Date of Award

Fall 2020

Degree Type

Masters Thesis

Committee Chair

Kevin Dillon

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Zachary Darnell

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Frank Hernandez

Committee Member 3 School

Ocean Science and Engineering

Abstract

The goal of this study was to determine the diet composition, trophic position and ecological role of red snapper (Lutjanus campechanus) in Mississippi state waters utilizing stable isotopes (δ13C and δ15N) and stomach content analysis. Stable isotope analysis of fish and their prey can provide information on species-specific basal resource utilization, diet composition and trophic position which can improve food web models and inform fisheries management decisions. Particulate organic matter (POM), the presumed base of the food web, red snapper muscle tissue, and red snapper stomach contents were collected from 25 sites in 2016 and 2017 for stable isotope analysis. POM δ13C values showed high variability for both years, with 2016 values being lower at deeper strata sites and steadily decreasing in surface and bottom water samples over the 7-month sampling period. POM δ13C values from both years may have been affected by increased riverine inputs. POM δ15N values showed unusual isotopic depletion during the summer months of 2016 and 2017. Stomach content analysis indicated shifts in red snapper diet between 2016 and 2017, with stomatopods and gastropods being the most abundant collected prey items in each year, respectively. Stable Isotope Analysis in R (SIAR) mixing models indicated crab and fish prey are the most isotopically significant contributors across depth strata. Red snapper δ13C values were highly variable and maybe related to riverine inputs, while red snapper δ15N values indicated that spatial baseline shifts were occurring in the depth strata possibly due to diet shifts.

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