Once abundant in the beds of inland lakes, kākahi [freshwater mussel] sightings are now few and far between, but their future looks more promising thanks to ongoing research taking place in Lake Wairarapa.
This year’s Kākahi Count marked ten years of study, supported by citizen scientists, the Greater Wellington Regional Council [GWRC] and the Wairarapa Moana Wetlands Project.
The annual survey has been conducted in Lake Wairarapa at two sites over the past decade, the Lake Domain and Western Lake Reserve.
Kākahi populations are currently threatened and even facing extinction, something GWRC biodiversity advisor Sarah-Jane Jensen said could be stopped if efforts to study the species are continued.
“Our dedicated community of citizen scientists have been getting their feet wet and hands dirty finding and measuring the kākahi of Lake Wairarapa for the last decade,” said Jensen.
“It’s not always clear what causes kākahi populations to decline, but the data we’ve collected illustrates an ecosystem in urgent need.”
Due to low numbers of juveniles or babies, Jensen said she believed that the kākahi were struggling to complete their lifestyles and reproduce.
“We know from local and iwi anecdotes that kākahi were once so plentiful you would cut your feet as you walked across the lakebed,” Jensen said.
“Now, the clock is ticking on the window for kākahi to recover.”
Volunteers helping with the surveys wade out into the shallow lake water and hand-collect the kākahi, where information such as species and length is recorded before the specimen is then gently returned to the water.
National Institute of Water and Atmospheric Research [NIWA] marine and freshwater ecologist Mark Fenwick joined the first Kākahi Count with his whānau in 2015 and said kākahi are a valuable indicator of the lake’s overall health.
At Lake Wairarapa, he said that the high sediment level meant that a lot of the animal’s energy was going into feeding rather than reproducing.
“Kākahi will only survive and flourish in certain environmental conditions,” Fenwick said.
“As filter-feeders, they’re sensitive to changes in water quality and very susceptible to high sediment levels.”
Fenwick noted that in a healthy waterbody, kākahi of all sizes would thrive.
“Shrinking kākahi populations can also signal the health of species like toitoi and other native fish, which the kākahi rely on to carry their spawn upstream,” Fenwick said.
“Monitoring kākahi is one way we collect long-term information about water quality or ecological changes to an environment.
“This decade of data can help freshwater resource managers understand the effectiveness of current ecological restoration efforts and consider alternatives.”
For next year’s count, GWRC’s Jensen said that data may be collected from a third site on the eastern side of the lake to help pinpoint which stressors are having the most impact on kākahi decline.
