Growth, Mortality, and Movement of Endemic Bartram's Bass and Invasive Alabama Bass in Upper Savannah River Basin Tributaries

Author

Tyler Zumwalt, Clemson UniversityFollow

Date of Award

5-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Forestry and Environmental Conservation

Committee Chair/Advisor

Dr. Brandon Peoples

Committee Member

Dr. Troy Farmer

Committee Member

Dr. Mark Scott

Abstract

Bartram’s Bass are an endemic to the Upper Savannah River basin in North Carolina, South Carolina, and Georgia. Bartram’s Bass are facing many risks, primary among them being hybridization with nonnative Alabama Bass. More recently, nonnative Alabama Bass and their hybrid congeners have been observed moving from reservoirs into tributaries where the remaining Bartram’s Bass populations exist. Thus, for Chapter 1 we sought to better understand the threat of nonnative gene spreading in tributary systems. To do this, we 1) quantified the movement of pure Alabama Bass, Bartram’s Bass, and their hybrids, 2) assessed correlations between movement and abiotic variables, and 3) quantified spreading potential of nonnative Alabama Bass genes into tributaries. We used radio telemetry and hook-and-line sampling in 2021 and 2022 to track the movement and river positions of all three species. Nonnative Alabama Bass and hybrids were located much further downstream than native Bartram’s Bass, but showed much higher movement rates than Bartram’s Bass. Hybrids showed increased movement rates at lower temperatures but shifted upstream in response to increased temperature. Alabama Bass showed the highest movement rate, but shifted downstream in response to increased temperature. Bartram’s Bass showed the lowest movement rate, but made larger upstream movements in response to increased temperature. Thus, temperature played a critical role on movement and nonnative gene spreading. Additionally, the mouth of Eastatoee Creek was used by nonnative bass as a movement corridor between Lake Keowee and upper sections of the stream, showing increased movement probabilities in the mouth at higher reservoir depths. Thus, high reservoir depths near the mouth also promoted upstream movement of nonnative bass. Inversely, nonnative bass rarely moved into the gorge section of Eastatoee Creek, regardless of reservoir depth. However, high probabilities of non-movement in the gorge section suggested that nonnative bass were much more likely to reside in the gorge once they did move there. Thus, nonnative gene spreading was much more gradual in the gorge, but still occurring. Therefore, our results provide critical insight on how nonnative gene spreading is section-specific, and the rate of spreading varies with environmental conditions. Furthermore, our results suggest that temperature and reservoir depth largely affect gene dispersal, and such factors should be considered for management of both nonnative bass and Bartram’s Bass. Barriers in Eastatoee Creek also proved to be critical in maintaining genetic integrity for Bartram’s Bass, and also should be considered in future management.

Beyond movement ecology and spreading of nonnative bass genes, very little information is known about the growth and mortality of Bartram’s Bass. Nonetheless, Bartram’s Bass can currently be harvested in Georgia and South Carolina. With this in mind, Chapter 2 sought to determine the different rates of mortality experienced by Bartram’s Bass. Specifically, our objectives were to 1) quantify the instantaneous and discrete total mortality rate of Bartram’s Bass, 2) quantify size-at-age and growth rates for Bartram’s Bass, and 3) quantify the natural mortality and fishing mortality for Bartram’s Bass. To do so, we conducted a mark-recapture survey using hook-and-line sampling in 2021 and 2022 to capture Bartram’s Bass. However, we did not want to sacrifice these individuals for ageing, and instead used aged otoliths of Bartram’s Bass collected in 2017. With the aged individuals, we created an age-length key to assign ages to Eastatoee Creek Bartram’s Bass. We then fit von Bertalanffy growth curves to our age data to estimate growth. We also created a catch curve to estimate total mortality. Then using empirical estimators, we used a weighted average approach to estimate natural mortality and fishing mortality. Growth of Bartram’s Bass was very slow and constant throughout their life span. Additionally, total discrete mortality was relatively low, most of the mortality was natural mortality, and essentially little to no fishing mortality occurred. Minimal fishing mortality suggests that current fishing regulations are not affecting Bartram’s Bass populations in Eastatoee Creek. While minimal fishing mortality occurred, slow growing species are particularly vulnerable to exploitation, and such vulnerability should be considered in management and harvest regulations of Bartram’s Bass. Furthermore, little is known about how Bartram’s Bass populations respond to the mortality rates we observed. Thus, current regulations, as well as future efforts, should further consider this lack of understanding of how various mortality rates may affect Bartram’s Bass population abundance.

Recommended Citation

Zumwalt, Tyler, "Growth, Mortality, and Movement of Endemic Bartram's Bass and Invasive Alabama Bass in Upper Savannah River Basin Tributaries" (2023). All Theses. 4024.
https://open.clemson.edu/all_theses/4024

Author ORCID Identifier

0009-0008-6351-5614