Community and Education news

The Tasman River
4 November 2019

2019 NZ River Story Finalist Tasman River, Canterbury

Cawthron is proud to be running the 2019 New Zealand River Awards. As part of the celebration, the River Story Award category sponsored by the Ministry for the Environment recognises interesting and compelling stories about individuals, businesses and communities working to improve the health of our rivers.

Each year Cawthron receives River Story entries that are representative of our collective desire to improve New Zealand waterways. The stories are inspirational projects that involve community collaboration, science and innovative ways to address freshwater-related challenges.

This year, eight stories were selected as finalists and from these, the judges have selected the top three stories. The work being done to restore Canterbury’s Tasman River is our first story.

The Tasman River starts below the famous Tasman Glacier and flows into Lake Pukaki. It’s a short, braided river seen from a distance by hundreds of thousands of visitors who travel to and from Aoraki Mt Cook each year.

For the past 15 years the Department of Conservation (DOC), power companies Meridian and Genesis, local landowners and other volunteers have been working to protect and restore the Tasman River’s natural ecosystem. The riverbed is being threatened by pest plants – mainly lupins and broom – and introduced predators are killing the native bird species that live there – kakī/black stilt, ngutu pare/wrybills, tūturiwhatu/banded dotterel and tarapirohe/black-fronted terns.    

The Tasman River is part of DOC’s River Recovery Project which has been going for more than 25 years and focuses on restoring the upper reaches of the South Island’s braided rivers.

The work on the Tasman River has two components: spraying out invasive plants such as Russell lupins and exotic broom that threaten significant areas of the riverbed; and trapping predators such as feral cats, stoats and hedgehogs that decimate the native bird populations living on the gravel islands in the river.

The spraying programme has cleared a substantial area of the riverbed of lupins and broom (approximately 6,000ha). This has resulted in the annual spraying costs falling from a peak of $70,000pa to now just over $30,000pa.

The predator control work is led by DOC, with cooperation from local landowners and residents from the Aoraki Mt Cook village to manage the trap lines. The community are certainly helping to provide a safer habitat for the native birds, particularly the iconic species, kakī/black stilt, that are permanent residents of the riverbed.

The predator control work is now in its 15th year. Statistics on the number and range of predators controlled over 2017/18 in the Tasman River highlight the importance of this programme – 1,152 land-based predators were dispatched last year. In 2013/14 DOC added the southern black-backed gull to the list of predators based on camera evidence that they were raiding the nests of black-fronted terns, and in the past four years they have eliminated around 1,500 gulls.

The ongoing offensive on predators is having a positive impact on native bird populations in the river. Tarapirohe/black-fronted tern numbers have increased from fewer than 100 ten years ago to more than 600 in 2017. Tūturiwhatu/banded dotterel numbers have remained stable over the past decade, while ngutu pare/wrybill numbers have risen slightly.

The work to restore the Tasman River to something akin to its natural state and the wider project to control pest plants and animals in our iconic braided rivers is a huge task requiring a big financial commitment and dedicated staff. Assistance from local landowners and community volunteers is also critical. Improved knowledge and technology is helping to reduce costs and increase the effectiveness of these programmes and therefore make them sustainable and successful over the long-term.