Defense Date

8-7-2025

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Tracey Sutton

Second Advisor

Estrella Malca

Third Advisor

Susana Caballero Gaitan

Keywords

Mesopelagic, bathypelagic, food webs, trophic ecology, vertical distribution, Nemichthyidae, snipe eels

Abstract

The Nemichthyidae (snipe eels) are ubiquitous in the deep-pelagic waters of tropical and temperate latitudes, and in some ecosystems are among the dominant fishes. In the deep waters of the Gulf of Mexico, the nemichthyid species Avocettina infans is one of the dominant large predators. This prompted the current study, where an extensive sample set was utilized to characterize the abundance of the family in total, and the vertical distribution and trophic ecology of A. infans specifically. The nemichthyid abundance from 0 – 1500 m was estimated at 1,106.58 individuals per billion cubic meters, the largest portion of which was contributed by A. infans (729.35 ind. 10-9m-3). For trophic analysis, 113 specimens were dissected, 69 of which contained prey. Prey identification revealed a high selectivity for pelagic macrocrustaceans, particularly decapods, and a complete avoidance of other prey such as zooplankton, fishes, and pelagic molluscs (e.g., cephalopods). No diel feeding pattern was evident, suggesting that A. infans feeds both during daytime and at night and/or digestion of macrocrustacean prey takes more than one diel cycle (i.e., 24 h). Estimation of feeding ration suggested a relatively high consumption rate, between 2.08 - 6.25% of their own body weight per day. These values, which are higher than typical deep-pelagic fishes, suggest that A. infans is a prolific predator and important contributor to carbon cycling. Morphometric analysis established allometry and a correlation between predator size and likelihood of prey presence.

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