This is also leading to a wider, shallower channel, with warmer water in summer causing more algae and slime to form on the river bed.
River raking is also being done in the main spawning streams, so even a relatively small rise in water level will start moving the river bed shingle where trout lay their eggs.
Last year the Forest & Bird organisation and other bird watchers were very upset when the raking was done through various nesting colonies, destroying eggs and chicks.
To their credit, at a well attended meeting in February 2017, HBRC fronted up to anglers and Forest & Bird, and agreed to stop raking in the bird nesting seasons. But the raking of the river beds is now being done at the height of the trout spawning run.
River raking was begun in the 1980s, before an environmental impact report was required.
The degrading and even possible loss of these fisheries to Hawke's Bay would be a disaster. On the other hand, the tourist revenue from a rejuvenated fishery would be a great boost to local economies and hard pressed farmers, home stays and for fishermen.
So much of the hard work going into Plan Change 6 to mitigate agricultural pollution could be wasted if the fishery collapses. Until a thorough environment impact survey is completed into river raking, this practice should be put on hold.
Hawke's Bay Regional Council replies:
There are a number of assertions by Fred Nichol that are incorrect, misleading or unsubstantiated.
HBRC has recently adopted a new riverbed Gravel Management Plan (GMP) and an Environmental Code of Practice (COP) for River Control and Waterway Works. This involved representatives of Fish and Game and anglers.
A number of studies have been carried out over the past six years to better understand the effects of gravel extraction and beach raking on the region's braided rivers.
These major studies included two reports: "Effects of Gravel Extraction and Beach Raking on Key Instream Species in Hawke's Bay Rivers: Cawthron" and "Gravel Review: Terrestrial Ecology Impact Assessment: Forbes Ecology".
The COP was developed around these reports, including guidelines on best river management practices to allow the council to carry out its flood control responsibilities with minimal environmental impact.
The Cawthron report highlighted no existing New Zealand-specific research on the instream ecological effects of gravel raking on instream ecology.
Equally there is a lack of fish population data, something the angling community through Fish and Game should measure to help understand the complex issues around river management and river ecology.
The report recommends a number of research studies to help understand some of the complexities. The council will carry out some of these recommendations over the coming years, hopefully with full support from the CHB Anglers Club.
HBRC operates using Ecological Management and Enhancement Plans developed for the rivers in the region. These supplement the COP with detailed descriptions and guidelines to manage the terrestrial and aquatic habitat in each managed river corridor.
They include for example times when beach raking can be carried out, requirements for inspection by a qualified ecologist and how to minimise any adverse effects.
It is worth noting that trout are not a native species.
HBRC strongly disputes Mr Nicol's statement that raking was carried out last year destroying nesting colonies.
The reference to beach raking during the nesting season referred to was carried out in the shoulder-breeding season before there was an ecological management plan finalised for the Tukituki River.
The ecological management plans currently in place dictate that no beach-raking can take place during the bird-nesting season.
Beach raking, as its name suggests, is not carried out in the rivers as implied by Mr Nichol; it is only carried out on gravel beaches (or islands) above the river level and half a metre from flowing water.
The main aim is to prevent stable islands or beach bars from forming. These cause lateral shifts in the flow meander. If stable armoured lateral channels develop, this increases the potential for river banks to erode by undercutting flood protection infrastructure along the banks.
Beach raking also helps to prevent pest vegetation (such as lupin) from establishing and ruining the open gravel habitat necessary for the survival of river birds that live and nest in the braided river network.
Sediment transport is a natural part of a river's function and in the case of some Hawke's Bay rivers there would be no highly-important braided rivers unless sediment was available to be transported. If beach raking was not carried out, the diversity and abundance of threatened native bird species currently supported by the managed reaches of these rivers would be compromised.
