Vital demographic statistics and management of the baldchin groper (Choerodon rubescens) from the Houtman Abrolhos Islands

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.