Marine bioregional plan for the South-west Marine Region - Draft for Consultation
Department of Sustainability, Environment, Water, Population and Communities, 2011
The South-west Marine Region comprises Commonwealth waters from the eastern end of Kangaroo Island in South Australia to Shark Bay in Western Australia (Figure 2.1). The region spans approximately 1.3 million square km of temperate and subtropical waters and abuts the coastal waters of South Australia and Western Australia. It extends from shallow waters on the continental shelf, 3 nautical miles (5.5 km) from shore, to the deep ocean environments at the edge of Australia's exclusive economic zone, 200 nautical miles from shore.
Figure 2.1: The South-west Marine Region
The main physical features of the region are:
- a narrow continental shelf on the west coast from the subtropics to temperate waters off south-west Western Australia
- a wide continental shelf dominated by sandy carbonate sediments of marine origin (i.e. crushed shells from snails and other small animals and calcareous algae) in the Great Australian Bight
- high wave energy on the continental shelf around the whole region
- a steep, muddy continental slope which include many canyons, the most significant being the Perth Canyon, the Albany canyon group and the canyons in the vicinity of Kangaroo Island
- large tracts of poorly understood abyssal plains at depths greater than 4000 m
- the Diamantina Fracture Zone, a rugged area of steep mountains and troughs off south-west Australia at depths greater than 4000 m
- the Naturaliste Plateau, an extension of Australia's continental mass that provides deep‑water habitat at depths of 2000–5000 m
- islands and reefs in both subtropical (Houtman Abrolhos Islands) and temperate waters (e.g. Recherche Archipelago)
- complex and unusual oceanographic patterns, driven largely by the Leeuwin Current and its associated currents, that have a significant influence on biodiversity distribution and abundance.
The remainder of this chapter describes the conservation values of the South-west Marine Region, including the Commonwealth marine environment, protected species and protected places.
By global standards, the marine environment of the South-west Marine Region has high biodiversity and large numbers of species native to the region (known as endemism). Particular hotspots for biodiversity are the Houtman Abrolhos Islands, the overlap between tropical and temperate fauna along the west coast, the Recherche Archipelago and the soft sediment ecosystems in the Great Australian Bight.
Several factors combine to contribute to the high level of biodiversity and endemism in the region. These include a long and stable period of geological isolation, a persistent high-energy environment, warm-water intrusion via the Leeuwin Current and areas where cold, nutrient-rich, deep ocean waters rise to the surface in the east of the region. The low-nutrient environment of the South-west Marine Region results in clear waters and high levels of light penetration, giving rise to a continental shelf characterised by high diversity of seagrass and algal species and benthic communities. These, in turn, provide habitats for a large variety of species and function as nurseries for a range of fish and invertebrates, which move further offshore in their adult stages.
The region is increasingly recognised as an area of global conservation significance for species of rare and endangered marine mammals and seabirds. It provides important calving regions for the endangered southern right whale and colonies (including pupping areas) of Australia's only endemic pinniped: Australian sea lion. The south-west corner of the region is an important area for beaked whales. Other protected species known to occur in the region include white shark, humpback whale and several species of albatross.
Despite its high biodiversity, the biological productivity of the South-west Marine Region is low compared with other Australian marine regions because of the effect of the Leeuwin Current in suppressing upwelling of nutrients from deeper cold waters and the absence of significant rivers contributing nutrients into the marine environment through run-off. Small seasonal upwellings occur regularly at known locations and, because of the overall nutrient-poor nature of the region's waters, these small hotspots of productivity have a disproportionate influence on the region's biodiversity. The main areas of higher seasonal productivity in the region are the Perth Canyon, Albany canyon group, Kangaroo Island canyons and pool, Cape Mentelle and eddy fields that spin off the Leeuwin Current along the west and south coasts of Western Australia.
The most significant known influence on ecosystem structure and function in the South-west Marine Region is the Leeuwin Current. The current originates in the warm, low-saline waters of the Indonesian archipelago, and brings warm waters south along the west coast of Australia before rounding capes Leeuwin and Mentelle and flowing east across the south coast. The current is stronger in winter than in summer and has three main influences on the south-west region:
- suppressing upwelling and therefore contributing to the low productivity of the region, and consequently the relatively small fisheries on the west coast
- maintaining warm-water communities much further south than they would normally occur—for example, corals and coral reef fish as far south as Rottnest Island
- driving inter annual variability in settlement of western rock lobster, which is a significant component of benthic communities on the west coast and a valuable fishery species.
