Australia might be our home girt by sea, but protecting agriculture from pests and diseases found abroad isn't as simple as watching the water.

Papua New Guinea gained independence half a century ago, and today only a few kilometres separate the mainland from Australia's closest point, the Torres Strait island of Saibai.

But the border - and the biosecurity situation - is more complicated than a matter of distance.

February marked 40 years since the Torres Strait Treaty came into effect, which gives some Papuan and Indigenous Australian communities special permissions to travel within the region without a passport or visa for traditional and cultural purposes.

It's this confluence of factors which makes it perhaps the most high-risk thoroughfare for threats to Australian agriculture.

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