February 12, 2020
Trout predation threat to mussel population
A shortage of native fish is being blamed for an alarming lack of juvenile kākahi or native mussels in Lake Wairarapa.
The annual Greater Wellington Regional Council kākahi monitoring survey at Wairarapa Lake Shore Scenic Reserve last Sunday found plenty of adult kākahi but less than a handful of the juvenile mollusc.
Freshwater ecologist Amber McEwan says kākahi rely on native fish, especially the kōaro, to spread their larvae, which latch onto passing fish using a hook at the top of their shell.
An explosion of pest fish in the lake such as perch, rudd and brown trout have decimated native host fish populations.
Historically, Māori used kākahi as a source of food and their shells were used as tools.
One kākahi can filter about one litre of water per hour, so in the past large beds of kākahi probably helped to maintain the clarity and ecological health of New Zealand’s waterways.
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