Back hoped the seal's visit was a short one as it could cause problems if he started to go ashore.
The Department of Conservation put up signs at the Town Basin warning people of the seal and letting them know what to do if he was spotted.
DoC spokeswoman Abi Monteith said the seal was being monitored.
Leopard seal research assistant Giverny Forbes said the seal had left B dock about 11.30am and was spotted nearby eating ducks. She said it was normal for seals to eat birds, including penguins.
Forbes said iwi would be contacted to see if they want to name the seal officially.
Scat samples showed feathers and indicated it had been feeding on the bird life around the harbour.
It would be the third leopard seal in Northland, excitingresearchers who are studying the animals closely.
Owha, the well-known female leopard seal was spotted at the Marsden Pt Marina yesterday. Another female, Novy, also visits, but there have been no recent sightings.
Leopard seals are typically found in the Antarctic and Subantarctic Islands and are regularly found around New Zealand.
Forbes said researchers were trying to find out how many leopard seals were in New Zealand and why they were here.
Hatea, estimated to be between 3 and 5 years old and weighing 80 to 100kg was first seen lounging on the pontoon outside The Quay on Monday.
He had a bite mark under his chin, which marine expert Dr Ingrid Visser said could be from a great white shark.
People are reminded if they see a leopard seal to stay 20m away.
