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RESEARCH ARTICLE
Contents Vol 60(9)

Assessing growth band counts from vertebrae and dorsal-fin spines for ageing sharks: comparison of four methods applied to Heterodontus portusjacksoni

Javier Tovar-Ávila A B C E , Christopher Izzo D , Terence I. Walker A B , J. Matías Braccini A B and Robert W. Day A
+ Author Affiliations
- Author Affiliations

A Department of Zoology, University of Melbourne, Parkville, Vic. 3052, Australia.

B Marine and Freshwater Fisheries Research Institute, Fisheries Victoria, Department of Primary Industries, PO Box 114, Queenscliff, Vic. 3225, Australia.

C Centro Regional de Investigaciones Pesqueras Bahía de Banderas, Instituto Nacional de Pesca, A.P. 59 Bucerías, Nayarit 63732, México.

D Southern Seas Ecology Laboratories, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, SA 5005, Australia.

E Corresponding author. Email: javiertovar.mx@gmail.com

Marine and Freshwater Research 60(9) 898-903 https://doi.org/10.1071/MF08206
Submitted: 15 July 2008  Accepted: 19 February 2009   Published: 22 September 2009

Abstract

Four methods for counting growth bands using vertebrae and dorsal-fin spines of the Port Jackson shark, Heterodontus portusjacksoni, are compared. Both calcified structures presented observable growth bands, allowing cross comparison among structures for the first time in a shark species. Whole and sectioned vertebrae and dorsal fin-spines possess highly visible growth bands and intra-reader band counts resulted in similar precision indices with little systematic bias. However, inter-reader growth band count plots showed possible biases in counts from sectioned vertebrae and sectioned dorsal-fin spines. Sectioned vertebrae and whole and sectioned dorsal-fin spines produced similar growth band counts, whereas whole vertebrae produced significantly lower counts. The similar readability, precision indices, growth band counts and apparent absence of biases between counts for a single reader would indicate that sectioned vertebrae and whole and sectioned dorsal-fin spines are both potentially useful and acceptable methods for band counting. However, inter-reader comparisons are necessary to avoid acceptance of biased estimations, resulting in over- or under-estimations of age. Validation for all age classes is essential to determining accurate age estimations for this and other species.

Additional keywords: age and growth, calcified structures, chondrichthyes, elasmobranchs, Port Jackson shark.


Acknowledgements

We thank the anonymous referees who improved this paper with their detailed comments and corrections and the following people for their contribution in collecting samples, material processing and statistical advice: Matt Reardon, Kate Rodda, Toby Bolton, observers and commercial fishers from Victoria and South Australia, staff of the Central Ageing Facility (MAFFRI) and Ann Grant. This research was supported by two Australian Fisheries Research and Development Corporation grants (FRDC Project 2002/033 to K. Rodda and FRDC Project 2003/023 to T.I.W.). The senior author was supported by a Postgraduate Scholarship from the National Science and Technology Council and the National Fisheries Institute from Mexico, and by a David Hay Writing Up Award from the University of Melbourne for preparation of this paper.


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