Wriggle room: Monitoring native fish passage for New Plymouth District Council

At a glance...

The client

New Plymouth District Council wanted to understand how the infrastructure in the city’s watercourses impacted fish passage.

The challenge

New Plymouth District Council had a range of fish passage solutions but wanted to know whether these had worked, so they needed native fish surveys.

The outcome

We have undertaken annual monitoring since 2017 to determine the success of fish passage solutions.


Taranaki is home to some of New Zealand’s most interesting and unique native fish species. But some of its infrastructure can block fish passage. New Plymouth District Council was aware of this and had put measures in place to better enable the passage of native fish in streams within the city.

The ask

New Plymouth District Council (NPDC) recognised that some of the city’s older instream structures might be posing a problem for its local native fish populations.

“They have a lot of culverts in the city that were probably installed a long time ago, before the protection of fish passage and streams was a priority. A lot of native New Zealand fish species are diadromous, which means that they move between sea and freshwater habitats. Perched culverts prevent the fish from getting into their adult habitat.”

Nick Carter | Senior Freshwater Scientist, Ecological Solutions

“Culverts can limit species diversity and habitat use. So NPDC wanted to see whether the measures they put in place to remedy this had worked. NPDC had employed a technique of retrofitting perched culverts with mussel spat rope. As the water dribbles down the rope, fish such as eels, bullies, kokopu and koaro can wriggle up it – and carry on upstream.”

Mussel spat rope can help some native fish to negotiate barriers. This rope was installed in the culverts to improve fish passage. But was it actually successful? Were the fish species of concern making their way up the ropes and successfully migrating?

That’s what we were tasked to find out.

Why us?

We were engaged for this project as a result of our relationship with NPDC staff built on doing quality work and getting results.

With plenty of experience in freshwater ecology and fish surveys, and working with unique native species in this region, we had the perfect blend of skills for the job.

Our solution

We undertook fish surveys to confirm the species that were migrating successfully. To do this, we used electric fishing methods to identify and measure the species captured, and then released unharmed.

In doing so, we were able to estimate the population size of the various species and determine whether the remediation works have been successful in allowing fish to move through the catchment.

With this information, NPDC was able to validate their approach and protect the fish communities in the streams around the city. And by extension, the residents of Taranki that rely on a healthy natural environment.


The results

“We’re finding most of the fish you’d expect to see upstream so they must be getting over the barriers, which is great! We’re even seeing some really nice adult short jaw kōkopu which is quite unusual, so it’s great that those fish are getting up there.”

Through our monitoring and identification efforts, we have been able to report back to NPDC that their measures were a success, how they are working, and which fish species were most impacted.

Native migratory fish are able to pass through the city’s infrastructure, protecting the health of the ecosystem as a result. This is an ongoing monitoring job which began in 2017 and will continue for a few more years to ensure long-term success.

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