Humpback whales appear to be getting a jump on their autumn travels.

The whales don't usually appear off the Victorian coast until April or May, when they migrate from chilly Antarctic waters to breed in the balmy seas off Queensland.

But two early sightings - one of a young calf off the Gippsland coast last month and another of three whales near Marengo this week - have scientists scratching their heads.

"We don't know why these whales are appearing early," said Mandy Watson, a Department of Sustainability and Environment senior biodiversity officer.

"It could be a response to climatic conditions or a result of population recovery, or both."

Victorians are being urged to keep an eye out for any marine mammals on the move in the first few weeks of autumn.

It's hoped this information will help scientists solve the mystery of why the whales have made such a quick start to the season.