Protecting kākahi - one catchment group at a time
- Konrad Kurta
- 6 days ago
- 2 min read
When you use the term ‘kākahi’, many people give you a blank stare. It’s the te reo name for our freshwater mussels. They’re surprisingly common across New Zealand, but are hard to spot given they spend much of their lives buried in sediment. The average Kiwi has never even seen one alive…though they might have seen mysterious shells on a stream bank and wondered where they came from.
In Auckland, there are two species:
Echyridella menziesii: Known for being much more robust and ‘fatter’.
Echyridella aucklandica: A streamlined, pointier species that is nationally vulnerable.
While they’re invisible to many people, they play an important role in our freshwater ecosystems - each mussel can filter up to a litre of water a day, helping to keep our streams, rivers and lakes clean.
These critters have an interesting way of reproducing and colonising new habitats. In their larval stage, called ‘glochidia’, kākahi are parasitic ‘pac-man’ looking creatures. Once released by mature females, they ‘hook’ onto a native fish (like kōaro, common bullies, or banded kōkopu) and become encysted on the fish’s tissue. There, they develop their internal organs - including a heart, liver, digestive tract, and the muscular ‘foot’ they will need as adults.
Once this metamorphosis is complete, the juvenile mussel ‘excysts’ (detaches) from the fish host. They drop into the water, sink, and start their life as a 3mm juvenile kākahi.
Historically, this strategy has been enough to populate rivers and streams across the country…even if many of us don’t know they’re there.
But in the last 20 years, there has been a concerning decline in kākahi numbers in the Auckland region. Predation from rats is a significant issue, as is sedimentation from heavy rainfall events.
Alarmingly, the status of both Auckland species might be masked by somewhat-healthy adult populations. Juvenile kākahi seem particularly vulnerable to poor water quality - especially sedimentation.
Recent heavy rainfall events may have done significant damage to younger kākahi populations. When the mature specimens die, we don’t currently have a good understanding of how many juveniles will be there to replace them.
Can catchment groups turn the tide for kākahi?
Enter Maddison Jones, a Freshwater Ecologist for Auckland Council. She works in rural areas with the Healthy Waters and Flood Resilience team. Given kākahi are such impressive natural water filters, Maddison and her Auckland Council colleagues took Waikato Regional Council’s kākahi monitoring protocol and streamlined it, with the intention of giving community groups an easily-digestible guide for monitoring their kākahi populations.
Together with Mountains to Sea Conservation Trust and the Wai Connection project, Maddison and her colleagues have trained the Arapārera Community Catchment Group to undertake their own monitoring.
It has been a resounding success.
With support from Mountains to Sea Catchment Coordinator Hana Aickin, the group has done extensive monitoring all over the catchment. Through this monitoring, they’re developing a good understanding of the health of their kākahi population. As they collate and interpret the data, they’ll be in a better position to engage their community and undertake protection and restoration efforts.
Could this be a blueprint for protecting kākahi populations - both in Auckland and around Aotearoa? See the video to find out more!
Comments