North Island (Houtman Abrolhos)

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North Island
Aerial photograph of the southern half of North Island, looking westwards
Aerial photograph of the southern half of North Island, looking westwards
Geography
Location Indian Ocean, off the coast of Western Australia
Coordinates 28°18′9″S 113°35′41″E / -28.3025, 113.59472Coordinates: 28°18′9″S 113°35′41″E / -28.3025, 113.59472[1][2]
Archipelago Houtman Abrolhos
Area 180 hectares
Length 2 kilometres (1¼ mi)
Width 1½ kilometres (1 mi)
Highest point Record Hill
13 metres (42 ft)
Administration
Flag of Australia Australia
State Western Australia
Demographics
Population Seasonally inhabited by about 130 lobster fishers (as of 2006)

North Island is the most northerly island in the Houtman Abrolhos.

Contents

[edit] History

[edit] Discovery

The first published map of North Island was an 1845 British Admiralty chart entitled "The Houtman Rocks".
The first published map of North Island was an 1845 British Admiralty chart entitled "The Houtman Rocks".

North Island was discovered in May 1840 during the third voyage of HMS Beagle, under the command of John Clements Wickham. The island was sighted from the peak of Flag Hill, East Wallabi Island in early May, and on 22 May it was visited and named North Island "from its relative position to the remainder of Houtman's Abrolhos". Before leaving the island, Wickham left a letter in a bottle atop the highest hill, which he named Record Hill for that reason.[3]

A map of the island first appeared in 1845 on a British Admiralty chart entitled "The Houtman Rocks". The following year, Wickham's lieutenant John Lort Stokes published the first account of the island in his Discoveries in Australia, describing it thus:[3]

"The island was about a mile across, and nearly circular. It was surrounded by a range of hills, with a flat in the centre, covered with coarse grass, where a great many quails were flushed, affording good sport, but not a single wallaby."

[edit] Development of infrastructure

The main thread in the history of North Island is the gradual development of a western rock lobster fishery on the island. There are records of the island being used as a base for crayfishers as early as 1902,[4] but it was not until the 1940s that a permanent seasonal camp was established there. By 1960 the island was seasonally inhabited by about 40 people,[5] and by 2003 this figure had increased to around 130. An airstrip was built on the island in 1979.[6]

[edit] Visits by naturalists

The island's history is punctuated by occasional visits by naturalists. The first such visit was that of the first Percy Sladen Trust Expedition to the Abrolhos Islands in 1913. This expedition spent very little time on North Island, as shore collecting was not very successful there, and other islands appeared better suited to their work. Nonetheless a substantial amount of information was published by the expedition members, including a description of the island's physiography[7] and an enumeration of its vertebrates.[8]

North Island was next visited by Dom Serventy in 1945, but no account of the visit was published. In 1959, the island was visited by a party from the University of Western Australia's Department of Zoology, accompanied by the English botanist Mary Gillham; the following year a brief article on North Island's physiography, vegetation and vertebrate fauna was published by Glen Storr.[5]

More recent visitors to North Island include P. R. Howden in 1974, Robert Ivan Taylor Prince in 1976, Ronald Eric Johnstone in 1981 and 1983,[9] Phillip Fuller in 1992,[10] and Judith Harvey and Vanda Longman in 1999.[11]

[edit] Geography

The Houtman Abrolhos and adjacent Western Australian coast; North Island is in the top left corner.
The Houtman Abrolhos and adjacent Western Australian coast; North Island is in the top left corner.

