Reef Watch - A Community Environmental Monitoring Project Based in South Australia

SPECIALITY PROGRAMS - BLUE GROPER SURVEYS

Western Blue Groper Surveys

The Western Blue Groper (Achoerodus gouldii - hereafter known as WBG) is a long-lived, slow growing, site-associated fish considered found on the exposed coasts of southern Australia from Cape Leeuwin, W.A. to Victoria but is rare east of the River Murray mouth. The name "Groper" is a misnomer as it is actually from the wrasse family. Little is known of the biology of the species, but much of it can be inferred from that of the eastern blue groper (Achoerodus viridis).

This species is considered by some fisheries researchers and conservation experts in SA to be potentially threatened. The recent Australian Conservation Overview of Marine and Estuarine Fish (Pogonoski et al. 2001) suggested that WBG be classified as Lower Risk - Conservation Dependent on an Australia-wide basis, because the continued survival of this species in southern Australian waters may rely on its protection from over-fishing by line (commercial and recreational) and spear-fishers (recreational).

Although protected in South Australia's Gulfs and Investigator Strait, commercial and recreational fishing occurs throughout the rest of the state.

Blue gropers have been described as "highly vulnerable to overexploitation". In the 1980's, divers reported that western blue groper numbers were rapidly declining in areas south of Adelaide, due to commercial and recreational fishing, including spear-fishing. Charter boats target them in some areas of SA. Gropers are caught as a bycatch in shark and Commonwealth scalefish fisheries.

For these reasons it has been included as one of the "In Peril" species for the Feral or In Peril program. Sightings of western blue groper can be reported through this program. Some incidental sightings submitted on DragonSearch reports have already been entered into the Feral or In Peril database, and there have been a number of further reports since the program began.

Previous observations suggest that the WBG may take up to 15 years before reaching sexual maturity, when it changes from greenish colour to blue. Initial studies by Dr Scoresby Shepherd show they feed on crabs, smaller crustaceans, sea urchins and molluscs. On one offshore island group, male gropers were found to be site-attached and wandered over a home-range of up to 8000 m². The blue groper, like other wrasses, may play a key role in coastal ecosystems by controlling the abundance of crabs (which predate on small abalone), and sea-urchins (which consume algae).

Between 2002 and 2005, Reef Watch coordinated and supported four surveys of WBG, on the nearshore rocky reef areas on the western and northern coasts of Kangaroo Island (see article), southern Yorke Peninsula, lower Eyre Peninsula and the west coast between Elliston and Streaky Bay. The surveys were undertaken by Dr Shepherd in conjunction with a total of twenty Reef Watch divers over the four trips. Funding was provided by Coastcare and the Coast and Marine Conservation Branch of the Department for Environment and Heritage.

During the surveys, divers and snorkellers counted and estimated the size of groper along several replicated 100m x 5m transects. This method was found to be suitable for sampling females and sub-adults (20-60 cm), which are site-attached and swim in loose aggregations. However, the transects were not long enough to adequately sample the less abundant juveniles (<20cm) and adults (> 60cm), the latter having home ranges of up to 16,000 m². To more accurately estimate the density of adult fish, at times the divers swam greater distances; covering up to 1 km of the coast, noting where the home range of one pair ended and another began.