Regional and annual variation in plasma steroids and metabolic indicators in female green turtles, Chelonia mydas
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Variation in environmental conditions at a foraging area or at a nesting rookery has the potential to impact reproductive output of green sea turtles (Chelonia mydas) by affecting food resources or the nesting substrate. In this paper we test whether turtles‘ physiological characteristics reflect variation in relevant environmental conditions. We did this by profiling metabolic and hormonal markers among (1) non-vitellogenic females from three different foraging areas and (2) nesting females from different rookeries and breeding seasons. Among the non-vitellogenic females, the highest plasma triglyceride concentrations (4.29 mmol/l) and the lowest plasma cholesterol concentrations (1.27 mmol/l) were found in non-vitellogenic females residing in Moreton Bay during the El Niño year of 1997. Furthermore, during 1997, these Moreton Bay females had higher plasma triglyceride and lower cholesterol concentrations than those recorded in non-vitellogenic females foraging at Heron Reef (triglyceride 1.22 mmol/l and cholesterol 4.53 mmol/l) and Shoalwater Bay (triglyceride 1.69 mmol/l and cholesterol 3.50 mmol/l) in the same year. Among nesting turtles, those nesting at Raine Island had low mean plasma triglyceride concentrations during the high density 1996 nesting season. For those nesting at Heron Island, the mean triglyceride concentrations were the lowest during the 1997 nesting season. This is the first time that hormone and metabolic markers have been used in concert to compare the physiological condition of nesting and foraging sea turtles and its relationship with the environment. Collectively, our data indicate that variation in the environmental conditions at both foraging and nesting areas are reflected at a physiological level. Moreover, our study indicates that turtles feeding during El Niño years are able to attain higher levels of body condition, and that physiological data combined with morphometric data is a useful proxy for assessing the condition of turtles in foraging areas.
KeywordsBody Condition Great Barrier Reef Green Turtle Plasma Metabolite Nest Season
This study was undertaken as part of the QPWS Turtle Conservation Project, funded by an ARC grant to JMW and CJL, and a small ARC (95/96) grant to JMW. Partial support for the passage to the northern Great Barrier Reef islands and for the collection of samples in Moreton Bay was provided by the Raine Island Corporation and Sea World Research and Rescue Foundation, respectively. P&O Resorts Australia provided transport of research staff and volunteers to and from Heron Island. The assistance of the Marine Parks staff of Gladstone, Roslyn Bay, Heron Island and Moreton Bay was invaluable. Additionally, this project also owes a considerable amount to many staff and volunteers of the QPWS Turtle Conservation Project, in particular I. Bell, D. Broderick, S. Clark, M. Forrest, D. Limpus and M. Read. This manuscript was improved following comments from C. Schäuble. The University of Queensland (ANAT/121/99/ARC/PHD) and QPWS animal ethics permits covered this project.
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