Kākahi shells. Whanganui Regional Museum Collection ref: 1802.5775.8
On display in the Whanganui Regional Museum exhibition Ngā Wai Honohono is an interesting tool that looks like a giant comb.
It's an intricately carved wooden bow-shape, with a row of long spiky wooden teeth attached. Next to it is a pile of black mussel shells. They are the empty
shells of kākahi, the endemic New Zealand freshwater mussel. The tool is a rou kākahi - a rake for gathering kākahi from the sandy bottoms of rivers and lakes.
Kākahi are an important traditional food source for Whanganui iwi. Formerly abundant throughout the Whanganui River and its tributaries, they were usually air-dried for use as a chewy, nutritious and portable snack.
Kākahi begin their lives as eggs. Unusually for a mollusc, the mother kākahi keeps her eggs inside her gills until they hatch into little wiggly larva that can swim freely. Next, they find a freshwater fish to attach themselves to, and hitch a ride.
A favourite host is the kōaro, one of our endemic and endangered freshwater fish, which begins its life near the sea and migrates inland as "whitebait". Kōaro that escape the whitebait nets will journey upstream to their eventual homes, sometimes with a little hitchhiker attached - the larva of a kākahi. When they arrive at a suitable habitat, the larvae drop off and burrow down into the sandy bottom of a nice clean stream or river. They hide buried under the sand for the first five years. Eventually, the young kākahi makes its way up through the sand to live, still partly buried, filtering food such as algae out of the water and growing very slowly for the next 50 years.
