Island Ecology

Islands are protected from many threats

Due to their remoteness and the absence of introduced predators such as foxes and cats, the islands off the south west coast support distinct ecosystems. As most of these islands are protected nature reserves, public access is restricted, favoring the establishment of seabird and seal breeding colonies.

Natural shelter for rare species

While the larger islands are vegetated by coastal heath, the smaller islands are composed of bare limestone, gneiss or granite rock. The islands are important breeding areas for the New Zealand Fur Seal (Arctocephalus forsteri), which has only reappeared in the Augusta area during the last 20 years after having been decimated by sealers last century. The islands are also important nesting areas for seabirds such as Bridled Terns (Onychoprion anaethetus), Caspian Terns (Sterna caspia), Fairy Terns (Sterna nereis), Flesh-footed Shearwaters (Puffinus carneipes) and Little Penguins (Eudyptula minor). Interestingly, a breeding colony of Red-tailed Tropicbirds (Phaethon rubricauda) exists on Sugarloaf Rock, over 2000 kilometers south of its more common distribution, as its name suggests, in the tropics!

 

Aim of study

Responsible for monitoring of threatened species in Western Australia, the Department of Environment and Conservation (DEC) obtained funding by the Natural Heritage Trust, West Australian and Australian Governments through the South West Catchments Council (SWCC) to monitor the diversity and abundance of flora and fauna on the islands off the south west coast in 2007 and 2008.

Taking measurements of a juvenile Pacific Gull

(Larus pacificus; courtesy of V. Steptoe, DEC)

Study area

Surveys of the offshore islands and rocky islets between Augusta and Hamelin Bay were undertaken in January and March 2008. In addition, annual monitoring of the Red-tailed Tropicbird (Phaethon rubricauda) was undertaken on Sugarloaf Rock throughout the 2007 and 2008 breeding seasons.

 

Objectives

· Quantify the number of New Zealand Fur Seals inhabiting the islands and rocks;

· Determine the diversity and density of seabirds inhabiting the islands, particularly breeding tropical seabirds extending their southerly distribution range;

· Conduct a general inspection and maintenance of the nature reserves;

· Determine flora species diversity of the larger islands; and

· Quantify the amount of marine debris on the islands.

Sugarloaf Rock Red-tailed Tropicbird monitoring
(courtesy of K. Onton, DEC)

This monitoring data serves as a baseline upon which further analysis can be undertaken to assess changes in island biodiversity and condition, and to identify and manage threats as required.

Results

Some of the key findings include:

 

· The presence of seal pups confirmed the use of several of the islands as breeding sites for the New Zealand Fur Seal.

· Bird observations confirmed that Bridled Tern were the most abundant breeding seabirds on the islands. Other breeding bird species observed included the Crested Tern, Sooty Oystercatcher (Haematopus fuliginosis), Pacific (Larus pacificus) and Silver Gulls (Larus novaehollandiae), Flesh-footed Shearwater and Little Penguin.

New Zealand Fur Seal colony (courtesy of D./F. Harvey)

· Red-tailed Tropicbird numbers in decline.

In each of the 2007 and 2008 breeding seasons, only a single pair of Red-tailed Tropicbird was observed at Sugarloaf Rock, marking the lowest counts of birds at the site on record and a continuation of the decreasing trend in tropicbird numbers. Although each pair was observed incubating an egg, both breeding attempts were unsuccessful.

Annual count of adult Red-tailed Tropicbirds at Sugarloaf Rock

 

· Change in vegetation diversity and structure.

A reduction of vegetation species from 23 in 1959 to 17 in 2008 was observed on St Alouarn Island, though a spring survey is required to identify annuals.

A change in vegetation composition and structure was observed on Seal Island. Woody species identified in 2008 were not present in 1959 and have the potential to transform the vegetation structure from a low herbaceous to an elevated scrub community, which may alter nesting seabird habitat.

 

An increase in weed species, particularly Mesembryanthemum crystallinum, was recorded for both islands.

Vegetation plot on Seal Island (courtesy of K. Onton, DEC)

How you can help the environment

Island ecosystems are fragile. It is important to avoid interfering with these ecosystems as they can easily be disturbed by humans who may displace wildlife and introduce invasive species.

Nature reserves are managed by the Department of Environment and Conservation under the Conservation and Land Management Act 1984. All activities in nature reserves are subject to the provisions of the act and its regulations. The islands of the south west are classified as Class A Nature Reserves and public access is mostly prohibited.

Signage on St Alouarn Island (courtesy of K. Onton, DEC)

Further information

Visit South West Catchments Council’s website to download the full technical report and/or contact

· DEC Conservation Officer (Marine & Coastal) Kim Onton on (08) 9725 5945 or This e-mail address is being protected from spambots. You need JavaScript enabled to view it or

· DEC South West Region’s Nature Conservation Program Leader Kim Williams on (08) 9725 5910 or This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

How to get involved in coastal conservation

To find out how to become a volunteer with DEC, please the DEC website.

To find out how to become involved in other Coastcare volunteer programs, please visit the South West and Peel Coastal Management Group’s website (www.coastswap.com).

 

Acknowledgements

We thank the Department of Environment and Conservation and Augusta Sea Search and Rescue for their efforts and collaboration on this project.

Sources

Department of Conservation and Land Management 2003 ‘The Capes - A diverse coastal and marine environment’. Landscope, Summer 2002-2003. Department of Conservation and Land Management, Perth.

Gillham, M. E. 1963 Association of nesting sea-birds and vegetation types on islands off Cape Leeuwin, South-Western Australia. Western Australian Naturalist Vol. 9, pp. 29-46.

Onton K 2009 South West Island Survey Report, report to the South West Catchments Council, Department of Environment and Conservation, Bunbury, Western Australia