"It's unusual to see them like that," said Niwa principal scientist Malcolm Francis.
"The odd thing is that they're right near the surface where people are seeing them."
The small sharks are "totally harmless" and are common throughout New Zealand he said.
"We'll often find them in our fish and chips as lemonfish."
They grow to about a metre and a half, and come into the harbour each spring or summer to give birth to their young, which will be about 30cm long.
"They have little paving-stone-like teeth which they use to crush up shellfish and worms, so they're not interested in people."
Anyone worried about going into the water while the rig sharks were around need not be afraid.
"There are other, bigger sharks that they may want to look out for, but they mostly occur out on the open coast around seal colonies and so on."
Francis was unsure why the rig sharks were coming so close to the shore, and said it could be to do with the warmer temperatures Wellington has been experiencing.
Rays have been spotted floating around the waterfront for the past few weeks, and over the weekend beachgoers glimpsed a pod of dolphins swimming in the harbour.
Reports of marine life sightings could also be higher because the scorching temperatures were driving more people into the water.