Located at 28°18′9″S 113°35′41″E / -28.3025, 113.59472,[1][2] North Island is an isolated, outlying island, separated from its nearest neighbours in the Wallabi Group by the 14 kilometre (9 mi) wide South Passage. Despite this separation, and despite not arising from the same carbonate platform as the rest of the Wallabi Group, it is usually considered as part of that group.[12]

The island is roughly oval in shape. It is approximately two kilometres (1¼ mi) long from south to north, and 1½ kilometres (1 mi) from west to east,[13] giving it an area of about 180 hectares (450 ac).[5]

Two high points are named Record Hill and Latitude Hill. These are the only gazetted places on the island, although some other features have informal names; for example, the most northerly and southerly point on the island have been called "North Point" and "South Point" respectively, and in 1960 a high point in the northwest corner of the island was referred to as "Northwest Hill".[5]

On the eastern side is a permanent seasonal fishers' camp consisting of fishing shacks, a number of jetties, a school for 24 children, a museum and a pub.[14] There is an unnamed lighthouse on the western side, a trig point on the eastern side, and a gravel airstrip near the centre.[15]

The island is surrounded by a coral reef flat. This extends about 1½ kilometres (1 mi) to the west of the island, and even further to the north and south, but the reef margin lies quite close to the island on the eastern side. Most of the reef is not navigable, but a passage through the reef just north of the island is named Suda Bay Passage, one just south of the island is named Barker Passage, and there are a few breaks or channels on the eastern side of the island where boats may obtain shelter in bad weather.[7]

An area of reef immediately north of the island is gazetted as an anchorage under the name The Flat, and at the northern extreme of the reef there is a breaker named The Big Breaker.[15] About 200 metres west of the island is a small rock informally known as "Shag Rock", but with no gazetted name; it is not to be confused with the gazetted Shag Rock in the Wallabi Group further south.

[edit] Geology and physiography

The basement of North Island is the Wallabi Limestone, a dense calcretised, coral limestone platform that underlies the entire Wallabi Group. This platform, which arises abruptly from a flat shelf, is about 40 metres thick, and is of Quaternary origin. Reef that formed during the Eemian interglacial (about 125,000 years ago), when sea levels were higher than at present, are now emergent in places, and constitute the basement of the group's central platform islands, namely West Wallabi Island, East Wallabi Island and North Island.[16][17]

North Island's basement for the most part does not exceed 1½ metres (5 ft) in elevation. Much of it is capped by aeolianite, and nearly all of it is covered with sand, but there are some exposed outcrops. The southern margin of the island, for example, takes the form of a low cliff, which in many places is severely undercut by the sea.[7]

There are extensive dunes of unconsolidated Holocene sand along both the western and eastern sides of the island. The topography of these dunes varies with time: in 1913 Dakin recorded the dunes as being a good deal higher in the east than in the west,[7] but in 1960 Storr found the eastern dunes to be severely eroded, apparently because of a fire that burnt out much of the island's vegetation in 1935.[5] In the centre of the island is a low plain, with a sinkhole in its southwest corner, and a small salt lake near its northern edge. The soil in the centre of the plain is shallow loam, whereas the rim is deeper and composed largely of shell fragments.[5]

[edit] Flora

See also: Flora of the Houtman Abrolhos
Typical dune vegetation on North Island
Typical dune vegetation on North Island

Most of North Island is dominated by chenopod shrubs, generally less than a metre (3 ft) high. The beach vegetation is largely Spinifex longifolius (Beach Spinifex), Salsola kali (Prickly Saltwort), Atriplex cinerea (Grey Saltbush) and naturalised Cakile maritima (Sea Rocket). Stable dunes are vegetated by Atriplex paludosa (Marsh Saltbush), Scaevola crassifolia (Thick-leaved Fan-flower), Olearia axillaris (Coastal Daisy-busy), Myoporum insulare (Blueberry Tree) and Exocarpos sparteus (Broom Ballart). Sheltered areas behind dunes support Salsola kali and Myoporum insulare and also Nitraria billardierei (Nitre Bush), the last of these being the only plant on the island to grow over 1½ metres (5 ft) high. In areas where limestone is close to the surface, the vegetation consists of Pimelea microcephala (Shrubby Rice-flower), Spyridium globulosum (Basket Bush) and Acanthocarpus preissii.[5]

