What’s in our freshwaters?



MĀORI: KĀKAHIENGLISH: Freshwater mussel

Kākahi are Aotearoa’s native freshwater mussels. They live in soft- bottomed lakes, rivers and streams where they feed by filtering water. They have complex life cycles with a parasitic larval stage. The young larvae called ‘glochidia’ live for 2-4 weeks attached to the fins or gills of native host fish (e.g kōaro, bully species, banded kōkopu, common smelt). Kākahi are taonga species for Māori and an important part of healthy freshwater ecosystems.


Threats and conservation

Freshwater mussels are under threat and declining in New Zealand and worldwide. There are three species of kākahi in New Zealand of which 2 can be found in the northern Auckland region: Echyridella menziesii (more round in shape) is classified as ‘At Risk – Declining’ and Echyridella aucklandica (generally more elongated) is ‘Threatened – Nationally Vulnerable’.

Threats to kākahi include habitat loss and degradation (too much fine sediment affects the filtration process), a decline of host fish populations (interrupted life cycle with failed recruitment), introduced fish (e.g. perch, trout), and terrestrial predators (rats, Pukeko).

Glochidium (© Michele Melchior)
Glochidia attached to common bully tail (© Michele Melchior)

Cool Facts

  • Some can live up to 50 years, and reach 13 cm in length
  • You can age kākahi by counting the growth rings in their shell
  • Unlike marine mussels which attach to rocks and can’t move, kākahi can move, anchor and burrow within soft sediment using their “foot” muscle
  • One kākahi can filter up to 1 litre of water per hour
Adult and juvenile kākahi © Michele Melchior

In our area

Kākahi can be found in streams and lakes in the North Rodney area. Important research is being done in Lake Rototoa (Kaipara South Head) by members of Aotearoa Lakes (a citizen science initiative) and Auckland Council. Some of the work includes;

  • 2620 square metres of kākahi beds in the lake have been surveyed
  • average of only 7.2 live mussels per square meter
  • all live individuals were adults (>51mm), no juveniles have been found thus far
  • working on various ways to encourage successful kākahi recruitment including exclusion pens to keep pest fish species out during spawning seasons
  • trying to identify kākahi habitat preferences and map out areas with the best conditions
  • actively searching the various habitat types for juveniles
Weweia Area map
Ebi Hussain from Aotearoa Lakes doing kākahi surveys in Lake Rototoa
Lake RototoaBryndlefly (https://commons.wikimedia.org/wiki/File:Lake_Rototoa_New_Zealand_1.JPG), https://creativecommons.org/licenses/by-sa/4.0/legalcode

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