Pristine islands off WA that harbour threatened species often found nowhere else in the world are at an unacceptable risk of being invaded by foreign pests, one of the State's leading biologists has warned.

Andrew Burbidge told a Senate committee investigating environmental biosecurity arrangements in Australia there was a lack of a "co-ordinated" plan for keeping out feral animals and plants from the country's islands.

Dr Burbidge, a former public servant who advises State and Federal governments, said the shortcoming was not good enough given Australia's "appalling" record of extinction.

He held up Christmas Island as a salutary lesson, saying the biosecurity performance there had been "shockingly inadequate" and led to the loss of many of its unique species.

He said unless governments set up a system to enable them to prioritise islands based on their environmental value and vulnerability to pest invasion, there was a risk of similar events happening again.

A spokeswoman for WA's Department of Parks and Wildlife noted the role many of the State's 3474 islands played as "arks" for threatened plants and animals.

The spokeswoman also pointed out the agency had been involved in many programs to eradicate pests from islands, including one under way on Dirk Hartog Island off the Gascoyne.

"The department is two years into a project that is working towards developing a prioritisation model for biosecurity measures for WA islands," she said.

Noting that most pests could not swim and were invariably brought to islands inadvertently on boats, Dr Burbidge recommended further regulation and education.

He said resource or tourist companies that visited islands should need to prepare quarantine plans, citing oil giant Chevron's example on Barrow Island as a model.

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Pests threaten WA islands