Greenpeace activists protested Tuesday as the last of six Japanese whaling ships returned to port from a five-month Antarctic mission marked by tense standoffs at sea with militant activists.Waiting on shore at Shimonoseki harbour, Greenpeace anti-whaling campaigners shouted and held up a placard that read: "Southern Ocean Whaling: Cover-ups, Lies, 1.2 billion yen (12 million dollars) in taxes."Japan kills whales using a loophole in a 1986 international moratorium on commercial whaling that allows "lethal research" on the mammals, and makes no secret of the fact that the animals' meat is then served as food.During their most recent mission, the whaling fleet's six ships were harassed by the environmentalist group the Sea Shepherd Conservation Society, resulting in a catch far smaller than the expected haul.The Japanese Fisheries Agency said the Sea Shepherds made it impossible for the whaling vessels to operate on 16 days of the 100-day whale hunt.Canadian Paul Watson, captain of the group's ship, the Steve Irwin, has vowed to "be their ongoing nightmare every year until they stop their horrific and unlawful slaughter of the great whales in the Southern Ocean Whale Sanctuary".The five other ships earlier arrived back in Japan -- including the Yushin Maru No. 3, which was damaged in a collision with the Steve Irwin -- and the Nisshin Maru factory ship sailed into Shimonoseki port on Tuesday.The Japanese Coast Guard immediately sent officers to inspect the vessel for signs of attacks by the Sea Shepherds, an official said.Shigetoshi Nishiwaki, the fleet's 'research leader', said the animal rights activists had thrown bottles of foul-smelling liquid and paint and tried to entangle ships' screws with rope, the Kyodo news agency reported.Sea Shepherd has accused Japan of deploying acoustic weapons, which send out high-frequency sound waves to disorient the activists.On their mission since November, the six ships caught 680 whales -- including 679 minke and just one fin whale -- well below a planned haul of between 765 and 935 of the giant mammals, the Fisheries Agency said.Greenpeace -- whose ships have faced off with whalers on nine past Antarctic missions -- said it stayed away this year to focus on another case, defending two of its activists set to go on trial on charges of stealing whale meat as part of a bid to expose alleged corruption involving whalers.The environmental group said it sought and failed to be allowed to document the offloading of the ship's cargo of whale meat this year.Greenpeace said that last year, boxes of the whale meat, some falsely labelled 'cardboard', were couriered to the homes of the ship?s crew and later declared "souvenirs" by authorities.The Greenpeace activists Junichi Sato and Toru Suzuki, who the group said first exposed the "embezzlement of whale meat", are on trial and facing up to ten years in prison, the statement said."If the 'souvenir' practice has been legitimised, the public should at least be told how much of the 1.2 billion yen it has spent subsidising the so-called scientific whaling expedition has been spent on buying gifts for the crew," said Junichi Sato, of Greenpeace Japan, in a statement."With warehouse full to over-flowing with whale meat from previous years' hunts, which can?t even be given away, this year's catch of 680 whales is still 680 too many," said Sato."The writing is on the wall for this economically and ecologically bankrupt practice. This must be the last of these so-called 'scientific' whaling expeditions."