Japan's Fisheries agency has spoken up about Australia-based Sea Shepherd's accusations that it "attacked" one of its ships on Feb 23. According to a report from a Japanese news agency, the Sea Shepherd has "seriously hampered" its whaling research programme in the Antarctic Ocean when ropes thrown by the anti-whaling group in front of the Yushin Maru No 3 and the Yushin Maru had become entangled in the ships' propellers.

The Japanese Fisheries Agency said one of its ships was damaged from the heavy metal weights attached to the ropes.

Anti-whaling organisation Sea Shepherd has claimed that the Japanese whaling ship "attacked" its ship in the dark in what it described as a "ruthless assault."

According to reports, the Japanese whaling fleet had allegedly disabled the Sea Shepherd ship in the Southern Ocean. The anti-whaling organisation based in Australia said two Japanese whaling ships had ambushed its ship, Bob Barker, on Feb 23. The Japanese whaling ships had reportedly tried to jam the Bob Barker's propellers and rubbers.

Peter Hammarstedt, captain of the Bob Barker, described what happened during the night of the attack. He said he had been following the Japanese whaling ship Nisshin Maru since the morning of Feb 23. The captain believes the Japanese crew had waited until nightfall to "launch their onslaught."

Sea Shepherd releases open letter to Greg Hunt

ABC has published an open letter from Captain Peter Hammarstedt of the Bob Barker, one of the Sea Shepherds ships in the Antartica's Souther Ocean Whale Santuary.

Here is an excerpt of the letter:

"Every year leading up to the Antarctic whaling season, the Governments of Australia, New Zealand, The Netherlands and the United States of America ask both parties in the struggle over the sanctity of the Southern Ocean Whale Sanctuary to show restraint. It's an easy way to skirt taking any actual responsibility for the clashes that occur in the Antarctic - why enforce the law against poachers when it's so much more convenient to just ask them to play nice?"

The Sea Shepherd captain urges Australian Environment Minister Greg Hunt to fulfill his promise during the elections and send an observer ship to the Southern Ocean.

Mr Hammarstedt also said in the letter that he is "losing hope" in the Australian government to protect Sea Shepherd ships. "When the whalers throw heavy metal objects at my crew, I instruct them to not throw anything back - not even in self-defense," said the Bob Barker captain.

He said he has realised the "attack" on his ship happened beyond the Australian Antarctic Territory, but he appealed for the safety of his crew who were also Australian citizens. The Australian government is still responsible for their safety.