For the purpose of this information, estuarine commercial fisheries (both fish and crustaceans) in Australia have been classified as being estuarine dependent or estuarine opportunist. Estuarine dependent commercial fisheries in Australia, defined as fisheries where the fish or crustaceans, as the case may be, are critically dependent on the estuarine environment for the survival of the species, include prawn fisheries such as the Northern Australian Prawn fishery, oyster fisheries such as the Sydney Rock oyster which is a native species of oyster located along the eastern seaboard as well as the Barramundi fishery and Mud Crab fisheries along the north east coast and the Gulf of Carpentaria. Because these fisheries are dependent on the ecosystem habitat provided by estuaries, such as mud flats, tidal creeks and seagrass areas, their continued survival is dependent on estuaries remaining largely unmodified.
Potter and Hyndes (1999) define estuarine opportunist fish, including such fish as Trevally and crustaceans such as Spanner Crabs, as those that spend at least a part of their life cycle, particularly as juveniles, in an estuarine environment but could equally use protected marine waters as nursery areas . These fisheries include some species of crab, the Australian Herring, the Australian Salmon and Whiting. Because these fish or crustaceans are not critically dependent on habitat areas provided by estuaries, their continued survival is not as threatened by the modification of estuaries. As the definition of estuaries for the information sheet is somewhat liberal, including a number of bays such as Shark Bay, Hervey Bay and Port Phillip Bay, the species specified here as estuarine opportunist is somewhat broad.
The following fisheries are examples of estuarine dependent fisheries. The information is far from exhaustive but serves to provide an indication of the value of a number of important fisheries.
Oyster fisheries are estuarine dependent. High quality water is critical to the edible oyster industry. For the most part, this fishery is located in estuaries that have not been substantially altered by human settlement and where the water quality is of a high standard. The NSW oyster industry produces the native Sydney Rock Oyster. The value as landed catch (excluding transport, processing, marketing and retailing of the product) is estimated to have been worth approximately $32m in 2000-2001. Production between 1998 and 2001 is estimated to have declined slightly by 150 tonnes. Exports from the industry are negligible whilst imports of edible oysters have been steadily increasing since 1995, mostly sourced from New Zealand . The increase in imports of oysters is a matter of some concern if this is due to a failure of producers to meet domestic demand due to reduced habitat. In South Australia and Tasmania, oyster fisheries produce Pacific Oysters, an introduced species. This species is regarded as an invasive pest capable of inflicting ecological damage to the native Sydney Rock Oyster as it competes with the native species for food and space. The Pacific Oyster industry is estimated to have been worth approximately $25.5m in 2000-2001. The value of this industry has increased by over $4.5m since 1999 .
Production of prawns from the Northern Australian Prawn fishery, the largest wild-harvested prawn fishery in Australia, is estimated to have been worth over $164.6m in 2000-2001. Production has increased from 5,605 tonnes in 1999-2000 to 9,752 tonnes in 2000-2001 . Prawn fisheries are especially reliant on estuarine habitat areas, particularly tidal creeks and mud flats, for spawning and for the development of juveniles and on substantial fresh water flows to flush adult prawns into marine areas for commercial harvesting. Native harvested prawn fisheries are located all around the Australian coastline with significant catches from Western Australia, Queensland, New South Wales and South Australia.
In Queensland, the volume and value of wild harvested prawns has increased from approximately 6,536 tonnes in 1999-2000 to 6,916 tonnes in 2000-2001 worth $101.7m. During the same time period, production from aquaculture increased very slightly from 2,505 tonnes in 1999-2000 to 2,525 tonnes in 2000-2001 .
In Western Australia, wild catch prawn fisheries were estimated to be worth over $46.4m in 2000-2001 with over half of this sourced from the Shark Bay Prawn Fishery and from the Exmouth Gulf Prawn Fishery, producing King and Tiger prawns which are mostly exported. Both of these fisheries are managed with spatial and temporal closures to protect spawning stock levels and catch sizes .
The value of prawn fisheries in NSW, producing King Prawns, School Prawns and Other Prawns is estimated to have been worth nearly $28.3m in 2000-2001 and in South Australia the catch is estimated to have been worth $42.6m in 2000-2001 .
In 2000-2001, Australia imported $174.6m of prawns, over one third of this coming from Thailand. Over the same period, Australia exported $291m of prawns sourced from both wild and aquaculture fisheries .
