The Great Australian Bight (GAB) is a massive oceanic indentation off the central and western parts of the southern Australian coastline. This immense bay hosts a marine environment recognized globally for its distinctive biodiversity. Defined by unique oceanographic conditions, the Bight’s waters support a wealth of life largely isolated from other global marine systems.
Geographical Definition and Extent
The Great Australian Bight stretches across the coasts of South Australia and Western Australia, spanning approximately 1,160 kilometers from Cape Pasley in the west to Cape Carnot in the east. The northern edge is defined by the sheer limestone cliffs of the Nullarbor Plain, including the iconic Bunda Cliffs. These uninterrupted cliffs can reach heights of up to 120 meters, forming a remote boundary between the arid continent and the ocean.
Geologically, the Bight is characterized by a wide continental shelf, extending over 200 nautical miles in some areas before dropping sharply into deeper waters. Below the shelf lies the Bight Basin, a large sedimentary basin where depths can exceed 4,000 meters. The Bight formed approximately 50 million years ago during the final breakup of Gondwana, separating Australia from Antarctica.
The Bight’s waters are typically considered part of the Indian Ocean, though the Australian Hydrographic Service classifies the area as part of the Southern Ocean. This area is the world’s longest stretch of ice-free, east-west coastline facing the Southern Ocean’s circum-polar waters.
Unique Marine Ecosystems
The Great Australian Bight is distinguished by an extraordinary level of endemism, with over 85% of its marine species found nowhere else on Earth. This unique biodiversity results from the region’s long period of geological isolation. Habitats include cold-water coral reefs, sponge gardens, and expansive beds of macroalgae, encompassing over 1,200 species.
The ecosystem is driven by two contrasting oceanographic forces, creating a highly productive environment. The warm, nutrient-poor Leeuwin Current flows into the western Bight from the north. Conversely, seasonal upwelling of cold, nutrient-rich water occurs in the eastern section, particularly around the Eyre Peninsula. This upwelling supports a massive population of zooplankton, forming the base of a rich food web.
The Bight serves as a sanctuary for endangered marine mammals. The Head of Bight is a globally recognized calving and nursery ground for the Southern Right Whale, which migrates here from sub-Antarctic waters between May and November. The Bight is also home to the endemic Australian Sea Lion, which breeds in colonies along the coast, and is a habitat for Blue Whales and Great White Sharks.
Economic Significance and Resource Use
The Great Australian Bight supports significant commercial activities, particularly fisheries. The seasonal surge of nutrients attracts vast schools of small pelagic fish, supporting the lucrative Southern Bluefin Tuna (SBT) fishery. Juvenile SBT are caught in the Bight and towed to coastal farms for fattening before harvest.
The Great Australian Bight Trawl Fishery operates along the continental shelf, targeting demersal species like deepwater flathead and Bight redfish. This specialized bottom trawling occurs in a narrow band of the upper continental slope, generally between 100 and 400 meters deep. The region also generates revenue through coastal tourism, primarily seasonal land-based whale watching at the Head of Bight.
The Bight Basin has long been considered a frontier for offshore oil and gas exploration due to its deep sedimentary structures. This potential has met with significant public and environmental opposition due to the risk of spills in the pristine environment. Major international companies, including BP, Chevron, and Equinor, previously held exploration permits but withdrew from proposed drilling projects, citing commercial non-competitiveness.
Conservation Status and Protected Areas
Protection of the Great Australian Bight is managed through a network of legal frameworks, including the Great Australian Bight Marine Park (GABMP). The GABMP covers approximately 45,926 square kilometers, composed of both Commonwealth and state-managed areas. The park aims to protect the area’s unique conservation values while allowing for ecologically sustainable resource use.
The GABMP utilizes a zoning system to regulate human activities and maintain biodiversity. These zones include a Marine National Park Zone, which restricts most human interference, and a Multiple Use Zone, which permits managed activities like commercial fishing. A Special Purpose Zone, including a Mining Exclusion area, was also implemented to provide protection against extractive industries.
This structured management approach ensures the preservation of the Bight’s unique features, particularly the calving habitat for the Southern Right Whale and the pupping sites for the Australian Sea Lion. The park network contributes to Australia’s National Representative System of Marine Protected Areas, providing a scientific reference area for monitoring environmental change.