Detectors that pick up on fish pheromones are being used to monitor piharau (lamprey) in a tributary of the Whanganui River.
Horizons Regional Council is using the detectors to survey piharau, a threatened native fish species that spends part of its life cycle in burrows in silty river edges and is suffering from the effects of habitat loss and in-stream barriers.
Horizons water-quality scientist Logan Brown says that this is the first time the pheromone detectors have been used in the region.
To assess populations, detectors are placed in water and left for a number of weeks during low flows. These detectors provide an estimate of population size by extracting the pheromones that juvenile piharau release into the water.
Techniques like spotlighting and electrofishing are effective for some fish species, but proved to be ineffective for juvenile piharau."
"The detectors themselves are really quite amazing as they're not overly complicated in design, but extremely helpful with the results they're able to produce," Mr Brown said.
As well as the Whanganui detector, Horizons placed them in two unnamed streams of the Manawatu River, the Turitea Stream, and the Makaretu Stream. He said the Turitea Stream results "were particularly promising, with approximately 200 juvenile piharau estimated."
"The results allow us to direct efforts to address concerns surrounding piharau, and the more data we can collect, the better we can assess where these efforts are made."
" A major focus will be on the Whanganui Catchment, where the adult piharau are a culturally-significant food source," says Mr Brown.
Horizons has recently been successful in obtaining funding from Envirolink to develop a monitoring protocol for piharau populations this summer, which will look at extending this method across the region.