The rim of the central plain is vegetated by a dense shrubland of Rhagodia baccata (Berry Saltbush), Atriplex paludosa and Threlkeldia diffusa (Coast Bonefruit). Nearer the centre, the vegetation consists of Frankenia pauciflora (Seaheath), Muellerolimon salicorniaceum and Tecticornia arbuscula (Bulli Bulli), although T. arbuscula is replaced by Tecticornia halocnemoides (Shrubby Samphire) where the soil is shallow. The most low-lying area of the central plain, south of the salt lake, is water-logged in winter; it is vegetated by a dense mat of Sarcocornia quinqueflora (Beaded Samphire), Sporobolus virginicus (Marine Couch) and Suaeda australis (Seablite).[5]

The dune, limestone and salt lake vegetation communities on North Island are all considered to have high conservation significance. The dune and limestone communities have high biodiversity, are highly sensitive to disturbance and regenerate slowly. The salt lake community is considered significant because of the rarity of salt lakes on offshore islands.[18]

According to survey published in 2001, the following vascular plants occur on North Island:[11]

  • Erodium cygnorum (Blue Heronsbill)
  • Euchiton sphaericus
  • Euphorbia tannensis
  • Exocarpos sparteus (Broom Ballart)
  • Ficinia nodosa (Knotted Club Rush)
  • Frankenia pauciflora (Seaheath)
  • Grevillea argyrophylla (Silvery-leaved Grevillea)
  • Hordeum leporinum (Barley Grass) (naturalised)
  • Hornungia procumbens (Oval Purse) (naturalised)
  • Juncus bufonius (Toad Rush) (naturalised)
  • Malva parviflora (Marshmallow) (naturalised)
  • Melilotus indicus (naturalised)
  • Mesembryanthemum crystallinum (Iceplant) (naturalised)
  • Muellerolimon salicorniaceum
  • Myoporum insulare (Blueberry Tree)
  • Nicotiana occidentalis subsp. hesperis (Native Tobacco)
  • Nitraria billardierei (Nitre Bush)
  • Olearia axillaris (Coastal Daisy Bush)
  • Parapholis incurva (Coast Barbgrass) (naturalised)
  • Parietaria debilis (Pellitory)
  • Phalaris minor (Lesser Canary Grass) (naturalised)
  • Pimelea microcephala (Shrubby Riceflower)
  • Plantago debilis
  • Podotheca angustifolia (Sticky Longheads)
  • Pseudognaphalium luteoalbum (Jersey Cudweed)

[edit] Fauna

[edit] Mammals

A Tammar Wallaby on North Island
A Tammar Wallaby on North Island
Much of North Island has been heavily overgrazed by Tammar Wallabies. Note the difference in vegetation density either side of the fence line.
Much of North Island has been heavily overgrazed by Tammar Wallabies. Note the difference in vegetation density either side of the fence line.

No land mammals are known to be native to North Island, but the Australian Sea Lion (Neophoca cinerea) occasionally hauls out on the island's beaches, and it has been suggested that the island once had a native population of the introduced Tammar Wallaby (Macropus eugenii).

Stokes explicitly stated the Tammar Wallaby to be absent from North Island in 1840,[3] and it was not recorded by the Percy Sladen Trust Expedition in 1913. However it was apparently introduced to the island in the 1920s, as early fishermen reported seeing it between 1928 and 1930. This introduction failed, possibly because the population overgrazed the island, then declined to extinction from lack of food and shelter.[6] The species was not found by Serventy during his 1945 visit, nor by Storr in 1959, but the latter found plenty of remains, mostly mandibles. Storr interpreted these remains as predating the 1920s introduction, suggesting that a native population of Tammars became extinct on the island before 1840.[5] Albert Russell Main agreed,[19] but the theory has not been accepted by later researchers.[6][20]

