After a day of swimming and snorkelling, Kyle Cooper got his drone out and made a prediction.
"I'm going to go find some sharks," he said, not knowing a school of smooth hammerheads cruised about 350m offshore in Northland's Taupō Bay.
Cooper, from Te Atatū South, said he'd seen sharks before when surfing, but never a school like the hammerheads in late January.
He told the Herald huge numbers of jellyfish were in the water that day near the campground he was at.
Cooper said people were in the water nearby and the sharks at one point probably cruised about 150m offshore at the bay's north end.
He used the drone for fishing and recreation and previously used it for professional photography.
Department of Conservation marine scientist Clinton Duffy said the sharks in Cooper's drone footage were juvenile smooth hammerheads.
He wouldn't expect the hammerheads to bother anybody swimming nearby.
"Juveniles present no risk to humans and there have been no reported attacks by adults in New Zealand waters."
"Globally reported attacks by this species are very rare, and in most cases, the species of hammerhead actually involved in the attack cannot be confirmed."
Duffy said juvenile smooth hammerheads, including newborn pups, were common around the upper half of the North Island.
"Comparing them to the jellyfish and floating seaweed visible in the video, most appear to be between 1m to 1.2m long."
This hammerhead species, with the scientific name Sphyrna zygaena, reached a maximum size of almost 4m.
Male smooth hammerheads usually matured at 2.5m and females when 3m long.
Duffy said adults mostly ate small fish, octopus and squid.
Large, loose schools of juveniles were often spotted around the upper North Island but their occurrence in any place could vary widely from year to year, Duffy said.
Eight hammerhead species were recognised worldwide but only four, including the smooth hammerhead, surpassed 1.5m in length.
Last month, a couple yachting saw a large school of sharks, believed to contain hammerheads, off Army Bay in Auckland.
According to Oceana, smooth hammerheads give birth to live young and sometimes eat sea snakes and other sharks.
Smooth hammerheads have special sensory cells in their heads to detect electric fields other fish produced.
A study from Simon Fraser University in British Columbia, Canada last month found oceanic shark and ray numbers had plummeted by 71 per cent from 1970 and 2018.
The smooth hammerhead was the only species with growing numbers but many other shark species faced a dire situation.
The International Union for Conservation of Nature said of 482 species assessed, less than one-third had a conservation status deemed of least concern.
And 79 species were endangered, with 10 critically endangered.
The man was not ordered to forfeit his passport.