Leopard seals were typically found in the Antarctic and sub-Antarctic Islands but were regularly seen in New Zealand too.
Three have been known to hang around Whangarei at various times in recent years.
One of them, a large female known as Owha, commuted between Auckland's Viaduct Harbour and Whangarei for some time and another female, Novy, was sighted in Northland occasionally, although not recently.
Hatea was estimated to be between 3 and 5 years old, and weigh 80kg to 100kg.
At that size, and with the speed seals were capable of, dock users and the public were warned not to get too close.
Some people with vessels berthed in the marina had to come ashore by different docks because of Hatea's presence.
The Department of Conservation (DoC) put up signs warning people of the seal and letting them know what to do if he was spotted.
People were asked not to go near seals when they came ashore.
As well as being treated by the public like a visiting film star or an unpredictable wild animal, the seal attracted scientific interest.
Research assistant Giverny Forbes was able to collect some of Hatea's droppings to find what his diet was and some other health information.
Feathers in the "scat" indicated the seal had been feeding on birdlife around the harbour, backing up local reports he was occasionally seen eating ducks.