Sophisticated DNA technology has detected a previously unknown population of critically threatened Clutha flathead galaxias fish in the Cardrona River.

Department of Conversation (DOC) river ranger Chris Kavazos said Central Otago is home to numerous galaxiid species that are found nowhere else in the world.

“Unfortunately, Clutha flatheads are one of the most endangered galaxias because of trout predation and habitat loss,” he said. 

“Given the threats these fish face, it’s amazing to discover a new population.

“[We] ...now have the chance to save a population that could have become extinct without us knowing it was ever there.”

The newly discovered population was found in the Cardrona River north of the Cardrona township.

DNA technology is the “gamechanger” which helped DOC discover the new galaxias, which are difficult to spot as they camouflage with gravels and cobbles in waterways.

An EDNA sample taken in the lower Tyre Gully (between Cardrona township and the Crown Range summit) detected the presence of Clutha flatheads up to five kilometres upstream.

Chris, who has done follow-up surveys of the area, said he thinks the Clutha flathead population is in the hundreds.

“The Tyre Gully population has healthy numbers compared to neighbouring waterways which probably 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.

“However, future flood events could make the waterfall useless as a trout barrier, meaning we could lose the entire Tyre Gully flathead population overnight.”

The removal of trout downstream is already underway and will offer better protection for the population in the long term, he said, and better barriers are helping too. 

WAI Wānaka, a driving force behind freshwater restoration efforts in the Cardrona Valley, has collaborated with Otago Polytechnic on a movable, adjustable fish passage barrier currently in use at Tyre Gully.

They’ve also received recent WWF Conservation Fund funding to support Tyre Gully efforts.

“All this work will increase the habitat available to flatheads, allowing re-occupation of habitats lost through trout predation,” Chris said.

Paulette Tamati-Elliffe of te Rūnanga o Ōtākou says the mauri of the Cardrona Valley’s waterways has been diminished with loss of taoka species, but the discovery of Clutha flatheads gives hope that mauri can be restored.

“By removing introduced species, Clutha flatheads are given a fighting chance to survive and even thrive.”

Cardrona Valley freshwater restoration efforts will continue to be a collaborative effort between WAI Wānaka, DOC, Otago Regional Council and Otago Fish & Game, with scope for wider community involvement.