The interesting aspects of the Heard Island and McDonald Island (HIMI) region don’t stop at the water’s edge.

The waters surrounding the islands provide important foraging areas for the seabirds and marine mammals that breed or haul out on the islands, but they also comprise a marine ecosystem that is unique and special in itself.

The special qualities of the marine area were recognised in the declaration of the HIMI Marine Reserve in 2002. The Reserve includes the islands, but 64,630 of the 65,000 square kilometres of the Reserve is marine, making the Reserve one of the largest marine protected areas in the world.

A fuller description of the marine component of the HIMI Marine Reserve is given below. The other pages in this section discuss the benthic communities (seabed communities), the fishes and cetaceans (whales, dolphins and porpoises) found in those areas. There is also a general description of the oceanography and ocean fronts of the HIMI region.

The HIMI waters

The marine area of the HIMI Marine Reserve can be broadly classified into five smaller marine areas described as the western, central, southern and north-eastern areas, plus the territorial sea (click here for a diagram of the marine area)

  • The territorial sea supports near shore marine species and is a foraging area for many flying birds based on the islands.
  • The southern area is likely to be highly productive, with a diverse range of benthic assemblages in depths of 500–1000 m.
  • The western area, including Coral Bank, displays diverse assemblages of benthic invertebrates, particularly gorgonian corals and barnacles.
  • The central area, including Discovery Bank and portions of the northern and southern plateaux, is habitat for long-lived glass and other erect sponges, and a nursery area for commercial fish species.
  • In the north-eastern area, Shell Bank supports a separate stock of mackerel icefish, small aggregations of a variety of other fish species, a diverse echinoderm assemblage and a unique shell-grit habitat different from the surface sediments found elsewhere in the region. This north-eastern area, including areas of the north-eastern plateau, is also an important foraging area for land-based marine predators in the HIMI region.

Collectively these areas contain unique features of the benthic environment surrounding HIMI, representative portions of the different habitat types in the HIMI region, and the near surface waters where land-based marine predators concentrate their local foraging activities.

Benthic communities

There is a diverse range of benthic (seabed) habitats in the HIMI region, caused by the varying submarine topography and the action of oceanic currents.

The sediments on the sea floor mainly comprise silica-rich diatom mud or ‘ooze’, with some areas containing quantities of calcareous sediments (calcium-rich shells of dead small marine animals).

A range of species are present on the sea bottom, with echinoderms (radially symmetrical marine invertebrates with an internal calcium-rich skeleton, such as sea urchins) being the most common, including seven species that possibly live only in the HIMI region. Other slow-growing and vulnerable benthic species, such as corals, sponges and barnacles are also found.

An analysis of the available information about benthic assemblages, substrate and the physical characteristics of the marine environment indicated that areas shallower than 1000 m can be divided into thirteen potentially unique units based on a combination of their biological and physical characteristics.

Nine of these ‘biophysical’ units are located within the HIMI Marine Reserve. Click on the following links for a diagram PDF or more detailed summary PDF.

A more thorough description of the biophysical units and benthic communities, including lists of benthic species found at HIMI, is given in the Australian Antarctic Division Report Conservation of marine habitats in the region of Heard Island and McDonald Islands PDF

Fishes

The near shore fish community (within 12 nautical miles of the coast) around Heard Island and the McDonald Islands (HIMI) is similar to those at other subantarctic islands.

The families Nototheniidae (Antarctic cods) and Channichthyidae (icefishes) dominate the near shore waters, both in number of species and in abundance. Most of the near shore species are found on the wider underwater Kerguelen Plateau around HIMI, although some species are only found close to shore.

In the deeper waters, and beyond the Kerguelen Plateau (greater the 500 m deep), dominant species or groups are toothfish, macrourids (grenadier fish, having an elongate tapering body and a compressed pointed tail) and skates, while myctophids (lantern fish) dominate the more distant oceanic waters.

An Australian commercial fishery has operated in the HIMI region since 1997. The fishery targets Patagonian toothfish (Dissostichus eleginoides) and mackerel icefish (Champsocephalus gunnari).

Cetaceans

Cetaceans are any members of the group of marine mammals that includes whales, dolphins and porpoises.

Records around Heard Island and McDonald Islands (HIMI) are sparse due to a lack of opportunities to conduct surveys. However, areas of nutrient rich waters in the region are believed to provide suitable feeding grounds for a range of cetaceans.

The remains of seven species of cetacean have been found washed ashore at Heard Island. These include skulls of pilot whales, strap-toothed beaked whales, spectacled porpoises, Minke whales, hourglass dolphins, and southern bottlenose whales. Additional records exist of sperm whale bones and two dolphin heads found on Heard Island in early December 1929.

