An expedition is being launched tomorrow to study the migration patterns of blue whales.

The team of six researchers from NIWA, the Department of Conservation and Blue Planet Marine will sail around Cook Strait and South Taranaki coast to find and tag the mammals.

The scientists will be at sea for two weeks.

NIWA marine ecologist Doctor Kim Goetz said the expedition is a first step in working out if there's a permanent population of blue whales in New Zealand waters, or if they only migrate through.

"So they're one of the populations of animals that were drastically reduced. So the numbers are now coming up but we have no idea how many there are."

Goetz said blue whales are heard all year around Taranaki, but it's not clear if that's a permanent population.

"I suspect they're migrating north and south and that the Taranaki area has upwelling's so it's a kind of a feeding hot spot for them."