An adult lamprey using its circular mouth to suck onto a person's arm. The dent in the top of the head is a single nostril - the lamprey has an extremely sensitive sense of smell. Photo: RNZ / Alison Ballance
Pheromone detectors are being used to track down a nationally vulnerable fish in Otago with hopes it will help to protect them in the future.
Kanakana or lamprey are a jawless, migratory fish that look like an eel and have existed for more than 360 million years.
They have a large 'sucker' full of teeth they use to climb steep waterfalls during their upstream journey to spawn and to latch onto larger fish and whales during a parasitic phase as adults.
The Department of Conservation and the Jobs for Nature Te Nukuroa o Matamata project team have deployed detectors in the mid and lower Taieri catchment to find them.
Kanakana are born upriver, spending three to four years in the waterways before travelling to the ocean as adults and clinging to hosts for several years.
They only breed at the end of their life and die a few months after spawning.
Adult kanakana use pheromones released by larvae from previous generations to find waterways with the specific nesting habitats - subterranean caves - they need and swim back upstream to spawn.
River restoration ranger Christopher Kavazos said using pheromone detectors would help them understand which tributaries were the most important breeding areas and should be protected and monitored.
"They're a little bit different to migratory fish which tend to come up a river and it's only certain periods of the year where we can really have detrimental effects on their life cycle.
"Where as with kanakana, they're in the larval phase for four years in the waterways so our effects on the river can really impact their life cycle."
It was important to maintain juvenile kanakana in waterways as adults might stop migrating to areas if their pheromone cue was lost, he said.
The project includes collaboration from iwi and other stakeholders
DOC has used eDNA sampling that captures the DNA fragments left behind by plants and animals that have been in the area recently, and has put out pheromone samplers in areas with positive results.
Weirs cause a major impediment to the migrating fish. Photo:
Those sensors stayed in the water for about three weeks and samples have been sent to NIWA for analysis.
The results were expected in the coming months.
The secretive fish can be hard to spot and face a variety of threats, including migration barriers, loss of habitat, poor water quality and some activities in streams like clearing drains.
"If there's a culvert put in the waterway or a weir or something that an adult kanakana can't overcome then they lose access to those habitats," Kavazos said.
"The adults are relying on that pheromone cue from the larvae coming down the waterway and you can imagine if you lose those larvae for whatever reason, such as drain clearing or a flood ... then you lose that pheromone cue.
"And when you lose that pheromone cue, the adult kanakana will no longer go up that waterway."
The next phase, which was expected to be rolled out by this time next year, was to develop a programme to annually monitor the fish.
While not on the cards any time soon, Christopher Kavazos said some countries with lamprey have released juveniles into tributaries with the right nesting habitat to encourage the adults to use it for spawning.
The project is funded by DOC's Ngā Awa river restoration programme.