Defense Date
5-2-2025
Document Type
Dissertation
Degree Type
Doctor of Philosophy
Degree Name
Oceanography/Marine Biology
First Advisor
Derek A. Burkholder, PhD
Second Advisor
Joana Figueiredo, PhD
Third Advisor
Bernhard M. Riegl, PhD
Fourth Advisor
Kristen M. Hart, PhD
Fifth Advisor
William Harford
Keywords
sea turtle, conservation, movement models, satellite tracking, isoscapes, stable isotopes, migration, internesting, foraging, origin, home range, marine protected areas
Abstract
The movements of animals in response to environmental variation influence the fitness of individuals and drive major ecological processes, while also varying their exposure level to anthropogenic risks. Understanding the movements and spatial distribution of imperiled species is critical for developing effective conservation strategies. This can be difficult for wide ranging and highly migratory species, such as sea turtles. Throughout their adult life stages, the females of most sea turtle species spend the majority of their time in their foraging areas for multiyear intervals between nesting periods. These foraging areas are typically widely dispersed and variable within nesting populations. To nest, females travel hundreds to over 1,000 km to nesting grounds, spending several months in internesting habitats before migrating back to foraging areas. Researching the impacts these large-scale movements have on population-level spatial distributions is challenging, often requiring large financial and human resource investment.
For sea turtles, satellite tracking can be an effective tool to understand the movements and habitat use of individuals. However, tracking data obtained through the most common tracking technology, which uses the Argos satellite system, is inherently noisy, with inconsistent temporal sampling rates and high spatial error estimates for the provided location data. But these challenges can often be effectively addressed by using switching state-space models to provide location estimates with high accuracy and at consistent, pre-defined periods. These data can then be used to investigate the wide-scale movements of tracked individuals. Due to fiscal limitations, satellite tracking studies are often only applied to a relatively small proportion of a population.
Fortunately, the insights gained from tagging studies can be extended to a larger proportion of the population by using the stable isotope values from tracked turtles to develop likelihood-based assignment models to predict the foraging areas of untracked turtles. Through intensive sampling efforts, this low-cost approach can provide insights into spatial distributions at the population-level.
In this dissertation, I applied these various approaches to investigate the internesting, migratory, and foraging movements of a previously unstudied population of loggerhead (Caretta caretta) and green (Chelonia mydas) turtles from a southeast Florida rookery. Using satellite tracking and state-space modelling, I characterized the post-nesting movements of loggerhead (Chapter 2) and green (Chapter 3) turtles that nest along Broward County beaches, identifying core-use areas for each species. Then, using stable isotopes, I employed both nominal and continuous approaches to predict the foraging areas of 177 untracked loggerhead turtles from Broward County and two other southern Florida nesting areas, providing a more representative assessment of the population-level spatial distribution in the region (Chapter 4).
Investigating the large-scale movements of individuals through satellite tracking revealed notably different preferences in habitat types used during the internesting and foraging periods, while they both made use of a major migratory corridor also commonly used by multiple sea turtle nesting populations throughout Florida. During the internesting period, both species spent the vast majority of their combined tracked internesting days in waters that lacked effective protection, increasing their exposure to anthropogenic threats associated with a high-density human population center and a major commercial port. The foraging distribution of loggerhead turtles was much more varied and widespread than the distribution of green turtles. While 72% of the tracked loggerheads used foraging areas outside of the US exclusive economic zone, 78% of green turtles used foraging areas within local marine protected areas. The use of predictive assignment models revealed broadscale insights into the foraging distribution for loggerhead turtles nesting in south Florida, which generally aligned with trends seen in the tracking data. Evaluations of model performance suggested various approaches that may improve model accuracy in future studies.
Taken together, this dissertation provides the first characterization of the movements of loggerhead and green turtles once they depart southeast Florida beaches, highlighting their conservation needs by offering insight into which characteristics are associated with critical, high-use habitats for each species as they move between these different behavioral states. Understanding the environmental characteristics that influence the movements of turtles during these periods is fundamental in developing effective conservation strategies for these imperiled species.
ORCID ID
https://orcid.org/0000-0003-4940-7605
Researcher ID
JCE-8407-2023
Appendix D
NSUWorks Citation
Glenn D. Goodwin. 2025. Using Satellite Tracking and Stable Isotopes to Characterize the Movements, Core-use Areas, and Distribution of Loggerhead and Green Turtles Nesting in South Florida, USA: Internesting, Foraging, and Migration. Doctoral dissertation. Nova Southeastern University. Retrieved from NSUWorks, . (208)
https://nsuworks.nova.edu/hcas_etd_all/208.
Comments
FWC MTP-255; NSU IACUC 2020.12.DB2-BBC; USGS/WARC/GNV 2017-04 and 2023-01