Date of Award

12-31-2022

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Marine Sciences and Technology

First Advisor

John W. Mandelman

Second Advisor

Jodie L. Rummer

Third Advisor

Helen Poynton

Abstract

Marine ectothermic fishes – fishes that do not regulate internal body temperature independent from the water temperature – are some of the most vulnerable organisms to rapid and alarming increases in environmental temperature occurring due to climate change mediated-ocean warming. For tropical fish species that live near their thermal maxima, this warming could be of grave consequence to individuals, populations, and whole marine ecosystems. Certain key life stages such as embryos and reproducing adults may be particularly vulnerable to warming given the excess energetic costs of these life stages, which may disallow compensation for extreme changes in temperature. One taxonomic group that may be vulnerable to warming is the tropical elasmobranch fishes (i.e., sharks and rays), where long generation times may impede these fishes from keeping pace with ocean warming. As such, the overall aim of this dissertation was to study the tropical epaulette shark (Hemiscyllium ocellatum), which is endemic to the Great Barrier Reef, to better understand basic life history physiological costs and to determine the interaction environmental temperature may have on these costs now and under ocean warming.

In chapter 2, I aimed to assess the influences of time of day and spring and summer current day temperature profiles on epaulette sharks. Next, in chapters 3 and 4, I assessed two measurements of energetics across life history stages, body condition and metabolic rate, and used a comparative approach to validate and study whole-organism, non-lethal energetics. In chapter 5, I assessed the upper thermal tolerance of wild epaulette sharks across common life history stages found on tidally influenced reef flat. Finally, in chapter 6 I assessed how future water temperatures predicted for the Great Barrier Reef impact the early growth, development, and physiological performance of this species. Together, my dissertation provides a better understanding of current day physiology, best practice non-lethal energetic comparisons, and assessment of the thermal response of this indicator shark species under future ocean warming conditions. Outcomes provide insight as to how these important marine predators will fair under ocean warming, key information to inform future conservation and protection efforts of this ecologically, economically, and culturally important taxon.

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