The Althorpe Islands are a group of islands in the Investigator Strait, off the south-western tip of Yorke Peninsula, South Australia. The group includes Althorpe Island and two rocky islets immediately to its west known as The Boobs. These are located 7.7 km south-southwest of Cape Spencer on the mainland. Closer inshore are Seal Island and Haystack Island, which together with Althorpe Island and The Boobs constitute the Althorpe Islands Conservation Park. A management plan for the Althorpe Islands Conservation Park was adopted in 2009. The islands are uninhabited and can only be accessed by sea or by helicopter.
Althorpe Island was described in 1879 as "no means an abode of bliss, for it is bare and bleak. The vegetation is nothing but scrubby bushes a few inches high, which seem afraid to grow any bigger lest they be blown off; and the flat summit of the now inhabited island rock is swept by the wild winds that chase the rollers into foam on the rocks beneath."
These islands support significant seabird colonies, including the state endangered white-bellied sea eagle (Haliaeetus leucogaster). The smaller islets of Althorpe Islands provide haul-out areas for nationally and state vulnerable Australian sea lion (Neophoca cinerea).
An early written account of the native wildlife of Althorpe Island was printed in the South Australian Register in 1879:
"Mutton birds make their 'holey' habitations on all sides of the Althorpes; seals sport in secluded spots; swift seagulls and solemn shags make the welkin (whatever instrument that is) ring consumedly ; penguins, like little lads in white pinafores, inhabit the nooks and crannies of the rocks... Sharks,sometimes of enormous size, may often be seen meandering softly round the ocean streets."
In 1951, a lighthouse keeper described the native wildlife at Althorpe Island:
"Penguins nest there in the mating season, and their young are to be seen in nooks and crannies around the shore. During the summer months, from September to March, mutton birds migrating from Siberia nest on the island in millions, digging their nests in the soil, under bushes and literally covering the ground... Years ago, seals were plentiful on the island, but owing to large scale slaughter during the early days of the State, few, if any, remain."
Little penguin colony
In 1845, penguins and Cape Barren geese were known to frequent Althorpe Island.
In 1883, W. Reddan described Althorpe Island's little penguin colony, stating:
"It is extraordinary the number of penguins on this island, they are everywhere."
In 1884, a visit of the Marine Board noted that "Down on the rocks the penguins waddle about in large numbers."
In 1886, the penguins of Althorpe Island were briefly mentioned in The Advertiser: "pairs of whom were found peering with pensive eyes out of holes in the sandy rocks."
In 1887, The South Australian Register also described them: "In crevices of the rocks innumerable birds find refuge, and in these and in holes in the sand the queer-shaped penguin also has its habitation."
In 1897, visitors described "the eerie cry of the penguins" of Althorpe Island.
The steep track from the jetty to the island's summit passes by a cave known as the "Penguin Hotel". In 1902, a visitor described the cave, writing "the whole of the interior was honey-combed by penguins."
Little penguin decline
The little penguin (Eudyptula minor) colony on Althorpe Island is in decline. This was initially inferred by contrasting historical accounts of their abundance with their relative scarcity, determined by a 2004 survey. In 2004, the population was 132 birds. In 2011, the colony was described as 'declining from “numerous” and “common” in 1982'. A survey conducted in 2013 estimated a population of 84 adult birds by counting burrow activity over half the island's breeding area. This survey confirmed the previously inferred decline.
The islands was first sighted by Europeans on Saturday 20 March 1802 from HMS Investigator whilst under the command of Matthew Flinders. They are reportedly named after the family home of George Spencer, 2nd Earl Spencer, also known as Viscount Althorp, in Northamptonshire which is actually spelled as ‘Althorp'.
Althorpe Island has played a significant part in South Australia’s maritime history. The lighthouse keepers’ cottages are of State Heritage significance and remain as evidence of the islands’ past use. Construction of the Althorpe Island Lighthouse began in 1877. An accident claimed the life of the foreman of works in 1878, slowing the project's progress. Once complete, the lighthouse was operated and maintained by resident keepers from its first light in 1879 until it was demanned in 1991. C. A. Unbehaun supervised the laying of a submarine telephone cable in 1886 from the Althorpes to Cape Spencer.
