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Digital archive of theses discussed at the University of Pisa

 

Thesis etd-12102010-231333


Thesis type
Tesi di dottorato di ricerca
Author
GALLI, SILVIA
URN
etd-12102010-231333
Thesis title
Oceanic navigation in sea turtles: role of environmental factors
Academic discipline
BIO/05
Course of study
BIOLOGIA
Supervisors
tutor Dott. Luschi, Paolo
Keywords
  • Caretta caretta
  • Chelonia mydas
  • Dermochelys coriacea
  • diving behaviour
  • environmental factors
  • migrations
  • navigation
  • ocean currents
Graduation session start date
14/01/2011
Availability
Withheld
Release date
14/01/2051
Summary
Adult sea turtles are known to accomplish extensive migrations that can range hundreds or thousands of kilometres, shuttling between individually-specific feeding and breeding sites The mechanisms that guide turtles in their travels within the apparently featureless open ocean is still object of study but, over the years, a number of reliable hypotheses about sea turtle navigation have been suggested.
Thanks to the development of satellite telemetry techniques, the movements of marine turtles are now known with some details and it is possible to reconstruct their migratory routes with good precision and accuracy, even for long periods of time. Recently, some studies have integrated the tracking data with information on a variety of environmental factors (e.g. ocean currents and winds) and have demonstrated the importance of these factors in affecting the spatial behaviour of these reptiles.
In this thesis the spatial behaviour of three different species of turtles (Dermochelys coriacea, Caretta caretta and Chelonia mydas) living in different parts of the world (South-East Indian Ocean, North Atlantic Ocean and Mediterranean Sea) was studied during different stages of their life cycle (post-nesting migrations and movements away from the reproductive period) and in experimental conditions (i.e. experimental displacements). The routes followed by these animals were reconstructed using satellite telemetry techniques and information on environmental parameters of the areas crossed by tracked individuals were obtained from satellite-derived data. In particular, I evaluated the influence that environmental factors like the atmospheric and oceanographic features, the Earth’s magnetic field or the light/dark cycle, have on the turtles’ migratory behaviour and on their navigational abilities during open sea movements.
The main results of this study reveal that sea turtles cannot perceive the currents they experienced during their open sea journeys and are able to overcome non favourable currents when moving toward a precise area, reaching it even in the presence of passive displacement due to currents flow. When swimming in the open ocean, sea turtles can maintain a fixed direction, both during night and day and when swimming at high depth. In addition, this study shows that turtles can rely on wind-borne cues to orient themselves towards an intended goal.
Since all sea turtle species are endangered, every research effort that can supply information regarding basic aspects of sea turtle biology, like how sea turtles navigate and which stimuli they use during their offshore movements, is valuable, as it provides basic information for the development of management and conservation measures to protect these animals during their prolonged, long-distance movements.

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