Seal Island is an

island An island (or isle) is an isolated piece of habitat that is surrounded by a dramatically different habitat, such as water. Very small islands such as emergent land features on atolls can be called islets, skerries, cays or keys. An island ...

located in

Investigator Strait Investigator Strait is a body of water in South Australia lying between the Yorke Peninsula, on the Australian mainland, and Kangaroo Island. It was named by Matthew Flinders after his ship, HMS ''Investigator'', on his voyage of 1801–1802. ...

off the south coast of

Yorke Peninsula The Yorke Peninsula is a peninsula located northwest and west of Adelaide in South Australia, between Spencer Gulf on the west and Gulf St Vincent on the east. The peninsula is separated from Kangaroo Island to the south by Investigator Strai ...

in the

Australian state The states and territories are federated administrative divisions in Australia, ruled by regional governments that constitute the second level of governance between the federal government and local governments. States are self-governing ...

South Australia South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...

about south south-west of Stenhouse Bay. Since 1972, it has been part of the

Althorpe Islands Conservation Park Althorpe Islands Conservation Park is a protected area in the Australian state of South Australia occupying the Althorpe Island, Haystack Island and Seal Island (Investigator Strait), Seal Island in Investigator Strait near the town of Stenhouse ...

Description

Seal Island is about south south-west of Stenhouse Bay. It is described as an ‘elevated hump’ rising to a height of with a series of ‘segmented islets’ at its west side. Seal Island is reported as being best accessed via its north coast and during the ‘calmest weather’. A number of sources consider Seal Island along with the Althorpe Islands and

Haystack Island Haystack Island is an island located in Investigator Strait off the south coast of Yorke Peninsula in the Australian state of South Australia about south-west of Stenhouse Bay. Since 1972, it has been part of the Althorpe Islands Conservatio ...

to be a group of islands known as the Althorpe Islands Group.

Formation, geology and oceanography

Seal Island was formed between 7500 and 8900 years ago after sea levels rose at the start of the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togethe ...

thereby separating

from

Kangaroo Island Kangaroo Island, also known as Karta Pintingga (literally 'Island of the Dead' in the language of the Kaurna people), is Australia's third-largest island, after Tasmania and Melville Island. It lies in the state of South Australia, southwest ...

. Seal Island is the remains of a

granite Granite () is a coarse-grained (phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies undergro ...

inselberg An inselberg or monadnock () is an isolated rock hill, knob, ridge, or small mountain that rises abruptly from a gently sloping or virtually level surrounding plain. In Southern Africa a similar formation of granite is known as a koppie, a ...

capped by a layer of Bridgewater Formation

calcarenite Calcarenite is a type of limestone that is composed predominantly, more than 50 percent, of detrital (transported) sand-size (0.0625 to 2 mm in diameter), carbonate grains. The grains consist of sand-size grains of either corals, shells, ooi ...

which has been extensively eroded by the action of the sea. Seal Island rises from a depth of within to its west and south shores, and within of its east shore.

Flora and fauna

Flora

A survey carried out in 1996 reported that 10 species of plants to be present including Nitre-bush, Grey Samphire, Roundleaved Pigface, Sea Celery,

Marsh Saltbush ''Atriplex paludosa'', commonly known as marsh saltbush, is a species of saltbush endemic to Australia. Description It grows as an erect shrub up to a metre high. Leaves are oval in shape, one to four centimetres long, and 2 to 15 millimetres wi ...

and

Ruby Saltbush ''Enchylaena tomentosa'', commonly known as barrier saltbush or ruby saltbush, is a small native shrub of Australia. Description ''Enchylaena tomentosa'' grows as a small perennial shrub, up to a meter in diameter. Leaves are slender and cylindr ...

and Australian Hollyhocks.

Fauna

A survey carried out in 1996 reported the following

vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

animals to be present -

Black-faced cormorant The black-faced cormorant (''Phalacrocorax fuscescens''), also known as the black-faced shag, is a medium-sized member of the cormorant family. Upperparts, including facial skin and bill, are black, with white underparts. It is endemic to coas ...

Little penguin The little penguin (''Eudyptula minor'') is a species of penguin from New Zealand. They are commonly known as little blue penguins or blue penguins owing to their slate-blue plumage and are also known by their Māori name . The Australian lit ...

Sooty oystercatcher The sooty oystercatcher (''Haematopus fuliginosus'') is a species of oystercatcher. It is a wading bird endemic to Australia and commonly found on its coastline. It prefers rocky coastlines, but will occasionally live in estuaries. All of its fea ...

Rock parrot The rock parrot (''Neophema petrophila'') is a species of grass parrot native to Australia. Described by John Gould in 1841, it is a small parrot long and weighing with predominantly olive-brown upperparts and more yellowish underparts. Its h ...

Silver gull The silver gull (''Chroicocephalus novaehollandiae'') is the most common gull of Australia. It has been found throughout the continent, but particularly at or near coastal areas. It is smaller than the Pacific gull (''Larus pacificus''), which ...

and

Fairy tern The fairy tern (''Sternula nereis'') is a small tern which is native to the southwestern Pacific. It is listed as " Vulnerable" by the IUCN and the New Zealand subspecies is " Critically Endangered". There are three subspecies: * Australian f ...

. The 1996 survey also noted the presence of

Galah The galah (; ''Eolophus roseicapilla''), also known as the pink and grey cockatoo or rose-breasted cockatoo, is the only species within genus ''Eolophus'' of the cockatoo family. Found throughout Australia, it is among the most common of the co ...

s and

Australian sea lion The Australian sea lion (''Neophoca cinerea''), also known as the Australian sea-lion or Australian sealion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently monotypic in the genus ''Neophoca'', with the e ...

s but assumed these animals were not residents of the island. Subsequent surveys found that Australian sea lions do use the island as a

haul-out Hauling-out is a ethology, behaviour associated with pinnipeds (true seals, sea lions, fur seals and walruses) temporarily leaving the water. Hauling-out typically occurs between periods of foraging activity. Rather than remain in the water, pin ...

area and possibly as a

rookery A rookery is a colony of breeding animals, generally gregarious birds. Coming from the nesting habits of rooks, the term is used for corvids and the breeding grounds of colony-forming seabirds, marine mammals (true seals and sea lions), and ev ...

, while the

Crested tern The greater crested tern Retrieved 28 February 2012 (''Thalasseus bergii''), also called crested tern or swift tern, is a tern in the family Laridae that nests in dense colonies on coastlines and islands in the tropical and subtropical Old World ...

has been observed as being present on the island.

Protected areas status

Since 1972, the island has been part of the Althorpe Islands Conservation Park. Since 2007, it has been a prohibited area where access is only allowed by permit in order to protect breeding population of seabirds. Since 2012, the waters surrounding its shores are part of a sanctuary zone located within the boundaries of the Southern Spencer Gulf Marine Park.

References

{{DEFAULTSORT:Seal Island (Investigator Strait) Islands of South Australia Uninhabited islands of Australia Investigator Strait