Biological parameters required for managing Western Blue Groper, Blue Morwong and Yellowtail Flathead

This study provides the sound quantitative data that are required by managers for developing plans for conserving the stocks of the Western Blue Groper Achoerodus gouldii, the Blue Morwong (previously Queen Snapper) Nemadactylus valenciennesi and the Yellowtail Flathead (previously Bar-tailed Flathead) Platycephalus endrachtensis in south-western Australian waters. The first two species are commercially and recreationally important in coastal waters and the third is one of the most important angling species in the Swan River Estuary. All three species have been identified by managers as requiring detailed studies of their biology, and Blue Morwong and Yellowtail Flathead are among a small suite of species selected as indicator species for the status of fish populations in marine and estuarine waters, respectively, in south-western Australia. As juveniles, Western Blue Groper typically occupy reef areas in protected inshore waters along the coast and around neighbouring islands. As the individuals of this species increase in size, they move offshore to deeper and more exposed waters over reefs. Spawning occurs in the latter environment, between early winter and mid-spring. The maximum length and age we recorded for Western Blue Groper were 1162 mm and 70 years, respectively, the latter age being the greatest by far yet recorded for any species of wrasse. However, most of the growth of this species occurs in the first 20 years of life. The Western Blue Groper is shown to be a monandric protogynous hermaphrodite, namely all of its individuals begin life as females and, after maturing, many subsequently change sex to males. Females typically first become mature at about 650 mm and 15-20 years and typically change to males at lengths of about 800-850 mm and ages of about 35- 39 years. As sex change takes place over a narrower range in lengths (650 to 900 mm) than in ages (15 to 49 years), that change is apparently related more to size than age. The fact that sex change i