In 1985, five Tammar Wallabies were introduced onto North Island, and this time the population established successfully. Possible reasons for this success include the absence of their natural predator the Carpet Python (Morelia spilota imbricata);[21] the availability of additional food and water from the fishers' huts, which are occupied during the harshest time of the year; and the presence of the air strip, which apparently provides additional food for them.[6] By the 2000s, there were over 450 Tammar Wallabies on the island.[22] The wallabies overgrazed and ringbarked the native vegetation, particularly in the area burnt in 1935,[6] thus reducing vegetation cover, and causing a serious decline in populations of some plant species. In 2003, residents asked the Department of Conservation and Land Management (now the Department of Environment and Conservation) for help in managing the issue. CALM staff visited the island in April and May of that year, and subsequently produced a report recommending an investigation into controlling population levels by the use of implanted contraceptives.[6] Exploration of this option began in 2005,[21] but in July 2007 the research was discontinued. Around 60 wallabies were removed to educational institutions for research purposes, and culling of the remainder was commenced.[23] By February 2008 the wallaby population had been reduced to around 25 individuals.[22]

The only other mammal known to occur on the island is the naturalised House Mouse (Mus Musculus).[20] Eight European Rabbits (Oryctolagus cuniculus) were introduced in 1934, and were found to be "exceedingly numerous" by 1945, but by 1960 they were extinct, apparently from predation by feral cats.[5] Neither rabbits nor cats are now reported as naturalised on the island.[20]

[edit] Reptiles

Reptiles recorded on North Island include Binoe's Prickly Gecko (Heteronotia binoei), the gecko Phyllodactylus marmoratus, the Jew Lizard (Pogona barbata), King's Skink (Egernia kingii), the Western Limestone Ctenotus (Ctenotus australis) the Western Worm Lerista (Lerista praepedita),[5] and the Common Dwarf Skink (Menetia greyii).[24] The Carpet Python was reported as present on the island in very low numbers prior to 1960, but it has never been observed there by naturalists,[5] and is now certainly absent.[21]

The Green Turtle (Chelonia mydas) has been observed in large numbers near the shore, and it has been claimed that they breed on the island,[5] but this has never been verified.[25] If this is true, then North Island would be the species' most southerly breeding site in Western Australia.[5]

[edit] Birds

The birds most often mentioned in relation to North Island are the Abrolhos Painted Button-quail (Turnix varia scintillans), a rare subspecies of Painted Button-quail (Turnix varia) known only from the Wallabi Group, and therefore protected under the Wildlife Conservation Act 1950; and the Brush Bronzewing (Phaps elegans), one of the most common birds on North Island, the mainland populations of which are decreasing.[18]

Other birds known to breed on North Island include the Osprey (Pandion haliaetus cristatus), Crested Tern (Sterna bergii),[18] Caspian Tern (S. caspia), Silver Gull (Larus novaehollandiae novaehollandiae), and Welcome Swallow (Hirunda neoxena). Birds commonly recorded as resident on the island but not recorded as breeding there include the Reef Heron (Egretta sacra), White-breasted Sea Eagle (Haliaeetun leucogaster), Red-capped Plover (Charadrius ruficapillus), Fairy Tern (Sterna nereis nereis), Richard's Pipit (Antus novaseelandiae australis) and Grey-breasted White-eye (Zosterops lateralis gouldi). The Sooty Oystercatcher (Haematopus fuliginosus fuliginosus) and White-backed Swallow (Cheramoeca leucosterna) have also rarely been observed as resident on the island.[9]

The most common visitors to the island are the Bar-tailed Godwit (Limosa lapponica baueri), Grey-tailed Tattler (Tringa brevipes), Ruddy Turnstone (Arenaria interpres interpres), Red-necked Stint (Calidris ruficollis) and Curlew Sandpiper (Calidris ferruginea). Other observed visitors include the Great Cormorant (Phalacrocorax carbo novaehollandiae), Australian Kestrel (Falco cenchroides cenchroides), Banded Plover (Vanellus tricolor), Large Sand Plover (Charadrius leschenaultii), Whimbrel (Numenius phaeopus variegatus), Greenshank (Tringa nebularia), Sanderling (Calidris alba), Willie Wagtail (Rhipidura leucophrys leucophrys) and Brown Songlark (Cincloramphus cruralis).[9]

[edit] Human uses

A Beechcraft aeroplane sits on the North Island airstrip.
A Beechcraft aeroplane sits on the North Island airstrip.

