Rangiora Tramping Club, July 25, 2017 Quantification of the weeds / birds battle on the Ashley-Rakahuri river Nick Ledgard and Grant Davey, Ashley-Rakahuri Rivercare Group Inc Rangiora Tramping Club, July 25, 2017

The only bird in the world with a bill which bends sideways The icon of rare and endangered braided river birds is the wrybill (ngutupare - bent bill) The only bird in the world with a bill which bends sideways It only breeds in Canterbury’s braided rivers

Other rare and endangered birds on the Ashley-Rakahuri river are: Black-fronted tern Black-billed gull Pied stilt Banded dotterel S. Is Pied Oystercatcher

Positive (mostly significant) increase in bird counts since 2000 ‘… management actions have contributed to these successes …’ Spurr and Ledgard (Notornis, 63(2), 2016)

BUT, over the last 2 years, an indication of a decline in bird populations. This appears to be associated with weeds invading bare gravel areas

Recent decline in bird numbers supported by most individual species analyses

Also supported by bird breeding data eg., wrybill

Relationship between bare gravel areas / 500m and sum of wrybill nests

How have we quantified the weed increase and loss of bare gravel areas? The river margins and bare gravel were digitized in 500m reaches using QGIS or Google Earth. QGIS was used to calculate areas. On the ground and in high resolution photos there is generally an obvious distinction between totally bare gravel (that measured) and gravel with weeds. This is harder to see on poorer quality images, but with experience it can be done with some confidence. A comparison of gravel areas  for half of the river was made between a 2015 Google Earth satellite image and high resolution air photos taken a few days apart. There was a 1% difference, with more variation for individual reaches.

Example of more detailed mapping for one stretch of riverbed Air or satellite photos from 2004, 2006, 2008, 2009, 2011, 2014 & 2015 used

Changes in the same stretch of riverbed over time Nov, 2011 Feb, 2017 Photo point

Photo point out from Groyne 2 Photo point over time in same stretch of riverbed Nov, 2014 Dec, 2015 Dec, 2016 Advance of weeds since 2014 Photo point out from Groyne 2

What are the reasons for this major increase in weed invasion since 2014? Probably, an increased source of weed seeds, a natural decrease in catchment maximum flows, and fewer large floods.

Of added concern is recent increase of more persistent woody weeds in the riverbed fairway – gorse, broom and shrubby willows The yellow tree lupin is a short-lived pioneer weed, readily removed by floods. Not so gorse, broom and willows Young gorse establishing Shrubby willows establishing from seed

In addition, important shallow water feeding areas are becoming choked with herbaceous weeds

So, what do we do about this bird decline associated with weed increase and bare gravel loss? If we do nothing we seriously risk losing the indigenous shore birds which breed on the Ashley-Rakahuri river – species which have been there for 10’s of thousands of years.

Will a return of floods do the job Will a return of floods do the job? Recent April 6, 2017, flood indicates it will help, but not be enough. April 6, 2017 It is estimated that this flood of 235 cumecs doubled the area of bare gravel from around 35ha to 70ha

The most recent flood of July 22, 2017 This was a 1-in-10 year event, with a peak flow of 572 cumecs. But it is too recent for us to quantify its effect on the extent of bare shingle.

Before and after floods - photos looking west from Cones Road bridge (Grant Davey) March 10, 2017 - before floods April 6, 2017 – during flood (235 cumecs) July 23, 2017 – after July 22 flood (572 cumecs)

Traditional bare gravel creation by commercial shingle extractors certainly helps Plenty of evidence that birds use weed-free gravel extraction sites for breeding

But regular large floods cannot be guaranteed, so there is no alternative other than to artificially manage weeds in the riverbed. Machine clearance of weeds has been tried in previous years August 2016 - before August 2016 - after Variable results on Ashley-Rakahuri, but success elsewhere (eg., Clarence and Waitaki) indicates further work warranted.

2017. Large clearances (50+ha) intended in sites historically favoured by birds Areas favoured by birds 2004 - 2015 Favoured sites often associated with past gravel extraction areas Proposed areas for clearance - 2017

Maintaining riverbed areas clear of weeds There is a far greater incidence and range of weeds in the Ashley- Rakahuri than there has been in the past. Floods might clear away weeds from shingle surfaces, but they also bring in large quantities of seed. There are many examples of where gravel areas cleared artificially or by floods has become reinfested with weeds within 2-3 years. Therefore, maintaining chosen breeding sites clear of weeds is absolutely vital. Fortunately, there are extensive control options available which allow us to do this relatively cheaply and in an environmentally acceptable manner (most likely chemicals).

The evidence is clear. Without direct action to increase and maintain bare gravel areas, we risk losing the indigenous shore birds which have bred on the Ashley Rakahuri river for centuries. “It is one thing to suffer the consequences of undetected changes – it is quite another, if no action is taken when the consequences are clearly indicated beforehand.”