A fresh(water) start

By Dr Nate Rigler

Did you know that the Kaiwharawhara is the only catchment in Wellington City with an open estuary connected to Wellington Harbour? A catchment is an area of land where rainfall flows into a common water source: for example a lake, wetland, or estuary. Beginning in Zealandia Te Māra a Tāne, the Kaiwharawhara catchment is home to many fish species which need to move between fresh and saltwater to complete their lifecycle.

One of these species is inanga (Galaxias maculatus) which is the most common species of whitebait, currently classified as ‘at-risk and declining’. Whitebait are the juveniles of five species of galaxiidae, a family of fish confined to the Southern Hemisphere. Whitebait are translucent in appearance and are around 4-5 cm long. Another of these five species is banded kōkopu, which are found at Zealandia.

The main threat that inanga are facing nationally is the loss of suitable habitat that they need to reproduce.

At the peak of the king tide (an exceptionally high tide), inanga will swim to the saltwater wedge of an estuary to find vegetation, like submerged native grasses, to which they attach their eggs. When the tide recedes, these eggs develop above the water for several weeks until the next king tide washes them out to sea. King tides typically occur during new or full moons or during specific seasons around the country. When these juvenile fish swim upstream once again, they’re often caught as whitebait.

In the Kaiwharawhara, and indeed so many other urban parts of Aotearoa New Zealand, there isn’t enough habitat remaining for inanga to attach their eggs to. That’s why Kia Mouriora te Kaiwharawhara Sanctuary to Sea, supported by Taranaki Whānui ki Te Ūpoko o Te Ika, Mountains to Sea Wellington, Trelissick Park Group, Predator Free Khandallah, and Te Ohu Kaiwharawhara businesses are working on restoring the Kaiwharawhara estuary. 

To begin, with help from Woods Waste, several large invasive wattle trees were removed from the stream bank. This allowed the rōpū/group to plant native grasses, sedges and rushes that inanga love. Predator traps were also installed throughout the stream bank, which Woods Waste has signed on to service to protect small eggs from introduced predators like mice and rats. 

Litter is a problem in parts of the catchment and, to play on the classic abandoned shopping trolley in an awa, we are trialling a new type of planter box for these plants. With help from McMud Earthworks, Living Room, Conservation Volunteers New Zealand, and Te Rito Gardens, we created four experimental planter boxes made from repurposed shopping trollies! We filled these trollies with more native plants and fastened them along the concrete channelised stream bank. This will provide inanga with more precious habitat and, if successful, will serve as a model for similar urbanised streams. If you want to take a sneak peek at these planters, they are near Spotlight— just cross the bridge and look into the awa/stream to see how they’re doing. Together, we're taking steps to enhance the mouri of the Kaiwharawhara. There is much to do so if you are interested in being involved, email sanctuarytosea@visitzealandia.com.