Investigator Group

Investigator Group Wilderness Protection Area protects a chain of remote offshore islands lying approximately 60 kilometres west of the Eyre Peninsula in the Great Australian Bight. Proclaimed in 2011, the wilderness encompasses the Ward Islands, Top Gallant Isles, and Pearson Isles, along with their surrounding marine environment. The islands provide critical nesting habitat for diverse seabird species and haul-out sites for Australian sea lions and New Zealand fur seals. The endemic Pearson Island black-footed rock-wallaby—found nowhere else on Earth—is the archipelago's most celebrated terrestrial resident. Great white sharks frequent the waters surrounding the islands to prey on the abundant seal colonies. The remote and windswept islands are accessible only by boat in suitable conditions and are closed to unauthorised access.

The Investigator Group is nationally significant for wildlife, particularly marine mammals and nesting seabirds. Australian sea lion breeding colonies on multiple islands represent a significant proportion of the global population of this endemic species. New Zealand fur seal colonies are also substantial. White-faced storm-petrels nest in burrows in their millions, and Cape Barren geese breed on vegetated island surfaces. Wedge-tailed shearwaters, crested terns, and pied oystercatchers are among the many seabird species present. The Pearson Island black-footed rock-wallaby—a distinct subspecies endemic to these islands—is monitored annually for population status. Great white sharks aggregate in the surrounding waters, one of their known hunting grounds.

The Investigator Group islands support vegetation communities adapted to exposed coastal conditions, salt spray, and seabird disturbance. Dense saltbush and samphire communities dominate the lower coastal terraces, while tussock grass, coastal daisy bush, and native herbs cover the upper island surfaces. Burrowing seabirds create significant soil disturbance, and the vegetation responds with nitrophilous species tolerant of nutrient-enriched soils. The Pearson Isles, the largest islands in the group, support the most diverse vegetation including patches of native shrubs and windswept trees that would otherwise be absent from the exposed outer islands. Weed invasion from historic visits is a management concern on some islands.

The Investigator Group sits on the continental shelf of the Great Australian Bight, representing remnant higher ground of the Eyre Peninsula exposed during glacial periods of lower sea level. The islands are composed of Precambrian metamorphic and igneous rocks that form the ancient Gawler Craton, some of the oldest rocks in Australia. Their isolation from the mainland has persisted for thousands of years, driving the divergence of endemic wildlife forms such as the Pearson Island rock-wallaby. Offshore reefs and rocky platforms provide diverse habitat for marine invertebrates and fish, supporting the food web that sustains the island's abundant predators.

The Investigator Group experiences a windy, cool-temperate maritime climate strongly influenced by Southern Ocean conditions. Annual rainfall is relatively low at 300–400 millimetres, concentrated in winter. The islands are exposed to persistent westerly and southwesterly winds throughout the year, creating treacherous seas around the shallow reefs. Summer temperatures are moderate due to maritime influence, rarely exceeding 25°C. Winter storms can make the islands inaccessible for weeks at a time. The exposure to Southern Ocean swell makes boat landings possible only in calm conditions.

The Investigator Group was named by English navigator Matthew Flinders during his circumnavigation of Australia in the ship HMS Investigator in 1802. Aboriginal peoples from the Eyre Peninsula likely visited the islands by raft or bark canoe in prehistoric times, though sustained occupation would have been challenging given the lack of freshwater. European sealers heavily exploited the fur seal and sea lion colonies throughout the 19th century, causing significant population declines that took many decades to recover. The remoteness and difficult access limited subsequent human impact, contributing to the preservation of the islands' exceptional wildlife.

The Investigator Group was proclaimed as a Wilderness Protection Area in 2011, recognising its outstanding natural character and the global significance of its Australian sea lion and seabird populations. The proclamation was part of South Australia's ongoing expansion of marine and island conservation. Access restrictions were formalised to prevent disturbance of sensitive breeding colonies. Research programs monitoring sea lion populations, seabird breeding success, and the endemic rock-wallaby were established in partnership with universities and conservation organisations. The area is co-managed with respect to the interests of the Nauo traditional owners of the adjacent Eyre Peninsula coast.

The Investigator Group is accessible only by private or chartered vessel, and landing is restricted to authorised research and management activities. Scenic cruises passing the islands from Port Lincoln or Streaky Bay allow viewing of sea lion colonies, seabird flocks, and dramatic coastal scenery without disturbance. Scuba diving and snorkelling in surrounding waters encounter diverse reef communities and, occasionally, great white sharks in a world-class shark diving experience. Aerial viewing from light aircraft provides perspectives on the island group's extent and the wildlife concentrated on their surfaces.

There are no visitor facilities on any of the Investigator Group islands. Access is strictly controlled and a permit from the Department for Environment and Water is required for landing. The islands are approximately 60 kilometres offshore from the Eyre Peninsula coast, requiring a substantial ocean crossing. Port Lincoln is the nearest major service centre with charter boat operators offering wildlife viewing tours to the outer islands. Great white shark cage diving operations based at Port Lincoln sometimes visit waters adjacent to the wilderness area. The islands are not accessible by public transport.

Conservation priorities focus on protecting Australian sea lion breeding colonies and the endemic Pearson Island rock-wallaby from disturbance and introduced species. Pest animal control—particularly rats, which can devastate seabird nesting colonies on offshore islands—is essential. Annual monitoring of sea lion pup production and adult survival tracks population trends for this nationally vulnerable species. Climate change poses risks through increased storm frequency and ocean warming affecting the fish prey of sea lions. The wilderness protection area classification provides the highest level of legislative protection against inappropriate development or access, ensuring the islands remain a refuge for their extraordinary wildlife.