New River Gorge National Park & Preserve (NERI) - that contain diverse aquatic landscapes within their borders. The objectives of this study were to assess decadal changes (2013-2014 vs. 2022-2023) in fish community occupancy and to better understand contemporary ecological drivers of species occupancy within these parks. Using a multispecies occupancy modeling framework, we found that community composition and occurrence probabilities for species in both parks have remained relatively constant over time, with current estimates of occupancy and detection ranging from 0.07 [90% CI = 0.02, 0.14] for Variegate Darter (Etheostoma variatum) to 0.73 [90% CI = 0.59, 0.85] for Blacknose Dace (Rhinichthys atratulus), and 0.26 [90% CI = 0.05, 0.61] for Green Sunfish (Lepomis cyanellus) to 0.99 [90% CI = 0.95, 1.00] for Blacknose Dace, respectively. However, changes in occupancy at DEWA were more prominent than at NERI, with Yellow Perch (Perca flavescens) and Pumpkinseed (Lepomis gibbosus) having posterior mean decadal differences in occupancy probabilities ranging from -0.17 [90% CI = -0.35, -0.01] to -0.20 [80% CI = -0.35, -0.05], respectively. Conversely, one species of conservation interest at DEWA, the American Eel (Anguilla rostrata), had a high posterior probability (>80%) of increasing in occupancy by at least 1%, with a posterior mean decadal difference of +0.12 [80% CI = -0.03, 0.28]. Landscape- and site-scale habitat variables were related to variation in community structure, but effects varied in significance, magnitude, and direction across species and parks. For example, reach slope, distance to a major river confluence, and stream temperature were significant predictors of species occupancy in both parks, and watershed size and developed land use were important at DEWA, whereas average stream depth was important at NERI. Over the past decade, we found relatively stable patterns in occupancy for 44 species of stream fish across two ecologically diverse landscapes. In addition to monitoring the status and trends of important U.S. National Park resources, quantifying changes and drivers of stream fish communities within these protected areas can serve as important reference points for understanding spatiotemporal differences observed in fish assemblages in non-protected areas with higher levels of environmental impacts.

Decadal changes in stream fish communities and contemporary ecological drivers of species occupancy in two Appalachian U.S. National Parks: A Thesis in Wildlife and Fisheries Science

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