A freshwater journey

Over the last few years, we have been focusing on restoring our freshwater ecosystems. From creating a safer environment by removing invasive species and bringing in endangered species to beginning the Kia Mouriora te Kaiwharawhara collaboration, we are beginning to see the impacts of this mahi/work with dragonflies and fish in abundance and a reduction in algal blooms in Roto Kawau. This month marks the beginning of our third (and likely final) toitoi/common bully translocation. The Zealandia population has established well since 2023 and if you peek into Roto Māhanga from the top dam, you are likely to see toitoi darting around on the bottom of the roto/lake.

In 2018 and 2022, we translocated kākahi/freshwater mussels into the waters of Roto Māhanga. Kākahi quietly transform the freshwater ecosystem around them, improving water quality by filter feeding—each kākahi can filter one litre of water per hour! Sadly, they are under threat and declining across Aotearoa New Zealand, due to water pollution and loss of host species, which makes it even more important to establish thriving populations in spaces such as Zealandia.

So where do toitoi fit into this? Toitoi have a very special relationship with kākahi. Kākahi use toitoi like ‘public transport’, shuttling their kids off to a different part of their freshwater home. Adult kākahi ‘sneeze’ their larvae, called 'glochidia', into the water. These larvae then attach onto the gills or fins of a nearby fish to catch a ride away from their parents. Along the way, toitoi provide the right environment and conditions for the larvae to change into juvenile kākahi. Once they are big enough, the kākahi drop off the toitoi into a new part of the lake and start the cycle all over again.

Before 2023, toitoi had disappeared completely from the Kaiwharawhara catchment. Since then, we have worked with Rōpū Tiaki (the co-management group for Parangarahu Lakes consisting of Taranaki Whānui ki Te Upoko o Te Ika and Greater Wellington Regional Council representatives) to bring both the kākahi and hundreds of toitoi from Parangarahu Lakes to Zealandia Te Māra a Tāne. The translocation in 2023 is likely the first time that freshwater fish have been moved within Aotearoa New Zealand solely for restoration reasons.

Last year, we trialled a traditional mātauranga Māori/Māori knowledge collection method called 'whakaweku', led by kaimahi Māori/Māori staff with help from NIWA freshwater ecologists.

Whakaweku are bundles of rārahu/bracken fern which are submerged in water for a few weeks. While in the water, the bundles act as habitat for ika/fish that live at the bottom of the lake, as well as insects and kōura/crayfish. The beauty of this method, especially when compared to western fishing methods, is that all the ika, kōura, and invertebrates that are caught in the whakaweku choose to inhabit this space and can come and go freely until it is pulled out of the water, which makes it less stressful for them. Drawing on mātauranga Māori in this project allowed staff and others involved to strengthen their connections with each other and with the natural world, all of which are especially important to a world in climate and biodiversity crisis.

This collection method was a success, and our aim for this year’s translocation is to try to use whakaweku exclusively as our collection method. Restoring these diverse ecosystems means they are more resilient to factors such as disease and climate change, and we are already seeing the impacts flow downstream and beyond.