Our restoration goal is to have a diverse and representative range of freshwater habitats, flora and fauna.
Zealandia encompasses the headwaters of the Kaiwharawhara stream catchment, which has its outlet into Wellington Harbour through Ngaio Gorge. In 1870 the stream was dammed at the lower end of the valley to create the lower lake. In 1906-08 a second dam was built 1km further up the valley. This, together with forest clearance and urban development along the Kaiwharawhara stream, has resulted in serious disturbances to the original freshwater stream habitat.
To assist with the restoration and management of wetlands in the sanctuary valley, four habitat zones have been identified. There are: upper freshwater streams (requiring little or no management), the upper lake (Roto Mahanga) and margins, central freshwater streams and the lower lake (Roto Kawau) and margins.
Lower Lake wetland restoration
The southern shoreline of the lower lake has been modified to establish shallow habitat suitable for a range of wetland plants. This is an important feeding area for wetland birds such as pāteke and scaup. Considerable planting has been undertaken around the margins, and artificial islands established. To promote the movement of fish between the lower lake and the wetland, a fish ladder has been constructed that joins that stream and wetland to the lower lake. Karori Sanctuary Trust is grateful to the Keith Taylor Charitable Trust for making this wetland development possible.
In addition to this development a native fish tank and interpretation about freshwater ecosystems is located here.
The lower lake suffers from algal blooms in the summer, resulting in an unpleasant smell and algal scum. While this is a natural event, there may be some management actions that can be undertaken to reduce the frequency and severity of these blooms.
Research is being conducted by Cawthorn Institute and Waikato University to understand the impact that exotic fish have on this phenomena.
Upper lake wetland restoration
Thanks to the Lions Club of Karori, artificial islands and viewing hides have been installed at the upper lake to increase the diversity of habitat for waterfowl and help the public view species such as scaup and pāteke. Considerable effort has gone into controlling exotic plants and planting native shrubs and grasses around the lake edge and on the artificial islands.
Wetland fauna restoration
Before the sanctuary valley was cleared and the stream dammed, there would have been limited wetland habitat. However, the two old water reservoirs provide us with the opportunity to develop wetland habitats and release a range of aquatic species that would be appropriate to this area.
We assumed that the aquatic fauna to be restored in the sanctuary valley should be characteristic of the southern lowland North Island. A list was generated of species known from this area before human settlement and those that have become naturally established since then.
This list includes 32 species of birds (of which 12 are now extinct), two amphibians (of which one is extinct), and approximately 10 fish (of which one is extinct).
When Karori Sanctuary (now Zealandia) was first established, seven species of birds (two shags, two gulls and two ducks) used the lakes and two species of native fish (banded kōkopu and shortfin eels) have been identified here since then. Two exotic fish species, brown trout and perch, are also found in the sanctuary valley and are a priority for eradication before any new species of native fish can be released*.
*Since this was written our upper lake and streams have been eradicated of brown trout.
The lakes, streams and wetland provide a variety of habitats that are attractive to a range of aquatic birds.
Nineteen aquatic birds have been identified as suitable for the sanctuary valley. A number may self-introduce when the habitat is right, but others will need to be transferred.
The first waterfowl releases have occurred: pāteke (brown teal), shoveler, and New Zealand scaup. These birds were sourced from captive breeding programmes. Further releases of shoveler will be required as the initial pair did not breed. As the wetland and lake habitats improve, the second wave of releases could include: Australian coot, grey teal and grey duck.
Some species, such as dabchick, marsh crake and spotless crake have never been transferred and techniques may need to be trialled first. Source populations will also need to be identified before transfers can begin.
Only two species of native of frogs (that may have been found in the sanctuary valley) are regarded as semi-aquatic, and one of these is extinct. The Maud Island frog was introduced here in 2006 – these frogs are mainly land-based.
Any fish species introduced to the sanctuary valley should be:
- able to breed in a small landlocked eco-system; or
- be able to climb through the predator-proof fence; or
- be able to be caught and transferred over the fence to complete their migration (in or out of the sanctuary valley).
Eight species including longfin eel, several species of bully and several species of galaxiid have been identified as meeting the criteria for release. However, before any native fish are released, exotic fish need to be successfully eradicated and habitat evaluated for the new species. You can view some species of native fish in the fish tank and display at the lower lake.
The quality of stream water at Zealandia is very high and there is a good diversity of freshwater invertebrates present, especially in the streams of the upper valley. Two new species of water beetle have been discovered here.
Any introductions of wetland invertebrates must be done with caution to protect existing species. The introduction of wetland invertebrates is an unknown science so any transfers will be carefully evaluated and monitored, and are unlikely to be undertaken until the exotic fish have been eradicated.
Wetland flora restoration
A comparison of plant species at Zealandia with similar sites in the Wellington region and with early herbarium records has helped us to determine which native species should be reintroduced.
As freshwater wetlands are rare in the Wellington Ecological District it is important that we accommodate as many appropriate wetland species as possible, to provide the diversity of habitat needed for aquatic fauna to establish.
While there are a few wetland plant species naturally occurring in the sanctuary valley, ongoing management is required to improve habitat diversity. Plant propagation for restoring and enhancing wetland areas has been a major undertaking.
Wetland trees & shrubs
Eight key species of wetland (riparian) trees and shrubs have been planted in the upper and central freshwater stream habitat zones. They include cabbage tree, tree fuchsia, swamp maire, kahikatea and pukatea and they have been planted to enhance the stream habitat. Exotic species such as buddleia and pampas are being removed to restore the habitat to a more natural state.
Grasses, sedges and rushes
Grasses, sedges and rushes form the most important component of wetland flora in the valley. They have been planted in large numbers around the lake edges and lower lake wetland. The 28 species identified for planting have been chosen because they are representative of a typical Wellington wetland and are important for wetland fauna. Key species include toetoe and kakaho (similar to toetoe).
An underwater survey of the lakes in 2002 shows that both lakes support a healthy and diverse cover of native vegetation, with only a few exotic species. Removal of the exotic species is not regarded as a priority because there would be continued reintroduction by waterfowl, and it appears that no artificial enhancement of native species is required.