A previously unknown population of a critically threatened fish has been found in Central Otago thanks to DNA technology.
Department of Conservation river ranger Chris Kavazos said Central Otago was home to numerous galaxiid species which were found nowhere else in the world.
Clutha flatheads were one of the most endangered galaxias because of trout predation and habitat loss, sharing the same threat status as kākāpō, Kavazos said.
They were often difficult to spot because they camouflaged with gravels and cobbles in waterways, but DNA technology was a game changer for helping to detect the elusive species, he said.
An environmental DNA sample of the upper Cardrona Valley detected the presence of Clutha flatheads up to 5 kilometres upstream, and a follow-up survey of Tyre Gully indicated a population in the hundreds, he said.
The population's numbers were healthy compared to neighbouring waterways which were believed to have only a handful of adults, he said.
"It turned out a small waterfall in Tyre Gully was the only thing stopping trout downstream from migrating up and predating the flatheads," Kavazos said.
"However, future flood events could make the waterfall useless as a trout barrier, meaning we could lose the entire Tyre Gully flathead population overnight.
"Given the threats these fish face, it's amazing to discover a new population. Now it's on us to ensure it survives."
Trout downstream are being removed to offer better protection for the population in the long term. Better barriers were helping too, Kavazos said.
WAI Wānaka have collaborated with Otago Polytechnic on a movable, adjustable fish passage barrier currently in use at Tyre Gully.