Date of Award

August 2020

Document Type


Degree Name

Master of Science (MS)


Forestry and Environmental Conservation

Committee Member

Troy Famer

Committee Member

Brandon Peoples

Committee Member

Dana Sackett


Southern Flounder (Paralichthys lethostigma) is an economically important species along the northern Gulf of Mexico. Over the last several years, Southern Flounder populations have experienced drastic declines. Analysis of natural tags, such as otolith chemistry and stable isotopes, can be used to examine habitat-specific contributions to commercial and recreational fisheries. A better understanding of habitat-use patterns and food web dynamics of this species could provide insight into habitat conservation and harvest regulations to promote sustainability of this species.

Water and otolith chemistry were used to quantify the proportional contributions of various residency patterns to the commercial and recreational harvest of historic (2004 – 2007) and recent (2018 – 2019) Southern Flounder populations. Otolith strontium to calcium (Sr:Ca) values from laser ablation inductively coupled plasma mass spectrometry were used to quantify age-specific and lifetime residency patterns for Southern Flounder across Alabama’s seasonal salinity gradient. Flounder were classified into one of three contingent types: freshwater, estuarine, or transient. Our results suggest that contributions to the commercial and recreational fisheries were predominately from estuarine habitats, and freshwater habitats were important during the settlement phase. Specifically, 3% of commercially and recreationally harvested flounder were lifetime freshwater contingents, but 57% utilized freshwater during the first year of life.

We used bulk carbon (δ13C) and nitrogen (δ15N) isotopes, compound specific δ15N isotopes (AA-CSIA), and stomach content analysis (SCA) to determine trophic ecology and food web dynamics of Southern Flounder. We assigned location of harvest for commercially and recreationally harvested flounder using δ13C and δ15N values from fishery-independent samples. In agreeance with otolith chemistry, isotope analysis results indicated greater contributions to commercial and recreational fisheries from estuarine habitats than freshwater habitats. Additionally, flounder harvested in lower portions of Mobile Bay appear to be consuming prey at higher trophic levels than other areas along Alabama’s coastal waters.



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