Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Rosanna Milligan, PhD

Second Advisor

Tracey Sutton, PhD

Third Advisor

Matthew Johnston, PhD


Biomass, Mesoscale, Mesopelagic Fishes, Length-Weight Regression, GAMLSS, Northern Gulf of Mexico


In recent years interest in mesopelagic fishes has grown due to their ecological significance and economic potential. A major outstanding question is how the assemblage is potentially structured by mesoscale (10 - 100s km) oceanographic features such as eddies, fronts, and riverine plumes. Mesoscale features are known to influence micronekton and zooplankton’s spatial distributions but data on individual mesopelagic fish species’ responses are limited. The Gulf of Mexico (GoM) is an area of particular interest due to its diverse mesopelagic fish assemblage, its well-defined mesoscale oceanographic features, its history of anthropogenic impacts such as oil spills, and its diverse mesopelagic fish assemblage. The most speciose group of mesopelagic fishes in the GoM is the order Stomiiformes, a hyper-diverse order that plays a major role in ecosystem functioning due to their roles as midwater predators and the trophic links they form between surface and deep-pelagic waters. The goal of this project was to determine whether mesoscale oceanographic features in the GoM such as the Loop Current, its associated eddies, and riverine plumes have a significant role in structuring the biomass distributions of Stomiiformes vertically in the water column and/or horizontally across depth strata. This project utilized Stomiiformes and oceanographic measurements obtained during the DEEPEND (Deep Pelagic Nekton Dynamics of the Gulf of Mexico) MOCNESS surveys that occurred between May 2015 – August 2018. Zero-adjusted generalized additive mixed-effects models (GAMMs) were constructed to analyze the effects of mesoscale oceanographic features on the distributions of each selected species. Most species analyzed displayed upward and/or downward shifts to their vertical distributions in response to water mass. In terms of horizontal distributions, four taxa displayed limited spatial structuring in response to distance to the 200-m isobath and/or mean monthly Chl-a with three displaying inverse relationships and one displaying a direct relationship. Current ecosystem models are mostly based on either abundance or acoustically derived estimates of mesopelagic fish biomass, with species-level biomass estimates rare but potentially useful. Alterations of individual mesopelagic fish species distributions have potential impacts on carbon sequestration that need to be considered in future ecosystem modeling and management efforts.

Creative Commons License

Creative Commons Attribution-Share Alike 4.0 International License
This work is licensed under a Creative Commons Attribution-Share Alike 4.0 International License.