Assessing fish populations in a stream near the Paparoa Ranges
Image: Suze Harris | DOC


A project to secure populations of shortjaw kōkopu, īnanga, longfin eel/tuna and lamprey across Aotearoa New Zealand.

Ngā Ika e Heke began in 2019 and provides a coordinated approach to managing migratory fish across the country. It extends the work we are already doing to conserve and manage native freshwater fish species. 

Download a factsheet summary of this project (PDF, 1,172K)

Species and conservation status

Ngā Ika e Heke is providing long-term support to help protect and restore populations of these migratory fish species in ecosystems across the country:

About the work

The species were chosen because their populations are threatened or in decline. Also, they are taonga species with special cultural significance and importance to Māori.

The fish are migratory and need to move freely between different freshwater habitats and the sea to complete their lifecycles. Work to secure their populations must consider all the habitats they use throughout their lifecycle, from the mountains to the sea.

Reducing threats and pressures on the species 

Populations of these fish are exposed to various threats and pressures, many of which are caused by human activities. These include habitat loss and degradation, sedimentation, pests, diseases, loss of water quality and quantity, artificial barriers in streams and rivers, climate change and genetic isolation. 

Actions that can be taken to reduce the pressures and threats on populations include:  

  • pest control 
  • planting riverbanks with natives to improve shade and spawning habitat and reduce the amount of sediment entering waterways
  • fencing off riverbanks to prevent stock from trampling vegetation
  • fixing or removing barriers to allow fish to move freely within waterways and to and from the sea
  • protecting and managing important habitats
  • exploring ways to reduce the effects of climate change at important sites.

Research strategy

More knowledge about the species will inform and help our work. Cost-effective methods and tools need to be developed because the populations must be managed at a landscape scale.

Our research is focussed in these areas:

  • species and populations – assessing and monitoring known populations, identifying new populations, understanding the ecology of all life stages and exploring species’ relationships to the environment
  • critical habitats – understanding the state and conservation of the habitats used at critical times and during vulnerable life stages
  • pressures and threats – responses to human-caused pressures and threats to the species
  • tools and methods for recovery and management – developing standards, methods and tools for intervention, such as improving fish passage.

Team and approach

The Ngā Ika e Heke team is made up of regional rangers and a North Island and a South Island coordinator, supported by national freshwater science and technical advisors. The rangers also have responsibilities for freshwater biosecurity and work closely with Ngā Awa river rangers.  

An important part of the work is building relationships with others involved in managing freshwater. Partnerships with iwi, hapū and whānau are being developed to decide on local work priorities and support existing projects.

Rangers are also connecting with regional councils, community groups, landowners and other organisations to identify existing fish populations and planning projects to secure them.

Data gathering and planning  

Shortjaw kōkopu 

Shortjaw kōkopu are rare and secretive. They are not seen often during the day and best detected at night using a spotlight. These fish use specific habitats and are often missed by routine freshwater fish monitoring.

As part of this project, we have re-surveyed known shortjaw kōkopu populations in different parts of New Zealand that have not been looked at for 10–20 years. This knowledge will inform and help prioritise our restoration efforts.

Little is known about the species or where they spawn. The only confirmed spawning sites were identified in Taranaki in early 2000. We have started intensive studies at sites with good numbers of fish to monitor the populations and identify when and where they spawn. Individual fish have been identified and their size and spawning condition tracked. We have also carried our egg searches at expected spawning times.

The new information we gather from this work will be applied to help secure other populations across the country.

Read about our shortjaw research on the West Coast.


Īnanga make up most of the native fish caught as whitebait. They spawn in thick vegetation on the side of riverbanks during high spring tides, hatch, and spend 4–6 months at sea before returning to the river to mature. During their development, eggs are vulnerable to drying out, being trampled by stock, or destroyed by mowing grass and work to control riverbank erosion.

Identifying and protecting īnanga spawning sites is an important action for this project. We are currently developing standard survey methods that will guide how to look for, and measure the extent of  īnanga spawning sites. Once finalised, the methodology will be used in all our survey work to ensure consistency across the country and provide data to support restoration work.

We are working with iwi, hapū and whānau, agencies, landowners and community groups to identify, enhance and protect spawning sites. Legally protecting sites is also an option through mechanisms in the Conservation Act 1987.

Ensuring īnanga and other migratory fish can move freely up and downstream enables them to complete their lifecycles. Īnanga are poor swimmers and unable to move past some culverts and swift rapids or climb weirs. Our work to improve fish passage includes fixing or removing barriers, and monitoring how well they are working.

Tuna / longfin eel 

Adult tuna / longfin eels leave New Zealand to spawn in ocean waters near Tonga. Their larvae return to rivers and streams as glass eels, migrate upstream and mature over several decades. Ensuring eels can migrate up and downstream safely is a priority for this work.

Monitoring glass eels as they return to rivers is one way to study their populations. Some information about their behaviour is available from studies in the Rangitaiki River in the Bay of Plenty. This project is identifying other rivers where more research can be carried out. Rangers also support activities to learn more about tuna populations in lakes, including Lake Brunner, and Lake Rotoroa in Nelson Lakes National Park.

Read about the cultural harvest at Lake Rotoroa

Lamprey / kanakana / piharau 

Lamprey is a mahinga kai species for Māori and an important traditional fishery.

Lamprey are a secretive species and can be very hard to find – they are often missed by standard fish survey methods. Recent research by NIWA scientists found better ways to detect and monitor lamprey using modified electric fishing methods, environmental DNA (eDNA) and pheromone samplers. These samplers can pick up pheromones in the water that were released by lamprey larvae.

We are using eDNA and pheromone samplers to confirm the presence and extent of known populations and identify new ones. As we learn more about the species and their distribution, we can focus our work to manage, protect and restore specific sites and populations.

Read about lamprey research and results from 2023 surveys.


We’d like to hear from you if your work aligns with ours or if there are opportunities to work collaboratively.


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