title: Shell walls: A new hope. Using barnacle shell isotopes as a conservation tool for understanding the movement ecology of threatened sea turtles
Creators: name: Pearson, Ryan
Publisher: name: Griffith University
Year: 2018
Subjects: subject: Barnacle shell isotopes
subject: Sea turtles
subject: Conservation
subject: Management
subject: South Pacific loggerhead turtles
subject: Caretta caretta
subject: Isotope ratios
subject: Barnacle shells
subject: Pelagic waters
subject: Estuarine habitats

description: Understanding the geographic distribution of sea turtles within their sub-populations could enhance conservation and management, especially for sub-populations that are the most threatened. Isotope techniques have been used for this purpose and have become popular in the past decade, with an increasing year-to-year trend in published studies. Via systematic literature review of all studies using isotopes to understand sea turtle ecology, this thesis first presents a robust understanding of the current state of the science, identifying knowledge gaps and priorities for future sea turtle conservation research (Chapter 2). This identified that very few stable isotope studies aimed at understanding foraging distributions have been completed on threatened sub-populations of sea turtles, whereas those considered of least concern by the IUCN have been the focus of many. I aimed to address this mismatch between stable isotope studies and conservation needs by developing, validating, and applying a novel isotope technique to understand the foraging distribution of critically endangered South Pacific loggerhead turtles (Caretta caretta), and in doing so identifying critical habitats for priority management. The technique presented uses isotope ratios from commensal barnacle shells, which vary with temperature (SST) and salinity (SSS) rather than turtle diet. Barnacle shells are formed sequentially, storing chemical information about of the surrounding conditions at the time of formation. This makes it possible to assign a date to samples, and compare isotope ratios with the spatial and temporal distribution of sea water parameters (SST and SSS), if the growth of the animal is well understood. Thus, in this thesis I tested the applicability of using barnacles to understand sea turtle foraging distribution by quantifying barnacle growth rates (Chapter 3), regional relationships between barnacle isotopes (C and O) and SST &amp; SSS (Chapter 5), and discriminating between foraging areas based on time dependent isoscapes for barnacle shell (Chapter 4, 5). Finally, the technique is applied to predict the home area of loggerhead turtles that nest in southern Queensland, Australia, identifying hotspots and relationships between nesting and foraging habitats (Chapter 6). This thesis demonstrates that isotopes from barnacle shells can be used to identify the origin and migration distances of host turtles at varying spatial scales, depending on water chemistry gradients present at the time and location of shell formation. In eastern Australia is it possible to assign turtles to home areas with &gt;86% accuracy when areas are separated by at least 400 km (Chapter 4). Globally, many coastal areas are likely to offer similar or better resolution to this, while pelagic waters will typically offer lower resolution. This thesis also shows that estuarine habitats are important foraging habitats for adult loggerhead turtles, probably more so for southern foragers, while marine habitats are clearly important in northern Australia. Future research should focus on developing isoscapes for barnacle shell in other regions, and combining barnacle analyses with other methods to improve the achievable resolution. I also expect that this technique can be applied widely to other taxa and objects that carry commensal barnacles throughout marine journeys.