Blue whales have arrived early and a rare sighting of an Antarctic minke whale was spotted in Geographe Bay.
Minke whales are usually sighted further offshore and Antarctic minke whales are not usually seen along the Western Australian coastline.
Natuaraliste Charters marine biologist Brodee Elsdon said over the last couple of years around five minke whales had been spotted in the bay.
Last week was the first time the crew spotted an Antarctic minke whale in Geographe Bay.
"It circled the boat, was spy hopping and blowing bubbles, it was really curious and hung around for longer than they usually do," Ms Elsdon said.
"When we see them it is usually a quick little glance."
Ms Elsdon said Antarctic minke whales were not a common species to encounter and not much was known about their distribution.
"We know there are more than 200,000 of them, their population has recovered, they were the whales that were heavily hunted during whaling days.
"More than 170,000 were hunted."
Ms Elsdon said there had been plentiful numbers of whales passing through Geographe Bay this year on their annual migration to Antarctica.
"Last week we had really good encounters on the boat with whales breaching and coming up closer than ever," she said.
"We started seeing mums and calves which have come down from Broome, they leave when they are just three months old and cruise in the clear waters at Castle Rock.
"By the time they reach Dunsborough they are around five months old and half the size of their mum (which is six to seven metres).
"We have also seen the most blue whales in a September month ever, in October you are almost guaranteed to see a blue whale each day.
"Last year 250 blue whales went through the bay."
Ms Elsdon said seeing blue whales earlier was an indicator that their population was increasing, however there were signs they were also leaving Antarctica earlier to travel north.
"It is not confirmed yet but it could be a sign there is a lack of food," she said.
"We have been hunting the krill and looking for krill oil. Over the last 20 years there has been a global reduction of 40 per cent, which is massive and not what we want.
"The mums do not feed on their migration, they are feeding their calves so they lose a lot of weight."