Northwest Australian Shelf large marine ecosystem
The Northwest Australia Large Marine Ecosystem (LME) is characterized by its tropical climate. It extends from North West Cape to the vicinity of the Timor Sea. The LME has a wide continental shelf and it includes topographical features such as the Exmouth Plateau, the Rowley Shelf and the Sahul Shelf. The LME is positioned on the path of the Indonesian Throughflow, a warm-water current flowing from the Pacific into the Indian Ocean. This current warms the LME’s sea surface and increases rainfall over Western Australia. Rainfall however is irregular, with occasional cyclonic disturbances and flash flooding resulting in brown sediments. The tropical waters are warm, and the coast includes reefs and extensive mangrove forests. Tropical cyclones are common seasonal events in this LME. Cyclones exert pronounced effects on the continental shelf and on coastal marine ecosystems. The rainfall that accompanies cyclonic weather systems can be a major source of freshwater to the region, causing widespread though episodic flooding.
The Northwest Australian Shelf Large Marine Ecosystem is considered a Class III, low productivity (< 150 gC/m2-yr) ecosystem based on SeaWiFS global primary productivity estimates. Temperature and salinity measurements of the Indonesian Throughflow and the South Equatorial Current were made as part of the World Ocean Circulation Experiment (WOCE). More information is provided in CSIRO Marine Research. The Northwest Australian Shelf system is characterized by a high-energy tidal regime. Tidally induced mixing is a major contributor to nutrient dynamics. Bottom friction acts in a manner analogous to wind stress on the surface to mix the water column. Shelf upwelling and cyclonic disruptions also contribute to nutrient inputs that support the productivity of this LME. The warm tropical waters are the home of corals, fish, starfish, sponges, turtles and shells. The continental shelf supports a diverse demersal fish community. For a general understanding of oceanographic processes affecting nutrient dynamics and the productivity of Australian marine ecosystems, see the State of the Environment Report, and Furnas.
Fish and Fisheries
Australian waters are relatively nutrient-poor and unable to sustain large fish populations. In the Northwest Australian Shelf LME, fish stocks are quite small. The level of endemicity in northern Australian LMEs is low, with most species distributed widely in the Indo-West Pacific region. Reef fisheries occur in the Rowley Shoals, a chain of coral atolls at the edge of the LME’s wide continental shelf. Demersal species that are fished in this LME include Lethrinus, Nemipterus, Saurida, and Lutjanus. These demersal species have historically been fished by foreign fleets. A small domestic trap fishery for Lethrinus, Lutjanus, and Epinephelus exists in areas subjected to little trawling. Until recently, fisheries resources were usually managed in separate fishery units. Under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act), the Commonwealth Government now has a framework that helps it to respond effectively to current and emerging environmental problems, and to ensure that any harvesting of marine species is managed for ecological sustainability. After examining several possible management regimes for this LME, the government of Australia divided the area into three zones and closed two of them to trawling. It is thought that there will be an expansion of trap fishing in the two closed areas after the species composition changes induced by trawling are reversed. For detailed fish catch statistics for this LME, see data collected by the University of British Columbia Fisheries Center. The Food and Agriculture Organization (FAO) website provides information on Australia’s fisheries industry.
Pollution and Ecosystem Health
The LME is threatened by an increase in shipping. Ships empty of cargo that enter the ports of Northwest Australia are ballasted with water collected in the last port of call. This ballast water has been shown to contain organisms including bacteria, viruses, algal cells, plankton, and the larval forms of many invertebrates and fish. There are accidental discharges of contaminants, such as spills and shipping accidents. This LME’s marine parks, home to a variety of plants, corals, fishes and marine mammals, are impacted by tourism. Activities associated with recreational fishing, SCUBA diving and boating have the potential to affect the environment through the pollution of water by boats and the disturbance of species and habitats. Recreational fishermen tend to target reef ecosystems and remove larger predatory species. The effects of this selective removal of fish are largely unknown. A source of environmental impacts is the provision of infrastructure to support tourism (airports, power generation facilities, accommodation, sewage treatment and disposal facilities, moorings, and marine transport). This infrastructure is being established in fragile or pristine environments that are susceptible to disturbance and fragmentation. For more information, see Environment Australia for marine and coastal pollution issues, and the State of the Environment Report.
Thousands are involved in the fisheries, aquaculture and processing sectors of the economy. The Food and Agriculture Organization (FAO) website provides information on the characteristics and socioeconomic benefits of Australia’s fishing industry. There has been exploration for oil and natural gas. Industry, shipping and tourism are major economic activities. Marine and coastal-based tourism is important in this LME both in terms of domestic and international tourism. A significant proportion of the Australian population is involved in recreational fishing, surfing, wind surfing, diving, snorkeling, and boating. Tourists from overseas prize the coral reefs and the natural and unspoiled marine environment. There are, however, social, cultural, economic and environmental impacts caused by tourism. Tourism may affect the lifestyle of residents in ways they perceive as intrusive. Negative social impacts may include real or perceived increases in crowding, prices, or crime, as well as increase conflict between commercial, recreational and indigenous interests.
The Northwest Australia LME lies off the coast of the state of Western Australia, not far from Indonesia. Some governance issues in this LME pertain to fisheries management and to the establishment of marine reserves (including Ningaloo Marine Park). Australian fisheries resources are managed under both Commonwealth and State/Territory legislation. The demarcation of jurisdiction and responsibilities among these various governments has been agreed to under the Offshore Constitutional Settlement (OCS). Under OCS, the state has jurisdiction over localized, inshore fisheries. The Commonwealth has jurisdiction over offshore fisheries. Foreign fisheries are managed by the Commonwealth fishery agencies. An important goal is to ensure that the exploitation of fisheries resources is conducted in a manner consistent with the principles of ecologically sustainable development. This includes the need to assess the impact of fishing activities on non-target species and the long-term sustainability of the marine environment. For more information on the governance of Australia’s fisheries, see the FAO website. Reserves have been declared to help protect rocky shore habitats and marine life, provide opportunities for research and education, conserve Australia’s cultural heritage and help boost ecotourism. The marine tourism industry has produced a code of conduct that covers issues such as anchoring, removal of rubbish, fish feeding and preservation of world heritage values. Australia declared a 200 nautical mile Exclusive Economic Zone in 1978. Australia is party to the following international agreements: Antarctic-Environmental Protocol, Antarctic Treaty, Biodiversity, Climate Change, Endangered Species, Environmental Modification, Hazardous Wastes, Law of the Sea, Marine Dumping, Marine Life Conservation, Nuclear Test Ban, Ozone Layer Protection, Ship Pollution, Tropical Timber 83, Wetlands, and Whaling.
Articles and LME Volumes
- Menon, H.B., 1998. Role of Oceanic fronts in promoting productivity in the Southern Indian Ocean. In: Kenneth Sherman, E. Okemwa and M. Ntiba. (eds.), Large Marine Ecosystems of the Indian Ocean: Assessment, Sustainability, and Management (Cambridge, MA: Blackwell Science) pp. 175-191. ISBN: 0632043180.
- Furnas, Miles J., Land-sea interactions and oceanographic processes affecting the nutrient dynamics and productivity of Australian marine ecosystems.
- Sainsbury, K.J., Campbell, R.A. and Whitelaw, A.W. 1993. Effects of trawling on the marine habitat on the Northwest Shelf of Australia and implications for sustainable fisheries management. In: Hancock, D.A. (editor), Sustainable fisheries through sustaining fish habitat. Australian society for fish biology workshop proceedings. Victor Harbor SA, August 1992. Australian Government Publishing Service, Canberra.
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