Rock art on the Wessel Islands, off the north-eastern tip of the Northern Territory, shows a whale's tail in the top left corner and a sailing boat in the middle. The art has been digitally enhanced using the DStretch method.(Supplied: Pastmasters)\

As the last of an inquisitive trio of humpback whales finally made its way down Kakadu's East Alligator River and out to sea this week, the whales' journey so far upstream 17 days earlier was being cited as a first in recorded history.

Key points:

• As whale populations increase, so do sightings along the NT coast
• Aboriginal rock art and oral history suggests foreign whale hunters have been visiting the area for hundreds, if not thousands, of years
• The whale is an important totem for Territory Aboriginal people

But a recently published short paper by PastMasters says an important rock art discovery suggests whales — albeit of the pelagic and not river-going variety — have been part of the Northern Territory's story for thousands of years.

WARNING: Aboriginal and Torres Strait Islander readers are advised that the following article contains images of people who have died.

Rock art discovered on the Wessel Islands several years ago — but only being brought to public attention now by researchers — depicts ancient hunters harpooning a large whale.

Paper author and anthropologist Dr Ian McIntosh says the discovery is of significant historical importance.

"This really is an astonishing find," Dr McIntosh said.