Date of Award

Winter 2022

Project Type


Program or Major

Biological Sciences

Degree Name

Master of Science

First Advisor

Easton R White

Second Advisor

Catherine C Macdonald

Third Advisor

Nathan Furey


Despite being economically, ecologically, and culturally important many species of marine megafauna are threatened with extinction. The reasons for the imperiled state of many marine megafauna include overfishing, habitat loss, pollution, and climate change. Marine Protected Areas (MPAs) are often proposed as a management tool for marine megafauna. However, it is difficult to monitor the efficacy of marine protected areas when it is unclear if abundance trends are due to management or environmental variability. Indeed, many studies to date on the efficacy of MPAs fail to account for environmental variability, or account for limited covariates. In this thesis, I examine the potential effects of environmental covariates and ecological shifts on multiple groups of marine megafauna. More specifically, I employ a set statistical models and equations on 27 years of data obtained by a small group of trained dive masters at Cocos Island, Costa Rica. In Chapter 1, I provide relevant background on the biology, ecology, and conservation of marine megafauna. In Chapter 2, I disentangle the potential impacts of oceanographic and environmental variability on whale sharks, manta rays, and mobula rays. Finally, in Chapter 3, I assess the effects of predation risk and environmental variability on marine turtle abundance trends. Notably, I found that water temperature increases are related to decreases in relative abundances of manta rays, mobula rays, and marine turtles. I also found that in contrast with our expectations, increased primary productivity is related to decreased relative abundances of several (whale sharks and marine turtles). In Chapter 3, hierarchical models revealed apparent interactions between tiger sharks and marine turtles at Cocos Island. Collectively, this work highlights the importance of accounting for environmental variability and trophic interactions when examining long-term abundance trends and evaluating the efficacy of marine protection.