Barramundi caught in the wild by commercial fishers are sourced exclusively from the Northern Territory and Queensland. Barramundi are a catadromous species growing to maturity in the upper reaches of freshwater rivers and streams thriving in ecosystem habitats that are largely unmodified. Because adults move downstream to estuaries and coastal waters for spawning, it is important that their movement is not hindered by in-stream water structures such as dams or barrages. It is reported that specimens captured from clean estuarine waters make excellent table fish. However, the quality of the flesh from specimens that have been captured in turbid and muddy water is less reliable . The wild harvested Barramundi fishery is estimated to have been worth nearly $12.8m in 1999-2000, ($5.5m from the Northern Territory and over $7.3m from Queensland). Production from this fishery is indicated to have been steadily increasing from approximately 1,745 tonnes in 1999-2000 to 2,088 tonnes in 2000-2001 . Barramundi is one of the most popular fish targeted by recreational fishers with over a third again of the commercial catch caught by recreational fishers. Recreational fishers are dealt with below.
A number of species of crab are estuarine dependent. These include mud crabs and blue swimmer crabs (sand crabs). In NSW and South Australia, commercial crab production in 2000-2001 was valued at over $8.2m and in Queensland it was worth $26.3m. Only in Queensland and the Northern Territory has the catch increased since 1997-98. The mud crab fishery is the Northern Territory's largest wild harvest commercial fishery, valued at over $10m in 2000-2001 .
The value of production from fisheries that use the protection of estuaries, but are not totally dependent on the conditions offered by estuaries is substantial. This valuation of commercial fisheries depends heavily on statistics provided by ABARE Fisheries. There are two notable shortcomings with reliance on this source. The first is that ABARE only publish specific species information about the more valuable commercial fisheries so there are many species of fish that are not individually identified, such as Flathead. The second shortcoming is that ABARE Fisheries statistics adopt the common name for fish rather than the biological name. In so doing, the estimates of fish catches could be adopting a common name that is not necessarily compatible with the biological name and which has a different local name in another state, for example the Jewfish. A summary table of the aggregate value of commercial estuarine opportunist fisheries in each state is provided below.
Lenanton and Potter (1987) estimated that in temperate Western Australia, estuarine opportunist commercial fisheries were worth $3.7m per annum . In Western Australia, these fisheries include Cobbler, Sea Mullet, Yelloweye Mullet, Australian Herring, Australian Salmon and Whiting. In 2000-2001 these fisheries are estimated to have been worth $3.7m .
In Queensland, these fisheries include Bream, Mullet, Snapper, Tailor and Whiting valued at $12.3m to commercial fishers in 2000-2001. Production from these fisheries in 2000-2001 has increased by almost 250% since 1999-2000 .
Estuarine opportunist commercial fisheries in NSW include Black and Yellowfin Bream, Australian Salmon, Rubberlip Morwong, Snapper and Sand Whiting. In 2000-2001, these fisheries were valued at $7.5m .
Victorian commercial fisheries that are estuarine opportunist, including Bream, Australian Salmon, King George Whiting, Pilchards, Snapper and Sea Garfish, have remained relatively stable over the period 1997-2000, valued at $5m in 2000-2001 .
Estuarine opportunist commercial fisheries in South Australia include the Australian Salmon, Mullet, Australian Herring, King George Whiting, Yellowfin Whiting, Pilchards, Snapper and Garfish. These fisheries were estimated to be worth over $17.2m in 2000-2001 .
Production in Tasmania from estuarine opportunist commercial fisheries, including Australian Salmon, Garfish, varieties of Morwong and Trumpeter fish as well as School Whiting were valued at $1.2m in 2000-2001. Catches have remained relatively stable between 1997-98 and 2000 .
In the Northern Territory, estuarine opportunist commercial fisheries include Jewfish, Snapper and Threadfin Salmon valued at $2.9m in 2000-2001 .
To conclude, it is apparent from these figures that commercial fisheries make a substantial economic contribution to the Australian economy. Needless to say that over exploitation of these fisheries beyond their maximum sustainable yield will result in lost production of these commercially exploitable species bringing about economic losses. However, it should not be assumed that this is where the economic consequences will end. Diminished production in one fishery could alter the balance of production in other parts of the marine ecosystem, resulting in wider economic repercussions. These economic repercussions could range from broad scale production losses in commercially exploitable fisheries to diminished regional tourism value due to the absence of previously present charismatic marine organisms like whales.