Althorpe Island has a number of heritage-listed structures:
- Althorpe Island Jetty and Railway for Trolley 
- Althorpe Island Lighthouse 
- Althorpe Island Lighthouse Keepers' Cottages 
- Property Location Browser V2 Government of South Australia. Accessed 2014-02-15.
- "Department of Environment & Heritage Management Plan - Althorpe Islands, Goose Island and Troubridge Island Conservation Parks 2009" Department of Environment and Heritage, Government of South Australia (2009). Retrieved 2014-02-15.
- "Annual inspection of lighthouses. Lighting the Althorpes." South Australian Register, South Australia (1879-02-18). Retrieved 2014-02-27.
- Holbert, Kendall "Life at Althorpe Lighthouse" Chronicle, South Australia (1951-07-26). Retrieved 2014-02-16.
- "Local News." South Australian, South Australia (1845-08-22). Retrieved 2014-02-27.
- Reddan, W. "A Trip to Althorpe Island" Kapunda Herald, South Australia (1883-10-30). Retrieved 2014-02-16.
- "The annual inspection of lighthouses" The South Australian Advertiser, South Australia (1884-01-08). Retrieved 2014-02-27.
- "South Australia's Jubilee - Fifty years of progress - The province as it is - The centre of settlement" South Australian Register, South Australia (1887-06-21). Retrieved 2014-02-26.
- "" South Australian Register, South Australia (1897-01-11). Retrieved 2014-02-26.
- "THE LIGHTHOUSES. AN INTERESTING TRIP. No. 1." The Advertiser, South Australia (1902-11-12). Retrieved 2014-02-16.
- Wiebken, Annelise "Conservation management priorities for little penguin populations in Gulf St Vincent" SARDI (2011-06). Retrieved 2014-02-12.
- Colombelli-Négrel, D. & Kleindorfer, S. Penguin monitoring and conservation activities in the Gulf St Vincent, July 2013 - July 2014, Report to the Adelaide and Mt Lofty Natural Resources Management Board, Flinders University, South Australia (2014-04). Retrieved 2014-07-28.
- Flinders, Matthew (1966) . A Voyage to Terra Australis : undertaken for the purpose of completing the discovery of that vast country, and prosecuted in the years 1801, 1802, and 1803 in His Majesty's ship the Investigator, and subsequently in the armed vessel Porpoise and Cumberland Schooner; with an account of the shipwreck of the Porpoise, arrival of the Cumberland at Mauritius, and imprisonment of the commander during six years and a half in that island. (Facsimile ed.). Adelaide; Facsimile reprint of: London : G. and W. Nicol, 1814 ed. In two volumes, with an Atlas (3 volumes): Libraries Board of South Australia. p. 249. Retrieved 21 June 2014.
- "Spencer, George John, Viscount Althorp (SPNR776GJ)". A Cambridge Alumni Database. University of Cambridge.
- Management Plan - Althorpe Islands, Goose Island and Troubridge Island Conservation Parks (PDF). Adelaide: Department of Environment & Heritage. 2009. p. 26. ISBN 978-1-921466-76-2.
- "Marine Board. Althorpe Island lighthouse." South Australian Chronicle & Weekly Mail, South Australia (1878-04-20). Retrieved 2014-02-16.
- "Adelaide's First Telephones". The Advertiser (Adelaide, SA : 1889 - 1931). Adelaide, SA: National Library of Australia. 7 February 1924. p. 10. Retrieved 1 November 2014.
- "Jetty & Railway for Trolley, Althorpe Islands Conservation Park". South Australian Heritage Register. Department of Environment, Water and Natural Resources. Retrieved 12 February 2016.
- "Althorpe Island Lighthouse, Althorpe Islands Conservation Park". South Australian Heritage Register. Department of Environment, Water and Natural Resources. Retrieved 12 February 2016.
- "Althorpe Island Lighthouse Keepers' Cottages, Althorpe Islands Conservation Park". South Australian Heritage Register. Department of Environment, Water and Natural Resources. Retrieved 12 February 2016.