Meet our Newest Arrivals

Kākahi / Freshwater Mussels

You may not see very much of the newest arrivals in the valley, but they are being carefully monitored all the same.

Two hundred kākahi (New Zealand freshwater mussels) have just been translocated from Wairarapa Moana and the Parangarahu lakes to the Upper Lake with the help of iwi partners, Taranaki Whānui, Ngāti Kahungunu, and Rangitāne o Wairarapa. Two different kākahi  species were included in the translocation: Echyridella menziesi and Echyridella aucklandica.

Amber McEwan, PhD student at VUW and Riverscapes Freshwater Ecology scientist, is conducting a three year research project looking at the effects of the translocation on the kākahi. Surprisingly little is known about kākahi, and “this is a super-exciting research opportunity”, she tells me when I meet up with her in the valley. While we’re talking, Amber is painstakingly attaching microchips to the shells of the kākahi with dental cement. She explains that the microchips will enable her to find out about kākahi survival rates, how they move around the lake and nearby streams, what habitats they choose to settle down in, and how the two species interact with each other. 

Amber McEwan (right), kākahi scientist and 'enthusiast'. Photo Credit: Linton Miller

One thing that is known about kākahi is that they are endangered, particularly Echyridella aucklandica. Kākahi are vulnerable to “everything that’s happening to freshwater” Amber says, such as contamination, sedimentation, and eutrophication. Kākahi rely on fish as part of their lifecycle and likely do better with native fish. Parent kākahi “sneeze out” their babies, which then attach themselves to passing fish to hitch a ride to a new home. In the past, our streams would have been full of native fish, but now the odds of a baby kākahi finding a fish to attach itself to are much lower. In ZEALANDIA at least, the banded kōkopu in the lakes and streams will do this job.

Amber is a kākahi enthusiast – “just look at them, they’re so cool” she says when I ask her why she was drawn to study them. She points out the different features of the kākahi that she is microchipping and I’m surprised to learn that they  can live for 50 years or possibly even longer. She estimates that the kākahi in her bucket might be 20 to 30 years old - they grow very slowly, accreting the ridges in their shells as they age.

Echyridella aucklandica (left) and Echyridella menziesi (right). Photo Credit: Leon Berard

The rate at which kākahi populations expand depends on their environment and so far, not much is known about this. Amber is hopeful that there could be quite a few more kākahi in ZEALANDIA in 5-10 years’ time, but it might be difficult to find them, as they burrow into the soft mud of lakes and streams.

Kākahi play an important role in the ecosystem by helping to keep freshwater clean – as filter feeders, they remove particles such as sediment and phytoplankton from the water. In ZEALANDIA, they are part of our ‘Sanctuary to sea’ project which aims to improve habitats in the catchment of the Kaiwharawhara stream. It is possible that the kākahi could even spread out into the Kaiwharawhara stream itself – athough generally they prefer slower-moving streams. They are also significant to Māori as mahinga kai, providing a valuable traditional food source. Amber’s research will help us understand more about how to conserve these easily-overlooked but important creatures.

This project is made possible by the Holdsworth Charitable Trust, our iwi partners Taranaki Whānui, Ngāti Kahungunu, and Rangitāne o Wairarapa, Riverscapes Freshwater Ecology, the Department of Conservation and Greater Wellington Regional Council. We are proud to be part of this partnership that involves many incredible people and organisations.

Article by Louise Slocombe.