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Advances in the aquatic sciences

Accepting final counts from repeat readings of otoliths: should a common criterion apply to the age estimation of fish?

Ross J. Marriott A F , Bruce D. Mapstone B , Aaron C. Ballagh C , Leanne M. Currey C , Ann Penny C , Ashley J. Williams C D , Gary Jackson A , Dongchun Lou E , Amos J. Mapleston C , Nicholas D. C. Jarvis A , Ian S. Keay A and Stephen J. Newman A
+ Author Affiliations
- Author Affiliations

A Western Australian Fisheries and Marine Research Laboratories, Department of Fisheries, Government of Western Australia, PO Box 20, North Beach, WA 6920, Australia.

B CSIRO Marine & Atmospheric Research, GPO Box 1538, Hobart, Tas. 7001, Australia.

C Fishing and Fisheries Research Centre, School of Earth and Environmental Science,James Cook University, Qld 4811, Australia.

D Oceanic Fisheries Program, Secretariat of the Pacific Community BP D5, 98848 Noumea Cedex, New Caledonia.

E School of Marine and Tropical Biology, James Cook University, Townsville, Qld 4811, Australia.

F Corresponding author. Email:

Marine and Freshwater Research 61(10) 1171-1184
Submitted: 3 November 2009  Accepted: 17 May 2010   Published: 14 October 2010


Multiple readings of otoliths are often carried out to assess the repeatability and reliability of increment counts for estimating fish age. Various criteria have been used to assign or discard age estimates from repeated counts when discrepancies occur although the reasons for doing so are usually not stated or justified. Trends in relative frequencies (percentage disagreement, PD) and magnitudes (inter-read discrepancy, IRD) of otolith-count discrepancies were explored for 15 species of fish collected from a range of locations around Australia to explore generality in the best explanatory model(s) for otolith-count discrepancies and, hence, the most appropriate criterion for accepting or rejecting age estimates from multiple-count data. Increasing discrepancies with increasing age, according to a constant per-increment probability of error, was the best-approximating model for 9 of the 15 species for PD data but for only two species for IRD data. Our results indicated disproportionately higher rates of rejection of estimates from older age groups if exact agreement between repeated counts was required for age acceptance. Results varied with the reader, region and the method of otolith reading, indicating that multiple criteria for accepting or rejecting counts from multiple readings may be required among or even within species.

Additional keywords: ageing precision, quality control.


We thank Andrea Molinari, Bob Mosse, Cameron Murchie, Campbell Davies, Garry Russ, Jake Kritzer and Jeffrey Norriss for sampling, preparing and reading otoliths to produce count data for several of the species studied. We also thank the ELF field team, Department of Fisheries (Government of Western Australia) research staff, and commercial and recreational fishers for assistance with sample collections in the eight study regions. Thanks also go to Samantha Bridgwood, Brett Molony, Kimberley A. Smith, Peter Marriott and one anonymous reviewer for constructive comments on earlier drafts. We acknowledge financial support from the Fisheries Research and Development Corporation for collection of data for S. semifasicatus (FRDC Project 2005/010), G. hebraicum and P. auratus (FRDC Project 2003/052), and from the Cooperative Research Centre for the Ecologically Sustainable Development of the Great Barrier Reef and from James Cook University. Sampling work was conducted under the following permits: GBRMPA permits G96/454, G01/603, G03/8896.1, QFMA Permit No 42294 and extensions, Queensland Fisheries Service permits PRM03517C, PRM02628J, JCU Ethics approval nos. A771_02, A566. This manuscript is a joint contribution from the CRC Reef Effects of Line Fishing Project and from the Department of Fisheries (Government of Western Australia).


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