Associated with the Leeuwin Current are fields of eddies that form at predictable locations in the region. These eddies can be either upwelling or downwelling; upwelling eddies enhance local biological productivity where they form, and downwelling eddies concentrate and transport communities away from the coast.
Key ecological features
Key ecological features are elements of the Commonwealth marine environment in the South-west Marine Region that, based on current scientific understanding, are considered to be of regional importance for either the region's biodiversity or ecosystem function and integrity. They may be physical features or species (see Table 2.1 and Figure 2.2).
Table 2.1: Key ecological features of the South-west Marine Region
|Commonwealth marine environment surrounding the Houtman Abrolhos Islands (and adjacent shelf break)||Values: High levels of biodiversity and endemism|
The Houtman Abrolhos Islands and surrounding reefs support a unique mix of temperate and tropical species, resulting from the southward transport of species by the Leeuwin Current over thousands of years. The Houtman Abrolhos Islands are the largest seabird breeding station in the eastern Indian Ocean. They support more than one million pairs of breeding seabirds.
|Perth Canyon and adjacent shelf break, and other west-coast canyons||Values: High biological productivity and aggregations of marine life, and unique seafloor features with ecological properties of regional significance |
The Perth Canyon is the largest known undersea canyon in Australian waters. Deep ocean currents rise to the surface, creating a nutrient-rich cold-water habitat attracting feeding aggregations of deep-diving mammals, such as pygmy blue whales and large predatory fish that feed on aggregations of small fish, krill and squid.
|Commonwealth marine environment within and adjacent to the west-coast inshore lagoons||Values: High productivity and aggregations of marine life|
These lagoons are important for benthic productivity, including macroalgae and seagrass communities, and breeding and nursery aggregations for many temperate and tropical marine species. They are important areas for the recruitment of commercially and recreationally important fishery species. Extensive schools of migratory fish visit the area annually, including herring, garfish, tailor and Australian salmon.
|Commonwealth marine environment within and adjacent to Geographe Bay||Values: High productivity and aggregations of marine life, and high levels of biodiversity and endemism|
Geographe Bay is known for its extensive beds of tropical and temperate seagrass that support a diversity of species, many of them not found anywhere else. The bay provides important nursery habitat for many species. It also an important resting area for migrating humpback whales.
|Cape Mentelle upwelling||Values: High productivity and aggregations of marine life|
The Cape Mentelle upwelling draws relatively nutrient-rich water from the base of the Leeuwin Current, up the continental slope and onto the inner continental shelf, where it results in phytoplankton blooms at the surface. The phytoplankton blooms provide the basis for an extended food chain characterised by feeding aggregations of small pelagic fish, larger predatory fish, seabirds, dolphins and sharks
|Naturaliste Plateau||Values: Unique seafloor feature with ecological properties of regional significance|
The Naturaliste Plateau is Australia's deepest temperate marginal plateau. The combination of its structural complexity, mixed water dynamics and relative isolation indicate that it supports deep-water communities with high species diversity and endemism.
|Diamantina Fracture Zone||Values: Unique seafloor feature with ecological properties of regional significance|
The Diamantina Fracture Zone is a rugged, deep-water environment of seamounts and numerous closely spaced troughs and ridges. Very little is known about the ecology of this remote, deep-water feature, but marine experts suggest that its size and physical complexity mean that it is likely to support deep-water communities characterised by high species diversity, with many species found nowhere else.
|Albany canyon group and adjacent shelf break||Values: High productivity and aggregations of marine life, and unique seafloor feature with ecological properties of regional significance|
The Albany canyon group is thought to be associated with small, periodic subsurface upwelling events, which may drive localised regions of high productivity. The canyons are known to be a feeding area for sperm whale and sites of orange roughy aggregations. Anecdotal evidence also indicates that this area supports fish aggregations that attract large predatory fish and sharks.
|The Commonwealth marine environment surrounding the Recherche Archipelago||Values: Aggregations of marine life and high levels of biodiversity and endemism|
The Recherche Archipelago is the most extensive area of reef in the South-west Marine Region. Its reef and seagrass habitat supports a high species diversity of warm temperate species, including 263 known species of fish, 347 known species of molluscs, 300 known species of sponges, and 242 known species of macroalgae. The islands also provide haul-out (resting areas) and breeding sites for Australian sea lions and New Zealand fur seals.
