Investigating life-history traits of adult Mediterranean sea turtles
Date: 9 December 2019
University of Exeter
PhD in Biological Sciences
The management of species of conservation concern requires high-quality life-history data to model and assess population stocks. This is particularly important for long-lived, migratory species with slow life-histories. In the case of sea turtles, the estimation of demographic parameters is a priority for the species globally and, in ...
The management of species of conservation concern requires high-quality life-history data to model and assess population stocks. This is particularly important for long-lived, migratory species with slow life-histories. In the case of sea turtles, the estimation of demographic parameters is a priority for the species globally and, in particular, in the Mediterranean Sea. In this thesis, I focus on green (Chelonia mydas) and loggerhead (Caretta caretta) turtles which nest sympatrically at Alagadi Beach, North Cyprus, where intensive monitoring and saturation tagging have been undertaken since 1993. This thesis aims to make use of this 26-year individual-based dataset both to further and to challenge current knowledge and theories surrounding life-history traits. More specifically, in Chapter 2, I review the state of knowledge of the growth strategy of adult sea turtles and life-history trade-offs. I highlight that, although studies of turtles in captivity have provided insights into changes in energy allocation at sexual maturity, there is a lack of data regarding the temporal variation in post-maturity growth rates in wild individuals. Thus, in Chapter 3, I provide evidence suggesting that, contrary to previous thinking, green and loggerhead turtles do not grow throughout their life. This clearly has implications for our understanding of ageing and longevity of the species. Additionally, in Chapter 4, I offer the first study of the effects of biologging device attachment on growth, reproduction and survival of nesting females. While the absence of an effect at this study site is promising considering how widely this technique is used in sea turtles, I stress the need for similar studies elsewhere to confirm this finding. Furthermore, I examine in Chapter 5 the importance of passive integrated transponder (PIT) tags and show that they greatly improve estimates of flipper tag loss and life-history and demographic parameters, essential for population assessments. Lastly, I use results from previous chapters in Chapter 6 to investigate the difference in recovery rates of the two species. I propose that high bycatch rates in the Mediterranean Sea are hampering the recovery of loggerhead turtles at this study site, whereas green turtles are showing signs of exponential recovery. In conclusion, this thesis emphasises the importance of long-term studies to refine life-history models and provides new and improved data for Mediterranean sea turtles, which can be used in regional and global IUCN Red List assessments.
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