Male loggerhead turtles (<I>Caretta caretta</I>) were observed in a shallow (< 2 m) lagoon. Preferred food sources were <I>Mytilus galloprovincialis, Posidonia oceanica</I> and discarded fish entrails. Foraging dives were of short duration, presumably because of the small lung volumes required to attain neutral buoyancy at shallow depths. In-water observations of juvenile hawksbill turtles (<I>Eretmocheyls imbricata</I>) were made. Curved carapace length was estimated to within 10 cm of actual size. Foraging grounds of adults and juveniles did not appear to overlap. Juvenile hawksbills alternated between short, shallow foraging dives and deeper, longer resting dives. Time depth recorders were attached to loggerhead turtles (<I>n</I> = 2). Dives to the seabed (< 20 m) accounted for 59% and 755 of the interesting interval. Benthic dives decreased markedly following or prior to a nesting event. This contrasted the predominance of open-water dives reported in Japan. Open-water resting may occur when turtles are travelling and, conservely, when little time is spent travelling turtles opt to remain predominantly on the seabed. Atypically deep v-dives were identified for loggerhead and green (<I>chelonia mydas</I>) turtles. These appeared pre-determined, within the physiological scope of the species and may allow direct bathymetric information to be gathered. Patterns of hatchling emergence were documented and related to in-nest thermal conditions. Variation existed between and within individual nests. Hatchlings from nests displaying large thermal range emerged over a longer time-scale than those with more uniform temperatures. Incubation during data were used as a proxy of sex ratios. Variation existed within and between nesting seasons with 'atypical' seasons characterised by predominantly male production. Egg failure and neonate mortality were investigated in loggerhead clutches. First clutches were more likely to contain a higher proportion of eggs displaying no gross signs of development. Possible factors underpinning this are explored as are its implications at population level.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637311 |
| Date | January 2002 |
| Creators | Houghton, J. D. R. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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