Leafy Seadragon Habitat Threatened

 

Protect the Western Blue Groper

 

Robert Browne

 

The habitats of the Leafy Seadragon are being threatened by the decimation of western blue groper populations. The western blue groper is a very special and magnificent fish essential to the ecological function of South Australian reefs and their surrounding areas.

 

The total protection of the western blue groper must be immediately implemented as recommended by the – South Australian Scalefish Fishery Management Committee - to sustainable mange the largest and most magnificent resident reef fish in South Australia, and our reefs ecology, recreational fishing and eco-tourism. 

 

South Australia is fortunate to have surviving populations of the western blue groper (Achoerodus gouldii).  The western blue groper is a giant member of the wrasse family and grows to 1.7 meters and 70 years of age.  The western blue groper is the largest reef-dwelling fish, in South Australia, and a slow grower taking 15 years to reach sexual maturity at 55-60 cm, and 70 years to reach a maximum length of 1.7 m.  Populations of western blue groper are very susceptible to fishing pressure and the shortest population doubling time is more than 14 years.

 

For divers, it is a special treat to see a groper swimming slowly and majestically in the water, approaching the diver fearlessly, and then following with disarming curiosity.  Whether a fisher or a diver we all like blue groper and want the minimal protection to sustainable manage the species and therefore restore numbers and foster older fish. 

 

We know that blue groper provide ecological balance to the system.  Blue groper eat large invertebrates including urchins, both grazing and predatory molluscs, and crustaceans.  These invertebrates in turn regulate the large seaweeds and other macroalgae that grow on reefs and thus influence the vegetation and community structure. 

 

For instance the blue groper is a major predator of the spiny sea-urchin.  In reef habitats across the globe - when uncontrolled - sea urchins have devastated reefs, leaving sea-urchin barrens devoid of algae. Sea urchin barrens are increasing along the east Tasmanian coasts reducing the productivity of the reefs by 80-90%.

 

The adults also have a remarkable bite-and-suck behaviour, by which they can dislocate their jaw and open it widely to bite large chunks of the algal mat, suck them into the gaping mouth cavity, and then filter out the tiny crustaceans living in the mat. This manner of feeding is difficult and exhausting, and it may not be only a friendly gesture when a groper takes a piece of abalone or other shellfish from a diver. 

 

Therefore, natural populations of the blue groper are necessary to provide ecological stability to reefs.  This then leads to the reefs being able to support and maintain the population of the many fish that aggregate on reefs like Trevally, Snapper, and other bottom feeders.

 

 

The blue groper is a wrasse. Wrasse are intelligent, inquisitive and active fish and many are brightly coloured with large scales.  Many smaller brightly coloured wrasse make delightful aquarium fish.  Most wrasse are territorial and many inhabit territories occupied by a family of males and females. Many wrasse that live in families have an interesting method to maximise egg production.  Most of the wrasse are females and when the dominant male dies the biggest female changes into a male. 

 

The blue groper has an interesting life history.  They spawn in spring and the larvae drift in the ocean for a couple of months then settle in shallow close inshore reefs.  These babies feed on tiny mussels scraped from the rocks or on small crustaceans.  As they grow to juveniles they brave deeper water of two to three meters depth and are a dull green-grey.  The juveniles then change to a uniform pale green and stay in sheltered waters and grow for ten years until they are sub-adults 20-60 cm long.  Along open coasts these sub-adults are not abundant and are at densities of one to eight every hundred meters of rocky coastline.

 

Once large blue gropers were common and the blue groper was abundant in its reef home.  However, years of fishing both deliberately and as incidental by catch have reduced their numbers. Marine conservationists have already initiated an educational process to alert concerned fishers to identify and release juvenile blue groper. 

 

In 1971 the blue groper was finally protected in Gulf St Vincent and Spencer Gulf.  There is a minimum 60 cm and maximum 100 cm size limit to blue groper. However, blue groper juveniles although protected are still captured by recreational fishers, and blue groper numbers are almost certainly less than they once were.  Even though concerned for blue groper conservation, many fishers do not recognize that the small greenish “rock cod” that they have caught is in fact a juvenile blue groper. On southern Yorke Peninsula, where adult blue groper were once common they are now rare.

