Vital demographic statistics and management of the baldchin groper (Choerodon rubescens) from the Houtman Abrolhos Islands
Kim Nardi A B D , Stephen J. Newman A , Michael J. Moran A and Geoffrey P. Jones CA Western Australian Fisheries and Marine Research Laboratories, Department of Fisheries, Government of Western Australia, PO Box 20, North Beach, WA 6920, Australia.
B Present address: Department of Fisheries, Government of Western Australia, 69–75 Connell Road, Geraldton, WA 6530, Australia.
C School of Marine Biology and Aquaculture, James Cook University of North Queensland, Townsville, Qld 4811, Australia.
D Corresponding author. Email: knardi@fish.wa.gov.au
Marine and Freshwater Research 57(5) 485-496 https://doi.org/10.1071/MF05187
Submitted: 19 September 2005 Accepted: 6 April 2006 Published: 29 June 2006
Abstract
In order to evaluate appropriate management strategies, the life history and demography of the baldchin groper (Choerodon rubescens) was examined from speared samples and commercial catches at the Houtman Abrolhos Islands, Western Australia. Ages were estimated from sections of sagittal otoliths, validated by oxytetracycline labelling of fish recaptured after a minimum of 12 months at liberty. Male C. rubescens (n = 147; 373–639 mm) ranged from ages 5 to 20 years, and females (n = 354; 226–610 mm) ranged from 2 to 13 years. The population underwent a transition in dominance from females to males at age 11–12 years and 500–550 mm total length. Gonad development was seasonal and spawning was evident from spring to summer (September–January), with evidence of aggregation behaviour. Indirect estimates of the annual instantaneous rate of natural mortality (M) ranged from 0.05 to 0.58 and total mortality (Z), ranged from 0.21 to 0.56, rendering stock assessment highly uncertain. The limited geographic range, slow growth, long potential life span, protogynous sex change, aggregative spawning and high discard mortality rates render C. rubescens susceptible to overfishing. In order to manage this mobile species successfully, marine protected areas must continue to be supplemented by strict catch controls in fished areas.
Extra keywords: age, age validation, growth, mortality, reproduction, sectioned otoliths.
Acknowledgments
This paper is dedicated to the memory of the late Colin Chalmers, Manager of the Fish and Fish Habitat Protection Program of the Department of Fisheries (Government of Western Australia), an active supporter of all aspects of this project. The authors gratefully acknowledge the funding and logistical support provided by the Department of Fisheries, Government of Western Australia. We would like to sincerely thank all the willing volunteers who helped dissect numerous fish at the fish markets or at the Abrolhos Islands, in particular, Nicole Horsman, Jackie Sauvage, Rod O’Halloran, Chris Dibden, Richard Sellers, Dr Lindsay Joll and Clinton Syers. The authors are thankful to the Geraldton fish processors and numerous professional fishermen who allowed us access to fish caught at the Abrolhos Islands in order to process samples. Technical assistance provided by Dr Michael Mackie and Lisa Farrington was appreciated. Constructive comments on the draft manuscript provided by our colleagues are greatly appreciated.
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