Swimming against extinction

The Canterbury mudfish (Neochanna burrowsius), also known as the Kōwaro, is found only on the Canterbury Plains and foothills and is the country’s most threatened freshwater fish.

The small, cigar-shaped fish, which is around 150mm fully grown, can look more like an eel than a fish and lives in wetlands, swampy streams, small waterways and drains that become seasonally dry.  However, they have the unique ability to survive for three months without water by burying into the stream bed.

The main threats to Canterbury mudfish are predatory fish - primarily the short fin eel and trout, environmental disturbances such as severe droughts, changing stream temperatures and destruction of in-stream vegetation from stock grazing and drain maintenance.

Sedimentation from harvesting and engineering works is also a potential damaging factor and Rayonier Matariki Forests is working with Selwyn District Council to implement a management plan to protect the mudfish and provide an opportunity for the species to thrive.

Theo Fowler, Rayonier Matariki Forests Canterbury Environmental Coordinator, says the Bush Gully Wetland is undergoing restoration and enhancement to help not just the mudfish but the other 37 indigenous and 45 introduced plant species living in the 10.5 hectare wetland area.

“Our harvesting operations have been carefully managed to ensure the Bush Gully Stream and Wetland is not affected.  Nearly all the trees neighbouring the wetland have now been harvested, which makes for an ideal time to retire some of the surrounding area and establish natives.  We planted around 8000 native trees over the course of one week late last year,” says Theo.

“We have removed a number of invasive hardwoods such as elderberry, rowan, cherry, and willow, and we continue to maintain a weeding and wilding pine programme as well as ongoing pest control.”

The Department of Conservation carries out biennial monitoring of the mudfish which involves trapping them overnight (adult mudfish are nocturnal) and counting, measuring and weighing them to check population growth and overall condition.

Department of Conservation Biodiversity Ranger, Allanah Purdie, says the mudfish population is constantly disappearing and reappearing however the ongoing monitoring is indicating that its range of habitat across Canterbury is declining overall.

“During monitoring in the Bush Gully Stream in 2019 we found two mudfish, in 2021 the population totalled 19 and last year it was zero.  So there is great variability and it is difficult to ascertain exact numbers,” says Allanah.

“The name ‘mudfish’ doesn’t really represent how special these little critters are.  They should be called ‘glitter fish’ as they have shiny scale-like reflective panels underneath their skin which, when they catch the light, they shine a beautiful iridescent green,” continues Allanah.

“Mudfish are an important part of the wider food network, being a food source for larger fish and birds - and they eat mosquito larvae.  The mudfish has a lot of nuanced ecosystems service roles that we don’t even know about and they are an indicator of general ecosystem health. 

“The local community should be proud of the healthy mudfish population they work hard to retain in the wider area.  The efforts that Rayonier Matariki Forests is making in the Bush Gully Wetland will greatly compliment this,” concludes Allanah.