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Movements, behaviors and threats to loggerhead turtles (Caretta caretta) in the Mediterranean Sea
Dissertation   Open access

Movements, behaviors and threats to loggerhead turtles (Caretta caretta) in the Mediterranean Sea

Samir Harshad Patel
Doctor of Philosophy (Ph.D.), Drexel University
Nov 2013
DOI:
https://doi.org/10.17918/etd-4379
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Abstract

Environmental sciences Loggerhead turtle--Behavior--Research--Mediterranean Sea Loggerhead turtle--Ecology--Mediterranean Sea
The purpose of this study was to determine the at-sea behavior of loggerhead turtles (Caretta caretta) in the Mediterranean Sea in order to gain a better understanding of the various environmental factors that play a role in their survival. By determining the environmental conditions that have a controlling force over foraging and nesting success, more accurate projections can be made on the future of this declining subpopulation of loggerheads. I deployed 20 satellite transmitters on postnesting adult loggerhead turtles from Rethymno, Crete, Greece, with 19 functioning through migration. Using a changepoint analysis model, I determined that loggerheads in the Mediterranean exhibited 5 behavior modes. Within these modes were migration, foraging and overwintering, along with newly discovered transition modes between each established sea turtle behavior. Overall, the turtles exhibited 3 unique postnesting strategies, 9 migrated to the North African coast, 6 migrated into the Aegean Sea and 4 remained within the waters of Crete. These three strategies corresponded to fitness differences between the turtles. The northern turtles were larger and had larger clutch sizes than those foraging near Crete and Africa. This corresponded to the abundance of prey from each region. The benthic environment of the Aegean had the largest prey abundance compared to the other sites. Around Crete there is very limited benthic environment to support loggerhead foraging, and in the Gulf of Gabes the prey abundances are reduced due to a high influx of industrial runoff. The Gulf of Gabes is home to ~40% of loggerheads nesting in Greece, and as global warming continues, the rising temperature is expected to exacerbate the deterioration of the benthic environment. Furthermore, there is already a strong female bias in sex ratio for Mediterranean loggerheads, which is expected to continue to get stronger as beach temperatures rise and precipitation declines. Loggerheads may be able to compensate for these changes, and I found that their nesting phenology is expected to shift earlier by as much as 52 - 74 days by 2100; however the factors threatening the survival of this species may be too strong to overcome.

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