In 2022, black rats reached a Great Barrier Reef island; four years later Australia declared it rat-free after an intensive eradication mission

In November 2022, campground hosts on North West Island noticed something that could have become a major threat to one of the Great Barrier Reef’s important wildlife refuges: black rats had arrived. The island, about 75 kilometres north-east of Gladstone, is part of Capricornia Cays National Park and supports important breeding populations of seabirds and nesting marine turtles. Rangers quickly confirmed that the rats had spread across the island using remote cameras and Black Trakka ink monitoring stations. The discovery came only three months after mice had been declared eradicated from North West Island, highlighting how quickly invasive pests can return. Over the next 18 months, Queensland Parks and Wildlife Service (QPWS) and Gidarjil Land and Sea Rangers carried out an intensive eradication programme using aerial baiting, bait stations and traps. After another 12 months of monitoring produced no evidence of rats, North West Island was officially declared rat-free in 2026.North West Island is isolated, but that isolation does not make it immune to invasive species. Rangers believe the black rats most likely arrived as stowaways on boats or inside camping equipment brought to the island by visitors. The timing made the discovery particularly frustrating: common house mice had been eradicated from the island only three months earlier. Once the possible infestation was reported in November 2022, rangers moved quickly to determine whether rats were actually present. Remote cameras and Black Trakka ink monitoring stations confirmed the animals and showed that they had spread throughout the island. A single breeding pair of black rats can produce a population numbering in the thousands within a year, making early intervention critical on isolated islands. The threat was particularly serious because North West Island is an important seabird and turtle rookery within the Great Barrier Reef World Heritage Area. Black rats are omnivores and can feed on seabirds, their eggs and chicks, turtle eggs and hatchlings, as well as vegetation. Their presence therefore had the potential to affect several parts of the island ecosystem at once.Removing rats from an entire island is considerably harder than trapping a few animals. North West Island’s size meant that aerial baiting by helicopter was considered the most effective primary treatment. However, the eradication team also used ground-based bait stations and trapping to help reduce potential impacts on seabirds and turtles. The operation lasted 18 months, and the team repeatedly adjusted its tactics as the rats changed their behaviour. This flexibility was an important part of the campaign because eradication depends on finding and eliminating the remaining animals rather than simply reducing their numbers. The project was carried out by QPWS and Gidarjil Land and Sea Rangers through the Reef Joint Field Management Program, with support from the Great Barrier Reef Marine Park Authority. Funding came through the Australian Government’s Reef Trust, including contributions from Australia Pacific LNG, QGC and Santos GLNG.The end of the baiting and trapping campaign did not immediately mean the island was considered safe. Rangers continued searching for surviving rats with remote cameras and Black Trakka monitoring traps. The island had to pass an extended period without evidence of the invasive animals before eradication could be confirmed. After 12 months of intensive monitoring produced no evidence of black rats, North West Island was officially declared rat-free in 2026. Queensland’s Department of the Environment, Tourism, Science and Innovation described the result as a major conservation win for the island’s threatened turtles and seabirds. The achievement is especially significant because North West Island had only recently experienced another successful pest eradication. It demonstrates both the vulnerability of isolated islands and the importance of continuing biosecurity after an eradication campaign ends.With the rats gone, the challenge has shifted from eradication to prevention. Rangers are urging visitors to thoroughly check boats, camping equipment and other belongings before travelling to North West Island. A small pest hidden in a boat or piece of equipment can undo years of conservation work. The Queensland Parks and Wildlife Service says the island’s rat-free status is an important step towards protecting its seabirds, marine turtles and wider ecosystem. The successful campaign also shows why island conservation often requires persistent monitoring long after an invasive species appears to have disappeared. For North West Island, the sequence is striking: black rats were detected in 2022, an intensive 18-month eradication campaign followed, and a further year of surveillance finally provided enough evidence to declare the island rat-free. What began as a few suspected stowaways had become a serious ecological threat; removing them required years of vigilance, cooperation and careful conservation work.