Several species of cetacean have also been observed at sea in the region, including blue whale, fin whale, killer whale, hourglass dolphin, strap-toothed beaked whale, spectacled porpoise, humpback whale, sperm whale, Minke whale, long-finned pilot whale, southern bottlenose whale, Commerson’s dolphin, dusky dolphin, Arnoux’s beaked whale and southern right whale.

Cetacean conservation

Each of the above cetacean species is a listed cetacean under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) and several are listed as threatened and/or migratory species. The Protection page in the Nature section has a table showing their conservation status and scientific names.

Under the EPBC Act recovery plans are in preparation for blue, fin, humpback and southern right whales. There is also an Action Plan for Australian Cetaceans.

The HIMI Marine Reserve lies within the Indian Ocean Whale Sanctuary, which was established under the International Convention for the Regulation of Whaling in 1979 to provide freedom from disturbance for migrating and breeding great whales in an area where whales were once hunted to the brink of extinction.

Marine oceanography

Heard Island and McDonald Islands (HIMI), Australia’s most remote island group, is located in the southern Indian Ocean.

Together with the French territory, Îles Kerguelen, Heard Island and the McDonald Islands comprise the only non-submerged part of the predominantly submarine Kerguelen Plateau.

The islands are situated over 4000 kilometres southwest of Perth in Western Australia and over 1700 kilometres north of Australia’s Mawson station on the Antarctic continent.

The northern and central parts of the Kerguelen Plateau are predominantly shallower than 1000 metres in depth while the southern plateau is characterised by deeper waters, ranging from 1500 to 3000 metres.

The plateau is surrounded by deep ocean basins. To the northwest is the Crozet Basin, to the northeast is the Australian-Antarctic Basin, the Labuan Basin is to the east, the 3500 metre deep Princess Elizabeth Trough is to the south, and to the southwest is the Enderby Abyssal Plain.

Several frontal systems have an important influence on the marine environment and ecosystems around HIMI.

HIMI’s remoteness has made marine research surveys in this area logistically difficult and relatively infrequent. Nevertheless, three comprehensive biological and oceanographic surveys were carried out during the early 1990s.

During the summer of 2003/04 an ambitious multi-disciplinary study was carried out integrating research on the foraging activities of predators with the oceanography and biology of the seas surrounding Heard Island.

Ocean fronts and circulation

The northern boundary of the Southern Ocean is defined by the subtropical front (STF) which separates warm, salty, subtropical waters in the north from the colder, subantarctic waters of the south.

Within the Southern Ocean, the vast and highly dynamic Antarctic Circumpolar Current (ACC) circles the globe and dominates the circulation. This current is driven by the globe’s strongest westerly winds between latitudes 45 and 55º S.

The Antarctic Circumpolar Current is associated with several narrow jets or fronts. These frontal regions are characterised by sharp horizontal gradients in hydrographic properties (such as temperature, salinity, density, oxygen and nutrients) that mark the boundaries of different water masses.

Three main fronts are continuous features of the Antarctic Circumpolar Current: the subantarctic front (SAF); the polar front (PF); and a deep-reaching front observed persistently to the south, the southern ACC front (SACCF).

The path of the Antarctic Circumpolar Current is mainly controlled by bottom topography, with major features such as ridges and plateaus acting as barriers that deflect and alter the flow. The Kerguelen Plateau is oriented north-west/south-east along the 70º E meridian and forms a large topographic barrier to the eastward flow of the Antarctic Circumpolar Current.

The subantarctic front and polar front are effectively merged as they pass to the north of the Kerguelen Plateau, while the southern Antarctic Circumpolar current front is deflected around the southern boundary of the Plateau, east of which, it turns northward to form a western boundary current along its eastern flank.

The most important front in the Heard Island region is the Antarctic Polar Front, which is typically defined as the northern limit of a temperature minimum of 2ºC at a depth of 100 to 300 metres.

The Polar Front is most often located just to the north of Îles Kerguelen and as a result that island ’s climate and biogeography is distinctly subantarctic. This is in contrast with Heard Island which is a typically Antarctic island.

The Polar Front follows a meandering course and may in some regions split into two separate jets, occasionally it may also be displaced to the south of Îles Kerguelen which has important implications for the biota and fisheries of the region.

Generally, the most biologically productive waters in the HIMI region are those to the north and east of Heard Island. These areas are high in phytoplankton, which often means that they would be areas high in secondary production such as zooplankton and fish. Highly productive regions like these are the most important local foraging areas for land-based marine predators.

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