Use of otolith chemistry to examine patterns of diadromy in the threatened Australian grayling Prototroctes maraena

Otolith chemical analyses (proton-induced X-ray emission and laser ablation inductively coupled plasma mass spectrometry) were used to examine patterns of diadromy in Australian grayling Prototroctes maraena collected from three rivers in south-eastern Australia. Concentrations of Sr:Ca and Ba:Ca were measured in the sagittal otoliths of 25 fish and in water samples collected on two occasions from multiple sites within freshwater, estuarine and marine reaches of the rivers. The results provide evidence of marine residency during the juvenile phase, with high Sr:Ca and low Ba:Ca in the inner region of the otoliths that were consistent across all three rivers. This general pattern was apparent for all individuals examined, suggesting that diadromous migration may be an obligate aspect of the life history. The chemical signatures of the outer regions of the otoliths were distinct between the three rivers, whilst there was no difference in the inner regions of the otoliths. This suggests that juveniles from different rivers may reside in a relatively homogenous chemical environment, such as the sea, and populations in coastal Victorian rivers may share a common marine recruitment source. (c) 2006 The Authors Journal compilation (c) 2006 The Fisheries Society of the British Isles.