The Eastern Blue Groper

Achoerodus viridis

Most divers would already know the Eastern Blue Groper. The Blue Groper is the largest reef and most well known fish in the waters around Sydney.

DISTRIBUTION
The Blue Groper is not a real ‘Groper’ as such but it is part of the Wrasses family. The Blue Groper is usually found on exposed reefs from about 0-40m deep. They range from Wilsons Promontory in Victoria up the east coast to around Hervey Bay Queensland. At most dive sites in Sydney, the banging of two rocks together will usually attract a Blue Groper (he thinks you are getting him something to eat!).

APPEARANCE
The Blue Groper male is the big blue fish that we all know and regularly see. The males also have orange coloured lines radiating out around their eyes. Look closely next time you see a Blue Groper while diving and see if you can notice the lines. The females are smaller and range from a brown colour to a reddish brown; they may also have a series of pale blotches along the side of their body. Juveniles start out as a green colour and then change to the brown of the female. Apart from colour the fish also has very large lips. The fish grows the max size of about 1m.

SEX CHANGE
The most interesting fact about the Blue Groper for me is that all Blue Groper start life as females and change into males later in life!! So a particular blue groper could breed as a female one year and then the next year turn into a male! Little is known about the factors which trigger this sex change however it is believed that they appear to change sex when they reach a certain size and age, or if the local male is removed from the reef the next biggest female will change to a male. It is also believed that if there is an increase in the female population a female may turn into a male if the threshold between the number of males and females is exceeded.

REPRODUCTION
The Eastern Blue Groper spawns over three months, starting around July and finishing up around October. So they should be spawning at the moment. There is not much information available in regards to their reproductive behaviour but recently on dives I have noticed the Blue groper males being particularly aggressive toward one another. Maybe this has something to do with it.

FOOD
Blue Groper love sea urchins, as most people would know. Please do not kill sea urchins to feed to the Blue Groper, no matter how tempting it may be. The sea urchins have their place in the reef ecosystem too. If you are tempted to feed them Akos Lumnitzer in his article on Blue Groper in the June/July edition of Sport Diving Magazine recommends boiled eggs and beach worms from the local tackle shop. Remember to watch your fingers if you try this. Apart from urchins their diet also consist of small crustaceans.

AGE
Blue Groper has been known to live as long as 35 years. Information by Bronwyn Gillanders in Under Southern Seas states that a 10 year old Blue groper will be approx. 48cm long and weight about 2.4kgs. At 20 years of age they will be approx. 62cm long and weight about 5.3kgs and at 30 years of age they will be approx. 73cm long and weight about 8.4kgs. So as you can see some of the Blue Gropers out at Oak Park must be at least 30 years old.

PROTECTED SPECIES
The Blue Groper is a friendly inquisitive fish that swims right up to divers; this is not a good characteristic for a fish, which is also large and tasty to eat. By the 1960s spear fishing had taken its toll and the blue groper has been a protected since 1969.