Wednesday, 1 November 2017

Evaluation of Christchurch City Council's riparian management trial

Christchurch City Council (CCC) recently conducted a riparian management trial involving cessation of riverbank vegetation clearance  A survey of īnanga (Galaxias maculatus) spawning habitat was completed in April 2017 to evaluate the effects of the trial. While the trial has wider objectives around improved environmental outcomes, īnanga spawning habitat is directly affected by bank cutting and other forms of vegetation clearance.

The trial produced demonstrable benefits in terms of increasing the availability of high quality spawning habitat. This was reflected by the discovery of new sites, expansion of the reach known to support post-quake spawning in the Heathcote/Ōpāwaho, and a relatively high area of occupation (AOO) of spawning sites being recorded from a single month of survey. However results from egg production measurements suggest a possible adult population decline  in the Heathcote/Ōpāwahoand and require follow-up to determine the actual trend using the other post-quake studies as a baseline. 

Overall, the 2017 study also contributes to our understanding of New Zealand’s largest known area of īnanga spawning habitat. The factors leading to its creation are now an important topic for investigation. This will help secure gains for īnanga conservation in Christchurch City and set a useful example for the management of habitat in other waterways.

The full report can be downloaded from the CCC website here:
Response of īnanga spawning habitat to riparian vegetation management