Native fish ‘hidden treasures’ in the Kaiwharawhara Stream
Our native fish are among the hidden treasures of New Zealand’s animal life because they are seldom seen. Yet the Kaiwharawhara Stream catchment is known to have 13 species of fish out of the 21 in the Wellington Region.
‘Sanctuary to Sea/Kia Mouriora te Kaiwharawhara’, a multi-stakeholder restoration project co-ordinated by ZEALANDIA staff, aims to improve fish habitats throughout this important catchment. Beginning within the ZEALANDIA sanctuary, the catchment is the largest in Wellington city, covering over 16 square kilometres.
It also is one of the few remaining tributaries with a natural estuary mouth into the harbour. The streams of this important valley provide habitat for eels, kōkopu and bullies, among others.
The ‘Sanctuary to Sea’ awa or river starts within the sanctuary; currently the lakes and streams within the sanctuary only have three native fish – banded kōkopu, longfin and shortfin eel. Naturally what happens at the headwaters affects what happens downstream. The Sanctuary to Sea project helps to coordinate efforts downstream to prevent further impacts on the waterways, and also improve aquatic habitats throughout the catchment and restore fish migration pathways. This is important because many native fish species need to migrate between freshwater and the sea (known as diadromy) during their lives; their survival depends on it.
Of the fish species recorded in the Kaiwharawhara catchment, five are classified as ‘at risk – declining’. These include the longfin eel, giant and kokopu, koaro, inanga, and bluegill bully. One species, the giant bully, is classified as ‘naturally uncommon”. The other three species – shortfin eel, banded kōkopu, and common bully are considered ‘not threatened’.
Greater Wellington Regional Council and Wellington City Council are running an on-going urban stream monitoring programme (including in the Kaiwharawhara catchment) to assess the condition of the fish communities over time and any to note any changes as a result of management interventions. Read or listen to the Radio New Zealand broadcast Streams Beneath our Streets to find out more.
Most of the fish species are found in the section of the stream that runs through Otari-Wilton bush and Trelissick Park, with some in the tributaries that feed into the stream from Mt Kaukau. There are fish barriers in the lower reaches of the stream that block the passage of fish getting up or downstream.
Several native fish lay their eggs on streamside plants in the lower reaches of rivers and streams. An example is inanga, which is one of five native freshwater fish species that are known as whitebait. Inanga are found in the Kaiwharawhara Estuary and the lower reaches of the stream.
Tuna hinahina (shortfin eels) and tuna kuwharuwharu (longfin eels) are also present in the Kaiwharawhara catchment. Longfin eels need to migrate downstream to spawn, and they then go far out into the sea between Tonga and New Caledonia.
We need to learn more about fish populations. The Sanctuary to Sea project will promote more research on areas like diversity, distribution, and movement. The Kaiwharawhara catchment is an important place for our threatened native fish.
Thanks to additional research by Evan Harrison (Greater Wellington) and Jazmine Ropner.