Billy Turner waited until after he'd been for a 20-minute swim with a 2.7m shark to tell his mother what he'd done.
The 18-year-old from Tairua was at Pauanui Beach in the Coromandel with friends on Monday evening when he decided to get in the water and film the bronze whaler swimming close to shore.
It was the latest of a series of bronze whalers spotted on the north east coast of the North Island.
Turner's "shark enthusiast" friends have been catching and tagging bronze whalers in the area to record their movements.
"When they were done, I thought this is my chance," Turner told the Herald.
"I knew I could put myself in danger but it was a timid shark. It had been swimming quietly, not snapping."
Turner, who grew up around the water, filmed the shark as he swam behind it.
"The water was clear so I grabbed my mate's Go Pro and held it as I swam behind it.
"The water went from being knee-deep to about three or four metres.
"I made sure I stayed out of [the shark's] way."
Turner believed the bronze whaler was aware he was swimming close to it.
"It was swimming really fast. I had to swim fast to keep up.
"I was probably swimming with it for about 20 minutes."
Turner said his mother commented on the video on his Facebook page that she worried about him when she didn't hear from him.
But she thought it was "pretty cool"; as did his father, who is a spear fisherman.