Mussel mania: our latest wildlife translocation

During April 2022 the team at Zealandia Te Māra a Tāne translocated kākahi/freshwater mussels into Roto Māhanga/the upper reservoir. 

But wait, what are kākahi?

Many people don’t know we have three species of endemic freshwater mussel in Aotearoa. While much attention is often paid to our feathery friends, the humble kākahi are quietly transforming the freshwater ecosystem around them, improving water quality by filter feeding— they are able to filter one litre of water per hour! They are also long-lived, with some species living up to 50-60 years.

Sadly, kākahi are under threat and declining, likely due to factors like habitat modification or destruction, water pollution, and possibly through the loss of host fish species which are critical for kākahi to complete their life cycles. This makes it all the more important to establish thriving populations of kākahi in protected sanctuary spaces like Zealandia Te Māra a Tāne. So, how did we translocate the kākahi?

Monitoring

First things first, we needed to check that the population of kākahi we were taking from was in a good enough shape to spare a few (150) individuals. To do this a small team from Zealandia Te Māra a Tāne, Taranaki Whānui, and Greater Wellington headed out at the end of March to Lake Kōhangapiripiri in East Harbour Regional Park to monitor the population we were planning to collect from.

This involved getting into the water and feeling around in the silt layer of the roto. While at least one person stayed ashore and kept their eyes on the safety of others, the rest were waist high in the water, reaching with hands into the silt layer of the roto in search of kākahi. They were quite lucky to have gone out on a beautifully sunny day, as reaching into the roto meant they were wet from neck to toe!

Throughout the day, a good range of sizes between kākahi individuals were found, which is exactly what we are looking for! This indicates a healthy, dynamic population where kākahi are surviving in good numbers (indicated by the bigger individuals) and that new kākahi are establishing to replace the older ones.

Collection

On Saturday 9 April, representatives from Zealandia Te Māra a Tāne, Taranaki Whānui, and Greater Wellington returned to Lake Lake Kōhangapiripiri.

After a karakia and a briefing around the kaupapa and health and safety, the rōpū/group made its way out along the gravel road past Pencarrow lighthouse, stopping near the roto/lake. We collected kākahi from two sites. Everyone had a role: there were the hardy collectors who waded and sometimes ended up swimming in the chilly water, the folks onshore who oversaw rinsing, measuring and placing the kākahi into a kete/basket within a bucket. The kete were specially designed and hand woven, drawing on rich archive of Māori knowledge of the natural world and protecting wildlife species.

Once the 150 kākahi had been collected and the collectors were all warmed up and fed/watered, the kākahi were carefully transported to Zealandia Te Māra a Tāne, where they stayed in quarantine until their release.

Release

While in quarantine, the water the kākahi were housed in was changed every day. This gave the mussels time to adjust to the water in Roto Māhanga and to filter through any unwanted organisms. Our operations team had to carry heavy buckets of water from Roto Māhanga back to the Zealandia offices where the kākahi were quarantining. On the 20 April, this bivalve bodybuilding came to an end as a small rōpū/group of Zealandia staff, mana whenua, and folks from te Roopu Rāranga o Manaia/Hīkoikoi weavers, Wellington City Council, and Greater Wellington Regional Council released the 150 kākahi from Kōhangapiripiri into Roto Māhanga/upper reservoir.

The rōpū made their way up to the top dam behind the vehicle carrying the kākahi, which, similar to their transport over to Zealandia, were nestled in kete contained within aerated buckets. A smaller team released the kākahi in the roto near the southwestern stream outflow to supplement the kākahi population already there, while the rest of the group watched on from the Upper Dam. To make sure they stayed safe as they settled into their new home, one of our rangers watched over them as they buried into the sediments, happy as clams....er, mussels.

It was a great end to a fantastic translocation. Like its outsized role as ecosystem engineer, over the course of the project this small, unassuming mussel has had a massive impact, bringing together a wide variety of folks from all around the Wellington region. It has also allowed us an opportunity to continually improve how we do translocations, making sure we were using a Te Tiriti-centered approach and following tikanga (Māori practices and guidelines of how to behave and treat one another—note these practices can vary by iwi and hapū) in all aspects of the project.

The ripple effects from these wee kākahi will be felt both in and outside the roto for many years to come!