Australia's longest maritime chase through freezing Antarctic seas finally ended yesterday in the South Atlantic where armed officers boarded a Uruguayan-flagged fishing trawler and began escorting it back to Australia.

The crew of the vessel - the Viarsa 1 - is suspected of poaching the highly prized Patagonian Toothfish in the remote Australian fishing zones around Heard and McDonald Islands. They were first sighted on August 7 and were finally stopped after a 21-day chase.

The chase ended after vessels from South Africa and Britain helped surround the Viarsa 1 some 2000 nautical miles south-west off Cape Town, South Africa. France also offered help. Lashed by gale force winds and 10-metre seas, an Australian customs boat had chased the Viarsa 1, with its suspected catch of the rare fish also known as Chilean sea bass, for 3,900 nautical miles.

Armed South African and Australian fisheries officers were able to board and arrest the Uruguayan captain and crew of 40 Uruguayan, Spanish and Chilean nationals, who are reported to have put up no resistance. If found guilty they could face a fine of up to A$550,000 for illegal fishing and 12 months in jail for failing to obey instructions from an authorised fisheries officer.

John Davis, compliance manager at the Australian Fisheries Management Authority, said no weapons were found on the Viarsa 1 but armed guards would remain on the trawler to ensure it stayed on course back to Australia which is expected to take around a month.

"This has been a difficult situation but they have managed to achieve something quite significant without any injury," Davis told a news conference.

Keith Johnson, superintendent for Australia's customs national marine unit, said fish had been found on board the Viarsa 1 but the type and amount had yet to be established. The captain's log showed there was 85 tonnes of fish on board: "But we are confident that there will be Patagonian Toothfish in the catch," he told the news conference.

The toothfish, which can grow to 2.2 m long and weigh 100 kg, have been dubbed "white gold" by fishermen. The demand for its white, flaky flesh has soared in recent years in Asia and the United States, with one shipload worth up to A$5 million.

But marine conservationists have warned the fish could become commercially extinct by 2007 because illegal fishing above quotas is depleting dwindling stocks.

So far no one from the six vessels seized by Australia since 1997 for toothfish poaching has been jailed - although the Russian captain of the Volga, caught in 2002, died while being detained after drinking an industrial alcohol.

Australia heralded the latest operation a major success: "This chase is a warning to the pirates and poachers...that Australia will pursue them to the end of the earth to stamp out this illegal activity," Fisheries Minister Ian Macdonald said.

While an Australian ministerial press release emphaised the boarding followed "cooperation and dialogue" between Australian and Uruguayan officials, Agençe France-Presse reports Uruguay has demanded jurisdiction over the trawler, claiming their authority has been affronted and they have been the subject of discriminatory treatment by the Australian authorities.

The chase is likely to bring heated debate at the Meeting of the Commission for the Conservation of Antarctic Marine Living Resources in Hobart later this year.