Defense Date

4-25-2024

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tracey Sutton, Ph.D.

Second Advisor

David Kerstetter, Ph.D.

Third Advisor

Amy Hirons, Ph.D.

Keywords

Gut content analysis, diet, ration

Abstract

The trophic ecology and vertical distribution of a deep-pelagic predatory fish, the longfin escolar (Scombriformes: Scombrolabrax heterolepis), from the Gulf of Mexico were examined. Deep-pelagic predators remain understudied because their larger size and higher mobility allow them to evade traditional, research-sized (i.e., relatively small) sampling nets. With the use of large midwater trawls, however, a substantial sample set was obtained. Quantitative gut content analysis revealed a wide range of prey types including teleost fishes and crustaceans, as well as a strong selective preference for cephalopods. This species appears to be a true “see it, eat it” generalist, a rarity among deep-pelagic fishes. Daily ration, which was estimated to be 3.9-7.9% of body weight consumed per day, in combination with a low vacuity index, suggests that S. heterolepis feeds far more often than other mesopelagic predatory fishes. While S. heterolepis inhabits epipelagic to mesopelagic waters and does not vertically migrate, it targets many prey taxa, such as Myctophidae, that do. Given that S. heterolepis is found circumglobally in low- to mid-latitude tropical regions, we propose that this species, and other “advanced” spiny-rayed fishes like it, exert a widespread, yet underappreciated predation effect on the oceanic biological pump.

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