LSU Master's Thesis: The Life History and Population Dynamics of Southern Flounder

Thesis Overview

Kenneth A. Erickson's thesis titled "The Life History and Population Dynamics of Southern Flounder" was submitted to Louisiana State University in December 2020 as a requirement for a Master of Science degree in Oceanography and Coastal Sciences.

Acknowledgements

The author expresses gratitude towards his advisor Dr. Steve Midway, committee members, Louisiana Department of Wildlife and Fisheries staff, colleagues, and family, emphasizing that their support was crucial for the completion of the thesis.

Abstract

This research examines Southern Flounder (Paralichthys lethostigma), a flatfish species in the Southeastern US, analyzing population dynamics due to reported declines in spawning stock biomass and recruitment. The study collected data on age, growth, and maturity of 327 Southern Flounder from Louisiana and historical data of 14,184 specimens. Results using a von Bertalanffy growth equation indicated local variations in growth and estimates of age and size at maturity. Generalized additive models identified a significant decline in relative abundance in 19 out of 31 estuaries, with environmental factors like temperature impacting population dynamics.

Chapter Highlights

Chapter 1: Life History Update

Southern Flounder inhabit estuaries and coastal waters, exhibiting sexual dimorphism with females growing larger than males. The thesis highlights concerns of overfishing and the need for updated biological data to inform management decisions. It defines life history as the suite of adaptations that affect survival and reproduction, emphasizing the importance of determining traits such as growth and maturity to manage fish stocks effectively.

Chapter 2: Climate Change and Population Dynamics

Investigates the implications of climate change on Southern Flounder populations, using ecological models to address the observed trends in age-0 fish across various coastal regions. It discusses potential biological responses to changing temperatures and their effects on reproductive success.

Methods

The study includes an extensive sampling methodology from various Louisiana estuaries, utilizing both fishery-independent and dependent data collections. Analyses employed Bayesian hierarchical frameworks to estimate growth parameters, maturity assessments through gonadosomatic indices, and a meta-analysis for historical comparisons of life history traits.

Results and Discussions

Findings detail specific parameters regarding growth rates and maturity: the estimated asymptotic lengths and growth coefficients reflect significant local variations. Logistic regression identified L50 (length for 50% maturity) as 353 mm, while maturity age estimates indicate that most females reach maturity between ages one and two. The results contribute to understanding population dynamics, aiding in future fishery management strategies and assessments.