Abstract
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ABSTRACT
The aim of this thesis is to study the migratory behaviour of some loggerhead sea turtles (Caretta caretta), monitored by satellite telemetry, through the observation of their movements across the Mediterranean Sea. The studied turtles were in the not-reproductive phase, one of the least-know period of their life cycle. In the last few years, the development of satellite telemetry technology made possible to follow the movements of relatively small size individuals and to reconstruct the accurately followed routes to obtain informations about their general behaviour during the initial stages of their life cycle.
In this work we examined six turtles (five young and one female adult) accidentally caught by fishing boats and brought to rehabilitation centres. Here they have been rescued and released near the catch location in different areas of the Adriatic Sea (Croatia, Italy and Slovenia) from 2006 to 2008.
Before releasing, radio transmitters linked to ARGOS system were glued on animals. Data obtained from the transmitters have been broadcast for a period from 4 to 15 months long. Location data were daily analyzed and filtered using special procedures to gain a set of reliable data that allowed us to reconstruct the routes followed by these animals. All these informations were finally integrated with remote sensing data, about environmental variables such as surface water temperature, chlorophyll and bathymetry, in order to assess their possible role in defining the overall behavioural pattern shown by turtles.
The reconstruction of the routes shown that movements take place mainly near the coast and often along direct routes. However, in some periods the animals stayed, even for long periods, in confined areas making short movements with frequent changes of direction. Young turtles travelled for the most of the time in the Adriatic Sea while the adult moved to the southern part of the Mediterranean Sea near the African coasts.
Two turtles made seasonal movements leaving northern areas as the cold season arrived to move towards southern latitudes. In opposition a young turtle remained in the northern Adriatic, probably entering in a period of hibernation.
Analyzing the behaviour in relation to environmental variables, we observed that young turtles were more affected by temperature than adult: in particular, a turtle
Abstract
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that remained in the northern Adriatic showed an evident decline in speed in correspondence to a significant decrease in temperature. Chlorophyll concentration remained almost constant along the routes of the turtles except for some peaks in specific areas, where turtles speed decreased. Finally, we analyzed the bathymetry of the areas frequented by the turtles to assess which kind of environment they prefer between neritic and oceanic. Young turtles seemed to prefer the neritic environment as expected for animals of their size at this stage of their life cycle. Adults spent the same time in both zones. Analysis of bathymetry and speed trends don’t show a common trend among studied turtles.
