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Abstract
Southern Flounder, Paralichthys lethostigma, are a coastal, estuarine-dependent flatfish species that inhabits the Southeastern US Atlantic Ocean and Gulf of Mexico. Throughout their range, Southern Flounder are exploited by both commercial and recreational fisheries. Recently, numerous sources have expressed concerns about Southern Flounder populations, with stock assessments indicating declines in spawning stock biomass and recruitment. To estimate life history traits needed for informed management, such as age, growth, and maturity, I collected 327 Southern Flounder from Louisiana and obtained 14,184 historical records from the Louisiana Department of Wildlife and Fisheries. Using a von Bertalanffy growth equation in a Bayesian hierarchical framework, I found local-scale differences in growth between estuaries and parameter differences from previous studies. Logistic regression estimated an L50 of 353mm, which is over 100mm larger than a previous estimate for Louisiana. Finally, I evaluated the variability in life history estimates from historical studies throughout the range.
I then used generalized additive models to quantify age-0 relative abundance trends in Texas, Louisiana, Alabama, Florida, South Carolina, and North Carolina. Of 31 estuaries modeled, a significant decline was found to be occurring in 19, indicating a range-wide population decline. Environmental covariates including growing degree days (GDD), wind, and winter severity were tested to explain the trends. GDD and winter severity appeared to have localized effects on Southern Flounder abundance, while wind was a significant explanatory factor in all 21 estuaries with available wind data. Additionally, I show that Southern Flounder are being exposed to warmer temperatures as they develop, which could cause sex ratios to masculinize. This research addresses fishery management needs and seeks to explain the population dynamics of Southern Flounder in the Gulf of Mexico and US Southeastern Atlantic.
