Date of Award

Fall 2019

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Ocean Science and Engineering

Committee Chair

Frank Hernandez

Committee Chair School

Ocean Science and Engineering

Committee Member 2

Kevin Dillon

Committee Member 2 School

Ocean Science and Engineering

Committee Member 3

Jesse Filbrun


All species of anguilliform eels have pelagic leptocephalus larval stages, which provides a means of monitoring the population dynamics of these otherwise cryptic and hard to study species. The goals of this study were to: 1) describe the distribution and abundance of anguilliform eel leptocephali across the northern Gulf of Mexico, and 2) examine the trophic ecology of leptocephali using stable isotope values of carbon and nitrogen (δ13C and δ15N). A 25-year (1990-2014) ichthyoplankton dataset provided by the National Oceanic and Atmospheric Administration (NOAA) Southeast Area Monitoring and Assessment Program (SEAMAP) was used to examine interannual variations in leptocephalus distribution, abundance, and occurrence. Family-level indices of abundance and occurrence were significantly and positively correlated over the time series within season (spring and fall) and gear types (bongo net and neuston net). Ten of the reported twelve eel families known from the Gulf of Mexico were collected during this time series. Decreases in abundance and occurrence for dominant families (Ophichthidae, Congridae, and Muraenidae) were observed during the latter part of the time series. Leptocephalus, zooplankton, and particulate organic matter (POM) samples were collected during the SEAMAP Fall Plankton Survey in 2016 and analyzed for stable isotopes. Variability in the isotope values of leptocephali was driven by variability in baseline POM isotope values. Diet composition analyses indicated leptocephali used POM and small zooplankton as diet sources. Information about leptocephali taxonomic diversity, abundance, distribution, and trophic ecology add to our understanding of their ecological role in the ocean.