Tiaki Kakahi | freshwater mussels

Kākahi are found in clean freshwater habitats where there are low levels of sediment

Monitoring work is crucial to better understand and protect these species

Tiaki Kākahi | Freshwater Mussels

Auckland's Kākahi, native freshwater mussels, play a crucial role in maintaining the health of our waterways by filtering and purifying our streams for many years. Unfortunately, their populations have significantly declined because of invasive pest fish, pollution and shifting water conditions.

Since 2021, Kaipātiki Project has been surveying kākahi after discovering that we have a relatively healthy colony of Echrydella menzesii in a local stream. We discovered that a healthy colony like ours is something of a rarity, not only in Auckland’s peri -urban streams, but increasingly rare throughout the Auckland Region, especially in our small lakes and major stream systems.

Our approach

Our approach to monitoring addresses many elements of the 2015 Freshwater Mussel Conservation Strategy NZ, including developing monitoring methods, being highly collaborative and protecting quality mussel habitat.

Key to the project are relationships that have been building over time, such as with mana whenua with interests in the area; Te Kawerau a Maki and Ngāti Whatua o Kaipara, represented by Nga Maunga Whakahii o Kaipara Ngahere. The work within Woodhill Forest and the northern section of Riverhead Forest is of particular significance to Ngā Maunga Whakahii o Kaipara, and the recognition of their role as kaitiaki and landowners. The inclusion of kaitaki in the project's survey efforts acknowledges the importance of mātaraunga Māori in shaping environmental conservation practices.

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Survey efforts and discoveries

We have undertaken surveys in streams in the Kāipatiki catchment and the Riverhead/ Coatesville catchment. Working with subject matter experts, we undertook a programme of designing and testing an eDNA protocol for small, slow-moving streams to assess the presence and absence of E menziesii.

In 2024, we surveyed streams on the Kaipara Harbour side of Riverhead Forest, receiving results from the eDNA testing that suggested one of these latter streams also held individuals of E aucklandica. Up until this discovery, there was little information available to suggest that this rare species was in the Kaipara catchment at all.

During our exploration of the stream and the subsequent discovery of not only large individuals, smaller post juvenile individuals and also recent post mortem evidence of at least one small juvenile, we became aware through communication with kākahi experts in New Zealand at DOC, NIWA, Auckland Council Healthy Waters and Te Papa, that juveniles were extremely hard to find and that as a result of an apparent failure to breed, there was great concern that in the Auckland Region at least, this rare species could be extinct within a very few years.

Upcoming work

Our upcoming work is to undertake a series of rapid stream surveys at a variety of sites within the wider Auckland Region, to provide assessments of the health of resident kākahi populations of not only Echrydella menzesii but also the rare, Threatened - Nationally Vulnerable species E aucklandica. We will focus our activities at localities where they are likely to be found together, based on historic evidence and more recent eDNA outcomes. These discoveries are based on our work, as well as a wide range of community groups and Auckland Council Healthy Waters.

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Assessing population health

Kākahi population health can be quickly assessed by locating younger juvenile bivalves, between 1.5 and 4cm in length, as well as in some circumstances, individuals less than 10mm in length. It is not uncommon to find numbers of larger adults at a site, some up to 100 mm long, but they can represent stagnating populations or remnants, living for up to fifty years but without successfully generating young.

By locating healthy functioning populations of both species and tying these results in with up-to-date knowledge of native fish presence in our local streams, we can:

Identify areas to actively protect kākahi from predators.
Maintain free from blockages to fish passage.

This work will assist the continuity of these important taonga species for years to come.

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Support this work to protect Kākahi

There are so many ways you can get involved:

VOLUNTEER to assist in the regeneration of local freshwater streams.
Join a local pest trapping group to help reduce the numbers of introduced predators.
Learn more about our community flood resilience programme.
Keep our streams clean and join our stream clean-ups.
DONATE or SPONSOR to support our initiatives!

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Ngā mihi nui to our incredible partners and funders

You strengthen the programme and help make it all possible!

Professor Charles Lee, from Te Tumu Whakaora Taiao Environmental Research Institute at The University of Waikato
A2E
Konstanze Steiner from the Cawthron Institute in Nelson
Brett Stansfield, Environmental Impact Assessment Ltd.

Ngati Whatua o Kaipara 10 5 cm Te Kawerau a Maku 10 5 cm Working with AC Lotto 10 5