A former US Marine helicopter pilot, who finds the whaling fleet so Sea Shepherd protesters can stop the hunt, says he has been denied a visa to join the activists in Australia.

Chris Aultman, who won official praise for his work on a polar search last summer, has been held up in Los Angeles as the countdown begins to this year's conflict.

Mr Aultman said by email that he had come to Australia for the past six years on an electronic travel authority visa, but this time was placed on hold, and then declined.

"I have not received any information about why it was denied or when it will be issued," he said. "I wish I knew."

The 38-year-old Gulf War veteran's work has been vital to Sea Shepherd finding the whaling fleet, and provided a critical platform for aerial footage used in the Whale Wars documentary series.

Mr Aultman won praise for conducting a 14-hour aerial search for missing Norwegian adventurers in the Ross Sea last summer, in conditions that forced the New Zealand Navy to withdraw.

A report by Maritime New Zealand into the tragedy commended Sea Shepherd for its work.

Sea Shepherd leader Paul Watson said he and first officer Peter Hammarstedt were denied visas two years ago before a petition, and intervention from Greens leader Bob Brown and former environment minister Ian Campbell.

"Now it appears that Australia is seeking to keep the Sea Shepherd helicopter grounded by denying a visa to our veteran pilot," Mr Watson said.

An Immigration Department spokeswoman said she was seeking further information, but cautioned that privacy laws prevented detailed discussion of individual cases.

Meanwhile, Mr Watson said it seemed likely that the factory ship Nisshin Maru would take on the remaining half of its fuel this week and leave Japan on Wednesday.

Sea Shepherd's three ships are being prepared to leave from Australia in about 10 days' time, with the Steve Irwin and Brigitte Bardot likely to embark from Albany, Western Australia, and the Bob Barker sailing from Hobart.

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