The shark which frightened a triathlete during training at Mount Maunganui was most likely curious rather than aggressive, experts say.

Department of Conservation shark biologist Clinton Duffy said it was common to see a bronze whaler in the Tauranga Harbour at this time of year, and people should not be alarmed.

"It's a seasonal thing. During the winter they are found further offshore during summer and females coming in first to pup closer to shore, sometimes in the harbour, definitely in the shallows around the coast. Then they hang around for most of the summer."

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Bronze whalers typical eat stingray, eagle ray, kahawai and snapper.

The only fatal incident with one in New Zealand involved a spear fisherman in 1976.

"I've spent a bit of time with them at Poor Knights' (Island), and they are certainly not aggressive."

On Saturday, Sarah O'Grady was training for Sunday's Classic Builders Tinman Triathlon when she discovered a shark had been chasing her and circled her before she fled the water. She believed the shark was a bronze whaler.

"They are definitely curious - most sharks are curious about things that are going on," Duffy said. "Unusual sounds and things like that will attract them."

Duffy said a person could dive or swim along with bronze whalers to observe them quietly with no issues. He dived with a school of about 13, including some larger than 3m long "and they never showed any interest in me whatsoever".

However, if someone found themselves in water with a shark and could not identify it, they should get out "quickly and quietly, with minimal fuss".

Swimmer Steve Morris said he knew there were plenty of bronze whalers in the harbour at this time of year but it would not put him off.

Morris is a member of the Seamen Ocean Swim Squad which regularly meet up to swim in and around Tauranga Harbour.

"We've actually ended up swimming with a pod of orca and swum with seals as well.

"Personally, I've never seen a live one. There are lots around, but they're scared of humans."