Neptune Islands
The Neptune Islands consist of two groups of islands located close to the entrance to Spencer Gulf in South Australia. They are well known as a venue for great white shark tourism.
Description
The Neptune Islands consists of two groups of islands, the North Neptune Islands and the South Neptune Islands. These both sit on the southern aspect of the Australasian continental shelf separated by a distance of.The North Neptune Islands which are south south-east from the mainland at Cape Catastrophe, consist of a large island of height and a small islet of height located from the main island's north-east point with a combined area of.
The South Neptune Islands which are south-south-east from the mainland at Cape Catastrophe are more evenly portioned in height with the northern island being high and the southern island rising to. The Southern group has an area of.
A third feature associated with the overall island group is an outcrop of rocks known as Low Rocks located about north-north-east of the northern group of islands.
Formation, geology and oceanography
The Neptune Islands were formed between 10,800 and 12,000 years ago when sea levels rose at the start of the Holocene.The islands are remnant igneous inselbergs which have survived the erosive process associated with sea level rise. The remnant rock is described as being "a porphyritic granite gneiss and pink granite intruded with dolerite dykes". Remnants of the once-overlying calcarenite layers are also present on the upper platforms of the island. The soil is mainly derived from the weathering of the granite with a minor contribution from the weathering of calcarenite strata.
The seabed falls steeply away from the coast of both island groups. Water depths of are reached within a distance of from the Northern group and within 1.5 km to from the Southern group.
Flora and fauna
Plants
While the low profile of the islands do limit what can grow due to wind exposure and salt spray, surveys have shown that the Northern island group has 35 plant species while the Southern group has 28 species on its north island while Lighthouse Island has 13 species. The latter is attributed to combination of the disturbance caused by activity associated with the formerly staffed lighthouse, airstrip, an introduced goat population that was eradicated in 1968, and burrows made by the large numbers of short-tailed shearwaters. Plant species include sea celery, leek lily, flax lily, coast tussock grass, salt couch, billy button daisies, variable groundsel and an introduced Northern Hemisphere grass, rat's-tail fescue.Terrestrial animals
The only mammals present are bush rats which are found on North Neptune Island.Birds of prey include white-bellied sea-eagles, peregrine falcon and swamp harrier with Australian kestrels mainly concentrated on the northern island in the South group. Breeding colonies of Cape Barren geese are present on the Northern group while short-tailed shearwaters, silver gull and greater crested tern are present on the South group island.
Other landbirds include white-fronted chats, masked plovers, rock parrots, welcome swallows, silvereyes and stubble quails. Sparrows, an introduced species, have established themselves on Lighthouse island.
Reptiles identified during surveys include marbled geckos on both island groups while the following are limited to the main island in the Northern group - four-toed earless skink, bull skinks and western brown snakes. The latter are believed to prey on bush rat and bull shinks.
Marine animals
and Australian sea lions are common on all islands, using the island group for breeding.Australian sea lions were already present in 1876 Australian sea lions were shot at the Neptune Islands for their hides and for "sport" during the 19th century. Large-scale hunting ceased in the 1920s, No baseline population data exists, but the species population and range have both decreased.
The introduction of the South Australian National Parks and Wildlife Act 1972 prohibited the killing of Australian sea lions statewide.
The Australian sea lion was listed as vulnerable under the Commonwealth Environment Protection and Biodiversity Conservation Act 1999 in 2005 and is also listed as a threatened species in each state in its range.
Nevertheless the presence of these pinniped colonies supports a migratory population of great white sharks.
Little penguin colony
s were present on the Neptune Islands in 1840, 1876, 1877, 1899, 1901, 1907, 1925 and 1934.In April 1877, the south island reportedly "swarmed with mutton-birds and penguin". A Mr Boucaut collected a pair of live penguins on this occasion to provide to the Botanical Garden.
In 1899, it was reported that South Neptune Island "abounded with penguin, and the sandy beach was a favourite resort of the hair seal." In 1901, a visiting party on the Governor Musgrave described the island thus: "Penguins are fairly numerous; but excepting an occasional seal or two the mutton birds monopolize the island." Another account of the visit said of the muttonbirds: "At night these birds create an indescribable din, in company with the penguins, of which also there is a large number about the various rocks of its coastline." In 1907, visitors landed in May and found a few penguins in burrows along with evidence of recent occupation.
Little penguin breeding sites were noted on North Neptune Island in a 1996 survey of South Australia's offshore islands.
None were found in 2006 and the colony is now believed to be extinct.
History
The islands were first sighted by Europeans on Sunday 21 February 1802 from HMS Investigator whilst under the command of Matthew Flinders. The islands were named Neptune's Isles, "for they seemed to be inaccessible to men".The islands were subsequently visited by John Lort Stokes in 1840 and later in 1873-74 by Captain F. Howard, RN as part of an ongoing South Australian Government program to map the colony’s waters, identify shipping hazards and assess the suitability of the coastline for settlement.
In the 19th century, the islands were visited by "sporting" parties who shot and killed Australian sea-lions and other wildlife.
During World War II, the Neptune Islands became a strategic military site due to its lighthouse’s location at the approaches to both Spencer Gulf and Investigator Strait. This is evident in the act of the placement of a mine field approximately west-south west of the Neptune Islands by the German auxiliary cruiser Pinguin during November 1940.
A naval depot including huts and observation towers was established on South Neptune Island along with a gun which was regularly fired.
The South Neptune Island Lighthouse Complex is listed on the South Australian Heritage Register.
In the 1970s, the Neptune Islands were a filming location where live-action shark sequences of the ground-breaking blockbuster Jaws were filmed.
In 2012, the Neptune Islands Conservation Park was designated as a marine park. To this day, it endures a popular location for cage diving with great white sharks.
Navigation aids
s have been located on islands within the Neptune Islands Group since the early 20th century.The need for a lighthouse in the Neptune Islands was considered for many years during the 19th century due to the islands' relatively low elevation. In 1901, the light tower from the Port Adelaide Entrance light was relocated to South Neptune Island. That was eventually replaced by a small brick tower in 1985, and the old tower was transported to Port Adelaide on to become part of the collection of the South Australian Maritime Museum, which opened in 1986. The new lighthouse was converted to automatic operation in 1990 resulting in the departure of the lighthouse keepers and their families.
Located on the largest island in the southern group, a light mounted on a tower commenced operation in 1983. It was removed in 2002-2003.