Defense Date

7-30-2020

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

Paul Arena, Ph.D

Keywords

Otoliths, Deep-pelagic, Age, Growth, Mesopelagic, Bathypelagic

Abstract

Mesopelagic and bathypelagic fishes provide important global ecosystem services, such as carbon sequestration via the biological pump and provision of food for economically important (billfishes and tuna) and federally protected (cetaceans and seabirds) species. These attributes are becoming increasingly recognized, while simultaneously mesopelagic fisheries are becoming of interest for direct harvest as coastal fisheries have become overexploited. Additionally, climate change, ocean acidification, and seabed mining threaten deep-sea fishes. With increasing interest in deep-sea fisheries and anthropogenic threats, age and growth information on these fishes is necessary for management and conservation. Currently ecosystem models lack data such as sexual maturity and lifespan on deep-pelagic fishes, hindering our ability to quantify production rates and resilience to disturbance. Here we examine four numerically dominant predatory fishes from the Gulf of Mexico exhibiting a range of trophic ecologies and vertical distributions: Lampanyctus lineatus (Myctophidae), Omosudis lowii (Omosudidae), Stomias affinis (Stomiidae), and Chauliodus sloani (Stomiidae). In this thesis, the otoliths (‘ear stones’) of each species were examined in order to estimate age and duration of specific life history stages (e.g. juvenile, intermediate, and adult) and landmarks (e.g., sexual maturity and determine longevity). Given that otolith ring validation was not possible (these fishes cannot be kept alive, marked and recaptured, and hourly sampling is not possible for species living at great depths), we present putative minimum and maximum estimates at landmarks based on two scenarios: 1) total rings = days of life; and 2) major (darkest) otolith increments = years of life). Comparing both estimates to available validated ages of their prey, we conclude that the maximum age scenario is most appropriate. Results of this study suggest that the deep-living myctophid species and higher-level predators investigated have relatively long generation times (L. lineatus one year, C. sloani 9 - 17 years, and S. affinis 10 – 19 years until sexual maturity), and thus likely have low resilience to population level-perturbation.

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