908 



Fishery Bulletin 101(4) 



the year than it is in the other three species. Similarly, the 

 apparent earlier timing of new ring creation in our study, 

 compared to the findings of Davis and West (1992) may have 

 been due to the fact that the translucent zone can probably 

 be detected closer to the time of formation in sectioned 

 otoliths than in urohyals (Reshetnikov and Claro, 1976). 



In summary, modeling the change in index of completion 

 over time enabled estimates to be made of the time of the 

 formation of a new growth ring (with confidence intervals) 

 for four tropical species. Although the index of completion 

 was modeled with a logistic function in the present study, 

 alternative functions (e.g. sine or linear), gave very similar 

 results. The technique is a useful addition to marginal in- 

 crement analysis because it can be used in place of previous 

 subjective methods to determine quantitatively the timing 

 of new ring formation. 



Acknowledgments 



This project was financed by the Fisheries Research and 

 Development Corporation (FRDC) (project 94/25) and the 

 Department of Fisheries, Western Australia where the 

 main author was employed for the duration of the project. 

 The authors thank Mike Moran (Department of Fisher- 

 ies, Western Australia) for obtaining FRDC funding and 

 providing critical advice and encouragement. The senior 

 author also thanks Robert Black (University of Western 

 Australia) for his valued suggestions and encouragement. 

 Stephen Newman (Department of Fisheries, Western 

 Australia) provided advice on reading and interpretation 

 of otolith bands, Iain Dunk (Department of Fisheries, 

 Western Australia) collected samples, sectioned otoliths, 

 and acted as the second reader for fish aging and mar- 

 ginal increment analysis. Tony Paust, Ken Bryers, Justin 

 Chidlow, Daryn Payne (Department of Fisheries, Western 

 Australia) assisted in sample collection. I also acknowledge 

 the assistance of M. G. Kailis, Kraus Fishing Company, and 

 Westmore Seafoods whose vessels were used for sample 

 collection, and two anonymous referees for their construc- 

 tive comments. 



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