Using traditional age and growth techniques in endangered species management: eastern freshwater cod, Maccullochella ikei
Gavin L. Butler A B and Stuart J. Rowland AA NSW Department of Primary Industries, Grafton Aquaculture Centre, PMB 2, Grafton, NSW 2460, Australia.
B Corresponding author. Email: Gavin.Butler@dpi.nsw.gov.au
Marine and Freshwater Research 59(8) 684-693 https://doi.org/10.1071/MF07188
Submitted: 15 October 2007 Accepted: 2 June 2008 Published: 22 August 2008
Abstract
Age and growth estimates can be difficult to obtain for endangered fishes owing to their relative low abundance and the ethics associated with sampling threatened populations. The eastern freshwater cod, Maccullochella ikei Rowland 1985, is an endangered freshwater fish endemic to the Clarence and Richmond Rivers of New South Wales, Australia. Bony parts were gathered from archival collections and hatcheries, as well as opportunistically from the wild, to determine age and growth. Examination of opercular bones and dorsal spine sections revealed no consistent annuli. Sectioned otoliths exhibited consistent bipartite rings throughout the structures and 106 otoliths were used to estimate the age of cod from 0+ to 15+ years. Edge increment analysis and known-age cod were used to validate the age estimates. The von Bertalanffy growth equation for M. ikei is Lt = 704.9 (1–exp (–0.20 (t + 0.14))). A length–weight relationship of W = 2.80 × 10–6 × L3.2467 was established from 372 cod collected using non-destructive techniques. Significant differences were found in the relative condition of cod in summer (Kn = 0.999) and winter (Kn = 1.026). The information presented in this paper will assist in the conservation of M. ikei and will provide a guide for future age and growth studies of threatened species.
Additional keywords: condition factor, length-at-age, length–weight relationship, validation.
Acknowledgements
This study is from PhD research undertaken by G. Butler and was supported by Southern Cross University, NSW Department of Primary Industries, the Australian Research Council and Rous Water. All sampling was undertaken in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes (Permit No: 04/12). We would particularly like to thank Kevin Clark, Ron Cockbain, Col Graham, Max Graham, Jack Rowland, Ian Wooden, Mike Gilbert, James Knight, Robert Predo, Peter Boyd and Andy Moore for their tireless assistance with fieldwork. We would also like to acknowledge Professor Peter Baverstock for providing support and guidance. Thanks also to Dr Danny Bucher, Dr Kevin Rowling, Dr John Stewart, Dr Dean Gilligan and the anonymous referees for their comments on drafts of this paper.
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