55 kilometres due west from the WA town of Geraldton is a unique group of islands, reefs and lagoons located near the Australian continental shelf-edge. These islands, known as the Abrolhos Islands or Houtman's Abrolhos, are the most southerly true coral reefs to be found in the Indian Ocean. In terms of biological diversity, they support a rare combination of both sub-tropical and temperate species located in close proximity.
Consisting of at least 122 small islands and islets, they sit atop the three carbonate platforms that comprise the Houtman Abrolhos. These are known as the Easter, Pelsart and Wallabi Groups. The groups spread northwest to southeast across 100 km of ocean and are separated from the mainland by the Geelvink Channel. The outlying North Island is considered as part of the Wallabi Group.
The Abrolhos Islands are an A-class Reserve managed by the Western Australian Department of Fisheries for the conservation of flora and fauna, for tourism, and for purposes associated with fishing industries. Tours to the islands are conducted out of Geraldton.
The names of these islands are a reflection of their significance in the early discovery and exploration of Australia. They were in fact one of the earliest Australian coastal features to make it onto maps used by European navigators, being first sighted by Frederick Houtman, the captain of the Dutch East India ship, D'Ordrecht, which sailed from Texel, Holland, in December 1618. On 17th July, 1619, Houtman sighted what he called 'The South Lands behind Java', somewhere between present day Mandurah and Bunbury.
Heavy surf caused Houtman to abandon an attempt to go ashore. Houtman left the coast the coast, sailing north, and on 29th July a 16 km a stretch of islands and broken reefs was encountered. Houtman marked his chart 'Abri voll olos', an internationally used Portuguese phrase literally translated as 'keep your eyes open', a recognised warning to navigators to keep clear - a call which has a similar effect to 'fore' with golfers. The name appeared on all subsequent charts as Houtman's Abrolhos.
Graveyard of Ships
The charts used by subsequent Dutch sailors using the East Indies shipping route had Houtman's Abrolhos clearly marked but it was only a matter of time before a Dutch sailing ship would come to grief on the islands - 10 years in fact. The story of the demise of the Dutch trading ship Batavia on Morning Reef in the Abrolhos Islands, on her maiden voyage in 1629, is one of the most tragic incidents in early Australian history. The Batavia, commanded by Commodore Francis Pelsart, was separated from her consorts by a storm, and during the night of the 4th of June struck on reefs on the Western Australian coast that were first marked on Dutch sailing charts by Frederick Houtman. The crew and passengers were landed on Beacon Island, and two small islets in the neighbourhood, and the ship broke up. What followed was a story of mutiny and a fight for survival.
The Wreck of the Batavia
In 1727, another Dutch ship, the Zeewijk, was lost on the reefs of the Houtman Abrolhos. The survivors managed to build a boat from the wreckage, calling it Sloepie, and sailing it to Batavia (Jakarta, Indonesia). Between the losses of the Batavia and Zeewijk, a number of other Dutch vessels went missing and have yet to be found; many believe their remains may well lie within the waters of the Abrolhos Islands just waiting to be discovered.
The Wreck of the Zeewijk
The largest vessel lost in the group was the 2892 tonne iron steamer Windsor, off Pelsart Island, 1908. Most of the vessels lost in the group are small luggers and fishing boats, with a number of larger sailing vessels: the fully-rigged iron ship Ben Ledi, 1107 tons, 1879, the American barque, Cochituate, 347 tons, 1861, the barque,Hadda, 334 tons, 1877, and the wooden barque, Ocean Queen, 268 tons, 1842.
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About The Islands
All but three of the islands are coral atolls formed over the millennia by the growth and break down of many species of coral. The existence of the warm Leeuwin current continues to carry with it a cargo of coral larvae and other marine life from as far north as Indonesia. This current maintains water temperatures at around 22 degrees, enabling corals and bright, colourful tropical fish species to thrive.
The islands are a mix of ancient reefs, sedimentary rocks, living reefs, lagoons, coral debris and sand that combine to form their unusual appearance. Each of the carbonate platforms rises 40 m or so from the shelf below. In general terms, each consists of a windward reef, leeward reef, and lagoon with a central platform. The islands - located on the central platforms or on the leeward reefs - are mainly rocky (composed of limestone or coral rubble) with scant vegetation cover and rise only 3 to 5 m above sea level.
The Wallabi Group
Located at the northern end of the group, 9 km northwest across the Middle Channel from the Easter Group and 58 km off the Australian mainland, is the Wallabi Group, consisting of North Island, East Wallabi Island, West Wallabi Island, Long Island, Beacon Island and a number of smaller islets and emergent rock outcrops. The entire formation upon which these islets and reefs reside measures 17 km in length (northwest to southeast) and up to 10 km in width. The separate formation of North Island lies in an isolated position a further 14 km to the northwest.
The Easter Group
The Easter Group, measuring 20 km by 12 km, lies at the centre of the chain and contains the largest island of the Houtman Abrolhos - Rat Island. Other significant landmasses include: Wooded Island, Morley Island, Suomi Island and Alexander Island.
The Pelsart Group
Situated 8 km southeast of the Easter Group, across the Zeewijk Channel, are the islands and reefs of the Pelsart Group - the southernmost true coral reefs of the Indian Ocean. Its main islands include Middle Islet, the Mangrove Islets, Square Islet and the elongated Pelsart Islet that stretches for 9 km along the eastern edge of the reef.
The islands' abundant bird and marine life provided the basis for the guano mining and fishing industries that emerged during Australia's colonial period. Guano, a fertiliser derived from bird excreta, was mined on a commercial scale from the 1880s to the 1920s, and again in the mid-1940s. Reminders of this industry include stone guano jetties on Pelsart, Gun and Big Rat islands, and the foundations of the small gauge railway on Big Rat and Pelsaert. Mounds of limestone tailings are cast into unusual shapes on Big Rat and Gun islands. Commercial fishing for trepang (sea cucumber) or beche-demer was conducted on a small scale at the Abrolhos for a period from the mid-1800s.
The Abrolhos was observed as a potential commercial crayfish (western rock lobster) site by the WA Government as early as 1904. Today, the western rock lobster (Panulirus cygnus) is the State's most valuable commercial fishery. The waters around the Abrolhos are an important lobster-breeding habitat - it has been estimated that about 50 per cent of the WA lobster fishery's egg production comes from the Abrolhos. Hence, careful management and conservation of these breeding stocks are of vital importance to the sustainability of the entire fishery.
Pearl farming is another Abrolhos industry. The highly-prized black pearl is produced from hatchery-raised black lipped pearl oysters at eight aquaculture sites in the archipelago. There are also licensed commercial finfish and scallop fisheries at the Abrolhos. 22 of the islands house fishermen who inhabit their island homes from March to June each year during the Abrolhos western rock lobster fishing season.