 

As sub-adults mature they change to a beautiful blue, the females being somewhat more greenish than males. They move to deeper water feeding on crabs, molluscs, sea-urchins, and worms and might even move offshore to deeper reefs of 30-50 m.

 

Juveniles blue groper are first seen at 5-10 cm size, and are called  juveniles to a length of 20 cm when they are aged about two years old, they then sub-adults from 20-60 cm length with an age range from 2-15 yrs.  Please release any blue groper you accidentally capture.

 

 

The blue groper lives in small families of a mature male and female and some sub-adults occupying a home range over several thousand square meters. Males fiercely combat for their territories but their valour is not protection against modern fishing methods.  Mostly the groper is a gentle creature and swims placidly over its territory, occasionally diving to the bottom to roll over boulders in search of small crabs, sea-urchins or molluscs.

 

When fishing for wrasse the large dominant males, if there are any left, are often the first caught. Blue gropers are large fish and do not handle catch-and- release well, particularly when large specimens are hauled up from depths.  Large males that may dominate a particular territory – even if they survive – would have their reproductive potential compromised.  So a male blue groper caught even if released is effectively worse than a dead fish; he is probably incompetent and preventing the dominant female from taking his place.

 

A blue throated wrasse. This species is related to the blue groper. 

Image courtesy of David Muirhead.
 

There are an increasing number of charter boats that are working the offshore islands.  The Charter boat fishery is able to take an increasingly large number of people to these sites, and catch and release would inevitably damage the blue groper population.  There is also increasing pressure on southern blue morwong, redfish, boarfish and other large reef fish.  However, the sustainable management of offshore reef charters is dependent on the total protection of the blue groper.

 

There have been many attempts over the last 40 years to protect the blue groper, beginning in the 60’s with Dr Scoresby Shepherd– order of Australia 2007 - and other early divers, then by SCUBA divers associations in the 70s and 80s, and by individual attempts since then.  In 2005 it was recommended to the South Australian Dept of Primary Industry and Resources that the blue groper be protected under the Fisheries Act, but this has not occurred. 

 

During the 1960s the new sport of spear fishing became popular.  At this stage even later marine conservationists like Rod Taylor and Jacques Cousteau loved spearing trophy fish.  Along with many other large resident fish across the world the blue groper – who would swim up to divers - were decimated.  Of course spear fishing divers would usually target the largest fish. 

 

Divers and fishers target the blue groper, a trophy, a prize; take a photo and show people.  Nowadays many would rather see blue gropers common again, to know that they are there, that there is a world where big blue gropers swim close to their original numbers and size. There used to places accessible to the public where you could feed blue gropers on the rocks. Blue groper look like grey ghosts rising from the depths then slowly assume shape, colour and texture as they reach the surface.

The total protection of the blue groper must occur now to protect both the largest and most magnificent reef fish in South Australia, to protect our reefs ecosystem for the sustainable management of reef fishing, and to provide for diving eco-tourism.

The recreational sector is very important to the people of South Australia and spends $419,000 every day of the year in pursuit of recreational angling, is the fifth largest employer supporting 15,000 jobs and has a total investment in excess of $1.2 billion in boats and tackle.

South Australian Recreational Fisheries Advisory Council (SARFAC) is a prescribed peak body recognized in Government Fishery Regulations, whose role is to advise government on recreational angling issues and to advocate on behalf of the 427,000 recreational anglers that fish in South Australia. 

SARFAC co-manages South Australia's fisheries with government, the commercial sector and community and co-ordinates eight government regional recreational fisheries committees.

The adequate implementation of the full protection of the blue groper will require the support of recreational fishers.

Acknowledgements:  This article is based on many years of work by Dr Scoresby Shepherd, South Australia, Reef Watch, MLSSA and many others that treasure the unique marine life of South Australia.