Groper; Baldchin
Choerdon rubescens
The baldchin groper has a variable body colour ranging from greenish-brown to pinkish-grey. The species is best recognised by the rounded head, small eye and white chin, particularly prominent in mature males. They also have a very high, sloping forehead and protruding tusk-like teeth in both jaws. Baldchin gropers grow to 90 centimetres in length and can weigh up to 14 kilograms. Large animals are generally confined to deep reefs, while juveniles live in shallow seagrass and algal beds, and occasionally shallow sandy areas near coral reefs. They are carnivorous using their powerful teeth to lift rocks off the bottom in search of molluscs and sea urchins, and they also feed on squid, octopus, and occasionally crustaceans.
Baldchin groper are endemic to Western Australia and can be found from Coral Bay to Geographe Bay, with the most abundant populations around the Abrolhos Islands, which is also their main known spawning ground.
Baldchin groper are slow-growing and long-lived species that reach a maximum age of approximately 22 years old. Because of their slow growth rate, baldchin groper populations are likely to take a long time to recover from sustained overfishing. As with most wrasses, they are classed as protogynous hermaphrodites, where they change sex from female to male at any time once they have reached maturity as a female (monandric), which is about two to three years of age and 29 centimetres in length. The size at sex change is variable (8 to 12 years) and occurs over a range of sizes (48 to 55 centimetres long), and what triggers this change in gender is still unknown to researchers. Although baldchin groper are more often a solitary species, they aggregate in large groups of up to 100 individuals to spawn. Populations of baldchin groper are considered to be resident within reef systems with movements between shallow and deep waterBaldchin groper are targeted by anglers along the central western Australian coast putting a lot of pressure on populations. Biological traits, such as the fact that they are slow-growing and reach sexual maturity as males quite late in life can put populations at risk, particularly if juveniles are captured. This along with the high mortality rates of bottom-dwelling fish suffering barotrauma, where gases’ expand in the fish’s body caused by rapid changes in pressure similar to the “bends” that humans experience after being brought to the surface rapidly. Due to their aggregating spawning habits, this makes them vulnerable to high levels of fishing, as does the fact that they tend to reside on the same reef throughout their life, making them easy for fishers to locate using GPS.
Occurrence at the Busselton Jetty
Solitary juvenile baldchin groper have been observed occasionally from the underwater observatory.
Image by: A. Gannaway
