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streams of the Golden Bay/ North West Nelson region surveyed by Department of
Conservation in 2001, it is only slightly greater than half of the average density, which
confirms this observation.

Sparse brown trout have been observed in large pools within the lowest section of the river
below the areas surveyed (R. Lamb pers. comm.; Department of Conservation 1999). Longfin
eels occurred throughout all areas of the survey reach at a low-moderate density. The
presence of a few quite large individuals indicated a lack of recent commercial harvest,
probably due to inaccessibility.

Proposed Flow reduction

Determining the exact level of fish habitat loss due to reduced flows, is problematic in an
environment such as the Parapara Gorge. Assumptions that are used for Instream Flow
Incremental Methodology (IFIM) flow modelling are violated due to the physical nature of the
riverbed. Flow reductions in such a high gradient environment, while causing habitat loss in
some areas, may actually also create suitable habitat in areas which are currently too swiftly
flowing for fish or invertebrates to inhabit. The potential effect of flow reduction on each of
the freshwater habitat types within the gorge is discussed below. Habitat types are grouped as
pool, run/riffle, and cascade habitat. In addition discussion of minimum flows required
immediately below the dam in the upper section of the gorge to ensure passage of diadromous
koaro and longfin eels, is included.

These potential effects have been assessed based on a proposal that is for a continuously
flowing and generating run of the river power scheme. If water-storage was built in and the
scheme operated on a peak power demand basis, there would be fluctuating flows downstream
of the power station. This would cause effects in the lower Parapara River that have not been
contemplated in this assessment.

Given the Parapara Gorge is unsuitable for IFIM, it is impossible to accurately predict habitat
loss under differing minimum flow regimes and therefore suggest an appropriate minimum
flow in this report. In this type of situation, other countries (such as the USA), often rely on
adaptive management to accurately assess flow effects. Adaptive management involves
monitoring actual effects of flow reductions before and after they are implemented, and then
reviewing these results using an ‘expert panel’ of stakeholders. Flows are then set at a level
where no major adverse effects occur, or appropriate off-site mitigation is provided for, if
flows cannot be set at this level without compromising economic viability of the development.
In the absence of adaptive management this report discusses river habitat within the gorge,
and attempts to provide estimates based on site visit observations, as to the likely effect of
flow reduction on these river habitat types.

Fish & Game New Zealand
Nelson Marlborough Region Sports Fish and Game Bird Management ...p21

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