|Ancient coastline between 90 and 120 m depth||Values: High productivity and aggregations of marine life, and high levels of biodiversity and endemism|
Benthic biodiversity and productivity occur where the ancient coastline forms a prominent escarpment, such as in the western Great Australian Bight, where the sea floor is dominated by sponge communities of significant biodiversity and structural complexity.
|Kangaroo Island Pool, canyons and adjacent shelf break, and Eyre Peninsula upwellings||Values: High productivity and aggregations of marine life, and the canyons and adjacent shelf break are unique seafloor features with ecological properties of regional significance|
The Kangaroo Island canyons are known for their seasonal upwellings of deep ocean waters that support aggregations of krill, small pelagic fish and squid, which, in turn, attract marine mammals (e.g. pygmy blue whales, fin whales, sperm whales, dolphins and New Zealand fur seals), sharks, large predatory fish and seabirds.
|Meso-scale eddies (several locations)||Values: High productivity and aggregations of marine life|
Driven by interactions between currents and bathymetry, persistent meso-scale eddies form in predictable locations within the meanders of the Leeuwin Current. They are important transporters of nutrients and plankton communities and are likely to attract a range of organisms from the higher trophic levels, such as marine mammals, seabirds, tuna and billfish. The eddies play a critical role in determining species distribution, as they influence the southerly range boundaries of tropical and subtropical species, the transport of coastal phytoplankton communities offshore and recruitment to fisheries.
|Demersal slope and associated fish communities of the Central Western Province||Values: Species groups that are nationally or regionally important to biodiversity|
The western demersal slope provides important habitat for demersal fish communities, with a high level of diversity and endemism. A diverse assemblage of demersal fish species below a depth of 400 m is dominated by relatively small benthic species such as grenadiers, dogfish and cucumber fish. Unlike other slope fish communities in Australia, many of these species display unique physical adaptations to feed on the sea floor (such as a mouth position adapted to bottom feeding), and many do not appear to migrate vertically in their daily feeding habits.
|Western rock lobste||Values: A species that plays a regionally important ecological role|
This species is the dominant large benthic invertebrate in the region. The lobster plays an important trophic role in many of the inshore ecosystems of the South-west Marine Region. Western rock lobsters are an important part of the food web on the inner shelf, particularly as juveniles.
|Benthic invertebrate communities of the eastern Great Australian Bight||Values: A species group or community that is nationally or regionally important to biodiversity|
The benthic invertebrate communities found on the shelf of the Great Australian Bight, particularly sponges, ascidians and bryozoans, have been described as among the world's most diverse soft-sediment ecosystems.
|Small pelagic fish||Values: A species group that has a regionally important ecological role|
This species group is considered important for ecological functioning and integrity, providing critical links between primary production and higher predators. Collectively, they are an important prey item for a diverse range of species, including tuna, whales, dolphins, seals, sea lions and numerous seabirds.
Figure 2.2: Key ecological features in the South-west Marine Region
Further information on the South-west Marine Region's key ecological features is available in the Commonwealth marine environment report card http://www.environment.gov.au/coasts/mbp/south-west/index.html.
The South-west Marine Region is an important area for protected species (see Section 1.5). Under the EPBC Act, species can be listed as threatened, migratory, cetaceans or marine.
Threatened species are, in broad terms, those species that have been identified as being in danger of becoming extinct. Species may be listed in the following categories:
- conservation dependent
- critically endangered
- extinct in the wild
Migratory species are those species that are listed under:
- the Convention on the Conservation of Migratory Species of Wild Animals (CMS or Bonn Convention)
- the Agreement between the Government of Australia and the Government of Japan for the Protection of Migratory Birds in Danger of Extinction and their Environment 1974 (JAMBA)
- the Agreement between the Government of Australia and the Government of the People's Republic of China for the Protection of Migratory Birds and their Environment 1986 (CAMBA)
- the Agreement between the Government of Australia and the Government of the Republic Of Korea on the Protection of Migratory Birds 2007 (ROKAMBA)
- any other international agreement, or instrument made under other international agreements approved by the Environment Minister.
Further information on the CMS, JAMBA, CAMBA and ROKAMBA is provided at www.environment.gov.au/biodiversity/migratory/index.html
Cetaceans—all cetaceans (whales, dolphins and porpoises) are protected under the EPBC Act in the Australian Whale Sanctuary (and, to some extent, beyond its outer limits).
