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History of Cobden Aromahana Ecological Restoration Group

A 2007 assessment of the West Coast's inanga spawning sites recommended that restoration of Cobden Island be carried out in order to enhance its values (Stengs 2007). This was followed by an ecological assessment of the island, mapping of vegetation types in 2011 and collating information about fauna for the Grey District Council. It was recommended that some of the former channels and river braids be re-instated (Stengs2011). This followed the successful restoration of another nearby coastal wetland by channel excavation and planting several years ago but on a smaller scale.

We have dug out nearly 400 m of channel and planted about 2600 indigenous species (mainly lowland flax) to date. Cobden Island is flood prone and it is managed in order to maximise egress of flood waters which could otherwise threaten the adjacent Greymouth and Cobden townships. Therefore channels and excavated spoil have been aligned parallel to flood flow. Flax bends under flood waters, therefore offers little resistance, yet is easy to plant, hardy and requires no subsequent management like releasing.

Inanga have started utilising the new channels straight away. Ten months after excavation grasses and other species that inanga prefer to spawn in have recolonised channel banks. We have also caught numerous rats and stoats in the predator traps we have set.

Lessons learned are that ongoing maintenance will always be an issue. For example weeds such as crack willow will remain a problem because of their sources of re-infestation in the catchment. Use of a helicopter to control them while expedient, results in herbicide being sprayed on non-target plants. Possibly better to use more selective methods such as basal bark treatment.

We have also made the excavated channels wide enough for canoeists and are configuring them so as to allow for round trips and possible development of walkways.

References:
Stengs, Henk 2007: West Coast Tai Poutini Conservancy inanga spawning site assessments with recommendations for restoration and protection. Department of Conservation, Greymouth.

Stengs, Henk 2011: Ecological assessment of the area between Cobden and the Grey River with recommendations for management. Report for Grey District Council. Department of Conservation, Greymouth.