Monitoring kōura

Kōura (freshwater crayfish, Paranephrops planifrons, P. zealandicus) are one of Aotearoa New Zealand’s original inhabitants. They have an ancient lineage that diverged from their Australian relatives about 60–109 million years ago. Because their entire life cycle requires freshwater, kōura are evidence that there has been continuous freshwater in Zealandia ever since our part of Gondwana broke up 60–80 million years ago. As far as our evolutionary history goes, kōura are as significant as tuatara, wētā and kiwi!

Kōura are a taonga species for Māori – they were once a staple food and a key trading commodity for iwi living in the Rotorua and Taupō regions. Ecologists regard kōura as an indicator species. Their presence signals a healthy ecosystem, while their absence is likely caused by poor water quality and/or disruptions caused by introduced plants and animals. While ecologists have a good understanding of stream-dwelling kōura, this hasn’t always been the case for kōura that live in wetlands (repo) associated with rivers and lakes.

Diagram of the modern day tau kōura

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The depth and length of tau are indicative and can be varied depending on lake depth.

Diagram based on an original in Te Reo o Te Repo – The Voice of the Wetland by Dr Ian Kusabs.

Rights: Crown copyright

A new use for a traditional practice

Conventional monitoring of roto and repo-dwelling kōura has a few drawbacks. Baited traps tend to catch large aggressive males so this method doesn’t accurately monitor smaller kōura or female kōura. Spotlighting, diving and underwater video monitoring also favour large males as they are easier to spot. These methods also require reasonable underwater visibility.

Fortunately, a conversation with kaumātua brought to light an old technique known as tau kōura – a way of collecting kōura that was still being used by two families from Ngāti Pikiao.

The tau kōura method involves placing bundles of bracken fern on the lake bed, creating a habitat or refuge for kōura. In a modern tau kōura, the fern bundles (called whakaweku in Te Arawa Lakes rohe and koere and tāruke in other rohe) are tied along a line (tāuhu) and placed on the lake bed for about 6 weeks. Alternatively, individual whakaweku can be left in streambeds for 2 weeks. To count the kōura, the whakaweku are lifted onto a kōrapa (net) so they cannot escape. Kōura are shaken from the fern, data about their size, gender and reproductive state are recorded and the kōura are returned to the water.

Using whakaweku to monitor kōura

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These images show the steps in using whakaweku to monitor kōura.

Sourced from Te Reo o Te Repo – The Voice of the Wetland.

Rights: Dr Ian Kusabs

Tau kōura represents over 500 years of mātauranga and rangahau (research). The technique is an effective yet inexpensive way for scientists, iwi and community groups to monitor kōura. The method has also been used successfully for monitoring freshwater crayfish in other countries! For example, freshwater ecologists in Staffordshire, England, are using whakaweku to collect endangered white-clawed crayfish for relocation to safer waterways. They’ve been able to safely collect crayfish of a wide size range and balanced sex ratios.

We retain the traditional names and history, and acknowledge the appropriate iwi and people, as we work to manage and sustain the kōura. We now have a scientifically robust method for sampling kōura that is being used in lakes and streams throughout New Zealand.

Dr Ian Kusabs (Te Arawa, Ngāti Tūwharetoa)

The value of kōrero in wetland restoration

For ecologists, iwi and community groups, the resurgence of tau kōura represents the importance of kōrero with kaumātua and whānau about their memories and current interactions with repo and wetland species.

If kōura were once mahinga kai, find out about the populations and/or harvesting practices. If there have been population declines, find out what may have caused the decline so that the causes can be addressed. Note that some whānau may not want to share the exact location of their harvesting areas, but they may be willing to answer questions about kōura populations and changes to habitat or land use.

The next step is to consider the ecology and environmental whakapapa of the repo system. Kōrero about the best areas to restore kōura. Habitat and water quality are key considerations. Preferred habitat includes undercut banks and lots of woody debris, good water quality and low levels of fine sediment. A monitoring and assessment survey will provide information about current conditions and can build a baseline to help monitor changes over time. Kōura are just one of many species that will benefit from repo restoration. Give some thought to how restoration might help native freshwater fish, aquatic insects and freshwater macroinvertebrates.

The Voice of the Wetlands

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The handbook Te Reo o Te Repo – The Voice of the Wetland forms the basis of the collection of resources funded by Manaaki Whenua – Landcare Research and MBIE’s Unlocking Curious Minds initiative.

Rights: Crown Copyright