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The Shoalwater Bay seagrass beds are likely to be significant to regional fisheries production. Commercially important prawns were found at each of the seagrass beds which were sampled and represented 99% of the prawns sampled. The western king prawn was the most abundant of the commercial species, but the true endeavour prawn, red endeavour prawn and brown tiger prawn were also common in the seagrass beds. The abundance of other invertebrates and juvenile fish found in beam trawl samples also indicate a significant source of food in local marine food webs.
Monitoring sites were established on selected meadows which are intended for survey every two years. A complete post-wet season mapping survey was undertaken in April 1996, the results of which are currently being analysed.
 Mumford Island in the north-east of Shoalwater Bay is typical of most of the islands in the area being made up of a series of granite/basalt islets with small beaches with a surrounding fringing reef. |
Eighteen reefs were surveyed and ranked according to their ecological value (Done 1995). Coral cover was very variable ranging from sparse (7%) on fringing reefs dominated by the macroalga, Sargassum, to high (66%). Most fringing reef community types were dominated by acroporids and Montipora species, but extensive stands of Turbinaria frondens were also common. For most species of coral, sizes were smaller than those found in most fringing reefs, but for plate-forming Acropora, many unusually large colonies were found (up to 5 m in diameter!). Many colonies of Turbinaria frondens were also found in the size class 2-5 m, the largest single colony measuring 4.55 m x 3.85 m! The best reefs (in terms of bioconstuction and biodiversity) were generally found in the north-east of Shoalwater Bay.
The diversity of corals was moderately low with a total of 87 species found in Shoalwater Bay (over a total of 25 diving hours), compared with 120 species found in inshore fringing reefs in the Cairns area (30 diving hours), 131 species at Dent Island in the Whitsunday area (2 diving hours) and 143 species around Cape Tribulation fringing reefs (10 diving hours). However, a number of species were found which are considered 'rare' on the Great Barrier Reef (Veron 1986), although some may be common in temperate waters. These include Acanthastrea hillae, Acanthastrea bowerbanki, Favia maritima, Acropora glauca, Acropora solitariensis and Turbinaria bifronds. These species were found at nearly all sites. Another interesting feature of coral diversity was the notable absence of many species, and indeed whole genera, which are found on most fringing reefs to the north. These include Echinopora (all species), Pectinia (all species), Oxypora (all species), Pavona (all species), Fungidae (all genera, except Podabacea crustacea), Millepora tenella, Merulina ampliata, Porites cylindrica, Acropora humilis and Acropora gemmifera.
In terms of the proportion of Queensland's total commercial fish catch, the Shoalwater Bay area contributes around 1% of the state's finfish, of which blue salmon is the dominant species. An average of 16 tonnes of blue salmon are caught annually, representing around 12% of Queensland catch. Other major species in the finfishery are shark, barramundi, mullet and grey mackerel, each representing between 0.3-3% of the state's catch (see figure 2 below). With the exception of shark and mackerel, almost all finfish are caught by gill netting. This has resulted in an unknown, but probably large, number of dugong deaths in the area. The restriction on gill netting on the foreshore in Shoalwater Bay, which was proclaimed in late 1995, may reduce future effort and catch in this fishery.
Figure 2. Average annual finfish catch and its relative importance to total Queensland production
The trawl fishery effort is concentrated immediately east of Shoalwater Bay between Townshend Island and Corio Bay with total prawn catches averaging 85 tonnes per annum, representing around 1% of the state's total prawn catch. Banana and endeavour prawns are the dominant species caught. Banana prawn are the major species caught and represent around 46% of the total prawn catch in the Shoalwater Bay area. However, catches have been highly variable from year to year, ranging from 7 to 85 tonnes between 1988 and 1994, and show a strong positive correlation with rainfall. By-catch from trawling is undocumented for this area, except for incidental capture of turtles. A voluntary logbook program (Queensland East Coast Otter Trawl Fishery) shows that 14 turtles were caught between 1991 and 1994 in the Shoalwater Bay area, but none died.
Other fisheries of note are the mud crab fishery which averaged around 29 tonnes per year between 1988 and 1994, which represents around 8% of the Queensland catch, and the oyster fishery which averaged around 7% of the state's catch.
The status of exploited fish stocks are unknown. Catch statistics from the Queensland commercial fishing database, C- FISH, show highly variable catches for most fisheries over the six years between 1988 and 1994 and allow no conclusions to be drawn.
Most of the commercial species caught are mangrove/ estuarine specialists and, given the vast area of mud banks, seagrass beds, couch flats and mangrove forests in Shoalwater Bay, it is likely that the intertidal habitats contribute appreciably to fisheries resources. However, the extent, value and nature of the interaction between nursery/habitat areas and fisheries production is unknown.
ReferencesDone, T.J. 1995, 'Ecological criteria for evaluating coral reefs and their implications for managers and researchers', Coral Reefs, 14:183-192.
Veron, J.E.N. 1986, Corals of Australia and the Indo- Pacific, University of Hawaii Press, Honolulu, 644 pp. |
Great Barrier Reef Marine Park Authority
PO Box 1379 TOWNSVILLE QLD 4810. Phone: (077) 500 700, Fax:
(077) 726 093
E-mail:
registry@gbrmpa.gov.au