Collaborative project provides boost for biodiversity in Kahuterawa

A joint effort by Horizons Regional Council and Palmerston North City Council to improve native fish passage in the Kahuterawa Stream has paid dividends for biodiversity.

The work was part of Horizons' Enhancing Native Fish Populations through Fish Passage Remediation project, which aims to remove barriers that prevent native migratory fish from getting upstream to suitable habitats to complete their lifecycle.
 
Horizons research associate Tui Wright says monitoring in Gordon Kear Forest in 2018 revealed several culverts acting as barriers through parts of the Kahuterawa catchment.
 
“While our native fish team identified a variety of migratory species, such as short-jaw kōkopu, banded kōkopu and kōaro (three of our five īnanga/whitebait species), downstream of the culverts, none of these species could be found above them,” she says.
 
“However, when the team recently carried out follow-up monitoring, we were really excited by the results. We found short-jaw kōkopu, banded kōkopu and kōaro above the culverts for the first time since monitoring began.”
 
Ms Wright says the improvement in native fish numbers is due to active efforts to improve fish passage.
 
“Native migratory fish are burst swimmers that work their way upstream by swimming short distances and then resting behind rocks and other natural structures before moving on. However, when they encounter a smooth-surfaced culvert in an area with high water velocity and no rest spots, or if the culvert is slightly higher than the stream level, they're unable to progress any further.
 
“These barriers to migration are one of the primary factors limiting the distribution of native fish in our region. For the Gordon Kear Forest area the solution involved installing a mixture of flexi-baffles and spat ropes (manufactured equipment designed to alter water flow and provide rest spots) in the existing culverts, or  completely replacing them.
 
"Finding native fish above the culverts now is a fantastic result. It shows the work we've undertaken has had an immediate impact on biodiversity in the Kahuterawa.
 
“Its success is a testament to our collective efforts and is likely to have significant ecological, economic and cultural benefits in the long term."
 
City Council Parks Operations Manager Dave Evans says most of the replaced culverts were older and undersized for the catchment, so an additional benefit is that the work has also improved the integrity of several access roads through the area, increasing their resilience to heavy rainfall and wear and tear.
 
“This increased resilience will help ensure access is maintained for the likes of emergency vehicles, pruning contractors and logging trucks,” says Mr Evans.
 
The project was initially funded by central government's Freshwater Improvement Fund and subsequently by the Jobs for Nature programme, with additional financial support provided by Horizons Regional Council and Palmerston North City Council. Local contractors Blenkiron Brothers Ltd carried out the culvert replacement work.
 
"This is a great example of organisations and local businesses collaborating through different funding streams to enhance biodiversity in our region," says Ms Wright