7. Outstanding fishery and fish habitat

This page has section seven of the New Zealand Fish and Game Council and the Otago Fish and Game Council application to amend the Water Conservation (Kawarau) River) Order. 

Backcountry Trout Fishery Values

7.1  Backcountry fishery values are now considered more important and deserving of greater recognition than given to those characteristics in the original water conservation order. The key characteristics of backcountry fishing are:

  • Remote from centres of population
  • Not easily accessible
  • Low angler density
  • Catch rate relatively high
  • Large size of fish
  • Largely unmodified catchment
  • Highly scenic setting.
    Angler fishing the Nevis
    Photo 1. Angler fishing the Nevis
    River upstream from Nevis Crossing,
    February 2005.

There has been significant research in this area in the last decade.  The SFGMP now provides a context for managing a spectrum of fishing opportunities with the highly valued backcountry fishing opportunity representing one end of that spectrum.  The main objective of backcountry fisheries management is to protect those key characteristics and that is being given much greater emphasis with the development of specific licences and in some cases regimes controlling angler density and advocacy to protect settings.  

7.2  Recent survey work in the Nevis (Trotter 2004, Olsen and Hayes 2006 – Appendix 6) has confirmed the backcountry values present. The pressure of angler use in the Nevis River is relatively low.  The river is fished extensively by non-resident anglers who make up 32% of angler use and over half of those non-residents are guided.  This confirms the river has an international reputation and is important for tourism as well as being outstanding in its own right.  39% of anglers were Otago residents and 29% were from elsewhere in New Zealand.  This again corroborates earlier work concluding that the angling opportunity is valued very highly (Unwin undated) and confirms its importance as an angling destination in the national context.

7.3  A good proportion of anglers (> 40%) considered that catching large fish was an important feature of the Nevis angling experience and an overwhelming majority (95%) of anglers considered that the natural environment and the scenery were an important feature of the experience (Trotter 2004).

Angler fishing the Nevis
Photo 2.  Large trout taken from river reach
upstream from Nevis Crossing, February 2005

7.4  The Nevis offers a diversity of angling opportunity with more accessible reaches adjacent to the road in the river from the Crossing to Nevis township and in the upper valley.  By comparison the upper gorge area, immediately below the crossing is more rugged and less accessible, and the Nevis Gorge itself, below Nevis Burn confluence offers challenging angling in a remote and rugged location with difficult access.  

Trout Habitat

7.5  New evidence (Trotter 2004 and 2006, Olsen and Hayes 2006) establishes that the trout habitat afforded by the Nevis is outstanding in that it sustains a headwater trophy brown trout fishery based on resident fish that have an average size that is far greater than most brown trout fisheries in Otago.  It is on a par with the two other trophy brown trout fisheries in Otago - the Upper Taieri River and the Upper Pomakaka River.  This is a special feature because the Nevis is a high altitude valley, the winter climate is severe, and the river is almost certainly not replenished with large adult trout migrating upstream from larger water bodies because of barriers to fish migration.  The large trophy trout present in the river grow to trophy size because of the productive nature of the instream habitat.

7.6  New evidence arising from an IFIM survey commissioned on the Nevis by Otago Regional Council (NIWA 2004) suggests adult brown trout habitat is maximised at 5 m3/sec in the lower gradient reach of the river upstream of Nevis Crossing.  Peak aquatic invertebrate food producing habitat occurs at 6.2 m3/sec in the same reach.

Trout Spawning and Rearing Areas

7.7  New information (Olsen and Hayes 2006) establishes that important areas of spawning habitat exist in the mainstem Nevis upstream of the Crossing and in tributary streams including Nevis Burn and Potters Creek.  Inundation of these areas is likely to have an adverse effect on these spawning areas, which will in turn adversely affect the fishery to the extent it is no longer outstanding, particularly in the reach of river from Nevis Crossing to Potters Creek and on downstream to the Kawarau where there is little suitable spawning habitat in the mainstem.

7.8  The river downstream from Nevis Crossing is rugged and some rapid sections pose a barrier to upstream trout migration from the Kawarau River (Olsen and Hayes 2006 – Appendix 6).  Thus the lower river will be dependant for recruitment on downstream migration of juvenile trout or trout rearing in tributary streams such as the Nevis Burn.

Native Fish Values

7.9  The Nevis River and its tributaries also support populations of non-migratory galaxiid fishes (Galaxias gollumoides).  The presence of this species is an example of species distribution consistent with river capture millions of years ago.  Apart from the Nevis population, G. gollumoides is otherwise found only in Southland.  It does not occur elsewhere in the Clutha catchment of which the Nevis is now a part. Its presence in the Nevis is interpreted as evidence that the catchment area was once part of the Mataura catchment, rather than the Clutha.  However, tectonic activity – the folding and faulting that occurs within the earths crust -  has tilted the landscape causing a reversal in the drainage direction and the capture of Nevis by the Clutha catchment as a result (Wallis and Waters 2003).  These native fishery values had not been identified in 1993 at the time of the original WCO decision.

7.10  Sub-populations of G. gollumoides would be threatened by flooding if a hydro dam were constructed downstream from the crossing.

Hydro Development and Impacts on Fishery Values

7.11  Fish and Game is concerned at the threat of potential hydro development of the Nevis.  To assess this risk, Fish and Game has used the description of the potential for hydro development in the recent report on hydro resources in New Zealand (East Harbour Management Services 2004).  The…“scheme consist of two dams on the Nevis River storing and diverting water to a power house further down the Nevis.  The upper Dam would be located at the Nevis Crossing and would provide water storage for the scheme.  The lower dam would be some 2 km. downstream and would divert the water into a 6.5 km tunnel.”

“A large volume storage lake would be obtained in the lower valley by an arch dam constructed just downstream of the Nevis Bridge.  An intake dam also of a concrete arch  construction would be erected at the mouth of the gorge about 2km downstream and would include the  additional, flow of the Nevis Burn stream.  The average flow here is 10.5 m3/s and the area to be drained is 510 km2.  At this point a concrete lined tunnel would be driven 8 km parallel to the river to a point above the power station and a steel penstock installed to carry water to it.  The head developed would be 300 m. and with 45MW, would give approximately 197 GWh p.a. (50% plant factor). The elevation is 300m.”

7.12  This type of development would cause significant adverse effects on the river (Olsen and Hayes 2006):

  1. The 6 km reach from the Nevis Crossing upstream will be inundated including some of the most accessible fishing areas and mainstem spawning grounds.  
  2. The 2km river reach upstream from the second dam will be inundated and spawning and rearing areas in the Nevis Burn will be flooded along with the low gradient reach of the river in The Dell.
  3. The river flow will be largely diverted into a tunnel below the second dam severely diminishing the flow over an 8.2 km reach of river.
  4. The 3.6 km river reach below the powerhouse to the Kawarau River will be subject to fluctuating flows.
  5. At present the Nevis River flows approximately 50 km from its source to its confluence with the Kawarau River without any significant modification to its flow.  The potential hydro development will see nearly half of the river either inundated (6.5km) substantially dewatered (7km) or subject to fluctuating flows (5km).
  6. Outstanding angling opportunities will be lost including the more challenging wilderness fishing in the Nevis Gorge and the more accessible water in The Dell and immediately upstream from Nevis Crossing.