Term of Award

Summer 2025

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Copyright Statement / License for Reuse

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

Department

Department of Biology

Committee Chair

Risa Cohen

Committee Member 1

James Roberts

Committee Member 2

Stephen Vives

Committee Member 3

Checo Colon Gaud

Abstract

The ecological complexity of southeastern Coastal Plain rivers is reflected in the diversity of fish communities they support, yet the processes structuring early life dynamics remain poorly understood. This thesis explores the influence of environmental gradients on larval fish assemblage composition and American Shad (Alosa sapidissima) spawning phenology across two Georgia Coastal Plain river systems.

In the unregulated Ogeechee River, I investigated spatial and temporal variation in larval fish communities by comparing mainstem and tributary habitats to understand the role of tributaries in watershed-wide larval production. Larvae were collected biweekly from May to September 2024 at eight paired mainstem-tributary sites using light traps and identified to family. Assemblages differed significantly between stream types and months, with greater temporal variability in mainstem. Atherinopsidae and Leuciscidae were more abundant in mainstems, while Centrarchidae dominated tributaries—a pattern likely driven by contrasting life-history traits. Tributaries also exhibited later and higher abundance peaks than the mainstem, suggesting a portfolio effect where asynchronous spawning may buffer recruitment variability. Canonical correspondence analysis identified drainage area, conductivity, dissolved oxygen, and pH as key correlates of assemblage variation, although 70% of variation was unexplained and likely tied to unmeasured landscape or biotic factors. These findings highlight the distinct and complementary role of tributaries in supporting larval production.

In the regulated Altamaha River, I examined the timing, magnitude, and environmental associations of American Shad spawning in its two largest dammed tributaries, the Oconee and Ocmulgee, where hydroelectric dams restrict upstream access and may alter downstream habitat. I indexed egg and larval CPUE from biweekly ichthyoplankton tows (January–June 2023–2024) across five sites. Densities were highest in the mainstem, followed by the Oconee, then Ocmulgee. Daily egg production exceeded 1.1 million in the mainstem and reached 480,000 in the Oconee. Spawning occurred at 13–18°C and 100–300 m³/s discharges, but generalized additive mixed models indicated day-of-year was a stronger predictor of CPUE, suggesting a photoperiod-linked cue. This study provides the first system-wide spawning comparison in the basin and shows that tributaries, particularly the Oconee, augment total output and extend the spawning season.

OCLC Number

1535337351

Research Data and Supplementary Material

No

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