Detectors provide insight for native fish

An innovative surveying method that detects piharau (lamprey) populations through their pheromones is proving promising in the Horizons Region.

Piharau (lamprey) is 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 Horizons Region.

“Our team is always on the lookout to improve monitoring techniques and find solutions if certain fish are difficult to monitor,” Mr Brown says.

Techniques like spotlighting and electrofishing are effective for some fish species, but proved to be ineffective for juvenile piharau.”

In order to better assess these populations, five piharau detectors were placed in streams around the Region 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 through membranes in the detectors.

“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 says.

The membranes were retrieved and sent to NIWA Hamilton, with results showing piharau populations in two of the five sites, with one detector malfunctioning.

“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.”

Horizons has recently been successful in obtaining funding from Envirolink to develop a monitoring protocol for piharau populations which will look at extending this method across the region. This work is to be undertaken this coming summer.

“We are excited to continue this work. A major focus will be on the Whanganui Catchment, where the adult piharau are a culturally significant food source,” says Mr Brown.

The detectors were placed in two unnamed streams of the Manawatu River, the Turitea Stream, an unnamed stream of the Whanganui River and the Makaretu Stream.

ENDS

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