The Houtman Abrolhos is wholly vested in Western Australia's Minister for Fisheries for purposes of "Conservation of Flora and Fauna, Tourism, and for Purposes Associated with the Fishing Industry".[26]

[edit] Conservation

North Island is considered to have high conservation value with respect to its populations of Brush Bronzewing and Abrolhos Painted Button-quail, and its dune, limestone and salt lake vegetation communities. The potential existence of historically significant artefacts on Record Hill, namely the bottle left by Wickham and Stokes in 1840, is yet to be assessed.[18]

A 514 hectare area of reef immediately south of North Island is designated a Reef Observation Areas (ROA), within which fishing is prohibited, except for the use of lobster pots. One of four ROAs in the Houtman Abrolhos, these protected areas are intended to help conserve species of territorial finfish that are fished elsewhere, and to provide divers with the opportunity to observe large populations of large finfish that are not frightened by their approach.[27]

[edit] Tourism

With extensive sand beaches, seabird breeding areas, and good dive sites in the Reef Observation Area to the south of the island, North Island is considered a attractive tourist site. However all of the island's limited anchorage and jetty space is already occupied by commercial fishers, so landings from private or charter boats are only possible by prior arrangement with one of them.[27] Moreover visitors are not permitted to camp on the island.[14] Nonetheless North Island accounts for about 3½% of private recreational boat trips to the Houtman Abrolhos, and about 1% of commercial charter boat trips.[28] The most recent tourism plan for the Houtman Abrolhos supported the continuation and improvement of access to North Island by private charter boats, and the use of the airstrip for tourism purposes, but recommended against the establishment of a land based tourist site there.[27]

[edit] Fishing industry

North Island's primary human use is as a seasonal camp for Western Rock Lobster fishers. During lobster season, which runs from 15 March to 30 June,[29] North Island's camp is occupied by about 130 fishers.[6] The camp is serviced by a carrier boat, the North Islander, which visits the island every three days, bringing supplies and taking about the catch and any domestic waste.[14][30]

