Defense Date


Document Type


Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tracey Sutton

Second Advisor

Andrew Bauman

Third Advisor

Amy Hirons


stomach content analysis, selectivity, chronology, ration


The ecology of deep-pelagic predatory fishes remains poorly understood despite their importance as ecosystem regulators and energy transfer vectors. This study investigated the trophic ecology of three species of the predatory fish genus Chiasmodon (“black swallowers”) in the Gulf of Mexico, a region that serves as an analog for the global low-latitude deep pelagial, the world’s largest cumulative ecosystem. Foraging habits (e.g., selectivity, chronology, daily ration) of an “advanced” evolutionary fish in a system that is otherwise dominated by basal fish taxa, were quantitatively estimated via high-resolution stomach content analysis. A quantitative dataset of both predator and prey abundance, the largest and most complete of its kind in existence, was utilized. A total of 337 Chiasmodon individuals were dissected, of which 138 had prey-positive stomachs (41%). Stomach content analysis revealed a strong selectivity for cephalopods as prey, while teleost fishes were consumed in proportions as predicted to those in the environment. Crustaceans, though highly abundant as potential prey, appeared to be actively avoided. Identifiable teleost prey taxa included Stomiidae (dragonfishes), Sternoptychidae (hatchetfishes), Dolicholagus (deep-sea smelts), Cyclothone (bristlemouths), and Bregmaceros (antenna codlets). These results differ substantially from the Stomiidae, another top mesopelagic predator in the Gulf of Mexico that have been shown to feed almost exclusively on Myctophidae, teleosts, and certain crustaceans. The preponderance of cephalopod predation within the same system for Chiasmodon is notable due to its rarity, and promotes future research opportunities comparing predation impact between these top predators. Daily ration was calculated as 3.64%, suggesting that Chiasmodon feeds more often than dominant “lie-in-wait” predators such as dragonfishes, and therefore likely exerts more top-down control per fish than more basal fishes.