IT'S that time of the year again.
Whales have been spotted off the Northern Beaches coastline as they begin their migration to warmer waters.
The whales are headed to the Great Barrier Reef area to mate and give birth after spending the summer feeding in the Antarctic.
While there is a chance you might catch a glimpse of white whale Migaloo, Southern Cross University researcher Peta Beeman said you're most likely to spot humpbacks swimming off-shore.
"Humpbacks are most visible because there are a lot of them and they're very active on the water's surface," Ms Beeman said.
Up to 20,000 whales are expected to pass by this year in their 10,000km migration round-trip.
Whale flukes, or the two lobes of a whale's tail, are so distinctive researchers are able to use them to identify the animals individually.
Ms Beeman encourages whale-spotters to send in any photos of flukes to assist in tracking whales.
"Thanks to all those citizen scientists out there I've got a really good collection of flukes," she said.
"By cataloguing these we're able to see whether the whales have been seen in the same place each year or different places, or we can hopefully track a whale along its migration path.
"There's still a lot we don't know about whales; tracking them allows us to understand the impact on whales as they encounter shipping traffic or get caught in fishing gear or shark nets."
Whale sightings are expected to increase over the next fortnight, with migration in full-swing by mid-June.
They typically make their journey south again when the weather warms up in October and November.
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