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Title: The reproductive ecology of marine turtles, Chelonia mydas and Caretta caretta, nesting at Alagadi, northern Cyprus, Eastern Mediterranean
Author: Broderick, Annette Cameron
ISNI:       0000 0001 3481 123X
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1997
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This thesis examines a wide range of subjects concerning the nesting and hatching of marine turtles, Chelonia mydas and Caretta caretta at Alagadi Beach on the north coast of the island of Cyprus (1993-1995). This is the most comprehensive study of its type to have been conducted in the Mediterranean, providing a unique opportunity to compare the two species nesting side by side. To date, 60 C. mydas and 99 C.caretta females have been tagged (1992-1996), allowing information to be gathered as to favoured remigration and inter-nesting intervals. Whilst C. mydas lay on average 2.4 clutches in any one season, C. caretta females lay, only 1.6. The latter require a greater period between laying subsequent clutches (13.5 days) compared to C. mydas (13 days). However, whilst some C. caretta females are able to lay in consecutive seasons and others favour an interval of 2 or 3 years, C. mydas females have only been recorded remigrating after 2 or 3 years. Females nesting at this site may require a greater remigration interval than the period of this study to prepare themselves for the reproductive process. The inter-species variations in nesting frequency recorded in this study may be a consequence of the larger size of C. mydas (curved carapace length range; 78-106 cm) in comparison to the smaller C. caretta (curved carapace length range; 65-87 cm) and the strong relationship recorded between female size and mean clutch size. C. caretta nesting in Greece and Turkey have been shown to be significantly smaller than those nesting outwith the Mediterranean. This was also found to be the case for this species in Cyprus, and additionally C. caretta was found to lay significantly smaller clutches in comparison to those recorded in Greece. Again this may be a reflection of their smaller size, which may possibly indicate earlier maturation in this population or a shortage of nutrients in their feeding areas, leading to slower growth. Although, in both species, larger females laid larger clutches, they did not lay significantly more clutches in one season than smaller females. However females, of both species, nesting earlier in a season were recorded to lay a greater number of clutches, but whilst larger C.caretta females were amongst the first nesters in a season, this was not the case for C. mydas. In the latter species, females showing a shorter inter-nesting interval between laying ultimately produced a greater number of clutches in a season. C. mydas females also oviposited into deeper nests and produced larger hatchlings than C. caretta, and both of these variables increased with the size of the female. No such relationships were recorded in C.caretta. however, nests of larger C. caretta females were found to have shorter incubation periods than smaller conspecifics. In addition, C. caretta nests which produced larger hatchlings had a greater hatching and hatchling emergence success. Likewise in deeper nests a higher level of success was recorded. The mean incubation period of C. caretta nests was shorter (47 days) than that of C. mydas (51 days) and those recorded elsewhere for these species in the Mediterranean. This is likely to be a result of the warmer temperatures prevailing in Cyprus. In some years, linear relationships were recorded as the incubation periods of nests decreased toward the end of the season, whilst in other years quadratic relationships were recorded, with nests laid at either end of the season requiring a longer incubation. Temperatures recorded by data-loggers ranged between 28.5-33°C in incubating C.mydas nests and 28.1-33°C in those of C.caretta. In nests of both species the majority of the incubation period was spent at temperatures above 29°C, which has been shown to be the pivotal temperature above which the sex ratio becomes increasingly skewed toward a greater proportion of females. If the temperatures in this small sample are typical and this is the pivotal temperature for these species in Cyprus, a greater number of hatchlings produced here will be female. However, seasonal and diurnal variations in the temperatures recorded in these nests may result in a different sex ratio than those achieved through artificial incubation at these temperatures. In light of the issue of global warming, interesting questions arise as to whether these species will be able to adapt to such climatic changes. Findings in this study, however, indicate that the timing of the onset of nesting is variable and may be governed by temperature and thus, in the event of global warming, these populations may shift their season so that it coincides with the correct temperatures for successftil incubation. The nesting behaviour of the two species is compared and the tagging procedure is critically examined as to its possible effects on subsequent behaviour and hatching success. C.mydas females spend on average twice as long in completing the nesting process than C.caretta. This is mainly a result of the longer time spent covering the nest. In C. mydas, a negative relationship was recorded between the time spent digging the egg chamber and the hatching and hatchling emergence success of the nest, possibly a result of females attempting to dig their egg chamber in an unsuitable substrate. Thus, not only is it more difficult to dig, but it is suboptimal for embryonic development, resulting in a lower level of success. This relationship was not recorded for C. caretta, however, individuals of this species laying larger clutches took a longer time to do so, a relationship that might be expected although was not recorded for C. mydas. No significant effect of tagging females of either species was recorded in their resultant behaviour or in the success of the nest.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nesting; Hatching