Anti-whaling activists have slammed the federal government for breaking a pre-election promise to send a ship to monitor Japanese whaling in the Southern Ocean.

Environment Minister Greg Hunt said on Sunday an A319 aircraft staffed by customs would instead be sent to observe whalers and environmental activists.

The Coalition's whale and dolphin protection plan, released two weeks before September's election, stated: ''Should the whaling season continue, the Coalition commits to sending a customs vessel to the Southern Ocean.''

Sea Shepherd Australian director Jeff Hansen, whose conservation society last week sent three vessels to intercept the Japanese whaling fleet, said that a plane was of no use.

''It's a broken promise. The promise was - to the whales and to the Australian public - to send a vessel. Sending a plane is really a waste of taxpayers' money.

Speaking on Frankston pier on Sunday, Mr Hunt said the purpose of using a plane was: ''Firstly, to ensure that there is observation and oversight and recording of any whaling which does occur; secondly, to ensure that there is a record and a chronicle if there is any conflict; and thirdly and most significantly, to ensure that the fact that we will be overhead and observing means that both whalers and protesters know they cannot breach the rules, they have to behave properly, they cannot put life and limb at risk and that there's an independent party to observe that,'' he said.