Marine species belong to taxa that the Australian Government has recognised as requiring protection to ensure their long-term conservation (in accordance with ss. 248–250 of the EPBC Act). Listed marine species occurring in the South-west Marine Region include species of:
- sea snakes (families Hydrophiidae and Laticaudidae)
- seals, both eared and true seals (families Otariidae and Phocidae)
- marine turtles (families Cheloniidae and Dermochelyidae)
- seahorses, sea dragons, pipefish and ghost pipefish (families Syngnathidae and Solenostomidae)
- seabirds (i.e. bird species that occur naturally in Commonwealth marine areas).
Protected species can be listed under more than one category.
Under the EPBC Act, species listed as threatened or migratory are matters of national environmental significance (although species listed as extinct or conservation dependent are not matters of national environmental significance—see Section 1.5). Information specific to species that occur in the region and are matters of national environmental significance is provided in Schedule 2.
Many of the species listed under the EPBC Act are also protected under state legislation. For example, white shark is protected under the EPBC Act and under South Australian and Western Australian legislation.
Species listed under the EPBC Act are also protected from adverse interactions with commercial fishing operations. All fisheries managed under Commonwealth legislation, and state-managed fisheries that have an export component, are assessed under the EPBC Act. These fishery assessments are conducted using the Guidelines for the Ecologically Sustainable Management of Fisheries. These guidelines specify that fisheries must be conducted in a manner that does not threaten bycatch species and that 'avoids mortality of, or injuries to, endangered, threatened or protected species'. Further information about fisheries assessments carried out under the EPBC Act is available at www.environment.gov.au/coasts/fisheries/publications/guidelines.html
The lists of protected species established under the EPBC Act are updated periodically. This plan refers to the current lists of protected species in the region included in the conservation values report cards http://www.environment.gov.au/coasts/mbp/south-west/index.html. The report cards include detailed information about species groups and species distribution and ecology in the South-west Marine Region.
Based on current data and expert advice, biologically important areas (see Section 1.5) are defined for some protected species. Biologically important areas and the data underpinning them are available in the South-west conservation values atlas http://www.environment.gov.au/coasts/mbp/south-west/index.html.
Protected places are those areas protected under the EPBC Act as matters of national environmental significance (places listed as world heritage properties, national heritage places or wetlands of international importance), Commonwealth marine reserves or places deemed to have heritage value in the Commonwealth marine environment (such as places on the Commonwealth Heritage List or shipwrecks under the Historic Shipwrecks Act 1976).
There are five historic shipwrecks in the region (Figure 2.3):
- HMAS Sydney II and HSK Kormoran: sunk in 1941 following a battle engagement approximately 250 km off the central coast of Western Australia
- SS Cambewarra: a steam-powered transport vessel that was wrecked in 1914 near Fisherman's Island, 80 km south of Dongara, Western Australia
- Lord Roberts: a cutter wrecked in 1902 in the Gulf St Vincent, South Australia
- Red Rover: a fishing boat wrecked near Coffin Bay, South Australia, in 1887.
The HMAS Sydney II and HSK Kormoran wrecks are also listed on the National Heritage List and Commonwealth Heritage List for their historic heritage values. By virtue of their listing on the National Heritage List, these two shipwrecks are also matters of national environmental significance.
There is one Commonwealth marine reserve in the South-west Marine Region: the Great Australian Bight Marine Park, which stretches from 200 km west of Ceduna in South Australia and follows the coast to the Western Australian border (Figure 2.3). The park includes a strip 20 nautical miles wide extending 200 nautical miles offshore.
The park comprises adjoining South Australian and Commonwealth protected areas. The Great Australian Bight Marine Park (Commonwealth Waters) is a Commonwealth reserve under the EPBC Act.
The Australian and South Australian governments manage the park cooperatively to protect conservation values (specifically, southern right whale, Australian sea lion, other species of conservation significance, and a transect representative of the seabed on the continental shelf and slope of the Great Australian Bight). Management of the park allows ecologically sustainable uses that are consistent with protecting these values and that contribute to regional and national development. Management plans regulate recreational, scientific and commercial uses of the park within four distinct management areas or zones: a sanctuary zone and a conservation zone (state waters); and a marine mammal protection zone and benthic protection zone (Commonwealth waters).