TOKYO (Reuters) - The main ship in Japan's whaling fleet set out for the Antarctic on Monday for its first hunt in the region since limping home with just over half its planned catch in April following clashes with militant anti-whaling activists, environmentalist group Greenpeace said.

The Nisshin Maru set out from Innoshima in western Japan, Greenpeace said, part of a plan to take about 850 minke whales and 50 fin whales. Last year six ships took part in the hunt.

The vessel's movements will be followed by a ship belonging to Sea Shepherd, an anti-whaling group that skirmished repeatedly with the fleet at sea last year in an attempt to halt the hunt.

Earlier on Monday, Australia urged Japan to abandon its yearly hunt, launching its own scientific whaling study in the Southern Ocean to prove it was not necessary to kill the ocean mammals to study them.

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"Modern-day research uses genetic and molecular techniques as well as satellite tags, acoustic methods and aerial surveys rather than grenade-tipped harpoons," Australian Environment Minister Peter Garrett told reporters in Canberra.

"Australia does not believe that we need to kill whales to understand them," Garrett said.

A Japanese Fisheries Agency official last week denied a newspaper report that Tokyo would cut by 20 percent the number of whales it planned to hunt due to anti-whaling protests.

But the official said that a moratorium on catching humpback whales would stay in place.

"Waved off only by the crew's families and whaling officials, the factory ship Nisshin Maru left Innoshima with no fanfare," Greenpeace said in a statement.

"Constant pressure on Japan's whaling industry by both Greenpeace and the international community has reduced the fleet to sneaking out of port in a fog of crisis and scandal, desperate to avoid attention," the statement quoted Sara Holden, Greenpeace International Whales Coordinator, as saying.

Japanese whaling officials declined to confirm the ship's departure, citing safety considerations, but a worker at a local hotel said about 10 people connected with the the Institute of Cetacean Research and whalers' families had stayed overnight.

DIPLOMATIC COMPLAINTS

Last season's row over whaling threatened to escalate when two of the group's members boarded a Japanese whaling ship without permission and were temporarily held by its crew.

The incident led to a string of diplomatic complaints between Japan and Australia, which has been a vocal critic of the whaling programme.

Canberra last year sent a customs and fisheries icebreaker to shadow anti-whaling activists and the Japanese fleet, gathering photo evidence of the yearly research hunt for a possible international legal case against Tokyo.

Australia's Garrett said on Monday a legal case was still under consideration, but no decision yet had been made on whether to send another patrol boat south this Antarctic summer.

Japan's Fisheries Agency blamed Sea Shepherd and a dearth of whale sightings for their catch of only 551 minke whales, compared with a target of 850 minkes and 50 fin whales last season. A plan to target humpback whales for the first time was dropped last year after protests from the United States.

Environmental group Greenpeace has said it will break with its tradition of sending a ship to follow the whalers this season, concentrating instead on a court case involving two of its activists in Japan, who are accused of stealing whalemeat.

The group says it took the meat to expose what it says are corrupt practices in the whaling industry.

Japan, which considers whaling a cultural tradition, abandoned commercial whaling after agreeing to an international whaling moratorium in 1986, but began what it calls a scientific research whaling programme the following year.

Critics say much of the meat ends up on dinner tables.

(Additional reporting by Rob Taylor in Canberra, Isabel Reynolds in Tokyo; Editing by Hugh Lawson)