[edit] References

The salt lake
The salt lake
Seals occasionally haul out on North Island.
Seals occasionally haul out on North Island.
  1. ^ a b Gazetteer of Australia (1996). Belconnen, ACT: Australian Surveying and Land Information Group.
  2. ^ a b North Island. Gazetteer of Australia online. Geoscience Australia, Australian Government.
  3. ^ a b c Stokes, John Lort (1846). Discoveries in Australia, Volume 2. London: T. and W. Boone. 
  4. ^ Gray, Howard (1999). The western rock lobster, Panulirus cygnus: Book 2, A history of the fishery. Geraldton: Westralian Books, 35. ISBN 0-9594105-6-2. 
  5. ^ a b c d e f g h i j k l m n Storr, G. M.. "The physiography, vegetation and vertebrate fauna of North Island, Houtman Abrolhos". Journal of the Royal Society of Western Australia 43: 59–62. 
  6. ^ a b c d e f g Morris, Keith; Sercombe, Nigel; Chant, Alanna. "A report on the management of Tammar Wallabies on North Island, Houtman Abrolhos". . Department of Conservation and Land Management, Western Australia
  7. ^ a b c d Dakin, W. J. (1919). "The Percy Sladen Trust Expeditions to the Abrolhos Islands (Indian Ocean)". Journal of the Linnean Society of London (Zoology) 34: 127–180. 
  8. ^ Alexander, Wilfred Backhouse (1922). The vertebrate fauna of Houtman's Abrolhos (Abrolhos Islands), Western Australia 34, 457–486. 
  9. ^ a b c Storr, G. M., Johnstone, R. E. and Griffin, P. (1986). "Birds of the Houtman Abholhos, Western Australia". Records of the Western Australian Museum (Supplement No. 24). 
  10. ^ Fuller, P. J.; Burbidge, A. A.; Owens, R. (1994). "Breeding seabirds of the Houtman Abrolhos, Western Australia". Corella 18 (4): 97–113. 
  11. ^ a b Harvey, J. M., Alford, J. J., Longman, V. M. and Keighery, G. J. (2001). "A flora and vegetation survey of the Houtman Abrolhos, Western Australia". CALMScience 3 (4): 521–623. 
  12. ^ Houtman Abrolhos. oceandots.com. Retrieved on 2007-10-13.
  13. ^ Google Earth. Retrieved on 2008-03-2008.
  14. ^ a b c Abrolhos Islands — North Island — album 1. eneabba.net. Retrieved on 2008-05-04.
  15. ^ a b Australia 1:100000 Topographic Survey, Map sheet 1641 (Edition 1): Wallabi
  16. ^ Collins, Lindsay B.; Zhu, Zhong Rong; Wyrwoll, Karl-Heinz (1998). "Late Tertiary-Quaternary Geological Evolution of the Houtman Abrolhos Carbonate Platforms, Northern Perth Basin", in Purcell, R. and Purcell, P. (eds): The sedimentary basins of Western Australia 2. Perth, Western Australia: Petroleum Exploration Society of Australia, 647-663. Retrieved on 2008-05-02. 
  17. ^ Collins, Lindsay B.; Zhu, Zhong Rong; Wyrwoll, Karl-Heinz (2004). "Geology of the Houtman Abrolhos Islands", in Vacher, Leonard and Quinn, Terrence (eds): Geology and hydrogeology of carbonate islands (Developments in Sedimentology 54). Elsevier Science, 811–834. 
  18. ^ a b c d . "Inventory of the Land Conservation Values of the Houtman Abrolhos Islands". . Department of Fisheries, Government of Western Australia. ISSN 0819-4327
  19. ^ Main, Albert Russell (1961). "The occurrence of Macropodidae on islands and its climatic and ecological implications". Journal of the Royal Society of Western Australia 44 (3): 84–89. 
  20. ^ a b c Burbidge, A. A.. "Introduced mammals on Western Australian islands: Improving Australia's ability to protect its island habitats from feral animals". . Department of Conservation and Land Management, Government of Western Australia Retrieved on 2007-12-21.
  21. ^ a b c 'Pill' plan for growing wallaby population. ABC News Online. Retrieved on 2007-12-21.
  22. ^ a b Wallabies — Culling. Minutes of the Western Australian Legislative Council, Tuesday 19 February 2008. Retrieved on 2008-05-03.
  23. ^ . "Science Division annual research activity report 2006 – 2007". 83–84. Department of Environment and Conservation, Government of Western Australia Retrieved on 2007-12-21.
  24. ^ Herpetofauna Assessment of Long Island, Wallabi Group – 8 November 2005. Retrieved on 2007-11-15.
  25. ^ . "Management of the Houtman Abrolhos". Fisheries Management Paper 117. . Fisheries WA Retrieved on 2008-05-02.
  26. ^ . "Management of the Houtman Abrolhos System: A Draft Review 2007 – 2017". Fisheries Management Paper No. 220. . Department of Fisheries, Government of Western Australia Retrieved on 2007-12-01.
  27. ^ a b c Fisheries Western Australia. "Sustainable tourism plan for the Houtman Abrolhos islands". Fisheries Management Paper No. 146. Retrieved on 2008-03-23.
  28. ^ Appendix 2: Tourist visitation to the Houtman Abrolhos Islands, 2002-6. Retrieved on 2007-11-15.
  29. ^ Department of Environment and Water Resources. "Assessment of the Western Rock Lobster Fishery". Retrieved on 2008-05-04.
  30. ^ David, Greg. "Abrolhos Islands Waste Management Coordinator's Report". Retrieved on 2008-05-04.

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