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."