Australia has launched a crackdown on illegal fishermen from Indonesia. The poachers are accused of depleting valuable fish stocks - and even of potentially exposing Australia to bird flu. This week, 29 fishermen were arrested at gunpoint near Darwin.

Illegal fishing boats could have plundered as many as a million sharks from waters in Australia's tropical north. That is according to state officials in Western Australia, who want the federal authorities to provide more patrol boats.

The Australian customs service already has its hands full trying to keep vast areas of ocean under surveillance.

It is an impossible job, and no one is quite sure how many foreign trawlers slip through unnoticed. Officials in Canberra believe that poaching is becoming more organized, and that criminal gangs in Indonesia, China and Korea are responsible.

Australia's worries, however, go far beyond fishing.

Australian customs officer Brian Hurrell says that illegal fishermen, who have been known to come ashore with dogs and other animals including chickens, are potentially bringing new diseases to Australia.

"What all border agencies are concerned about is the increasing approach to our shores, in terms of quarantine threat, particularly up here in the north," Mr. Hurrell said. "I think anything that would upset the balance in remote Australia would be a problem for us, and anything like animals coming ashore or other pests brought ashore from any of the boats could be a real problem for us."

Australia has been watching nervously as Indonesia, its giant neighbor to the north, grapples with a form of bird flu that has killed more than 60 people in Southeast Asia since 2003.

The World Health Organization says the bird flu virus could mutate into a form that passes easily and quickly among humans, threatening tens of millions worldwide.

Opposition politicians have claimed that foreign vessels bring with them the threat of avian influenza, or bird flu, and that the government is not ready to deal with the problem.

This week 29 foreign fishermen were arrested near Darwin in dramatic circumstances.

The captain of one Indonesian vessel tried to resist, forcing Australian customs officers to fire a machinegun across the boat's bow. No one was injured, but the episode has highlighted Australia's determination to crack down on the illegal fishing trade.

The men are suspected of taking huge quantities of shark and reef fish.