People are being warned to stay away from a leopard seal basking among the rocks at the entrance of Moturiki/Leisure Island.

The seal, dubbed Cecil by members of the public, was spotted on the beach at 7am by local Mark Clayson.

The leopard seal, which has been nicknamed Cecil by members of the public, on Mount Main Beach. Photos: Chris Callinan.

Mark is concerned because it's a popular area for people to walk dogs and the seal is hidden among the rocks.

Unlike normal seals which can be bothered by dogs, leopard seals are more aggressive.

Mark relates a story from the Chatham Island where a dog was antagonising a leopard seal, and the owner ignored a warning to keep his dog away.

'The dog got really close and the leopard seal just grabbed it by the back of the neck and flung it in the air. It kept hold of the skin and just ripped a big chunk of skin out of it.

'They are lethal things,” Mark says referring to leopard seals.

He thinks the leopard seal is grazing on the local blue penguin population. There are between 12-1400 little blue penguins roosting around the Mount, Moturiki and Rabbit Islands, and penguins are one of the leopard seals' favourite foods.

DOC community ranger Kate Miller says dogs should be kept on a lead and people should not approach closer than 20 metres.

It's believed the seal is feeding on The Mount's little blue penguin population.

'We have 800 little blue penguins living on Mauao, about 200 on Moturiki and there's a seal colony on Plate Island near Motiti, plus I understand there are often seals around the back of Motuotau (Rabbit) Island plus another population of about 400 penguins,” says Rosalie Crawford.

Rosalie says the local Little Blue penguin population was unknown until the Rena Oil Spill crisis.

There were 350 oiled penguins – mostly from Mauao, Moturiki and Motuotau - caught, cleaned and released back into their original environment after the rocks were cleared of oil.

"It was during this time that we 'discovered” the local population was much bigger than we had imagined. An estimated 800 nest on Mauao, 200 on Moturiki and 400 on Motuotau.

"We have discovered that the Little Blue penguins can nest twice during the spring/summer breeding season – probably due to the warmer climate and abundance of food."