Date of Award
8-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Wildlife and Fisheries Biology
Committee Chair/Advisor
Dr. Luke Bower
Committee Member
Dr. Troy Farmer
Committee Member
Dr. Kyle Barrett
Abstract
A majority of the world's rivers are impounded, severely reducing connectivity between stream reaches, altering natural environmental gradients, and altering biotic communities. Consequently, dams significantly impact riverine ecosystems and overall freshwater biodiversity, including fishes. While numerous studies have examined the effects of dams on adult fish, a critical knowledge gap exists regarding the effect of dams on vulnerable early life stages of fishes. The early life stages of fishes experience high mortality rates, with year-class strength and recruitment ultimately influencing adult population dynamics. Migratory fish species in particular are negatively influenced by dams, as they restrict access to and degrade historic spawning grounds. American Shad, Alosa sapidissima, is a large, anadromous Clupeid native to coastal rivers along the East Coast of North America. American Shad are an integral component of the ecosystems they are a part of, and population declines often result in ecological destabilization. Historically, American Shad migrated over 600 km from the Atlantic Ocean through the Santee-Cooper River Basin to the Broad River in South Carolina. Due to extensive damming, American Shad access to the Broad River was halted until the installation of a fishway at the Columbia Diversion Dam. American Shad have been documented passing through the Columbia fishway; however, it remains unknown whether they spawn in the Broad River reach between Columbia Dam and Parr Shoals Dam. To examine the influence of dams in the lower Broad River on larval fish assemblages and American Shad, we conducted biweekly ichthyoplankton sampling using bongo nets, benthic sleds, and light traps from March through July in 2024 and 2025. The first objective of this study was to investigate if American Shad spawning occurred in the Broad River. Despite collecting over 15,000 larval fish, no American Shad eggs or larvae were detected. We suggest that the lack of evidence of spawning is likely due to a combination of a low density of mature adults successfully migrating into the Broad River, the Allee effect, and unfavorable habitat conditions created by dams for both American Shad spawning and egg and larvae survival. To further investigate the influence of dams on early life stages of fishes, our second objective explored the spatial and temporal patterns of larval fish assemblage structure across the highly regulated Broad River and identified environmental variables associated with the observed patterns. The temporal patterns of larval fish occurrence and density were similar between years, with Catostomidae and Percidae reaching peak density earlier in the season compared to Leuciscidae, Centrarchidae, and Ictaluridae. The later seasonal peak in Leuciscidae, Centrarchidae, and Ictaluridae suggests they are associated with the stable river conditions characteristic of summer months. We suggest that the spatial patterns of larval fish assemblages were influenced by the presence of the largest dam on the Broad River, with lotic conditions present above dams contributing to disrupted larval drift and transport. Flow and temperature influenced the presence and density of two of the most abundant larval taxa collected, suggesting these two components were crucial in shaping both assemblage and family level responses. This study provides valuable insights into periods of heightened vulnerability for larval fish, particularly in response to environmental disturbances such as dam releases. These findings can inform future management strategies and contribute to the conservation of at-risk fish populations and species of concern.
Recommended Citation
Niles, Madison B., "Patterns of Larval Fish Assemblage Structure Across a Regulated River" (2026). All Theses. 4850.
https://open.clemson.edu/all_theses/4850