University of Twente Student Theses


Influence of the aquatic environment on the nesting ecology of the Loggerhead Sea Turtle (Caretta caretta) in the Mediterranean Sea

Venegas Li, Rubén (2009) Influence of the aquatic environment on the nesting ecology of the Loggerhead Sea Turtle (Caretta caretta) in the Mediterranean Sea.

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Abstract:Loggerhead turtle populations in the Mediterranean have been depleted due to over fishing and to the degradation of their nesting habitats, their protection requires a better understanding of the utilization of the different ecosystems that they exploit. So far, most studies on sea turtle biology have been carried out on the terrestrial part of their nesting areas, even though they spend modes of their lives in the ocean. How this aquatic environment affects sea turtle behaviour has not been evidently understood yet. The main objective of this study is to investigate how the aquatic environment of loggerhead turtles’ nesting and foraging areas in the Mediterranean influences their nesting ecology. Two main approaches were taken, 1) the aquatic environment in which loggerhead turtle nesting areas can be found was modelled using MAXENT (a presence only modelling approach); separately, Multiple Linear regression was used to establish the relationship between Sea Surface Temperature (SST) in foraging areas and the reproductive effort and phenology of turtles nesting in Zakynthos, Greece. Results of the Maxent model suggest that the following aquatic environment enhances the suitability of an area to hold nesting colonies of loggerhead turtles in the Mediterranean: a) warmer sea surface temperatures (SST) at the start (month of May) and at the end (month of September) of the nesting season, b) lower concentrations of chlorophyll a at the start and end of the nesting seasons (may and September respectively), and c) steeper ocean floors (represented by the distance to the 50m and 500m isobaths in this study. It is suggested that SST could be related with higher metabolic rates that allow turtles to take advantage of the warmest months of the summer for incubation of eggs, while chlorophyll and bathymetry could be related with a strategy of predator avoidance. On the other hand, data for Zakynthos nesting population was correlated with SST from the Adriatic Sea and the Gulf of Gabès, the two major foraging grounds for this population. In general, warmer waters in the year prior to the nesting season is positively correlated to the number of nests and to an earlier start and end of the nesting seasons, while relationships with more than a year lagged SST are negatively correlated. Understanding how environmental conditions affect population dynamics could be an aid in enhancing biodiversity conservation measures.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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